| 1 | // Package lsp is a minimal Language Server Protocol client: it spawns a language |
| 2 | // server per language on demand, syncs queried documents from disk, and adapts a |
| 3 | // few read-only capabilities (definition, references, hover, diagnostics) to the |
| 4 | // tool.Tool interface. Servers are not bundled — they resolve on PATH and a clear |
| 5 | // install hint is returned when one is missing. |
| 6 | package lsp |
| 7 | |
| 8 | import ( |
| 9 | "bufio" |
| 10 | "context" |
| 11 | "encoding/json" |
| 12 | "fmt" |
| 13 | "io" |
| 14 | "strconv" |
| 15 | "strings" |
| 16 | "sync" |
| 17 | ) |
| 18 | |
| 19 | type rpcError struct { |
| 20 | Code int `json:"code"` |
| 21 | Message string `json:"message"` |
| 22 | } |
| 23 | |
| 24 | func (e *rpcError) Error() string { return fmt.Sprintf("lsp error %d: %s", e.Code, e.Message) } |
| 25 | |
| 26 | type outMsg struct { |
| 27 | JSONRPC string `json:"jsonrpc"` |
| 28 | ID *int64 `json:"id,omitempty"` |
| 29 | Method string `json:"method,omitempty"` |
| 30 | Params any `json:"params,omitempty"` |
| 31 | Result any `json:"result,omitempty"` |
| 32 | } |
| 33 | |
| 34 | type inMsg struct { |
| 35 | ID *int64 `json:"id"` |
| 36 | Method string `json:"method"` |
| 37 | Result json.RawMessage `json:"result"` |
| 38 | Error *rpcError `json:"error"` |
| 39 | Params json.RawMessage `json:"params"` |
| 40 | } |
| 41 | |
| 42 | // conn speaks LSP framing (Content-Length headers) over a subprocess's |
| 43 | // stdin/stdout. A single read-pump goroutine demultiplexes the stream: |
| 44 | // id-bearing responses wake the matching call; method-only messages are |
| 45 | // notifications (diagnostics); id+method messages are server→client requests |
| 46 | // that must be answered or some servers stall during initialize. |
| 47 | type conn struct { |
| 48 | w io.Writer |
| 49 | writeMu sync.Mutex |
| 50 | |
| 51 | mu sync.Mutex |
| 52 | nextID int64 |
| 53 | pending map[int64]chan inMsg |
| 54 | |
| 55 | onNotify func(method string, params json.RawMessage) |
| 56 | onRequest func(id int64, method string, params json.RawMessage) |
| 57 | |
| 58 | closeOnce sync.Once |
| 59 | closed chan struct{} |
| 60 | err error |
| 61 | } |
| 62 | |
| 63 | func newConn(w io.Writer, r io.Reader, |
| 64 | onNotify func(string, json.RawMessage), |
| 65 | onRequest func(int64, string, json.RawMessage)) *conn { |
| 66 | c := &conn{ |
| 67 | w: w, |
| 68 | pending: map[int64]chan inMsg{}, |
| 69 | onNotify: onNotify, |
| 70 | onRequest: onRequest, |
| 71 | closed: make(chan struct{}), |
| 72 | } |
| 73 | go c.readLoop(r) |
| 74 | return c |
| 75 | } |
| 76 | |
| 77 | func (c *conn) call(ctx context.Context, method string, params any) (json.RawMessage, error) { |
| 78 | c.mu.Lock() |
| 79 | c.nextID++ |
| 80 | id := c.nextID |
| 81 | ch := make(chan inMsg, 1) |
| 82 | c.pending[id] = ch |
| 83 | c.mu.Unlock() |
| 84 | defer func() { |
| 85 | c.mu.Lock() |
| 86 | delete(c.pending, id) |
| 87 | c.mu.Unlock() |
| 88 | }() |
| 89 | |
| 90 | if err := c.writeMsg(outMsg{JSONRPC: "2.0", ID: &id, Method: method, Params: params}); err != nil { |
| 91 | return nil, err |
| 92 | } |
| 93 | select { |
| 94 | case <-ctx.Done(): |
| 95 | return nil, ctx.Err() |
| 96 | case <-c.closed: |
| 97 | return nil, c.err |
| 98 | case m := <-ch: |
| 99 | if m.Error != nil { |
