[Mlir-commits] [mlir] [mlir-lsp] Abstract input and output of the `JSONTransport` (PR #129320)

[River Riddle]

================
@@ -43,14 +43,86 @@ enum JSONStreamStyle {
   Delimited
 };
 
+/// An abstract class used by the JSONTransport to read JSON message.
+class JSONTransportInput {
+public:
+  explicit JSONTransportInput(JSONStreamStyle style = JSONStreamStyle::Standard)
+      : style(style) {}
+  virtual ~JSONTransportInput() = default;
+
+  virtual bool getError() const = 0;
+  virtual bool isEndOfInput() const = 0;
+
+  /// Read in a message from the input stream.
+  virtual LogicalResult readMessage(std::string &json) {
+    return style == JSONStreamStyle::Delimited ? readDelimitedMessage(json)
+                                               : readStandardMessage(json);
+  }
+  virtual LogicalResult readDelimitedMessage(std::string &json) = 0;
+  virtual LogicalResult readStandardMessage(std::string &json) = 0;
+
+private:
+  /// The JSON stream style to use.
+  JSONStreamStyle style;
+};
+
+/// An abstract class used by the JSONTransport to write JSON messages.
+class JSONTransportOutput {
+public:
+  explicit JSONTransportOutput() = default;
+  virtual ~JSONTransportOutput() = default;
+
+  virtual void sendMessage(const llvm::json::Value &msg) = 0;
+};
+
+/// Concrete implementation of the JSONTransportInput that reads from a file.
+class JSONTransportInputOverFile : public JSONTransportInput {
+public:
+  explicit JSONTransportInputOverFile(
+      std::FILE *in, JSONStreamStyle style = JSONStreamStyle::Standard)
+      : JSONTransportInput(style), in(in) {}
+
+  bool getError() const final { return ferror(in); }
+  bool isEndOfInput() const final { return feof(in); }
+
+  LogicalResult readDelimitedMessage(std::string &json) final;
+  LogicalResult readStandardMessage(std::string &json) final;
+
+private:
+  std::FILE *in;
+};
+
+/// Concrete implementation of the JSONTransportOutput that writes to a stream.
+class JSONTransportOutputOverStream : public JSONTransportOutput {
----------------
River707 wrote:

With these kinds of things I'd really prefer to avoid abstracting until we need to. Most of the time it ends up not being necessary. For example, why would you need/want colors for a transport class? You generally aren't observing the data being transferred outside of logging/testing (or shouldn't be at least). 

https://github.com/llvm/llvm-project/pull/129320