feat: publish the Hime-san Beta 2 LSP

Add the standard-library language server, editor-neutral protocol contract, additive version feature discovery, and bounded security regressions while leaving the Sando runtime unchanged. Material design and implementation assistance was provided by OpenAI Codex.

Signed-off-by: Cole Speelman <crspeelman@gmail.com>

internal/lsp/protocol.go

@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package lsp
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+const (
+	maxMessageBytes = 16 << 20
+	maxHeaderBytes  = 64 << 10
+	maxHeaderLines  = 64
+)
+
+type rpcMessage struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      json.RawMessage `json:"id,omitempty"`
+	Method  string          `json:"method,omitempty"`
+	Params  json.RawMessage `json:"params,omitempty"`
+	Result  any             `json:"result,omitempty"`
+	Error   *rpcError       `json:"error,omitempty"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+func validRequestID(id json.RawMessage) bool {
+	if len(id) == 0 {
+		return true
+	}
+	var value any
+	if err := json.Unmarshal(id, &value); err != nil {
+		return false
+	}
+	switch value := value.(type) {
+	case string:
+		return true
+	case float64:
+		return value == math.Trunc(value)
+	default:
+		return false
+	}
+}
+
+const (
+	errParse            = -32700
+	errInvalidRequest   = -32600
+	errMethodNotFound   = -32601
+	errInvalidParams    = -32602
+	errInternal         = -32603
+	errRequestCancelled = -32800
+)
+
+type frameReader struct{ reader *bufio.Reader }
+
+func newFrameReader(input io.Reader) *frameReader {
+	return &frameReader{reader: bufio.NewReaderSize(input, 64<<10)}
+}
+
+func (reader *frameReader) read() ([]byte, error) {
+	contentLength := -1
+	headerBytes := 0
+	headerLines := 0
+	for {
+		line, err := reader.reader.ReadString('\n')
+		if err != nil {
+			return nil, err
+		}
+		headerBytes += len(line)
+		headerLines++
+		if headerBytes > maxHeaderBytes || headerLines > maxHeaderLines {
+			return nil, errors.New("LSP headers exceed configured limits")
+		}
+		if len(line) > 8<<10 {
+			return nil, errors.New("LSP header line exceeds 8 KiB")
+		}
+		line = strings.TrimSuffix(strings.TrimSuffix(line, "\n"), "\r")
+		if line == "" {
+			break
+		}
+		name, value, ok := strings.Cut(line, ":")
+		if !ok {
+			return nil, errors.New("malformed LSP header")
+		}
+		if strings.EqualFold(strings.TrimSpace(name), "Content-Length") {
+			if contentLength >= 0 {
+				return nil, errors.New("duplicate Content-Length header")
+			}
+			parsed, parseErr := strconv.Atoi(strings.TrimSpace(value))
+			if parseErr != nil || parsed < 0 || parsed > maxMessageBytes {
+				return nil, errors.New("invalid or excessive Content-Length")
+			}
+			contentLength = parsed
+		}
+	}
+	if contentLength < 0 {
+		return nil, errors.New("missing Content-Length header")
+	}
+	payload := make([]byte, contentLength)
+	if _, err := io.ReadFull(reader.reader, payload); err != nil {
+		return nil, err
+	}
+	return payload, nil
+}
+
+type frameWriter struct {
+	mu     sync.Mutex
+	output io.Writer
+}
+
+func (writer *frameWriter) write(message rpcMessage) error {
+	payload, err := json.Marshal(message)
+	if err != nil {
+		return err
+	}
+	var frame bytes.Buffer
+	fmt.Fprintf(&frame, "Content-Length: %d\r\n\r\n", len(payload))
+	frame.Write(payload)
+	writer.mu.Lock()
+	defer writer.mu.Unlock()
+	written, err := writer.output.Write(frame.Bytes())
+	if err == nil && written != frame.Len() {
+		return io.ErrShortWrite
+	}
+	return err
+}
+
+type Position struct {
+	Line      int `json:"line"`
+	Character int `json:"character"`
+}
+
+type Range struct {
+	Start Position `json:"start"`
+	End   Position `json:"end"`
+}
+
+type Location struct {
+	URI   string `json:"uri"`
+	Range Range  `json:"range"`
+}
+
+type lspDiagnostic struct {
+	Range    Range  `json:"range"`
+	Severity int    `json:"severity,omitempty"`
+	Code     string `json:"code,omitempty"`
+	Source   string `json:"source,omitempty"`
+	Message  string `json:"message"`
+}
+
+type textDocumentIdentifier struct {
+	URI string `json:"uri"`
+}
+
+type versionedTextDocumentIdentifier struct {
+	URI     string `json:"uri"`
+	Version int    `json:"version"`
+}
+
+type textDocumentPositionParams struct {
+	TextDocument textDocumentIdentifier `json:"textDocument"`
+	Position     Position               `json:"position"`
+}