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Transport options

LspCpp supports several ways to move JSON-RPC messages between client and server.

stdio (recommended for editors)

The standard LSP transport: the editor launches your server as a subprocess and communicates over stdin/stdout. stderr is free for logging.

lsp::LanguageSession server;
server.startStdio();  // equivalent to start(make_stdin_stream(), make_stdout_stream())

Or with explicit streams:

server.start(lsp::make_stdin_stream(), lsp::make_stdout_stream());

Messages use the LSP content-length header framing defined by the protocol. LspCpp handles framing, parsing, and serialization automatically.

Custom in-memory streams (testing)

For unit tests, use feedable input and capturing output streams. See tests/test_helpers.h for FeedableIStream and StringOStream:

auto input = std::make_shared<test::FeedableIStream>();
auto output = std::make_shared<test::StringOStream>();
server.start(input, output);

input->append(test::MakeLspFrame(R"({"jsonrpc":"2.0","id":1,"method":"initialize","params":{}})"));
// inspect output->snapshot()

TCP

For remote or multi-client scenarios, use TcpServer from LibLsp/JsonRpc/TcpServer.h. See examples/TcpServerExample.cpp:

#include "LibLsp/JsonRpc/TcpServer.h"

lsp::TcpServer server("127.0.0.1", "9333", protocol_json_handler, endpoint, log);
server.point.registerHandler(/* ... */);
server.run();  // blocks until stop() is called

The example listens on 127.0.0.1:9333 by default and runs server.run() on a background thread so the test client can connect in the same process.

Build with the default configuration; TCP support is always included.

WebSocket

WebSocket transport is built when LSPCPP_BUILD_WEBSOCKETS=ON (the default). See examples/WebsocketExample.cpp.

WebSocket support depends on the bundled IXWebSocket library (or a system/vcpkg copy when USE_EXTERNAL_IXWEBSOCKET=ON).

Disable WebSocket support to reduce dependencies:

cmake -DLSPCPP_BUILD_WEBSOCKETS=OFF ..

JSON stream styles

LanguageSession and RemoteEndPoint accept a JSONStreamStyle parameter:

lsp::LanguageSession server(lsp::JSONStreamStyle::Standard);

Use Standard for normal LSP content-length framing. Other styles exist for legacy or test scenarios; most users should keep the default.

Worker threads

Both LanguageSession and RemoteEndPoint accept a max_workers parameter (default 2) controlling how many threads process incoming messages concurrently. Increase this if handlers are CPU-bound and independent; keep it low if handlers share mutable state without synchronization.

Choosing a transport

Transport Best for
stdio Editor integration (VS Code, Neovim, etc.)
TCP Custom clients, debugging with netcat, remote development
WebSocket Browser-based editors, web IDEs
Custom streams Automated tests, embedding in another process

For production editor plugins, stdio is almost always the right choice.