Cthulhu is no longer a fork. Now it is a screen reader written in Golang.

internal/nvda2cthulhu/protocol.go

@@ -0,0 +1,154 @@
+// Package nvda2cthulhu accepts the local WebSocket protocol used by NVDA
+// compatibility bridges and routes it to Cthulhu's speech and braille queues.
+package nvda2cthulhu
+
+import (
+	"bytes"
+	"errors"
+	"strconv"
+	"strings"
+
+	"github.com/gorilla/websocket"
+)
+
+func (server *Server) deliver(request bridgeRequest) {
+	switch request.kind {
+	case "SpeakText":
+		if server.handler.SpeakText(request.text, true) {
+			server.logger.Debug("NVDA to Cthulhu speech accepted", "bytes", len(request.text))
+		} else {
+			server.logger.Warn("NVDA to Cthulhu speech rejected", "bytes", len(request.text))
+		}
+	case "BrailleText":
+		if server.handler.BrailleMessage(request.text) {
+			server.logger.Debug("NVDA to Cthulhu braille accepted", "bytes", len(request.text))
+		} else {
+			server.logger.Debug("NVDA to Cthulhu braille unavailable")
+		}
+	case "CancelSpeech":
+		if server.handler.CancelSpeech() {
+			server.logger.Debug("NVDA to Cthulhu cancellation accepted")
+		} else {
+			server.logger.Warn("NVDA to Cthulhu cancellation rejected")
+		}
+	}
+}
+
+type bridgeRequest struct {
+	kind, text string
+}
+
+func decodeRequest(messageType int, payload []byte) (bridgeRequest, error) {
+	if len(payload) > maxPayload {
+		return bridgeRequest{}, errors.New("message exceeds 64 KiB")
+	}
+	switch messageType {
+	case websocket.TextMessage:
+		return parseRequest(string(payload))
+	case websocket.BinaryMessage:
+		reader := bytes.NewReader(payload)
+		value, err := decodeMessagePack(reader)
+		if err != nil {
+			return bridgeRequest{}, err
+		}
+		if reader.Len() != 0 {
+			return bridgeRequest{}, errors.New("trailing MessagePack data")
+		}
+		return parseRequest(value)
+	default:
+		return bridgeRequest{}, errors.New("unsupported WebSocket message type")
+	}
+}
+
+func parseRequest(value any) (bridgeRequest, error) {
+	switch payload := value.(type) {
+	case string:
+		if strings.TrimSpace(payload) == "" {
+			return bridgeRequest{}, errors.New("blank text request")
+		}
+		if payload == "CancelSpeech" {
+			return bridgeRequest{kind: "CancelSpeech"}, nil
+		}
+		return bridgeRequest{kind: "SpeakText", text: payload}, nil
+	case map[any]any:
+		if len(payload) != 1 {
+			return bridgeRequest{}, errors.New("map request must contain exactly one entry")
+		}
+		for key, value := range payload {
+			return keyedRequest(coerceText(key), value)
+		}
+	case map[string]any:
+		if len(payload) != 1 {
+			return bridgeRequest{}, errors.New("map request must contain exactly one entry")
+		}
+		for key, value := range payload {
+			return keyedRequest(key, value)
+		}
+	case []any:
+		if len(payload) == 0 {
+			return bridgeRequest{}, errors.New("array request is empty")
+		}
+		kind := coerceText(payload[0])
+		if kind == "CancelSpeech" {
+			return bridgeRequest{kind: "CancelSpeech"}, nil
+		}
+		if len(payload) < 2 {
+			return bridgeRequest{}, errors.New("array request has no value")
+		}
+		return keyedRequest(kind, payload[1])
+	}
+	return bridgeRequest{}, errors.New("unsupported MessagePack payload")
+}
+
+func keyedRequest(kind string, value any) (bridgeRequest, error) {
+	switch kind {
+	case "CancelSpeech":
+		return bridgeRequest{kind: "CancelSpeech"}, nil
+	case "SpeakText", "BrailleText":
+		if strings.TrimSpace(coerceText(value)) == "" {
+			return bridgeRequest{}, errors.New("blank text request")
+		}
+		return bridgeRequest{kind: kind, text: coerceText(value)}, nil
+	default:
+		return bridgeRequest{}, errors.New("unsupported request kind")
+	}
+}
+
+func coerceText(value any) string {
+	switch text := value.(type) {
+	case string:
+		return text
+	case messagePackBinary:
+		return string(text)
+	case nil:
+		return ""
+	case bool:
+		return strconv.FormatBool(text)
+	case int:
+		return strconv.Itoa(text)
+	case int8:
+		return strconv.FormatInt(int64(text), 10)
+	case int16:
+		return strconv.FormatInt(int64(text), 10)
+	case int32:
+		return strconv.FormatInt(int64(text), 10)
+	case int64:
+		return strconv.FormatInt(text, 10)
+	case uint:
+		return strconv.FormatUint(uint64(text), 10)
+	case uint8:
+		return strconv.FormatUint(uint64(text), 10)
+	case uint16:
+		return strconv.FormatUint(uint64(text), 10)
+	case uint32:
+		return strconv.FormatUint(uint64(text), 10)
+	case uint64:
+		return strconv.FormatUint(text, 10)
+	case float32:
+		return strconv.FormatFloat(float64(text), 'g', -1, 32)
+	case float64:
+		return strconv.FormatFloat(text, 'g', -1, 64)
+	default:
+		return ""
+	}
+}