[Lldb-commits] [lldb] [lldb] Adding A new Binding helper for JSONTransport. (PR #159160)

John Harrison via lldb-commits lldb-commits at lists.llvm.org
Tue Sep 16 17:52:27 PDT 2025


https://github.com/ashgti updated https://github.com/llvm/llvm-project/pull/159160

>From b91cad6dc7ea4c40c61a0cfe9bb45be03de32254 Mon Sep 17 00:00:00 2001
From: John Harrison <harjohn at google.com>
Date: Wed, 10 Sep 2025 10:42:56 -0700
Subject: [PATCH] [lldb] Adding A new Binding helper for JSONTransport.

This adds a new Binding helper class to allow mapping of incoming and outgoing requests / events to specific handlers.

This should make it easier to create new protocol implementations and allow us to create a relay in the lldb-mcp binary.
---
 lldb/include/lldb/Host/JSONTransport.h        | 387 ++++++++++++++++--
 lldb/include/lldb/Protocol/MCP/Protocol.h     |   8 +
 lldb/include/lldb/Protocol/MCP/Server.h       |  73 ++--
 lldb/include/lldb/Protocol/MCP/Transport.h    |  77 +++-
 lldb/source/Host/common/JSONTransport.cpp     |  10 +
 .../Protocol/MCP/ProtocolServerMCP.cpp        |  42 +-
 .../Plugins/Protocol/MCP/ProtocolServerMCP.h  |  20 +-
 lldb/source/Protocol/MCP/Server.cpp           | 211 +++-------
 lldb/tools/lldb-dap/DAP.h                     |   6 +-
 lldb/tools/lldb-dap/Protocol/ProtocolBase.h   |   6 +-
 lldb/tools/lldb-dap/Transport.h               |   6 +-
 lldb/unittests/DAP/DAPTest.cpp                |  20 +-
 lldb/unittests/DAP/Handler/DisconnectTest.cpp |   4 +-
 lldb/unittests/DAP/TestBase.cpp               |  42 +-
 lldb/unittests/DAP/TestBase.h                 | 122 +++---
 lldb/unittests/Host/JSONTransportTest.cpp     | 338 +++++++++++----
 .../Protocol/ProtocolMCPServerTest.cpp        | 280 +++++++------
 .../Host/JSONTransportTestUtilities.h         |  96 ++++-
 18 files changed, 1170 insertions(+), 578 deletions(-)

diff --git a/lldb/include/lldb/Host/JSONTransport.h b/lldb/include/lldb/Host/JSONTransport.h
index 210f33edace6e..da1ae43118538 100644
--- a/lldb/include/lldb/Host/JSONTransport.h
+++ b/lldb/include/lldb/Host/JSONTransport.h
@@ -18,6 +18,7 @@
 #include "lldb/Utility/IOObject.h"
 #include "lldb/Utility/Status.h"
 #include "lldb/lldb-forward.h"
+#include "llvm/ADT/FunctionExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
@@ -25,8 +26,13 @@
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/raw_ostream.h"
+#include <functional>
+#include <mutex>
+#include <optional>
 #include <string>
 #include <system_error>
+#include <type_traits>
+#include <utility>
 #include <variant>
 #include <vector>
 
@@ -50,17 +56,70 @@ class TransportUnhandledContentsError
   std::string m_unhandled_contents;
 };
 
+class InvalidParams : public llvm::ErrorInfo<InvalidParams> {
+public:
+  static char ID;
+
+  explicit InvalidParams(std::string method, std::string context)
+      : m_method(std::move(method)), m_context(std::move(context)) {}
+
+  void log(llvm::raw_ostream &OS) const override;
+  std::error_code convertToErrorCode() const override;
+
+private:
+  std::string m_method;
+  std::string m_context;
+};
+
+// Value for tracking functions that have a void param or result.
+using VoidT = std::monostate;
+
+template <typename T> using Callback = llvm::unique_function<T>;
+
+template <typename T>
+using Reply = typename std::conditional<
+    std::is_same_v<T, VoidT> == true, llvm::unique_function<void(llvm::Error)>,
+    llvm::unique_function<void(llvm::Expected<T>)>>::type;
+
+template <typename Result, typename Params>
+using OutgoingRequest = typename std::conditional<
+    std::is_same_v<Params, VoidT> == true,
+    llvm::unique_function<void(Reply<Result>)>,
+    llvm::unique_function<void(const Params &, Reply<Result>)>>::type;
+
+template <typename Params>
+using OutgoingEvent = typename std::conditional<
+    std::is_same_v<Params, VoidT> == true, llvm::unique_function<void()>,
+    llvm::unique_function<void(const Params &)>>::type;
+
+template <typename Id, typename Req>
+Req make_request(Id id, llvm::StringRef method,
+                 std::optional<llvm::json::Value> params = std::nullopt);
+template <typename Req, typename Resp>
+Resp make_response(const Req &req, llvm::Error error);
+template <typename Req, typename Resp>
+Resp make_response(const Req &req, llvm::json::Value result);
+template <typename Evt>
+Evt make_event(llvm::StringRef method,
+               std::optional<llvm::json::Value> params = std::nullopt);
+template <typename Resp>
+llvm::Expected<llvm::json::Value> get_result(const Resp &resp);
+template <typename Id, typename T> Id get_id(const T &);
+template <typename T> llvm::StringRef get_method(const T &);
+template <typename T> llvm::json::Value get_params(const T &);
+
 /// A transport is responsible for maintaining the connection to a client
 /// application, and reading/writing structured messages to it.
 ///
 /// Transports have limited thread safety requirements:
 ///  - Messages will not be sent concurrently.
 ///  - Messages MAY be sent while Run() is reading, or its callback is active.
-template <typename Req, typename Resp, typename Evt> class Transport {
+template <typename Id, typename Req, typename Resp, typename Evt>
+class JSONTransport {
 public:
   using Message = std::variant<Req, Resp, Evt>;
 
-  virtual ~Transport() = default;
+  virtual ~JSONTransport() = default;
 
   /// Sends an event, a message that does not require a response.
   virtual llvm::Error Send(const Evt &) = 0;
@@ -90,8 +149,6 @@ template <typename Req, typename Resp, typename Evt> class Transport {
     virtual void OnClosed() = 0;
   };
 
-  using MessageHandlerSP = std::shared_ptr<MessageHandler>;
-
   /// RegisterMessageHandler registers the Transport with the given MainLoop and
   /// handles any incoming messages using the given MessageHandler.
   ///
@@ -100,22 +157,302 @@ template <typename Req, typename Resp, typename Evt> class Transport {
   virtual llvm::Expected<MainLoop::ReadHandleUP>
   RegisterMessageHandler(MainLoop &loop, MessageHandler &handler) = 0;
 
-  // FIXME: Refactor mcp::Server to not directly access log on the transport.
-  // protected:
+protected:
   template <typename... Ts> inline auto Logv(const char *Fmt, Ts &&...Vals) {
     Log(llvm::formatv(Fmt, std::forward<Ts>(Vals)...).str());
   }
   virtual void Log(llvm::StringRef message) = 0;
+
+  /// Function object to reply to a call.
+  /// Each instance must be called exactly once, otherwise:
+  ///  - the bug is logged, and (in debug mode) an assert will fire
+  ///  - if there was no reply, an error reply is sent
+  ///  - if there were multiple replies, only the first is sent
+  class ReplyOnce {
+    std::atomic<bool> replied = {false};
+    const Req req;
+    JSONTransport *transport;               // Null when moved-from.
+    JSONTransport::MessageHandler *handler; // Null when moved-from.
+
+  public:
+    ReplyOnce(const Req req, JSONTransport *transport,
+              JSONTransport::MessageHandler *handler)
+        : req(req), transport(transport), handler(handler) {
+      assert(handler);
+    }
+    ReplyOnce(ReplyOnce &&other)
+        : replied(other.replied.load()), req(other.req),
+          transport(other.transport), handler(other.handler) {
+      other.transport = nullptr;
+      other.handler = nullptr;
+    }
+    ReplyOnce &operator=(ReplyOnce &&) = delete;
+    ReplyOnce(const ReplyOnce &) = delete;
+    ReplyOnce &operator=(const ReplyOnce &) = delete;
+
+    ~ReplyOnce() {
+      if (transport && handler && !replied) {
+        assert(false && "must reply to all calls!");
+        (*this)(make_response<Req, Resp>(
+            req, llvm::createStringError("failed to reply")));
+      }
+    }
+
+    void operator()(const Resp &resp) {
+      assert(transport && handler && "moved-from!");
+      if (replied.exchange(true)) {
+        assert(false && "must reply to each call only once!");
+        return;
+      }
+
+      if (llvm::Error error = transport->Send(resp))
+        handler->OnError(std::move(error));
+    }
+  };
+
+public:
+  class Binder;
+  using BinderUP = std::unique_ptr<Binder>;
+
+  /// Binder collects a table of functions that handle calls.
+  ///
+  /// The wrapper takes care of parsing/serializing responses.
+  class Binder : public JSONTransport::MessageHandler {
+  public:
+    explicit Binder(JSONTransport &transport)
+        : m_transport(transport), m_seq(0) {}
+
+    Binder(const Binder &) = delete;
+    Binder &operator=(const Binder &) = delete;
+
+    /// Bind a handler on transport disconnect.
+    template <typename Fn, typename... Args>
+    void disconnected(Fn &&fn, Args &&...args) {
+      m_disconnect_handler = [&, args...]() mutable {
+        std::invoke(std::forward<Fn>(fn), std::forward<Args>(args)...);
+      };
+    }
+
+    /// Bind a handler on error when communicating with the transport.
+    template <typename Fn, typename... Args>
+    void error(Fn &&fn, Args &&...args) {
+      m_error_handler = [&, args...](llvm::Error error) mutable {
+        std::invoke(std::forward<Fn>(fn), std::forward<Args>(args)...,
+                    std::move(error));
+      };
+    }
+
+    template <typename T>
+    static llvm::Expected<T> parse(const llvm::json::Value &raw,
+                                   llvm::StringRef method) {
+      T result;
+      llvm::json::Path::Root root;
+      if (!fromJSON(raw, result, root)) {
+        // Dump the relevant parts of the broken message.
+        std::string context;
+        llvm::raw_string_ostream OS(context);
+        root.printErrorContext(raw, OS);
+        return llvm::make_error<InvalidParams>(method.str(), context);
+      }
+      return std::move(result);
+    }
+
+    /// Bind a handler for a request.
+    /// e.g. `bind("peek", &ThisModule::peek, this, std::placeholders::_1);`.
+    ///  Handler should be e.g. `Expected<PeekResult> peek(const PeekParams&);`
+    /// PeekParams must be JSON parsable and PeekResult must be serializable.
+    template <typename Result, typename Params, typename Fn, typename... Args>
+    void bind(llvm::StringLiteral method, Fn &&fn, Args &&...args) {
+      assert(m_request_handlers.find(method) == m_request_handlers.end() &&
+             "request already bound");
+      if constexpr (std::is_void_v<Params> || std::is_same_v<VoidT, Params>) {
+        m_request_handlers[method] =
+            [fn,
+             args...](const Req &req,
+                      llvm::unique_function<void(const Resp &)> reply) mutable {
+              llvm::Expected<Result> result = std::invoke(
+                  std::forward<Fn>(fn), std::forward<Args>(args)...);
+              if (!result)
+                return reply(make_response<Req, Resp>(req, result.takeError()));
+              reply(make_response<Req, Resp>(req, toJSON(*result)));
+            };
+      } else {
+        m_request_handlers[method] =
+            [method, fn,
+             args...](const Req &req,
+                      llvm::unique_function<void(const Resp &)> reply) mutable {
+              llvm::Expected<Params> params =
+                  parse<Params>(get_params<Req>(req), method);
+              if (!params)
+                return reply(make_response<Req, Resp>(req, params.takeError()));
+
+              llvm::Expected<Result> result = std::invoke(
+                  std::forward<Fn>(fn), std::forward<Args>(args)..., *params);
+              if (!result)
+                return reply(make_response<Req, Resp>(req, result.takeError()));
+
+              reply(make_response<Req, Resp>(req, toJSON(*result)));
+            };
+      }
+    }
+
+    /// Bind a handler for a event.
+    /// e.g. `bind("peek", &ThisModule::peek, this);`
+    /// Handler should be e.g. `void peek(const PeekParams&);`
+    /// PeekParams must be JSON parsable.
+    template <typename Params, typename Fn, typename... Args>
+    void bind(llvm::StringLiteral method, Fn &&fn, Args &&...args) {
+      assert(m_event_handlers.find(method) == m_event_handlers.end() &&
+             "event already bound");
+      if constexpr (std::is_void_v<Params> || std::is_same_v<VoidT, Params>) {
+        m_event_handlers[method] = [fn, args...](const Evt &) mutable {
+          std::invoke(std::forward<Fn>(fn), std::forward<Args>(args)...);
+        };
+      } else {
+        m_event_handlers[method] = [this, method, fn,
+                                    args...](const Evt &evt) mutable {
+          llvm::Expected<Params> params =
+              parse<Params>(get_params<Evt>(evt), method);
+          if (!params)
+            return OnError(params.takeError());
+          std::invoke(std::forward<Fn>(fn), std::forward<Args>(args)...,
+                      *params);
+        };
+      }
+    }
+
+    /// Bind a function object to be used for outgoing requests.
+    /// e.g. `OutgoingRequest<Params, Result> Edit = bind("edit");`
+    /// Params must be JSON-serializable, Result must be parsable.
+    template <typename Result, typename Params>
+    OutgoingRequest<Result, Params> bind(llvm::StringLiteral method) {
+      if constexpr (std::is_void_v<Params> || std::is_same_v<VoidT, Params>) {
+        return [this, method](Reply<Result> fn) {
+          std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+          Id id = ++m_seq;
+          Req req = make_request<Req, Resp>(id, method, std::nullopt);
+          m_pending_responses[id] = [fn = std::move(fn),
+                                     method](const Resp &resp) mutable {
+            llvm::Expected<llvm::json::Value> result = get_result<Resp>(resp);
+            if (!result)
+              return fn(result.takeError());
+            fn(parse<Result>(*result, method));
+          };
+          if (llvm::Error error = m_transport.Send(req))
+            OnError(std::move(error));
+        };
+      } else {
+        return [this, method](const Params &params, Reply<Result> fn) {
+          std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+          Id id = ++m_seq;
+          Req req =
+              make_request<Id, Req>(id, method, llvm::json::Value(params));
+          m_pending_responses[id] = [fn = std::move(fn),
+                                     method](const Resp &resp) mutable {
+            llvm::Expected<llvm::json::Value> result = get_result<Resp>(resp);
+            if (llvm::Error err = result.takeError())
+              return fn(std::move(err));
+            fn(parse<Result>(*result, method));
+          };
+          if (llvm::Error error = m_transport.Send(req))
+            OnError(std::move(error));
+        };
+      }
+    }
+
+    /// Bind a function object to be used for outgoing events.
+    /// e.g. `OutgoingEvent<LogParams> Log = bind("log");`
+    /// LogParams must be JSON-serializable.
+    template <typename Params>
+    OutgoingEvent<Params> bind(llvm::StringLiteral method) {
+      if constexpr (std::is_void_v<Params> || std::is_same_v<VoidT, Params>) {
+        return [this, method]() {
+          if (llvm::Error error =
+                  m_transport.Send(make_event<Evt>(method, std::nullopt)))
+            OnError(std::move(error));
+        };
+      } else {
+        return [this, method](const Params &params) {
+          if (llvm::Error error =
+                  m_transport.Send(make_event<Evt>(method, toJSON(params))))
+            OnError(std::move(error));
+        };
+      }
+    }
+
+    void Received(const Evt &evt) override {
+      std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+      auto it = m_event_handlers.find(get_method<Evt>(evt));
+      if (it == m_event_handlers.end()) {
+        OnError(llvm::createStringError(
+            llvm::formatv("no handled for event {0}", toJSON(evt))));
+        return;
+      }
+      it->second(evt);
+    }
+
+    void Received(const Req &req) override {
+      ReplyOnce reply(req, &m_transport, this);
+
+      std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+      auto it = m_request_handlers.find(get_method<Req>(req));
+      if (it == m_request_handlers.end()) {
+        reply(make_response<Req, Resp>(
+            req, llvm::createStringError("method not found")));
+        return;
+      }
+
+      it->second(req, std::move(reply));
+    }
+
+    void Received(const Resp &resp) override {
+      std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+      auto it = m_pending_responses.find(get_id<Id, Resp>(resp));
+      if (it == m_pending_responses.end()) {
+        OnError(llvm::createStringError(
+            llvm::formatv("no pending request for {0}", toJSON(resp))));
+        return;
+      }
+
+      it->second(resp);
+      m_pending_responses.erase(it);
+    }
+
+    void OnError(llvm::Error err) override {
+      std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+      if (m_error_handler)
+        m_error_handler(std::move(err));
+    }
+
+    void OnClosed() override {
+      std::scoped_lock<std::recursive_mutex> guard(m_mutex);
+      if (m_disconnect_handler)
+        m_disconnect_handler();
+    }
+
+  private:
+    std::recursive_mutex m_mutex;
+    JSONTransport &m_transport;
+    Id m_seq;
+    std::map<Id, Callback<void(const Resp &)>> m_pending_responses;
+    llvm::StringMap<Callback<void(const Req &, Callback<void(const Resp &)>)>>
+        m_request_handlers;
+    llvm::StringMap<Callback<void(const Evt &)>> m_event_handlers;
+    Callback<void()> m_disconnect_handler;
+    Callback<void(llvm::Error)> m_error_handler;
+  };
 };
 