| 100 | return nil, m.Error |
| 101 | } |
| 102 | return m.Result, nil |
| 103 | } |
| 104 | } |
| 105 | |
| 106 | func (c *conn) notify(method string, params any) error { |
| 107 | return c.writeMsg(outMsg{JSONRPC: "2.0", Method: method, Params: params}) |
| 108 | } |
| 109 | |
| 110 | func (c *conn) reply(id int64, result any) error { |
| 111 | return c.writeMsg(outMsg{JSONRPC: "2.0", ID: &id, Result: result}) |
| 112 | } |
| 113 | |
| 114 | func (c *conn) writeMsg(v any) error { |
| 115 | b, err := json.Marshal(v) |
| 116 | if err != nil { |
| 117 | return err |
| 118 | } |
| 119 | c.writeMu.Lock() |
| 120 | defer c.writeMu.Unlock() |
| 121 | if _, err := fmt.Fprintf(c.w, "Content-Length: %d\r\n\r\n", len(b)); err != nil { |
| 122 | return err |
| 123 | } |
| 124 | _, err = c.w.Write(b) |
| 125 | return err |
| 126 | } |
| 127 | |
| 128 | func (c *conn) readLoop(r io.Reader) { |
| 129 | br := bufio.NewReader(r) |
| 130 | for { |
| 131 | body, err := readFrame(br) |
| 132 | if err != nil { |
| 133 | c.fail(err) |
| 134 | return |
| 135 | } |
| 136 | var m inMsg |
| 137 | if json.Unmarshal(body, &m) != nil { |
| 138 | continue |
| 139 | } |
| 140 | switch { |
| 141 | case m.Method != "" && m.ID != nil: |
| 142 | if c.onRequest != nil { |
| 143 | c.onRequest(*m.ID, m.Method, m.Params) |
| 144 | } |
| 145 | case m.Method != "": |
| 146 | if c.onNotify != nil { |
| 147 | c.onNotify(m.Method, m.Params) |
| 148 | } |
| 149 | case m.ID != nil: |
| 150 | c.mu.Lock() |
| 151 | ch := c.pending[*m.ID] |
| 152 | c.mu.Unlock() |
| 153 | if ch != nil { |
| 154 | ch <- m |
| 155 | } |
| 156 | } |
| 157 | } |
| 158 | } |
| 159 | |
| 160 | func (c *conn) fail(err error) { |
| 161 | c.closeOnce.Do(func() { |
| 162 | c.err = err |
| 163 | close(c.closed) |
| 164 | }) |
| 165 | } |
| 166 | |
| 167 | // maxFrameBytes caps a single LSP message body. Generous for any real response |
| 168 | // (document symbols, semantic tokens for a huge file) while stopping a corrupt or |
| 169 | // desynced Content-Length from triggering an unbounded allocation that OOMs the |
| 170 | // whole process. |
| 171 | const maxFrameBytes = 64 << 20 // 64 MiB |
| 172 | |
| 173 | // readFrame reads one LSP message: header lines terminated by a blank line, then |
| 174 | // exactly Content-Length bytes of JSON body. |
| 175 | func readFrame(r *bufio.Reader) ([]byte, error) { |
| 176 | n := -1 |
| 177 | for { |
| 178 | line, err := r.ReadString('\n') |
| 179 | if err != nil { |
| 180 | return nil, err |
| 181 | } |
| 182 | line = strings.TrimRight(line, "\r\n") |
| 183 | if line == "" { |
| 184 | break |
| 185 | } |
| 186 | if v, ok := strings.CutPrefix(line, "Content-Length:"); ok { |
| 187 | parsed, err := strconv.Atoi(strings.TrimSpace(v)) |
| 188 | if err != nil { |
| 189 | return nil, fmt.Errorf("bad Content-Length %q: %w", v, err) |
| 190 | } |
| 191 | n = parsed |
| 192 | } |
| 193 | } |
| 194 | if n < 0 { |
| 195 | return nil, fmt.Errorf("missing Content-Length header") |
| 196 | } |
| 197 | if n > maxFrameBytes { |
| 198 | return nil, fmt.Errorf("Content-Length %d exceeds the %d-byte frame cap", n, maxFrameBytes) |
| 199 | } |
| 200 | buf := make([]byte, n) |
| 201 | if _, err := io.ReadFull(r, buf); err != nil { |
| 202 | return nil, err |
| 203 | } |
| 204 | return buf, nil |
| 205 | } |
| 206 |