fix: chat stream returns an error response with a 'data: ' prefix (#396)

* fix: chat stream resp has 'data: ' prefix

* fix: lint error

* fix: lint error

* fix: lint error

chat_stream_test.go

@@ -178,6 +178,45 @@ func TestCreateChatCompletionStreamError(t *testing.T) {
 	t.Logf("%+v\n", apiErr)
 }
 
+func TestCreateChatCompletionStreamErrorWithDataPrefix(t *testing.T) {
+	client, server, teardown := setupOpenAITestServer()
+	defer teardown()
+	server.RegisterHandler("/v1/chat/completions", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+
+		// Send test responses
+		//nolint:lll
+		dataBytes := []byte(`data: {"error":{"message":"The server had an error while processing your request. Sorry about that!", "type":"server_ error", "param":null,"code":null}}`)
+		dataBytes = append(dataBytes, []byte("\n\ndata: [DONE]\n\n")...)
+
+		_, err := w.Write(dataBytes)
+		checks.NoError(t, err, "Write error")
+	})
+
+	stream, err := client.CreateChatCompletionStream(context.Background(), ChatCompletionRequest{
+		MaxTokens: 5,
+		Model:     GPT3Dot5Turbo,
+		Messages: []ChatCompletionMessage{
+			{
+				Role:    ChatMessageRoleUser,
+				Content: "Hello!",
+			},
+		},
+		Stream: true,
+	})
+	checks.NoError(t, err, "CreateCompletionStream returned error")
+	defer stream.Close()
+
+	_, streamErr := stream.Recv()
+	checks.HasError(t, streamErr, "stream.Recv() did not return error")
+
+	var apiErr *APIError
+	if !errors.As(streamErr, &apiErr) {
+		t.Errorf("stream.Recv() did not return APIError")
+	}
+	t.Logf("%+v\n", apiErr)
+}
+
 func TestCreateChatCompletionStreamRateLimitError(t *testing.T) {
 	client, server, teardown := setupOpenAITestServer()
 	defer teardown()

stream_reader.go

@@ -10,6 +10,11 @@ import (
 	utils "github.com/sashabaranov/go-openai/internal"
 )
 
+var (
+	headerData  = []byte("data: ")
+	errorPrefix = []byte(`data: {"error":`)
+)
+
 type streamable interface {
 	ChatCompletionStreamResponse | CompletionResponse
 }
@@ -34,12 +39,16 @@ func (stream *streamReader[T]) Recv() (response T, err error) {
 	return
 }
 
+//nolint:gocognit
 func (stream *streamReader[T]) processLines() (T, error) {
-	var emptyMessagesCount uint
+	var (
+		emptyMessagesCount uint
+		hasErrorPrefix     bool
+	)
 
 	for {
 		rawLine, readErr := stream.reader.ReadBytes('\n')
-		if readErr != nil {
+		if readErr != nil || hasErrorPrefix {
 			respErr := stream.unmarshalError()
 			if respErr != nil {
 				return *new(T), fmt.Errorf("error, %w", respErr.Error)
@@ -47,9 +56,14 @@ func (stream *streamReader[T]) processLines() (T, error) {
 			return *new(T), readErr
 		}
 
-		var headerData = []byte("data: ")
 		noSpaceLine := bytes.TrimSpace(rawLine)
-		if !bytes.HasPrefix(noSpaceLine, headerData) {
+		if bytes.HasPrefix(noSpaceLine, errorPrefix) {
+			hasErrorPrefix = true
+		}
+		if !bytes.HasPrefix(noSpaceLine, headerData) || hasErrorPrefix {
+			if hasErrorPrefix {
+				noSpaceLine = bytes.TrimPrefix(noSpaceLine, headerData)
+			}
 			writeErr := stream.errAccumulator.Write(noSpaceLine)
 			if writeErr != nil {
 				return *new(T), writeErr