[lldb][lldb-vscode] Pretty print JSON to log files

[DavidSpickett]

Summary

This makes anlysing test failures much more easy.

For SendJSON this is simple, just use llvm::format instead.

For GetNextObject/ReadJSON it's a bit more tricky.

• Print the "Content-Length:" line in ReadJSON, but not the json.
• Back in GetNextObject, if the JSON doesn't parse, it'll be printed as a normal string along with an error message.
• If we didn't error before, we have a JSON value so we pretty print it.
• Finally, if it isn't an object we'll log an error for that, not including the JSON.

Before:

<--
Content-Length: 81

{"command":"disconnect","request_seq":5,"seq":0,"success":true,"type":"response"}

After:

<--
Content-Length: 81

{
  "command": "disconnect",
  "request_seq": 5,
  "seq": 0,
  "success": true,
  "type": "response"
}

There appear to be some responses that include strings that are themselves JSON,
and this won't pretty print those but I think it's still worth doing.

[DavidSpickett]

The one disadvantage here is that pretty printing adds more characters, so before you could copy paste the single JSON line and (I presume) it would have the same number of characters.

If that's a required use case then instead I can do the printing in the testing wrapper in lldb, by just going line by line and anything beginning with {, attempt to parse as JSON. I just figured that this formatting may be useful outside of the lldb context.

[wallace]

nice improvement for sure

lldb/tools/lldb-vscode/VSCode.cpp

 // Send the JSON in "json_str" to the "out" stream. Correctly send the
 // "Content-Length:" field followed by the length, followed by the raw
 // JSON bytes.
 void VSCode::SendJSON(const std::string &json_str) {
   output.write_full("Content-Length: ");
   output.write_full(llvm::utostr(json_str.size()));
   output.write_full("\r\n\r\n");
   output.write_full(json_str);
-
-  if (log) {
-    *log << "<-- " << std::endl
-         << "Content-Length: " << json_str.size() << "\r\n\r\n"
-         << json_str << std::endl;
-  }
 }
 
 // Serialize the JSON value into a string and send the JSON packet to
 // the "out" stream.
 void VSCode::SendJSON(const llvm::json::Value &json) {
   std::string s;
   llvm::raw_string_ostream strm(s);
   strm << json;
   static std::mutex mutex;
   std::lock_guard<std::mutex> locker(mutex);
-  SendJSON(strm.str());
+  std::string json_str = strm.str();
+  SendJSON(json_str);
+
+  if (log) {
+    *log << "<-- " << std::endl
+         << "Content-Length: " << json_str.size() << "\r\n\r\n"
+         << llvm::formatv("{0:2}", json).str() << std::endl;
+  }
 }
 
 // Read a JSON packet from the "in" stream.
 std::string VSCode::ReadJSON() {
   std::string length_str;
   std::string json_str;
   int length;
 
   if (!input.read_expected(log.get(), "Content-Length: "))
     return json_str;
 
   if (!input.read_line(log.get(), length_str))
     return json_str;
 
   if (!llvm::to_integer(length_str, length))
     return json_str;
 
   if (!input.read_expected(log.get(), "\r\n"))
     return json_str;
 
   if (!input.read_full(log.get(), length, json_str))
     return json_str;
 
-  if (log) {
-    *log << "--> " << std::endl
-         << "Content-Length: " << length << "\r\n\r\n"
-         << json_str << std::endl;
-  }
+  if (log)
+    *log << "--> " << std::endl << "Content-Length: " << length << "\r\n\r\n";
 
   return json_str;
 }
 
 // "OutputEvent": {
 //   "allOf": [ { "$ref": "#/definitions/Event" }, {
 //     "type": "object",
 //     "description": "Event message for 'output' event type. The event
if (log) {
       llvm::raw_string_ostream strm(error_str);
       strm << error;
       strm.flush();
       *log << "error: failed to parse JSON: " << error_str << std::endl
            << json << std::endl;
     }
     return PacketStatus::JSONMalformed;
   }
+
+  if (log) {
+    *log << llvm::formatv("{0:2}", *json_value).str() << std::endl;
+  }
+
   llvm::json::Object *object_ptr = json_value->getAsObject();
   if (!object_ptr) {
     if (log)
       *log << "error: json packet isn't a object" << std::endl;
     return PacketStatus::JSONNotObject;
   }
   object = *object_ptr;
   return PacketStatus::Success;