-/// A JSONTransport will encode and decode messages using JSON.
-template <typename Req, typename Resp, typename Evt>
-class JSONTransport : public Transport<Req, Resp, Evt> {
+/// A IOTransport will encode and decode messages using an IOObject like a
+/// file or a socket.
+template <typename Id, typename Req, typename Resp, typename Evt>
+class IOTransport : public JSONTransport<Id, Req, Resp, Evt> {
 public:
-  using Transport<Req, Resp, Evt>::Transport;
-  using MessageHandler = typename Transport<Req, Resp, Evt>::MessageHandler;
+  using Message = typename JSONTransport<Id, Req, Resp, Evt>::Message;
+  using MessageHandler =
+      typename JSONTransport<Id, Req, Resp, Evt>::MessageHandler;
 
-  JSONTransport(lldb::IOObjectSP in, lldb::IOObjectSP out)
+  IOTransport(lldb::IOObjectSP in, lldb::IOObjectSP out)
       : m_in(in), m_out(out) {}
 
   llvm::Error Send(const Evt &evt) override { return Write(evt); }
@@ -127,7 +464,7 @@ class JSONTransport : public Transport<Req, Resp, Evt> {
     Status status;
     MainLoop::ReadHandleUP read_handle = loop.RegisterReadObject(
         m_in,
-        std::bind(&JSONTransport::OnRead, this, std::placeholders::_1,
+        std::bind(&IOTransport::OnRead, this, std::placeholders::_1,
                   std::ref(handler)),
         status);
     if (status.Fail()) {
@@ -140,7 +477,7 @@ class JSONTransport : public Transport<Req, Resp, Evt> {
   /// detail.
   static constexpr size_t kReadBufferSize = 1024;
 
-  // FIXME: Write should be protected.
+protected:
   llvm::Error Write(const llvm::json::Value &message) {
     this->Logv("<-- {0}", message);
     std::string output = Encode(message);
@@ -148,7 +485,6 @@ class JSONTransport : public Transport<Req, Resp, Evt> {
     return m_out->Write(output.data(), bytes_written).takeError();
   }
 
-protected:
   virtual llvm::Expected<std::vector<std::string>> Parse() = 0;
   virtual std::string Encode(const llvm::json::Value &message) = 0;
 
@@ -175,9 +511,8 @@ class JSONTransport : public Transport<Req, Resp, Evt> {
       }
 
       for (const std::string &raw_message : *raw_messages) {
-        llvm::Expected<typename Transport<Req, Resp, Evt>::Message> message =
-            llvm::json::parse<typename Transport<Req, Resp, Evt>::Message>(
-                raw_message);
+        llvm::Expected<Message> message =
+            llvm::json::parse<Message>(raw_message);
         if (!message) {
           handler.OnError(message.takeError());
           return;
@@ -202,10 +537,10 @@ class JSONTransport : public Transport<Req, Resp, Evt> {
 };
 
 /// A transport class for JSON with a HTTP header.
-template <typename Req, typename Resp, typename Evt>
-class HTTPDelimitedJSONTransport : public JSONTransport<Req, Resp, Evt> {
+template <typename Id, typename Req, typename Resp, typename Evt>
+class HTTPDelimitedJSONTransport : public IOTransport<Id, Req, Resp, Evt> {
 public:
-  using JSONTransport<Req, Resp, Evt>::JSONTransport;
+  using IOTransport<Id, Req, Resp, Evt>::IOTransport;
 
 protected:
   /// Encodes messages based on
@@ -231,8 +566,8 @@ class HTTPDelimitedJSONTransport : public JSONTransport<Req, Resp, Evt> {
       for (const llvm::StringRef &header :
            llvm::split(headers, kHeaderSeparator)) {
         auto [key, value] = header.split(kHeaderFieldSeparator);
-        // 'Content-Length' is the only meaningful key at the moment. Others are
-        // ignored.
+        // 'Content-Length' is the only meaningful key at the moment. Others
+        // are ignored.
         if (!key.equals_insensitive(kHeaderContentLength))
           continue;
 
@@ -269,10 +604,10 @@ class HTTPDelimitedJSONTransport : public JSONTransport<Req, Resp, Evt> {
 };
 
 /// A transport class for JSON RPC.
-template <typename Req, typename Resp, typename Evt>
-class JSONRPCTransport : public JSONTransport<Req, Resp, Evt> {
+template <typename Id, typename Req, typename Resp, typename Evt>
+class JSONRPCTransport : public IOTransport<Id, Req, Resp, Evt> {
 public:
-  using JSONTransport<Req, Resp, Evt>::JSONTransport;
+  using IOTransport<Id, Req, Resp, Evt>::IOTransport;
 
 protected:
   std::string Encode(const llvm::json::Value &message) override {
diff --git a/lldb/include/lldb/Protocol/MCP/Protocol.h b/lldb/include/lldb/Protocol/MCP/Protocol.h
index 6e1ffcbe1f3e3..1e0816110b80a 100644
--- a/lldb/include/lldb/Protocol/MCP/Protocol.h
+++ b/lldb/include/lldb/Protocol/MCP/Protocol.h
@@ -14,6 +14,7 @@
 #ifndef LLDB_PROTOCOL_MCP_PROTOCOL_H
 #define LLDB_PROTOCOL_MCP_PROTOCOL_H
 
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/JSON.h"
 #include <optional>
 #include <string>
@@ -324,4 +325,11 @@ bool fromJSON(const llvm::json::Value &, CallToolResult &, llvm::json::Path);
 
 } // namespace lldb_protocol::mcp
 
+namespace llvm::json {
+inline Value toJSON(const lldb_protocol::mcp::Void &) { return Object(); }
+inline bool fromJSON(const Value &, lldb_protocol::mcp::Void &, Path) {
+  return true;
+}
+} // namespace llvm::json
+
 #endif
diff --git a/lldb/include/lldb/Protocol/MCP/Server.h b/lldb/include/lldb/Protocol/MCP/Server.h
index 1f916ae525b5c..df2a4810ce620 100644
--- a/lldb/include/lldb/Protocol/MCP/Server.h
+++ b/lldb/include/lldb/Protocol/MCP/Server.h
@@ -9,7 +9,6 @@
 #ifndef LLDB_PROTOCOL_MCP_SERVER_H
 #define LLDB_PROTOCOL_MCP_SERVER_H
 
-#include "lldb/Host/JSONTransport.h"
 #include "lldb/Host/MainLoop.h"
 #include "lldb/Protocol/MCP/Protocol.h"
 #include "lldb/Protocol/MCP/Resource.h"
@@ -19,74 +18,66 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/Signals.h"
-#include <functional>
 #include <memory>
 #include <string>
 #include <vector>
 
 namespace lldb_protocol::mcp {
 
-class Server : public MCPTransport::MessageHandler {
+class Server {
+
+  using MCPTransportUP = std::unique_ptr<lldb_protocol::mcp::MCPTransport>;
+
+  using ReadHandleUP = lldb_private::MainLoop::ReadHandleUP;
+
 public:
-  Server(std::string name, std::string version,
-         std::unique_ptr<MCPTransport> transport_up,
-         lldb_private::MainLoop &loop);
+  Server(std::string name, std::string version, LogCallback log_callback = {});
   ~Server() = default;
 
-  using NotificationHandler = std::function<void(const Notification &)>;
-
   void AddTool(std::unique_ptr<Tool> tool);
   void AddResourceProvider(std::unique_ptr<ResourceProvider> resource_provider);
-  void AddNotificationHandler(llvm::StringRef method,
-                              NotificationHandler handler);
 
-  llvm::Error Run();
+  llvm::Error Accept(lldb_private::MainLoop &, MCPTransportUP);
 
 protected:
-  ServerCapabilities GetCapabilities();
-
-  using RequestHandler =
-      std::function<llvm::Expected<Response>(const Request &)>;
+  MCPTransport::BinderUP Bind(MCPTransport &);
 
-  void AddRequestHandlers();
-
-  void AddRequestHandler(llvm::StringRef method, RequestHandler handler);
-
-  llvm::Expected<std::optional<Message>> HandleData(llvm::StringRef data);
-
-  llvm::Expected<Response> Handle(const Request &request);
-  void Handle(const Notification &notification);
-
-  llvm::Expected<Response> InitializeHandler(const Request &);
+  ServerCapabilities GetCapabilities();
 
-  llvm::Expected<Response> ToolsListHandler(const Request &);
-  llvm::Expected<Response> ToolsCallHandler(const Request &);
+  llvm::Expected<InitializeResult> InitializeHandler(const InitializeParams &);
 
-  llvm::Expected<Response> ResourcesListHandler(const Request &);
-  llvm::Expected<Response> ResourcesReadHandler(const Request &);
+  llvm::Expected<ListToolsResult> ToolsListHandler();
+  llvm::Expected<CallToolResult> ToolsCallHandler(const CallToolParams &);
 
-  void Received(const Request &) override;
-  void Received(const Response &) override;
-  void Received(const Notification &) override;
-  void OnError(llvm::Error) override;
-  void OnClosed() override;
+  llvm::Expected<ListResourcesResult> ResourcesListHandler();
+  llvm::Expected<ReadResourceResult>
+  ResourcesReadHandler(const ReadResourceParams &);
 
-  void TerminateLoop();
+  template <typename... Ts> inline auto Logv(const char *Fmt, Ts &&...Vals) {
+    Log(llvm::formatv(Fmt, std::forward<Ts>(Vals)...).str());
+  }
+  void Log(llvm::StringRef message) {
+    if (m_log_callback)
+      m_log_callback(message);
+  }
 
 private:
   const std::string m_name;
   const std::string m_version;
 
