go-lsp-bridge documentation

A pure-Go (no cgo) bridge that relays JSON-RPC LSP traffic between a WebSocket and a language-server subprocess's stdio. The module path is github.com/go-lsp-bridge/lspbridge.

It owns the Content-Length framing on the stdio side so each WebSocket text frame carries one bare JSON object — exactly what browser LSP clients such as codemirror-languageserver and @open-rpc/codemirror-lsp expect. A web editor gets real completions, hovers, diagnostics and go-to-definition from an actual language server (texlab, gopls, pyright, typescript-language-server, rust-analyzer, …) behind a single HTTP handler.

The only dependency is github.com/coder/websocket.

Status: complete and released

HandleWS relays JSON-RPC in both directions with correct Content-Length framing; DefaultServers() ships launchers for latex / go / python / typescript / javascript / rust with neutral LSPBRIDGE_* env overrides; WithSubject drives the per-user concurrency cap; AvailableLanguages() reports resolvable servers; EncodeError surfaces setup failures. Validated by a hermetic WS → subprocess → WS round-trip against the bundled cmd/fake-lsp stub at 100% coverage including error branches, gofmt + go vet clean, CI green across the six 64-bit Go targets.

The wire shape

server → client : one JSON-RPC object per WS text frame
client → server : one JSON-RPC object per WS text frame

The bridge is the only party that touches the stdio framing. On the way in it prepends Content-Length: <n>\r\n\r\n to each WS payload before writing it to the server's stdin; on the way out it parses that header off the server's stdout and forwards the bare body as a single WS text frame. The editor and the language server never see each other's transport.

A bridge, not a client

go-lsp-bridge transports JSON-RPC untouched — it never parses or rewrites the LSP messages themselves, only the transport framing. That keeps it protocol -version agnostic: as the LSP spec and individual servers evolve, the bridge needs no changes.

Quick taste

http.HandleFunc("/lsp/", func(w http.ResponseWriter, r *http.Request) {
    lang := r.PathValue("lang")
    r = r.WithContext(lspbridge.WithSubject(r.Context(), subjectOf(r)))
    lspbridge.HandleWS(w, r, lang, slog.Default(), acceptOpts)
})

See Wiring the bridge for the full handler, and Server registry & configuration for choosing and overriding language servers.

Install

go get github.com/go-lsp-bridge/lspbridge

License

BSD-3-Clause. Copyright the go-lsp-bridge/lspbridge authors.