[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:

That's not the goal of the output stream abstraction, implementations of raw_ostream describe the capabilities of the stream, it's up to the user to decide which capabilities it wants to take advantage of. That is an example of a good abstraction, because it's reusable across different use-cases and domains. Consider, for example, if we needed to provide an output abstraction for file output for everything that may write to a file. Consider the ease of use today for raw_ostream, if an implementation already exists for your output type (which is the case most often) you have nothing else to do to take advantage of the API.

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