-  std::unique_ptr<MCPTransport> m_transport_up;
-  lldb_private::MainLoop &m_loop;
+  LogCallback m_log_callback;
+  struct Client {
+    ReadHandleUP handle;
+    MCPTransportUP transport;
+    MCPTransport::BinderUP binder;
+  };
+  std::map<MCPTransport *, Client> m_instances;
 
   llvm::StringMap<std::unique_ptr<Tool>> m_tools;
   std::vector<std::unique_ptr<ResourceProvider>> m_resource_providers;
-
-  llvm::StringMap<RequestHandler> m_request_handlers;
-  llvm::StringMap<NotificationHandler> m_notification_handlers;
 };
 
 class ServerInfoHandle;
@@ -120,7 +111,7 @@ class ServerInfoHandle {
   ServerInfoHandle &operator=(const ServerInfoHandle &) = delete;
   /// @}
 
-  /// Remove the file.
+  /// Remove the file on disk, if one is tracked.
   void Remove();
 
 private:
diff --git a/lldb/include/lldb/Protocol/MCP/Transport.h b/lldb/include/lldb/Protocol/MCP/Transport.h
index 47c2ccfc44dfe..55b2e8fa0a7f2 100644
--- a/lldb/include/lldb/Protocol/MCP/Transport.h
+++ b/lldb/include/lldb/Protocol/MCP/Transport.h
@@ -10,22 +10,95 @@
 #define LLDB_PROTOCOL_MCP_TRANSPORT_H
 
 #include "lldb/Host/JSONTransport.h"
+#include "lldb/Protocol/MCP/MCPError.h"
 #include "lldb/Protocol/MCP/Protocol.h"
 #include "lldb/lldb-forward.h"
 #include "llvm/ADT/FunctionExtras.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+
+namespace lldb_private {
+/// Specializations of the JSONTransport protocol functions for MCP.
+/// @{
+template <>
+inline lldb_protocol::mcp::Request
+make_request(int64_t id, llvm::StringRef method,
+             std::optional<llvm::json::Value> params) {
+  return lldb_protocol::mcp::Request{id, method.str(), params};
+}
+template <>
+inline lldb_protocol::mcp::Response
+make_response(const lldb_protocol::mcp::Request &req, llvm::Error error) {
+  lldb_protocol::mcp::Error protocol_error;
+  llvm::handleAllErrors(
+      std::move(error),
+      [&](const lldb_protocol::mcp::MCPError &err) {
+        protocol_error = err.toProtocolError();
+      },
+      [&](const llvm::ErrorInfoBase &err) {
+        protocol_error.code = lldb_protocol::mcp::MCPError::kInternalError;
+        protocol_error.message = err.message();
+      });
+
+  return lldb_protocol::mcp::Response{req.id, std::move(protocol_error)};
+}
+template <>
+inline lldb_protocol::mcp::Response
+make_response(const lldb_protocol::mcp::Request &req,
+              llvm::json::Value result) {
+  return lldb_protocol::mcp::Response{req.id, std::move(result)};
+}
+template <>
+inline lldb_protocol::mcp::Notification
+make_event(llvm::StringRef method, std::optional<llvm::json::Value> params) {
+  return lldb_protocol::mcp::Notification{method.str(), params};
+}
+template <>
+inline llvm::Expected<llvm::json::Value>
+get_result(const lldb_protocol::mcp::Response &resp) {
+  if (const lldb_protocol::mcp::Error *error =
+          std::get_if<lldb_protocol::mcp::Error>(&resp.result))
+    return llvm::make_error<lldb_protocol::mcp::MCPError>(error->message,
+                                                          error->code);
+  return std::get<llvm::json::Value>(resp.result);
+}
+template <> inline int64_t get_id(const lldb_protocol::mcp::Response &resp) {
+  return std::get<int64_t>(resp.id);
+}
+template <>
+inline llvm::StringRef get_method(const lldb_protocol::mcp::Request &req) {
+  return req.method;
+}
+template <>
+inline llvm::StringRef get_method(const lldb_protocol::mcp::Notification &evt) {
+  return evt.method;
+}
+template <>
+inline llvm::json::Value get_params(const lldb_protocol::mcp::Request &req) {
+  return req.params;
+}
+template <>
+inline llvm::json::Value
+get_params(const lldb_protocol::mcp::Notification &evt) {
+  return evt.params;
+}
+/// @}
+
+} // end namespace lldb_private
 
 namespace lldb_protocol::mcp {
 
 /// Generic transport that uses the MCP protocol.
-using MCPTransport = lldb_private::Transport<Request, Response, Notification>;
+using MCPTransport =
+    lldb_private::JSONTransport<int64_t, Request, Response, Notification>;
 
 /// Generic logging callback, to allow the MCP server / client / transport layer
 /// to be independent of the lldb log implementation.
 using LogCallback = llvm::unique_function<void(llvm::StringRef message)>;
 
 class Transport final
-    : public lldb_private::JSONRPCTransport<Request, Response, Notification> {
+    : public lldb_private::JSONRPCTransport<int64_t, Request, Response,
+                                            Notification> {
 public:
   Transport(lldb::IOObjectSP in, lldb::IOObjectSP out,
             LogCallback log_callback = {});
diff --git a/lldb/source/Host/common/JSONTransport.cpp b/lldb/source/Host/common/JSONTransport.cpp
index c4b42eafc85d3..f809ef478c8f7 100644
--- a/lldb/source/Host/common/JSONTransport.cpp
+++ b/lldb/source/Host/common/JSONTransport.cpp
@@ -30,3 +30,13 @@ void TransportUnhandledContentsError::log(llvm::raw_ostream &OS) const {
 std::error_code TransportUnhandledContentsError::convertToErrorCode() const {
   return std::make_error_code(std::errc::bad_message);
 }
+
+char InvalidParams::ID;
+
+void InvalidParams::log(llvm::raw_ostream &OS) const {
+  OS << "invalid parameters for method '" << m_method << "': '" << m_context
+     << "'";
+}
+std::error_code InvalidParams::convertToErrorCode() const {
+  return std::make_error_code(std::errc::invalid_argument);
+}
diff --git a/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp b/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
index d3af3cf25c4a1..46a7a96cc5fc0 100644
--- a/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
+++ b/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
@@ -52,11 +52,6 @@ llvm::StringRef ProtocolServerMCP::GetPluginDescriptionStatic() {
 }
 
 void ProtocolServerMCP::Extend(lldb_protocol::mcp::Server &server) const {
-  server.AddNotificationHandler("notifications/initialized",
-                                [](const lldb_protocol::mcp::Notification &) {
-                                  LLDB_LOG(GetLog(LLDBLog::Host),
-                                           "MCP initialization complete");
-                                });
   server.AddTool(
       std::make_unique<CommandTool>("command", "Run an lldb command."));
   server.AddTool(std::make_unique<DebuggerListTool>(
@@ -66,7 +61,7 @@ void ProtocolServerMCP::Extend(lldb_protocol::mcp::Server &server) const {
 
 void ProtocolServerMCP::AcceptCallback(std::unique_ptr<Socket> socket) {
   Log *log = GetLog(LLDBLog::Host);
-  std::string client_name = llvm::formatv("client_{0}", m_instances.size() + 1);
+  std::string client_name = llvm::formatv("client_{0}", m_client_count++);
   LLDB_LOG(log, "New MCP client connected: {0}", client_name);
 
   lldb::IOObjectSP io_sp = std::move(socket);
@@ -74,16 +69,9 @@ void ProtocolServerMCP::AcceptCallback(std::unique_ptr<Socket> socket) {
       io_sp, io_sp, [client_name](llvm::StringRef message) {
         LLDB_LOG(GetLog(LLDBLog::Host), "{0}: {1}", client_name, message);
       });
-  auto instance_up = std::make_unique<lldb_protocol::mcp::Server>(
-      std::string(kName), std::string(kVersion), std::move(transport_up),
-      m_loop);
-  Extend(*instance_up);
-  llvm::Error error = instance_up->Run();
-  if (error) {
-    LLDB_LOG_ERROR(log, std::move(error), "Failed to run MCP server: {0}");
-    return;
-  }
-  m_instances.push_back(std::move(instance_up));
+
+  if (auto error = m_server->Accept(m_loop, std::move(transport_up)))
+    LLDB_LOG_ERROR(log, std::move(error), "{0}:");
 }
 
 llvm::Error ProtocolServerMCP::Start(ProtocolServer::Connection connection) {
@@ -114,13 +102,20 @@ llvm::Error ProtocolServerMCP::Start(ProtocolServer::Connection connection) {
       llvm::join(m_listener->GetListeningConnectionURI(), ", ");
 
   ServerInfo info{listening_uris[0]};
-  llvm::Expected<ServerInfoHandle> handle = ServerInfo::Write(info);
-  if (!handle)
-    return handle.takeError();
+  llvm::Expected<ServerInfoHandle> server_info_handle = ServerInfo::Write(info);
+  if (!server_info_handle)
+    return server_info_handle.takeError();
+
+  m_client_count = 0;
+  m_server = std::make_unique<lldb_protocol::mcp::Server>(
+      std::string(kName), std::string(kVersion), [](StringRef message) {
+        LLDB_LOG(GetLog(LLDBLog::Host), "MCP Server: {0}", message);
+      });
+  Extend(*m_server);
 
   m_running = true;
-  m_server_info_handle = std::move(*handle);
-  m_listen_handlers = std::move(*handles);
+  m_server_info_handle = std::move(*server_info_handle);
+  m_accept_handles = std::move(*handles);
   m_loop_thread = std::thread([=] {
     llvm::set_thread_name("protocol-server.mcp");
     m_loop.Run();
@@ -145,9 +140,10 @@ llvm::Error ProtocolServerMCP::Stop() {
   if (m_loop_thread.joinable())
     m_loop_thread.join();
 
+  m_accept_handles.clear();
+
+  m_server.reset(nullptr);
   m_server_info_handle.Remove();
-  m_listen_handlers.clear();
-  m_instances.clear();
 
   return llvm::Error::success();
 }
diff --git a/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.h b/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.h
index 0251664a2acc4..d34b22e29765f 100644
--- a/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.h
+++ b/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.h
@@ -12,19 +12,23 @@
 #include "lldb/Core/ProtocolServer.h"
 #include "lldb/Host/MainLoop.h"
 #include "lldb/Host/Socket.h"
-#include "lldb/Protocol/MCP/Protocol.h"
 #include "lldb/Protocol/MCP/Server.h"
 #include <thread>
 
 namespace lldb_private::mcp {
 
 class ProtocolServerMCP : public ProtocolServer {
+
+  using ServerUP = std::unique_ptr<lldb_protocol::mcp::Server>;
+
+  using ReadHandleUP = MainLoop::ReadHandleUP;
+
 public:
   ProtocolServerMCP();
-  virtual ~ProtocolServerMCP() override;
+  ~ProtocolServerMCP() override;
 
-  virtual llvm::Error Start(ProtocolServer::Connection connection) override;
-  virtual llvm::Error Stop() override;
+  llvm::Error Start(ProtocolServer::Connection connection) override;
+  llvm::Error Stop() override;
 
   static void Initialize();
   static void Terminate();
@@ -48,16 +52,18 @@ class ProtocolServerMCP : public ProtocolServer {
 
   bool m_running = false;
 
-  lldb_protocol::mcp::ServerInfoHandle m_server_info_handle;
   lldb_private::MainLoop m_loop;
   std::thread m_loop_thread;
+  unsigned m_client_count = 0;
   std::mutex m_mutex;
 
   std::unique_ptr<Socket> m_listener;
+  std::vector<ReadHandleUP> m_accept_handles;
 
-  std::vector<MainLoopBase::ReadHandleUP> m_listen_handlers;
-  std::vector<std::unique_ptr<lldb_protocol::mcp::Server>> m_instances;
+  ServerUP m_server;
+  lldb_protocol::mcp::ServerInfoHandle m_server_info_handle;
 };
+
 } // namespace lldb_private::mcp
 
 #endif
diff --git a/lldb/source/Protocol/MCP/Server.cpp b/lldb/source/Protocol/MCP/Server.cpp
index a08874e7321af..d3c970e6b7efc 100644
--- a/lldb/source/Protocol/MCP/Server.cpp
+++ b/lldb/source/Protocol/MCP/Server.cpp
@@ -13,6 +13,7 @@
 #include "lldb/Host/JSONTransport.h"
 #include "lldb/Protocol/MCP/MCPError.h"
 #include "lldb/Protocol/MCP/Protocol.h"
+#include "lldb/Protocol/MCP/Transport.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/JSON.h"
@@ -109,48 +110,9 @@ Expected<std::vector<ServerInfo>> ServerInfo::Load() {
   return infos;
 }
 
-Server::Server(std::string name, std::string version,
-               std::unique_ptr<MCPTransport> transport_up,
-               lldb_private::MainLoop &loop)
+Server::Server(std::string name, std::string version, LogCallback log_callback)
     : m_name(std::move(name)), m_version(std::move(version)),
-      m_transport_up(std::move(transport_up)), m_loop(loop) {
-  AddRequestHandlers();
-}
-
-void Server::AddRequestHandlers() {
-  AddRequestHandler("initialize", std::bind(&Server::InitializeHandler, this,
-                                            std::placeholders::_1));
-  AddRequestHandler("tools/list", std::bind(&Server::ToolsListHandler, this,
-                                            std::placeholders::_1));
-  AddRequestHandler("tools/call", std::bind(&Server::ToolsCallHandler, this,
-                                            std::placeholders::_1));
-  AddRequestHandler("resources/list", std::bind(&Server::ResourcesListHandler,
-                                                this, std::placeholders::_1));
-  AddRequestHandler("resources/read", std::bind(&Server::ResourcesReadHandler,
-                                                this, std::placeholders::_1));
-}
-
-llvm::Expected<Response> Server::Handle(const Request &request) {
-  auto it = m_request_handlers.find(request.method);
-  if (it != m_request_handlers.end()) {
-    llvm::Expected<Response> response = it->second(request);
-    if (!response)
-      return response;
-    response->id = request.id;
-    return *response;
-  }
-
-  return llvm::make_error<MCPError>(
-      llvm::formatv("no handler for request: {0}", request.method).str());
-}
-
-void Server::Handle(const Notification &notification) {
-  auto it = m_notification_handlers.find(notification.method);
-  if (it != m_notification_handlers.end()) {
-    it->second(notification);
-    return;
-  }
-}
+      m_log_callback(std::move(log_callback)) {}
 
 void Server::AddTool(std::unique_ptr<Tool> tool) {
   if (!tool)
@@ -165,48 +127,62 @@ void Server::AddResourceProvider(
   m_resource_providers.push_back(std::move(resource_provider));
 }
 
