opencatd-open/backend/internal/proxy/convert/stream.go

package convert

import (
	"bufio"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
)

// SSEWriter writes Server-Sent Events
type SSEWriter struct {
	writer io.Writer
	flusher http.Flusher
}

// NewSSEWriter creates a new SSE writer
func NewSSEWriter(w http.ResponseWriter) *SSEWriter {
	flusher, _ := w.(http.Flusher)
	return &SSEWriter{
		writer:  w,
		flusher: flusher,
	}
}

// WriteEvent writes a single SSE event
func (w *SSEWriter) WriteEvent(event string, data interface{}) error {
	var dataStr string
	switch v := data.(type) {
	case string:
		dataStr = v
	default:
		b, err := json.Marshal(v)
		if err != nil {
			return err
		}
		dataStr = string(b)
	}

	_, err := fmt.Fprintf(w.writer, "event: %s\ndata: %s\n\n", event, dataStr)
	if err != nil {
		return err
	}

	if w.flusher != nil {
		w.flusher.Flush()
	}
	return nil
}

// WriteChunk writes a streaming chunk in SSE format
func (w *SSEWriter) WriteChunk(chunk interface{}) error {
	b, err := json.Marshal(chunk)
	if err != nil {
		return err
	}

	_, err = fmt.Fprintf(w.writer, "data: %s\n\n", string(b))
	if err != nil {
		return err
	}

	if w.flusher != nil {
		w.flusher.Flush()
	}
	return nil
}

// WriteDone writes the [DONE] marker
func (w *SSEWriter) WriteDone() error {
	_, err := fmt.Fprintf(w.writer, "data: [DONE]\n\n")
	if err != nil {
		return err
	}

	if w.flusher != nil {
		w.flusher.Flush()
	}
	return nil
}

// SSEParser parses Server-Sent Events from a reader
type SSEParser struct {
	reader *bufio.Reader
}

// NewSSEParser creates a new SSE parser
func NewSSEParser(r io.Reader) *SSEParser {
	return &SSEParser{
		reader: bufio.NewReader(r),
	}
}

// SSEEvent represents a parsed SSE event
type SSEEvent struct {
	Event string
	Data  string
}

// ReadEvent reads the next SSE event
func (p *SSEParser) ReadEvent() (*SSEEvent, error) {
	event := &SSEEvent{}

	for {
		line, err := p.reader.ReadString('\n')
		if err != nil {
			return nil, err
		}

		line = strings.TrimRight(line, "\r\n")

		if line == "" {
			// Empty line means end of event
			if event.Data != "" || event.Event != "" {
				return event, nil
			}
			continue
		}

		if strings.HasPrefix(line, "event:") {
			event.Event = strings.TrimSpace(line[6:])
		} else if strings.HasPrefix(line, "data:") {
			data := strings.TrimSpace(line[5:])
			if event.Data != "" {
				event.Data += "\n" + data
			} else {
				event.Data = data
			}
		}
		// Ignore comments (lines starting with :) and unknown fields
	}
}

// ParseChatStreamChunk parses an OpenAI Chat Completions streaming chunk
func ParseChatStreamChunk(data string) (*ChatCompletionStreamChunk, error) {
	if data == "[DONE]" {
		return nil, io.EOF
	}

	var chunk ChatCompletionStreamChunk
	err := json.Unmarshal([]byte(data), &chunk)
	if err != nil {
		return nil, err
	}
	return &chunk, nil
}

// ParseMessagesStreamEvent parses an Anthropic Messages streaming event
func ParseMessagesStreamEvent(data string) (*AnthropicStreamEvent, error) {
	var event AnthropicStreamEvent
	err := json.Unmarshal([]byte(data), &event)
	if err != nil {
		return nil, err
	}
	return &event, nil
}

// ParseResponsesStreamChunk parses an OpenAI Responses API streaming chunk
func ParseResponsesStreamChunk(data string) (*ResponsesStreamEvent, error) {
	if data == "[DONE]" {
		return nil, io.EOF
	}

	var event ResponsesStreamEvent
	err := json.Unmarshal([]byte(data), &event)
	if err != nil {
		return nil, err
	}
	return &event, nil
}