-void Server::AddRequestHandler(llvm::StringRef method, RequestHandler handler) {
-  m_request_handlers[method] = std::move(handler);
-}
+MCPTransport::BinderUP Server::Bind(MCPTransport &transport) {
+  MCPTransport::BinderUP binder =
+      std::make_unique<MCPTransport::Binder>(transport);
+  binder->bind<InitializeResult, InitializeParams>(
+      "initialize", &Server::InitializeHandler, this);
+  binder->bind<ListToolsResult, void>("tools/list", &Server::ToolsListHandler,
+                                      this);
+  binder->bind<CallToolResult, CallToolParams>("tools/call",
+                                               &Server::ToolsCallHandler, this);
+  binder->bind<ListResourcesResult, void>("resources/list",
+                                          &Server::ResourcesListHandler, this);
+  binder->bind<ReadResourceResult, ReadResourceParams>(
+      "resources/read", &Server::ResourcesReadHandler, this);
+  binder->bind<void>("notifications/initialized",
+                     [this]() { Log("MCP initialization complete"); });
+  return binder;
+}
+
+llvm::Error Server::Accept(MainLoop &loop, MCPTransportUP transport) {
+  MCPTransport::BinderUP binder = Bind(*transport);
+  MCPTransport *transport_ptr = transport.get();
+  binder->disconnected([this, transport_ptr]() {
+    assert(m_instances.find(transport_ptr) != m_instances.end() &&
+           "Client not found in m_instances");
+    m_instances.erase(transport_ptr);
+  });
+
+  auto handle = transport->RegisterMessageHandler(loop, *binder);
+  if (!handle)
+    return handle.takeError();
 
-void Server::AddNotificationHandler(llvm::StringRef method,
-                                    NotificationHandler handler) {
-  m_notification_handlers[method] = std::move(handler);
+  m_instances[transport_ptr] =
+      Client{std::move(*handle), std::move(transport), std::move(binder)};
+  return llvm::Error::success();
 }
 
-llvm::Expected<Response> Server::InitializeHandler(const Request &request) {
-  Response response;
+Expected<InitializeResult>
+Server::InitializeHandler(const InitializeParams &request) {
   InitializeResult result;
   result.protocolVersion = mcp::kProtocolVersion;
   result.capabilities = GetCapabilities();
   result.serverInfo.name = m_name;
   result.serverInfo.version = m_version;
-  response.result = std::move(result);
-  return response;
+  return result;
 }
 
-llvm::Expected<Response> Server::ToolsListHandler(const Request &request) {
-  Response response;
-
+llvm::Expected<ListToolsResult> Server::ToolsListHandler() {
   ListToolsResult result;
   for (const auto &tool : m_tools)
     result.tools.emplace_back(tool.second->GetDefinition());
 
-  response.result = std::move(result);
-
-  return response;
+  return result;
 }
 
-llvm::Expected<Response> Server::ToolsCallHandler(const Request &request) {
-  Response response;
-
-  if (!request.params)
-    return llvm::createStringError("no tool parameters");
-  CallToolParams params;
-  json::Path::Root root("params");
-  if (!fromJSON(request.params, params, root))
-    return root.getError();
-
+llvm::Expected<CallToolResult>
+Server::ToolsCallHandler(const CallToolParams &params) {
   llvm::StringRef tool_name = params.name;
   if (tool_name.empty())
     return llvm::createStringError("no tool name");
@@ -223,125 +199,50 @@ llvm::Expected<Response> Server::ToolsCallHandler(const Request &request) {
   if (!text_result)
     return text_result.takeError();
 
-  response.result = toJSON(*text_result);
-
-  return response;
+  return text_result;
 }
 
-llvm::Expected<Response> Server::ResourcesListHandler(const Request &request) {
-  Response response;
-
+llvm::Expected<ListResourcesResult> Server::ResourcesListHandler() {
   ListResourcesResult result;
   for (std::unique_ptr<ResourceProvider> &resource_provider_up :
        m_resource_providers)
     for (const Resource &resource : resource_provider_up->GetResources())
       result.resources.push_back(resource);
 
-  response.result = std::move(result);
-
-  return response;
+  return result;
 }
 
-llvm::Expected<Response> Server::ResourcesReadHandler(const Request &request) {
-  Response response;
-
-  if (!request.params)
-    return llvm::createStringError("no resource parameters");
-
-  ReadResourceParams params;
-  json::Path::Root root("params");
-  if (!fromJSON(request.params, params, root))
-    return root.getError();
-
-  llvm::StringRef uri_str = params.uri;
+Expected<ReadResourceResult>
+Server::ResourcesReadHandler(const ReadResourceParams &params) {
+  StringRef uri_str = params.uri;
   if (uri_str.empty())
-    return llvm::createStringError("no resource uri");
+    return createStringError("no resource uri");
 
   for (std::unique_ptr<ResourceProvider> &resource_provider_up :
        m_resource_providers) {
-    llvm::Expected<ReadResourceResult> result =
+    Expected<ReadResourceResult> result =
         resource_provider_up->ReadResource(uri_str);
     if (result.errorIsA<UnsupportedURI>()) {
-      llvm::consumeError(result.takeError());
+      consumeError(result.takeError());
       continue;
     }
     if (!result)
       return result.takeError();
 
-    Response response;
-    response.result = std::move(*result);
-    return response;
+    return *result;
   }
 
   return make_error<MCPError>(
-      llvm::formatv("no resource handler for uri: {0}", uri_str).str(),
+      formatv("no resource handler for uri: {0}", uri_str).str(),
       MCPError::kResourceNotFound);
 }
 
 ServerCapabilities Server::GetCapabilities() {
   lldb_protocol::mcp::ServerCapabilities capabilities;
   capabilities.supportsToolsList = true;
+  capabilities.supportsResourcesList = true;
   // FIXME: Support sending notifications when a debugger/target are
   // added/removed.
-  capabilities.supportsResourcesList = false;
+  capabilities.supportsResourcesSubscribe = false;
   return capabilities;
 }
-
-llvm::Error Server::Run() {
-  auto handle = m_transport_up->RegisterMessageHandler(m_loop, *this);
-  if (!handle)
-    return handle.takeError();
-
-  lldb_private::Status status = m_loop.Run();
-  if (status.Fail())
-    return status.takeError();
-
-  return llvm::Error::success();
-}
-
-void Server::Received(const Request &request) {
-  auto SendResponse = [this](const Response &response) {
-    if (llvm::Error error = m_transport_up->Send(response))
-      m_transport_up->Log(llvm::toString(std::move(error)));
-  };
-
-  llvm::Expected<Response> response = Handle(request);
-  if (response)
-    return SendResponse(*response);
-
-  lldb_protocol::mcp::Error protocol_error;
-  llvm::handleAllErrors(
-      response.takeError(),
-      [&](const MCPError &err) { protocol_error = err.toProtocolError(); },
-      [&](const llvm::ErrorInfoBase &err) {
-        protocol_error.code = MCPError::kInternalError;
-        protocol_error.message = err.message();
-      });
-  Response error_response;
-  error_response.id = request.id;
-  error_response.result = std::move(protocol_error);
-  SendResponse(error_response);
-}
-
-void Server::Received(const Response &response) {
-  m_transport_up->Log("unexpected MCP message: response");
-}
-
-void Server::Received(const Notification &notification) {
-  Handle(notification);
-}
-
-void Server::OnError(llvm::Error error) {
-  m_transport_up->Log(llvm::toString(std::move(error)));
-  TerminateLoop();
-}
-
-void Server::OnClosed() {
-  m_transport_up->Log("EOF");
-  TerminateLoop();
-}
-
-void Server::TerminateLoop() {
-  m_loop.AddPendingCallback(
-      [](lldb_private::MainLoopBase &loop) { loop.RequestTermination(); });
-}
diff --git a/lldb/tools/lldb-dap/DAP.h b/lldb/tools/lldb-dap/DAP.h
index 71681fd4b51ed..0c921e5b72d74 100644
--- a/lldb/tools/lldb-dap/DAP.h
+++ b/lldb/tools/lldb-dap/DAP.h
@@ -79,10 +79,10 @@ enum DAPBroadcasterBits {
 enum class ReplMode { Variable = 0, Command, Auto };
 
 using DAPTransport =
-    lldb_private::Transport<protocol::Request, protocol::Response,
-                            protocol::Event>;
+    lldb_private::JSONTransport<protocol::Id, protocol::Request,
+                                protocol::Response, protocol::Event>;
 
-struct DAP final : private DAPTransport::MessageHandler {
+struct DAP final : public DAPTransport::MessageHandler {
   /// Path to the lldb-dap binary itself.
   static llvm::StringRef debug_adapter_path;
 
diff --git a/lldb/tools/lldb-dap/Protocol/ProtocolBase.h b/lldb/tools/lldb-dap/Protocol/ProtocolBase.h
index 0a9ef538a7398..92e41b1dbf595 100644
--- a/lldb/tools/lldb-dap/Protocol/ProtocolBase.h
+++ b/lldb/tools/lldb-dap/Protocol/ProtocolBase.h
@@ -30,6 +30,8 @@ namespace lldb_dap::protocol {
 
 // MARK: Base Protocol
 
+using Id = int64_t;
+
 /// A client or debug adapter initiated request.
 struct Request {
   /// Sequence number of the message (also known as message ID). The `seq` for
@@ -39,7 +41,7 @@ struct Request {
   /// associate requests with their corresponding responses. For protocol
   /// messages of type `request` the sequence number can be used to cancel the
   /// request.
-  int64_t seq;
+  Id seq;
 
   /// The command to execute.
   std::string command;
@@ -76,7 +78,7 @@ enum ResponseMessage : unsigned {
 /// Response for a request.
 struct Response {
   /// Sequence number of the corresponding request.
-  int64_t request_seq;
+  Id request_seq;
 
   /// The command requested.
   std::string command;
diff --git a/lldb/tools/lldb-dap/Transport.h b/lldb/tools/lldb-dap/Transport.h
index 4a9dd76c2303e..6462c155eb9af 100644
--- a/lldb/tools/lldb-dap/Transport.h
+++ b/lldb/tools/lldb-dap/Transport.h
@@ -24,9 +24,9 @@ namespace lldb_dap {
 
 /// A transport class that performs the Debug Adapter Protocol communication
 /// with the client.
-class Transport final
-    : public lldb_private::HTTPDelimitedJSONTransport<
-          protocol::Request, protocol::Response, protocol::Event> {
+class Transport final : public lldb_private::HTTPDelimitedJSONTransport<
+                            protocol::Id, protocol::Request, protocol::Response,
+                            protocol::Event> {
 public:
   Transport(llvm::StringRef client_name, lldb_dap::Log *log,
             lldb::IOObjectSP input, lldb::IOObjectSP output);
diff --git a/lldb/unittests/DAP/DAPTest.cpp b/lldb/unittests/DAP/DAPTest.cpp
index 2090fe6896d6b..4fd6cd546e6fa 100644
--- a/lldb/unittests/DAP/DAPTest.cpp
+++ b/lldb/unittests/DAP/DAPTest.cpp
@@ -9,13 +9,10 @@
 #include "DAP.h"
 #include "Protocol/ProtocolBase.h"
 #include "TestBase.h"
-#include "llvm/Testing/Support/Error.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <optional>
 
-using namespace llvm;
-using namespace lldb;
 using namespace lldb_dap;
 using namespace lldb_dap_tests;
 using namespace lldb_dap::protocol;
@@ -24,18 +21,7 @@ using namespace testing;
 class DAPTest : public TransportBase {};
 
 TEST_F(DAPTest, SendProtocolMessages) {
-  DAP dap{
-      /*log=*/nullptr,
-      /*default_repl_mode=*/ReplMode::Auto,
-      /*pre_init_commands=*/{},
-      /*no_lldbinit=*/false,
-      /*client_name=*/"test_client",
-      /*transport=*/*transport,
-      /*loop=*/loop,
-  };
-  dap.Send(Event{/*event=*/"my-event", /*body=*/std::nullopt});
-  loop.AddPendingCallback(
-      [](lldb_private::MainLoopBase &loop) { loop.RequestTermination(); });
-  EXPECT_CALL(client, Received(IsEvent("my-event", std::nullopt)));
-  ASSERT_THAT_ERROR(dap.Loop(), llvm::Succeeded());
+  dap->Send(Event{/*event=*/"my-event", /*body=*/std::nullopt});
+  EXPECT_CALL(client, Received(IsEvent("my-event")));
+  Run();
 }
diff --git a/lldb/unittests/DAP/Handler/DisconnectTest.cpp b/lldb/unittests/DAP/Handler/DisconnectTest.cpp
index c6ff1f90b01d5..88d6e9a69eca3 100644
--- a/lldb/unittests/DAP/Handler/DisconnectTest.cpp
+++ b/lldb/unittests/DAP/Handler/DisconnectTest.cpp
@@ -31,7 +31,7 @@ TEST_F(DisconnectRequestHandlerTest, DisconnectTriggersTerminated) {
   DisconnectRequestHandler handler(*dap);
   ASSERT_THAT_ERROR(handler.Run(std::nullopt), Succeeded());
   EXPECT_CALL(client, Received(IsEvent("terminated", _)));
-  RunOnce();
+  Run();
 }
 
 TEST_F(DisconnectRequestHandlerTest, DisconnectTriggersTerminateCommands) {
@@ -53,5 +53,5 @@ TEST_F(DisconnectRequestHandlerTest, DisconnectTriggersTerminateCommands) {
   EXPECT_CALL(client, Received(Output("(lldb) script print(2)\n")));
   EXPECT_CALL(client, Received(Output("Running terminateCommands:\n")));
   EXPECT_CALL(client, Received(IsEvent("terminated", _)));
-  RunOnce();
+  Run();
 }
diff --git a/lldb/unittests/DAP/TestBase.cpp b/lldb/unittests/DAP/TestBase.cpp
index ba7baf2103799..3721e09d8b699 100644
--- a/lldb/unittests/DAP/TestBase.cpp
+++ b/lldb/unittests/DAP/TestBase.cpp
@@ -32,23 +32,9 @@ using lldb_private::FileSystem;
 using lldb_private::MainLoop;
 using lldb_private::Pipe;
 
-Expected<MainLoop::ReadHandleUP>
-TestTransport::RegisterMessageHandler(MainLoop &loop, MessageHandler &handler) {
-  Expected<lldb::FileUP> dummy_file = FileSystem::Instance().Open(
-      FileSpec(FileSystem::DEV_NULL), File::eOpenOptionReadWrite);
-  if (!dummy_file)
-    return dummy_file.takeError();
-  m_dummy_file = std::move(*dummy_file);
-  lldb_private::Status status;
-  auto handle = loop.RegisterReadObject(
-      m_dummy_file, [](lldb_private::MainLoopBase &) {}, status);
-  if (status.Fail())
-    return status.takeError();
-  return handle;
-}
+void TransportBase::SetUp() {
+  std::tie(to_client, to_server) = TestDAPTransport::createPair();
 
-void DAPTestBase::SetUp() {
-  TransportBase::SetUp();
   std::error_code EC;
   log = std::make_unique<Log>("-", EC);
   dap = std::make_unique<DAP>(
@@ -57,16 +43,30 @@ void DAPTestBase::SetUp() {
       /*pre_init_commands=*/std::vector<std::string>(),
       /*no_lldbinit=*/false,
       /*client_name=*/"test_client",
-      /*transport=*/*transport, /*loop=*/loop);
+      /*transport=*/*to_client, /*loop=*/loop);
+
+  auto server_handle = to_server->RegisterMessageHandler(loop, *dap.get());
+  EXPECT_THAT_EXPECTED(server_handle, Succeeded());
+  handles[0] = std::move(*server_handle);
+
+  auto client_handle = to_client->RegisterMessageHandler(loop, client);
+  EXPECT_THAT_EXPECTED(client_handle, Succeeded());
+  handles[1] = std::move(*client_handle);
 }
 
+void TransportBase::Run() {
+  loop.AddPendingCallback(
+      [](lldb_private::MainLoopBase &loop) { loop.RequestTermination(); });
+  EXPECT_THAT_ERROR(loop.Run().takeError(), llvm::Succeeded());
+}
+
+void DAPTestBase::SetUp() { TransportBase::SetUp(); }
+
 void DAPTestBase::TearDown() {
-  if (core) {
+  if (core)
     ASSERT_THAT_ERROR(core->discard(), Succeeded());
-  }
-  if (binary) {
+  if (binary)
     ASSERT_THAT_ERROR(binary->discard(), Succeeded());
-  }
 }
 
 void DAPTestBase::SetUpTestSuite() {
diff --git a/lldb/unittests/DAP/TestBase.h b/lldb/unittests/DAP/TestBase.h
index c19eead4e37e7..aaeab3b3d2cd9 100644
--- a/lldb/unittests/DAP/TestBase.h
+++ b/lldb/unittests/DAP/TestBase.h
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "DAP.h"
+#include "DAPLog.h"
 #include "Protocol/ProtocolBase.h"
 #include "TestingSupport/Host/JSONTransportTestUtilities.h"
 #include "TestingSupport/SubsystemRAII.h"
@@ -14,66 +15,41 @@
 #include "lldb/Host/HostInfo.h"
 #include "lldb/Host/MainLoop.h"
 #include "lldb/Host/MainLoopBase.h"
-#include "lldb/lldb-forward.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/JSON.h"
-#include "llvm/Testing/Support/Error.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <memory>
+#include <optional>
+
+/// Helpers for gtest printing.
+namespace lldb_dap::protocol {
+
+inline void PrintTo(const Request &req, std::ostream *os) {
+  *os << llvm::formatv("{0}", toJSON(req)).str();
+}
+
+inline void PrintTo(const Response &resp, std::ostream *os) {
+  *os << llvm::formatv("{0}", toJSON(resp)).str();
+}
+
+inline void PrintTo(const Event &evt, std::ostream *os) {
+  *os << llvm::formatv("{0}", toJSON(evt)).str();
+}
+
+inline void PrintTo(const Message &message, std::ostream *os) {
+  return std::visit([os](auto &&message) { return PrintTo(message, os); },
+                    message);
+}
+
+} // namespace lldb_dap::protocol
 
 namespace lldb_dap_tests {
 
-class TestTransport final
-    : public lldb_private::Transport<lldb_dap::protocol::Request,
-                                     lldb_dap::protocol::Response,
-                                     lldb_dap::protocol::Event> {
-public:
-  using Message = lldb_private::Transport<lldb_dap::protocol::Request,
-                                          lldb_dap::protocol::Response,
-                                          lldb_dap::protocol::Event>::Message;
-
-  TestTransport(lldb_private::MainLoop &loop, MessageHandler &handler)
-      : m_loop(loop), m_handler(handler) {}
-
-  llvm::Error Send(const lldb_dap::protocol::Event &e) override {
-    m_loop.AddPendingCallback([this, e](lldb_private::MainLoopBase &) {
-      this->m_handler.Received(e);
-    });
-    return llvm::Error::success();
-  }
-
-  llvm::Error Send(const lldb_dap::protocol::Request &r) override {
-    m_loop.AddPendingCallback([this, r](lldb_private::MainLoopBase &) {
-      this->m_handler.Received(r);
-    });
-    return llvm::Error::success();
-  }
-
-  llvm::Error Send(const lldb_dap::protocol::Response &r) override {
-    m_loop.AddPendingCallback([this, r](lldb_private::MainLoopBase &) {
-      this->m_handler.Received(r);
-    });
-    return llvm::Error::success();
-  }
-
-  llvm::Expected<lldb_private::MainLoop::ReadHandleUP>
-  RegisterMessageHandler(lldb_private::MainLoop &loop,
-                         MessageHandler &handler) override;
-
-  void Log(llvm::StringRef message) override {
-    log_messages.emplace_back(message);
-  }
-
-  std::vector<std::string> log_messages;
-
-private:
-  lldb_private::MainLoop &m_loop;
-  MessageHandler &m_handler;
-  lldb::FileSP m_dummy_file;
-};
+using TestDAPTransport =
+    TestTransport<int64_t, lldb_dap::protocol::Request,
+                  lldb_dap::protocol::Response, lldb_dap::protocol::Event>;
 
 /// A base class for tests that need transport configured for communicating DAP
 /// messages.
@@ -82,22 +58,38 @@ class TransportBase : public testing::Test {
   lldb_private::SubsystemRAII<lldb_private::FileSystem, lldb_private::HostInfo>
       subsystems;
   lldb_private::MainLoop loop;
-  std::unique_ptr<TestTransport> transport;
-  MockMessageHandler<lldb_dap::protocol::Request, lldb_dap::protocol::Response,
-                     lldb_dap::protocol::Event>
+  lldb_private::MainLoop::ReadHandleUP handles[2];
+
+  std::unique_ptr<lldb_dap::Log> log;
+
+  std::unique_ptr<TestDAPTransport> to_client;
+  MockMessageHandler<int64_t, lldb_dap::protocol::Request,
+                     lldb_dap::protocol::Response, lldb_dap::protocol::Event>
       client;
 
-  void SetUp() override {
-    transport = std::make_unique<TestTransport>(loop, client);
-  }
+  std::unique_ptr<TestDAPTransport> to_server;
+  std::unique_ptr<lldb_dap::DAP> dap;
+
+  void SetUp() override;
+
+  void Run();
 };
 
 /// A matcher for a DAP event.
-template <typename M1, typename M2>
+template <typename EventMatcher, typename BodyMatcher>
 inline testing::Matcher<const lldb_dap::protocol::Event &>
-IsEvent(const M1 &m1, const M2 &m2) {
-  return testing::AllOf(testing::Field(&lldb_dap::protocol::Event::event, m1),
-                        testing::Field(&lldb_dap::protocol::Event::body, m2));
+IsEvent(const EventMatcher &event_matcher, const BodyMatcher &body_matcher) {
+  return testing::AllOf(
+      testing::Field(&lldb_dap::protocol::Event::event, event_matcher),
+      testing::Field(&lldb_dap::protocol::Event::body, body_matcher));
+}
+
+template <typename EventMatcher>
+inline testing::Matcher<const lldb_dap::protocol::Event &>
+IsEvent(const EventMatcher &event_matcher) {
+  return testing::AllOf(
+      testing::Field(&lldb_dap::protocol::Event::event, event_matcher),
+      testing::Field(&lldb_dap::protocol::Event::body, std::nullopt));
 }
 
 /// Matches an "output" event.
@@ -110,8 +102,6 @@ inline auto Output(llvm::StringRef o, llvm::StringRef cat = "console") {
 /// A base class for tests that interact with a `lldb_dap::DAP` instance.
 class DAPTestBase : public TransportBase {
 protected:
-  std::unique_ptr<lldb_dap::Log> log;
-  std::unique_ptr<lldb_dap::DAP> dap;
   std::optional<llvm::sys::fs::TempFile> core;
   std::optional<llvm::sys::fs::TempFile> binary;
 
@@ -126,12 +116,6 @@ class DAPTestBase : public TransportBase {
   bool GetDebuggerSupportsTarget(llvm::StringRef platform);
   void CreateDebugger();
   void LoadCore();
-
-  void RunOnce() {
-    loop.AddPendingCallback(
-        [](lldb_private::MainLoopBase &loop) { loop.RequestTermination(); });
-    ASSERT_THAT_ERROR(dap->Loop(), llvm::Succeeded());
-  }
 };
 
 } // namespace lldb_dap_tests
diff --git a/lldb/unittests/Host/JSONTransportTest.cpp b/lldb/unittests/Host/JSONTransportTest.cpp
index 445674f402252..0228e13b61909 100644
--- a/lldb/unittests/Host/JSONTransportTest.cpp
+++ b/lldb/unittests/Host/JSONTransportTest.cpp
@@ -9,6 +9,7 @@
 #include "lldb/Host/JSONTransport.h"
 #include "TestingSupport/Host/JSONTransportTestUtilities.h"
 #include "TestingSupport/Host/PipeTestUtilities.h"
+#include "TestingSupport/SubsystemRAII.h"
 #include "lldb/Host/File.h"
 #include "lldb/Host/MainLoop.h"
 #include "lldb/Host/MainLoopBase.h"
@@ -25,6 +26,7 @@
 #include <chrono>
 #include <cstddef>
 #include <memory>
+#include <optional>
 #include <string>
 
 using namespace llvm;
@@ -32,20 +34,35 @@ using namespace lldb_private;
 using testing::_;
 using testing::HasSubstr;
 using testing::InSequence;
+using testing::Ref;
+
+namespace llvm::json {
+static bool fromJSON(const Value &V, Value &T, Path P) {
+  T = V;
+  return true;
+}
+} // namespace llvm::json
 
 namespace {
 
 namespace test_protocol {
 
 struct Req {
+  int id = 0;
   std::string name;
+  std::optional<json::Value> params;
 };
-json::Value toJSON(const Req &T) { return json::Object{{"req", T.name}}; }
+json::Value toJSON(const Req &T) {
+  return json::Object{{"name", T.name}, {"id", T.id}, {"params", T.params}};
+}
 bool fromJSON(const json::Value &V, Req &T, json::Path P) {
   json::ObjectMapper O(V, P);
-  return O && O.map("req", T.name);
+  return O && O.map("name", T.name) && O.map("id", T.id) &&
+         O.map("params", T.params);
+}
+bool operator==(const Req &a, const Req &b) {
+  return a.name == b.name && a.id == b.id && a.params == b.params;
 }
-bool operator==(const Req &a, const Req &b) { return a.name == b.name; }
 inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Req &V) {
   OS << toJSON(V);
   return OS;
@@ -58,14 +75,19 @@ void PrintTo(const Req &message, std::ostream *os) {
 }
 
 struct Resp {
-  std::string name;
+  int id = 0;
+  std::optional<json::Value> result;
 };
-json::Value toJSON(const Resp &T) { return json::Object{{"resp", T.name}}; }
+json::Value toJSON(const Resp &T) {
+  return json::Object{{"id", T.id}, {"result", T.result}};
+}
 bool fromJSON(const json::Value &V, Resp &T, json::Path P) {
   json::ObjectMapper O(V, P);
-  return O && O.map("resp", T.name);
+  return O && O.map("id", T.id) && O.map("result", T.result);
+}
+bool operator==(const Resp &a, const Resp &b) {
+  return a.id == b.id && a.result == b.result;
 }
-bool operator==(const Resp &a, const Resp &b) { return a.name == b.name; }
 inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Resp &V) {
   OS << toJSON(V);
   return OS;
@@ -79,11 +101,14 @@ void PrintTo(const Resp &message, std::ostream *os) {
 
 struct Evt {
   std::string name;
+  std::optional<json::Value> params;
 };
-json::Value toJSON(const Evt &T) { return json::Object{{"evt", T.name}}; }
+json::Value toJSON(const Evt &T) {
+  return json::Object{{"name", T.name}, {"params", T.params}};
+}
 bool fromJSON(const json::Value &V, Evt &T, json::Path P) {
   json::ObjectMapper O(V, P);
-  return O && O.map("evt", T.name);
+  return O && O.map("name", T.name) && O.map("params", T.params);
 }
 bool operator==(const Evt &a, const Evt &b) { return a.name == b.name; }
 inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Evt &V) {
@@ -107,41 +132,64 @@ bool fromJSON(const json::Value &V, Message &msg, json::Path P) {
     P.report("expected object");
     return false;
   }
-  if (O->get("req")) {
-    Req R;
-    if (!fromJSON(V, R, P))
+
+  if (O->find("id") == O->end()) {
+    Evt E;
+    if (!fromJSON(V, E, P))
       return false;
 
-    msg = std::move(R);
+    msg = std::move(E);
     return true;
   }
-  if (O->get("resp")) {
-    Resp R;
+
+  if (O->get("name")) {
+    Req R;
     if (!fromJSON(V, R, P))
       return false;
 
     msg = std::move(R);
     return true;
   }
-  if (O->get("evt")) {
-    Evt E;
-    if (!fromJSON(V, E, P))
-      return false;
 
-    msg = std::move(E);
-    return true;
-  }
-  P.report("unknown message type");
-  return false;
+  Resp R;
+  if (!fromJSON(V, R, P))
+    return false;
+
+  msg = std::move(R);
+  return true;
 }
 
-} // namespace test_protocol
+struct MyFnParams {
+  int a = 0;
+  int b = 0;
+};
+json::Value toJSON(const MyFnParams &T) {
+  return json::Object{{"a", T.a}, {"b", T.b}};
+}
+bool fromJSON(const json::Value &V, MyFnParams &T, json::Path P) {
+  json::ObjectMapper O(V, P);
+  return O && O.map("a", T.a) && O.map("b", T.b);
+}
 
-template <typename T, typename Req, typename Resp, typename Evt>
-class JSONTransportTest : public PipePairTest {
+struct MyFnResult {
+  int c = 0;
+};
+json::Value toJSON(const MyFnResult &T) { return json::Object{{"c", T.c}}; }
+bool fromJSON(const json::Value &V, MyFnResult &T, json::Path P) {
+  json::ObjectMapper O(V, P);
+  return O && O.map("c", T.c);
+}
+
+using Transport = TestTransport<int, Req, Resp, Evt>;
+using MessageHandler = MockMessageHandler<int, Req, Resp, Evt>;
+
+} // namespace test_protocol
 
+template <typename T> class JSONTransportTest : public PipePairTest {
 protected:
-  MockMessageHandler<Req, Resp, Evt> message_handler;
+  SubsystemRAII<FileSystem> subsystems;
+
+  test_protocol::MessageHandler message_handler;
   std::unique_ptr<T> transport;
   MainLoop loop;
 
@@ -191,8 +239,8 @@ class JSONTransportTest : public PipePairTest {
 };
 
 class TestHTTPDelimitedJSONTransport final
-    : public HTTPDelimitedJSONTransport<test_protocol::Req, test_protocol::Resp,
-                                        test_protocol::Evt> {
+    : public HTTPDelimitedJSONTransport<
+          int, test_protocol::Req, test_protocol::Resp, test_protocol::Evt> {
 public:
   using HTTPDelimitedJSONTransport::HTTPDelimitedJSONTransport;
 
@@ -204,9 +252,7 @@ class TestHTTPDelimitedJSONTransport final
 };
 
 class HTTPDelimitedJSONTransportTest
-    : public JSONTransportTest<TestHTTPDelimitedJSONTransport,
-                               test_protocol::Req, test_protocol::Resp,
-                               test_protocol::Evt> {
+    : public JSONTransportTest<TestHTTPDelimitedJSONTransport> {
 public:
   using JSONTransportTest::JSONTransportTest;
 
@@ -222,7 +268,7 @@ class HTTPDelimitedJSONTransportTest
 };
 
 class TestJSONRPCTransport final
-    : public JSONRPCTransport<test_protocol::Req, test_protocol::Resp,
+    : public JSONRPCTransport<int, test_protocol::Req, test_protocol::Resp,
                               test_protocol::Evt> {
 public:
   using JSONRPCTransport::JSONRPCTransport;
@@ -234,9 +280,7 @@ class TestJSONRPCTransport final
   std::vector<std::string> log_messages;
 };
 
-class JSONRPCTransportTest
-    : public JSONTransportTest<TestJSONRPCTransport, test_protocol::Req,
-                               test_protocol::Resp, test_protocol::Evt> {
+class JSONRPCTransportTest : public JSONTransportTest<TestJSONRPCTransport> {
 public:
   using JSONTransportTest::JSONTransportTest;
 
@@ -248,8 +292,71 @@ class JSONRPCTransportTest
   }
 };
 
+class TestTransportBinder : public testing::Test {
+protected:
+  SubsystemRAII<FileSystem> subsystems;
+
+  std::unique_ptr<test_protocol::Transport> to_remote;
+  std::unique_ptr<test_protocol::Transport> from_remote;
+  std::unique_ptr<test_protocol::Transport::Binder> binder;
+  test_protocol::MessageHandler remote;
+  MainLoop loop;
+
+  void SetUp() override {
+    std::tie(to_remote, from_remote) = test_protocol::Transport::createPair();
+    binder = std::make_unique<test_protocol::Transport::Binder>(*to_remote);
+
+    auto binder_handle = to_remote->RegisterMessageHandler(loop, remote);
+    EXPECT_THAT_EXPECTED(binder_handle, Succeeded());
+
+    auto remote_handle = from_remote->RegisterMessageHandler(loop, *binder);
+    EXPECT_THAT_EXPECTED(remote_handle, Succeeded());
+  }
+
+  void Run() {
+    loop.AddPendingCallback([](auto &loop) { loop.RequestTermination(); });
+    EXPECT_THAT_ERROR(loop.Run().takeError(), Succeeded());
+  }
+};
+
 } // namespace
 
+namespace lldb_private {
+using namespace test_protocol;
+template <>
+inline test_protocol::Req make_request(int id, llvm::StringRef method,
+                                       std::optional<json::Value> params) {
+  return test_protocol::Req{id, method.str(), params};
+}
+template <> inline Resp make_response(const Req &req, llvm::Error error) {
+  llvm::consumeError(std::move(error));
+  return Resp{req.id, std::nullopt};
+}
+template <> inline Resp make_response(const Req &req, json::Value result) {
+  return Resp{req.id, std::move(result)};
+}
+template <>
+inline Evt make_event(llvm::StringRef method,
+                      std::optional<json::Value> params) {
+  return Evt{method.str(), params};
+}
+
+template <> inline llvm::Expected<json::Value> get_result(const Resp &resp) {
+  return resp.result;
+}
+
+template <> inline int get_id(const Resp &resp) { return resp.id; }
+template <> inline llvm::StringRef get_method(const Req &req) {
+  return req.name;
+}
+template <> inline llvm::StringRef get_method(const Evt &evt) {
+  return evt.name;
+}
+template <> inline json::Value get_params(const Req &req) { return req.params; }
+template <> inline json::Value get_params(const Evt &evt) { return evt.params; }
+
+} // namespace lldb_private
+
 // Failing on Windows, see https://github.com/llvm/llvm-project/issues/153446.
 #ifndef _WIN32
 using namespace test_protocol;
@@ -269,35 +376,47 @@ TEST_F(HTTPDelimitedJSONTransportTest, MalformedRequests) {
 }
 
 TEST_F(HTTPDelimitedJSONTransportTest, Read) {
-  Write(Req{"foo"});
-  EXPECT_CALL(message_handler, Received(Req{"foo"}));
+  Write(Req{6, "foo", std::nullopt});
+  EXPECT_CALL(message_handler, Received(Req{6, "foo", std::nullopt}));
   ASSERT_THAT_ERROR(Run(), Succeeded());
 }
 
 TEST_F(HTTPDelimitedJSONTransportTest, ReadMultipleMessagesInSingleWrite) {
   InSequence seq;
-  Write(Message{Req{"one"}}, Message{Evt{"two"}}, Message{Resp{"three"}});
-  EXPECT_CALL(message_handler, Received(Req{"one"}));
-  EXPECT_CALL(message_handler, Received(Evt{"two"}));
-  EXPECT_CALL(message_handler, Received(Resp{"three"}));
+  Write(
+      Message{
+          Req{6, "one", std::nullopt},
+      },
+      Message{
+          Evt{"two", std::nullopt},
+      },
+      Message{
+          Resp{2, std::nullopt},
+      });
+  EXPECT_CALL(message_handler, Received(Req{6, "one", std::nullopt}));
+  EXPECT_CALL(message_handler, Received(Evt{"two", std::nullopt}));
+  EXPECT_CALL(message_handler, Received(Resp{2, std::nullopt}));
   ASSERT_THAT_ERROR(Run(), Succeeded());
 }
 
 TEST_F(HTTPDelimitedJSONTransportTest, ReadAcrossMultipleChunks) {
   std::string long_str = std::string(
-      HTTPDelimitedJSONTransport<Req, Resp, Evt>::kReadBufferSize * 2, 'x');
-  Write(Req{long_str});
-  EXPECT_CALL(message_handler, Received(Req{long_str}));
+      HTTPDelimitedJSONTransport<int, test_protocol::Req, test_protocol::Resp,
+                                 test_protocol::Evt>::kReadBufferSize *
+          2,
+      'x');
+  Write(Req{5, long_str, std::nullopt});
+  EXPECT_CALL(message_handler, Received(Req{5, long_str, std::nullopt}));
   ASSERT_THAT_ERROR(Run(), Succeeded());
 }
 
 TEST_F(HTTPDelimitedJSONTransportTest, ReadPartialMessage) {
-  std::string message = Encode(Req{"foo"});
+  std::string message = Encode(Req{5, "foo", std::nullopt});
   auto split_at = message.size() / 2;
   std::string part1 = message.substr(0, split_at);
   std::string part2 = message.substr(split_at);
 
-  EXPECT_CALL(message_handler, Received(Req{"foo"}));
+  EXPECT_CALL(message_handler, Received(Req{5, "foo", std::nullopt}));
 
   ASSERT_THAT_EXPECTED(input.Write(part1.data(), part1.size()), Succeeded());
   loop.AddPendingCallback(
@@ -309,12 +428,12 @@ TEST_F(HTTPDelimitedJSONTransportTest, ReadPartialMessage) {
 }
 
 TEST_F(HTTPDelimitedJSONTransportTest, ReadWithZeroByteWrites) {
-  std::string message = Encode(Req{"foo"});
+  std::string message = Encode(Req{6, "foo", std::nullopt});
   auto split_at = message.size() / 2;
   std::string part1 = message.substr(0, split_at);
   std::string part2 = message.substr(split_at);
 
-  EXPECT_CALL(message_handler, Received(Req{"foo"}));
+  EXPECT_CALL(message_handler, Received(Req{6, "foo", std::nullopt}));
 
   ASSERT_THAT_EXPECTED(input.Write(part1.data(), part1.size()), Succeeded());
 
@@ -366,20 +485,21 @@ TEST_F(HTTPDelimitedJSONTransportTest, InvalidTransport) {
 }
 
 TEST_F(HTTPDelimitedJSONTransportTest, Write) {
-  ASSERT_THAT_ERROR(transport->Send(Req{"foo"}), Succeeded());
-  ASSERT_THAT_ERROR(transport->Send(Resp{"bar"}), Succeeded());
-  ASSERT_THAT_ERROR(transport->Send(Evt{"baz"}), Succeeded());
+  ASSERT_THAT_ERROR(transport->Send(Req{7, "foo", std::nullopt}), Succeeded());
+  ASSERT_THAT_ERROR(transport->Send(Resp{5, "bar"}), Succeeded());
+  ASSERT_THAT_ERROR(transport->Send(Evt{"baz", std::nullopt}), Succeeded());
   output.CloseWriteFileDescriptor();
   char buf[1024];
   Expected<size_t> bytes_read =
       output.Read(buf, sizeof(buf), std::chrono::milliseconds(1));
   ASSERT_THAT_EXPECTED(bytes_read, Succeeded());
-  ASSERT_EQ(StringRef(buf, *bytes_read), StringRef("Content-Length: 13\r\n\r\n"
-                                                   R"({"req":"foo"})"
-                                                   "Content-Length: 14\r\n\r\n"
-                                                   R"({"resp":"bar"})"
-                                                   "Content-Length: 13\r\n\r\n"
-                                                   R"({"evt":"baz"})"));
+  ASSERT_EQ(StringRef(buf, *bytes_read),
+            StringRef("Content-Length: 35\r\n\r\n"
+                      R"({"id":7,"name":"foo","params":null})"
+                      "Content-Length: 23\r\n\r\n"
+                      R"({"id":5,"result":"bar"})"
+                      "Content-Length: 28\r\n\r\n"
+                      R"({"name":"baz","params":null})"));
 }
 
 TEST_F(JSONRPCTransportTest, MalformedRequests) {
@@ -395,17 +515,18 @@ TEST_F(JSONRPCTransportTest, MalformedRequests) {
 }
 
 TEST_F(JSONRPCTransportTest, Read) {
-  Write(Message{Req{"foo"}});
-  EXPECT_CALL(message_handler, Received(Req{"foo"}));
+  Write(Message{Req{1, "foo", std::nullopt}});
+  EXPECT_CALL(message_handler, Received(Req{1, "foo", std::nullopt}));
   ASSERT_THAT_ERROR(Run(), Succeeded());
 }
 
 TEST_F(JSONRPCTransportTest, ReadMultipleMessagesInSingleWrite) {
   InSequence seq;
-  Write(Message{Req{"one"}}, Message{Evt{"two"}}, Message{Resp{"three"}});
-  EXPECT_CALL(message_handler, Received(Req{"one"}));
-  EXPECT_CALL(message_handler, Received(Evt{"two"}));
-  EXPECT_CALL(message_handler, Received(Resp{"three"}));
+  Write(Message{Req{1, "one", std::nullopt}}, Message{Evt{"two", std::nullopt}},
+        Message{Resp{3, "three"}});
+  EXPECT_CALL(message_handler, Received(Req{1, "one", std::nullopt}));
+  EXPECT_CALL(message_handler, Received(Evt{"two", std::nullopt}));
+  EXPECT_CALL(message_handler, Received(Resp{3, "three"}));
   ASSERT_THAT_ERROR(Run(), Succeeded());
 }
 
@@ -413,19 +534,22 @@ TEST_F(JSONRPCTransportTest, ReadAcrossMultipleChunks) {
   // Use a string longer than the chunk size to ensure we split the message
   // across the chunk boundary.
   std::string long_str =
-      std::string(JSONTransport<Req, Resp, Evt>::kReadBufferSize * 2, 'x');
-  Write(Req{long_str});
-  EXPECT_CALL(message_handler, Received(Req{long_str}));
+      std::string(IOTransport<int, test_protocol::Req, test_protocol::Resp,
+                              test_protocol::Evt>::kReadBufferSize *
+                      2,
+                  'x');
+  Write(Req{42, long_str, std::nullopt});
+  EXPECT_CALL(message_handler, Received(Req{42, long_str, std::nullopt}));
   ASSERT_THAT_ERROR(Run(), Succeeded());
 }
 
 TEST_F(JSONRPCTransportTest, ReadPartialMessage) {
-  std::string message = R"({"req": "foo"})"
+  std::string message = R"({"id":42,"name":"foo","params":null})"
                         "\n";
   std::string part1 = message.substr(0, 7);
   std::string part2 = message.substr(7);
 
-  EXPECT_CALL(message_handler, Received(Req{"foo"}));
+  EXPECT_CALL(message_handler, Received(Req{42, "foo", std::nullopt}));
 
   ASSERT_THAT_EXPECTED(input.Write(part1.data(), part1.size()), Succeeded());
   loop.AddPendingCallback(
@@ -455,20 +579,21 @@ TEST_F(JSONRPCTransportTest, ReaderWithUnhandledData) {
 }
 
 TEST_F(JSONRPCTransportTest, Write) {
-  ASSERT_THAT_ERROR(transport->Send(Req{"foo"}), Succeeded());
-  ASSERT_THAT_ERROR(transport->Send(Resp{"bar"}), Succeeded());
-  ASSERT_THAT_ERROR(transport->Send(Evt{"baz"}), Succeeded());
+  ASSERT_THAT_ERROR(transport->Send(Req{11, "foo", std::nullopt}), Succeeded());
+  ASSERT_THAT_ERROR(transport->Send(Resp{14, "bar"}), Succeeded());
+  ASSERT_THAT_ERROR(transport->Send(Evt{"baz", std::nullopt}), Succeeded());
   output.CloseWriteFileDescriptor();
   char buf[1024];
   Expected<size_t> bytes_read =
       output.Read(buf, sizeof(buf), std::chrono::milliseconds(1));
   ASSERT_THAT_EXPECTED(bytes_read, Succeeded());
-  ASSERT_EQ(StringRef(buf, *bytes_read), StringRef(R"({"req":"foo"})"
-                                                   "\n"
-                                                   R"({"resp":"bar"})"
-                                                   "\n"
-                                                   R"({"evt":"baz"})"
-                                                   "\n"));
+  ASSERT_EQ(StringRef(buf, *bytes_read),
+            StringRef(R"({"id":11,"name":"foo","params":null})"
+                      "\n"
+                      R"({"id":14,"result":"bar"})"
+                      "\n"
+                      R"({"name":"baz","params":null})"
+                      "\n"));
 }
 
 TEST_F(JSONRPCTransportTest, InvalidTransport) {
@@ -477,4 +602,59 @@ TEST_F(JSONRPCTransportTest, InvalidTransport) {
                     FailedWithMessage("IO object is not valid."));
 }
 
+// Out-bound binding request handler.
+TEST_F(TestTransportBinder, OutBoundRequests) {
+  auto addFn = binder->bind<MyFnResult, MyFnParams>("add");
+  addFn(MyFnParams{1, 2}, [](Expected<MyFnResult> result) {
+    EXPECT_THAT_EXPECTED(result, Succeeded());
+    EXPECT_EQ(result->c, 3);
+  });
+  EXPECT_CALL(remote, Received(Req{1, "add", MyFnParams{1, 2}}));
+  // Queue a reply that will be sent during 'Run'.
+  EXPECT_THAT_ERROR(from_remote->Send(Resp{1, toJSON(MyFnResult{3})}),
+                    Succeeded());
+  Run();
+}
+
+// In-bound binding request handler.
+TEST_F(TestTransportBinder, InBoundRequests) {
+  binder->bind<MyFnResult, MyFnParams>(
+      "add",
+      [](const int captured_param,
+         const MyFnParams &params) -> Expected<MyFnResult> {
+        return MyFnResult{params.a + params.b + captured_param};
+      },
+      2);
+  EXPECT_THAT_ERROR(from_remote->Send(Req{2, "add", MyFnParams{3, 4}}),
+                    Succeeded());
+  EXPECT_CALL(remote, Received(Resp{2, MyFnResult{9}}));
+  Run();
+}
+
+// Out-bound binding event handler.
+TEST_F(TestTransportBinder, OutBoundEvents) {
+  auto emitEvent = binder->bind<MyFnParams>("evt");
+  emitEvent(MyFnParams{1, 2});
+  EXPECT_CALL(remote, Received(Evt{"evt", MyFnParams{1, 2}}));
+  Run();
+}
+
+// In-bound binding event handler.
+TEST_F(TestTransportBinder, InBoundEvents) {
+  bool called = false;
+  binder->bind<MyFnParams>(
+      "evt",
+      [&](const int captured_arg, const MyFnParams &params) {
+        EXPECT_EQ(captured_arg, 42);
+        EXPECT_EQ(params.a, 3);
+        EXPECT_EQ(params.b, 4);
+        called = true;
+      },
+      42);
+  EXPECT_THAT_ERROR(from_remote->Send(Evt{"evt", MyFnParams{3, 4}}),
+                    Succeeded());
+  Run();
+  EXPECT_TRUE(called);
+}
+
 #endif
diff --git a/lldb/unittests/Protocol/ProtocolMCPServerTest.cpp b/lldb/unittests/Protocol/ProtocolMCPServerTest.cpp
index f686255c6d41d..0958af87a9402 100644
--- a/lldb/unittests/Protocol/ProtocolMCPServerTest.cpp
+++ b/lldb/unittests/Protocol/ProtocolMCPServerTest.cpp
@@ -6,9 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "ProtocolMCPTestUtilities.h"
+#include "ProtocolMCPTestUtilities.h" // IWYU pragma: keep
 #include "TestingSupport/Host/JSONTransportTestUtilities.h"
-#include "TestingSupport/Host/PipeTestUtilities.h"
 #include "TestingSupport/SubsystemRAII.h"
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/HostInfo.h"
@@ -28,20 +27,21 @@
 #include "llvm/Testing/Support/Error.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
-#include <chrono>
-#include <condition_variable>
+#include <future>
+#include <memory>
+#include <optional>
 
 using namespace llvm;
 using namespace lldb;
 using namespace lldb_private;
 using namespace lldb_protocol::mcp;
+using testing::_;
 
 namespace {
 
-class TestServer : public Server {
-public:
-  using Server::Server;
-};
+template <typename T> Response make_response(T &&result, Id id = 1) {
+  return Response{id, std::forward<T>(result)};
+}
 
 /// Test tool that returns it argument as text.
 class TestTool : public Tool {
@@ -118,175 +118,209 @@ class FailTool : public Tool {
   }
 };
 
-class ProtocolServerMCPTest : public PipePairTest {
+class TestServer : public Server {
+public:
+  using Server::Bind;
+  using Server::Server;
+};
+
+using Transport = TestTransport<int64_t, lldb_protocol::mcp::Request,
+                                lldb_protocol::mcp::Response,
+                                lldb_protocol::mcp::Notification>;
+
+class ProtocolServerMCPTest : public testing::Test {
 public:
   SubsystemRAII<FileSystem, HostInfo, Socket> subsystems;
 
-  std::unique_ptr<lldb_protocol::mcp::Transport> transport_up;
-  std::unique_ptr<TestServer> server_up;
   MainLoop loop;
-  MockMessageHandler<Request, Response, Notification> message_handler;
+  lldb_private::MainLoop::ReadHandleUP handles[2];
 
-  llvm::Error Write(llvm::StringRef message) {
-    llvm::Expected<json::Value> value = json::parse(message);
-    if (!value)
-      return value.takeError();
-    return transport_up->Write(*value);
-  }
+  std::unique_ptr<Transport> to_server;
+  Transport::BinderUP binder;
+  std::unique_ptr<TestServer> server_up;
 
-  llvm::Error Write(json::Value value) { return transport_up->Write(value); }
+  std::unique_ptr<Transport> to_client;
+  MockMessageHandler<int64_t, Request, Response, Notification> client;
 
-  /// Run the transport MainLoop and return any messages received.
-  llvm::Error
-  Run(std::chrono::milliseconds timeout = std::chrono::milliseconds(200)) {
-    loop.AddCallback([](MainLoopBase &loop) { loop.RequestTermination(); },
-                     timeout);
-    auto handle = transport_up->RegisterMessageHandler(loop, message_handler);
-    if (!handle)
-      return handle.takeError();
+  std::vector<std::string> logged_messages;
 
-    return server_up->Run();
+  /// Runs the MainLoop a single time, executing any pending callbacks.
+  void Run() {
+    loop.AddPendingCallback(
+        [](MainLoopBase &loop) { loop.RequestTermination(); });
+    EXPECT_THAT_ERROR(loop.Run().takeError(), Succeeded());
   }
 
   void SetUp() override {
-    PipePairTest::SetUp();
-
-    transport_up = std::make_unique<lldb_protocol::mcp::Transport>(
-        std::make_shared<NativeFile>(input.GetReadFileDescriptor(),
-                                     File::eOpenOptionReadOnly,
-                                     NativeFile::Unowned),
-        std::make_shared<NativeFile>(output.GetWriteFileDescriptor(),
-                                     File::eOpenOptionWriteOnly,
-                                     NativeFile::Unowned));
+    std::tie(to_client, to_server) = Transport::createPair();
 
     server_up = std::make_unique<TestServer>(
         "lldb-mcp", "0.1.0",
-        std::make_unique<lldb_protocol::mcp::Transport>(
-            std::make_shared<NativeFile>(output.GetReadFileDescriptor(),
-                                         File::eOpenOptionReadOnly,
-                                         NativeFile::Unowned),
-            std::make_shared<NativeFile>(input.GetWriteFileDescriptor(),
-                                         File::eOpenOptionWriteOnly,
-                                         NativeFile::Unowned)),
-        loop);
+        [this](StringRef msg) { logged_messages.push_back(msg.str()); });
+    binder = server_up->Bind(*to_client);
+    auto server_handle = to_server->RegisterMessageHandler(loop, *binder);
+    EXPECT_THAT_EXPECTED(server_handle, Succeeded());
+    binder->error([](llvm::Error error) {
+      llvm::errs() << formatv("Server transport error: {0}", error);
+    });
+    handles[0] = std::move(*server_handle);
+
+    auto client_handle = to_client->RegisterMessageHandler(loop, client);
+    EXPECT_THAT_EXPECTED(client_handle, Succeeded());
+    handles[1] = std::move(*client_handle);
+  }
+
+  template <typename Result, typename Params>
+  Expected<json::Value> Call(StringRef method, const Params &params) {
+    std::promise<Response> promised_result;
+    Request req = make_request<int64_t, lldb_protocol::mcp::Request>(
+        /*id=*/1, method, toJSON(params));
+    EXPECT_THAT_ERROR(to_server->Send(req), Succeeded());
+    EXPECT_CALL(client, Received(testing::An<const Response &>()))
+        .WillOnce(
+            [&](const Response &resp) { promised_result.set_value(resp); });
+    Run();
+    Response resp = promised_result.get_future().get();
+    return toJSON(resp);
+  }
+
+  template <typename Result>
+  Expected<json::Value>
+  Capture(llvm::unique_function<void(Reply<Result>)> &fn) {
+    std::promise<llvm::Expected<Result>> promised_result;
+    fn([&promised_result](llvm::Expected<Result> result) {
+      promised_result.set_value(std::move(result));
+    });
+    Run();
+    llvm::Expected<Result> result = promised_result.get_future().get();
+    if (!result)
+      return result.takeError();
+    return toJSON(*result);
+  }
+
+  template <typename Result, typename Params>
+  Expected<json::Value>
+  Capture(llvm::unique_function<void(const Params &, Reply<Result>)> &fn,
+          const Params &params) {
+    std::promise<llvm::Expected<Result>> promised_result;
+    fn(params, [&promised_result](llvm::Expected<Result> result) {
+      promised_result.set_value(std::move(result));
+    });
+    Run();
+    llvm::Expected<Result> result = promised_result.get_future().get();
+    if (!result)
+      return result.takeError();
+    return toJSON(*result);
   }
 };
 
 template <typename T>
-Request make_request(StringLiteral method, T &&params, Id id = 1) {
-  return Request{id, method.str(), toJSON(std::forward<T>(params))};
-}
-
-template <typename T> Response make_response(T &&result, Id id = 1) {
-  return Response{id, std::forward<T>(result)};
+inline testing::internal::EqMatcher<llvm::json::Value> HasJSON(T x) {
+  return testing::internal::EqMatcher<llvm::json::Value>(toJSON(x));
 }
 
 } // namespace
 
 TEST_F(ProtocolServerMCPTest, Initialization) {
-  Request request = make_request(
-      "initialize", InitializeParams{/*protocolVersion=*/"2024-11-05",
-                                     /*capabilities=*/{},
-                                     /*clientInfo=*/{"lldb-unit", "0.1.0"}});
-  Response response = make_response(
-      InitializeResult{/*protocolVersion=*/"2024-11-05",
-                       /*capabilities=*/{/*supportsToolsList=*/true},
-                       /*serverInfo=*/{"lldb-mcp", "0.1.0"}});
-
-  ASSERT_THAT_ERROR(Write(request), Succeeded());
-  EXPECT_CALL(message_handler, Received(response));
-  EXPECT_THAT_ERROR(Run(), Succeeded());
+  EXPECT_THAT_EXPECTED(
+      (Call<InitializeResult, InitializeParams>(
+          "initialize",
+          InitializeParams{/*protocolVersion=*/"2024-11-05",
+                           /*capabilities=*/{},
+                           /*clientInfo=*/{"lldb-unit", "0.1.0"}})),
+      HasValue(make_response(
+          InitializeResult{/*protocolVersion=*/"2024-11-05",
+                           /*capabilities=*/
+                           {
+                               /*supportsToolsList=*/true,
+                               /*supportsResourcesList=*/true,
+                           },
+                           /*serverInfo=*/{"lldb-mcp", "0.1.0"}})));
 }
 
 TEST_F(ProtocolServerMCPTest, ToolsList) {
   server_up->AddTool(std::make_unique<TestTool>("test", "test tool"));
 
-  Request request = make_request("tools/list", Void{}, /*id=*/"one");
-
   ToolDefinition test_tool;
   test_tool.name = "test";
   test_tool.description = "test tool";
   test_tool.inputSchema = json::Object{{"type", "object"}};
 
-  Response response = make_response(ListToolsResult{{test_tool}}, /*id=*/"one");
-
-  ASSERT_THAT_ERROR(Write(request), llvm::Succeeded());
-  EXPECT_CALL(message_handler, Received(response));
-  EXPECT_THAT_ERROR(Run(), Succeeded());
+  EXPECT_THAT_EXPECTED(Call<ListToolsResult>("tools/list", Void{}),
+                       HasValue(make_response(ListToolsResult{{test_tool}})));
 }
 
 TEST_F(ProtocolServerMCPTest, ResourcesList) {
   server_up->AddResourceProvider(std::make_unique<TestResourceProvider>());
 
-  Request request = make_request("resources/list", Void{});
-  Response response = make_response(ListResourcesResult{
-      {{/*uri=*/"lldb://foo/bar", /*name=*/"name",
-        /*description=*/"description", /*mimeType=*/"application/json"}}});
-
-  ASSERT_THAT_ERROR(Write(request), llvm::Succeeded());
-  EXPECT_CALL(message_handler, Received(response));
-  EXPECT_THAT_ERROR(Run(), Succeeded());
+  EXPECT_THAT_EXPECTED(Call<ListResourcesResult>("resources/list", Void{}),
+                       HasValue(make_response(ListResourcesResult{{
+                           {
+                               /*uri=*/"lldb://foo/bar",
+                               /*name=*/"name",
+                               /*description=*/"description",
+                               /*mimeType=*/"application/json",
+                           },
+                       }})));
 }
 
 TEST_F(ProtocolServerMCPTest, ToolsCall) {
   server_up->AddTool(std::make_unique<TestTool>("test", "test tool"));
 
-  Request request = make_request(
-      "tools/call", CallToolParams{/*name=*/"test", /*arguments=*/json::Object{
-                                       {"arguments", "foo"},
-                                       {"debugger_id", 0},
-                                   }});
-  Response response = make_response(CallToolResult{{{/*text=*/"foo"}}});
-
-  ASSERT_THAT_ERROR(Write(request), llvm::Succeeded());
-  EXPECT_CALL(message_handler, Received(response));
-  EXPECT_THAT_ERROR(Run(), Succeeded());
+  EXPECT_THAT_EXPECTED(
+      (Call<CallToolResult, CallToolParams>("tools/call",
+                                            CallToolParams{
+                                                /*name=*/"test",
+                                                /*arguments=*/
+                                                json::Object{
+                                                    {"arguments", "foo"},
+                                                    {"debugger_id", 0},
+                                                },
+                                            })),
+      HasValue(make_response(CallToolResult{{{/*text=*/"foo"}}})));
 }
 
 TEST_F(ProtocolServerMCPTest, ToolsCallError) {
   server_up->AddTool(std::make_unique<ErrorTool>("error", "error tool"));
 
-  Request request = make_request(
-      "tools/call", CallToolParams{/*name=*/"error", /*arguments=*/json::Object{
-                                       {"arguments", "foo"},
-                                       {"debugger_id", 0},
-                                   }});
-  Response response =
-      make_response(lldb_protocol::mcp::Error{eErrorCodeInternalError,
-                                              /*message=*/"error"});
-
-  ASSERT_THAT_ERROR(Write(request), llvm::Succeeded());
-  EXPECT_CALL(message_handler, Received(response));
-  EXPECT_THAT_ERROR(Run(), Succeeded());
+  EXPECT_THAT_EXPECTED((Call<CallToolResult, CallToolParams>(
+                           "tools/call", CallToolParams{
+                                             /*name=*/"error",
+                                             /*arguments=*/
+                                             json::Object{
+                                                 {"arguments", "foo"},
+                                                 {"debugger_id", 0},
+                                             },
+                                         })),
+                       HasValue(make_response(lldb_protocol::mcp::Error{
+                           eErrorCodeInternalError, "error"})));
 }
 
 TEST_F(ProtocolServerMCPTest, ToolsCallFail) {
   server_up->AddTool(std::make_unique<FailTool>("fail", "fail tool"));
 
-  Request request = make_request(
-      "tools/call", CallToolParams{/*name=*/"fail", /*arguments=*/json::Object{
-                                       {"arguments", "foo"},
-                                       {"debugger_id", 0},
-                                   }});
-  Response response =
-      make_response(CallToolResult{{{/*text=*/"failed"}}, /*isError=*/true});
-
-  ASSERT_THAT_ERROR(Write(request), llvm::Succeeded());
-  EXPECT_CALL(message_handler, Received(response));
-  EXPECT_THAT_ERROR(Run(), Succeeded());
+  EXPECT_THAT_EXPECTED((Call<CallToolResult, CallToolParams>(
+                           "tools/call", CallToolParams{
+                                             /*name=*/"fail",
+                                             /*arguments=*/
+                                             json::Object{
+                                                 {"arguments", "foo"},
+                                                 {"debugger_id", 0},
+                                             },
+                                         })),
+                       HasValue(make_response(CallToolResult{
+                           {{/*text=*/"failed"}},
+                           /*isError=*/true,
+                       })));
 }
 
 TEST_F(ProtocolServerMCPTest, NotificationInitialized) {
-  bool handler_called = false;
-  std::condition_variable cv;
-
-  server_up->AddNotificationHandler(
-      "notifications/initialized",
-      [&](const Notification &notification) { handler_called = true; });
-  llvm::StringLiteral request =
-      R"json({"method":"notifications/initialized","jsonrpc":"2.0"})json";
-
-  ASSERT_THAT_ERROR(Write(request), llvm::Succeeded());
-  EXPECT_THAT_ERROR(Run(), Succeeded());
-  EXPECT_TRUE(handler_called);
+  EXPECT_THAT_ERROR(to_server->Send(lldb_protocol::mcp::Notification{
+                        "notifications/initialized",
+                        std::nullopt,
+                    }),
+                    Succeeded());
+  Run();
+  EXPECT_THAT(logged_messages,
+              testing::Contains("MCP initialization complete"));
 }
diff --git a/lldb/unittests/TestingSupport/Host/JSONTransportTestUtilities.h b/lldb/unittests/TestingSupport/Host/JSONTransportTestUtilities.h
index 5a9eb8e59f2b6..4dbcd614e400b 100644
--- a/lldb/unittests/TestingSupport/Host/JSONTransportTestUtilities.h
+++ b/lldb/unittests/TestingSupport/Host/JSONTransportTestUtilities.h
@@ -6,19 +6,105 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLDB_UNITTESTS_TESTINGSUPPORT_HOST_NATIVEPROCESSTESTUTILS_H
-#define LLDB_UNITTESTS_TESTINGSUPPORT_HOST_NATIVEPROCESSTESTUTILS_H
+#ifndef LLDB_UNITTESTS_TESTINGSUPPORT_HOST_JSONTRANSPORTTESTUTILITIES_H
+#define LLDB_UNITTESTS_TESTINGSUPPORT_HOST_JSONTRANSPORTTESTUTILITIES_H
 
+#include "lldb/Host/FileSystem.h"
 #include "lldb/Host/JSONTransport.h"
+#include "lldb/Host/MainLoop.h"
+#include "lldb/Utility/FileSpec.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Testing/Support/Error.h"
 #include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include <cstddef>
+#include <memory>
+#include <utility>
 
-template <typename Req, typename Resp, typename Evt>
+template <typename Id, typename Req, typename Resp, typename Evt>
+class TestTransport final
+    : public lldb_private::JSONTransport<Id, Req, Resp, Evt> {
+public:
+  using MessageHandler =
+      typename lldb_private::JSONTransport<Id, Req, Resp, Evt>::MessageHandler;
+
+  static std::pair<std::unique_ptr<TestTransport<Id, Req, Resp, Evt>>,
+                   std::unique_ptr<TestTransport<Id, Req, Resp, Evt>>>
+  createPair() {
+    std::unique_ptr<TestTransport<Id, Req, Resp, Evt>> transports[2] = {
+        std::make_unique<TestTransport<Id, Req, Resp, Evt>>(),
+        std::make_unique<TestTransport<Id, Req, Resp, Evt>>()};
+    return std::make_pair(std::move(transports[0]), std::move(transports[1]));
+  }
+
+  explicit TestTransport() {
+    llvm::Expected<lldb::FileUP> dummy_file =
+        lldb_private::FileSystem::Instance().Open(
+            lldb_private::FileSpec(lldb_private::FileSystem::DEV_NULL),
+            lldb_private::File::eOpenOptionReadWrite);
+    EXPECT_THAT_EXPECTED(dummy_file, llvm::Succeeded());
+    m_dummy_file = std::move(*dummy_file);
+  }
+
+  llvm::Error Send(const Evt &evt) override {
+    EXPECT_TRUE(m_loop && m_handler)
+        << "Send called before RegisterMessageHandler";
+    m_loop->AddPendingCallback([this, evt](lldb_private::MainLoopBase &) {
+      m_handler->Received(evt);
+    });
+    return llvm::Error::success();
+  }
+
+  llvm::Error Send(const Req &req) override {
+    EXPECT_TRUE(m_loop && m_handler)
+        << "Send called before RegisterMessageHandler";
+    m_loop->AddPendingCallback([this, req](lldb_private::MainLoopBase &) {
+      m_handler->Received(req);
+    });
+    return llvm::Error::success();
+  }
+
+  llvm::Error Send(const Resp &resp) override {
+    EXPECT_TRUE(m_loop && m_handler)
+        << "Send called before RegisterMessageHandler";
+    m_loop->AddPendingCallback([this, resp](lldb_private::MainLoopBase &) {
+      m_handler->Received(resp);
+    });
+    return llvm::Error::success();
+  }
+
+  llvm::Expected<lldb_private::MainLoop::ReadHandleUP>
+  RegisterMessageHandler(lldb_private::MainLoop &loop,
+                         MessageHandler &handler) override {
+    if (!m_loop)
+      m_loop = &loop;
+    if (!m_handler)
+      m_handler = &handler;
+    lldb_private::Status status;
+    auto handle = loop.RegisterReadObject(
+        m_dummy_file, [](lldb_private::MainLoopBase &) {}, status);
+    if (status.Fail())
+      return status.takeError();
+    return handle;
+  }
+
+protected:
+  void Log(llvm::StringRef message) override {};
+
+private:
+  lldb_private::MainLoop *m_loop = nullptr;
+  MessageHandler *m_handler = nullptr;
+  // Dummy file for registering with the MainLoop.
+  lldb::FileSP m_dummy_file = nullptr;
+};
+
+template <typename Id, typename Req, typename Resp, typename Evt>
 class MockMessageHandler final
-    : public lldb_private::Transport<Req, Resp, Evt>::MessageHandler {
+    : public lldb_private::JSONTransport<Id, Req, Resp, Evt>::MessageHandler {
 public:
-  MOCK_METHOD(void, Received, (const Evt &), (override));
   MOCK_METHOD(void, Received, (const Req &), (override));
   MOCK_METHOD(void, Received, (const Resp &), (override));
+  MOCK_METHOD(void, Received, (const Evt &), (override));
   MOCK_METHOD(void, OnError, (llvm::Error), (override));
   MOCK_METHOD(void, OnClosed, (), (override));
 };



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