fix: stream return EOF when openai return error (#184)

* fix: stream return EOF when openai return error

* perf: add error accumulator

* fix: golangci-lint

* fix: unmarshal error possibly null

* fix: error accumulator

* test: error accumulator use interface and add test code

* test: error accumulator add test code

* refactor: use stream reader to re-use stream code

* refactor: stream reader use generics

stream_reader.go

@@ -0,0 +1,71 @@
+package openai
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+type streamable interface {
+	ChatCompletionStreamResponse | CompletionResponse
+}
+
+type streamReader[T streamable] struct {
+	emptyMessagesLimit uint
+	isFinished         bool
+
+	reader         *bufio.Reader
+	response       *http.Response
+	errAccumulator errorAccumulator
+	unmarshaler    unmarshaler
+}
+
+func (stream *streamReader[T]) Recv() (response T, err error) {
+	if stream.isFinished {
+		err = io.EOF
+		return
+	}
+
+	var emptyMessagesCount uint
+
+waitForData:
+	line, err := stream.reader.ReadBytes('\n')
+	if err != nil {
+		if errRes, _ := stream.errAccumulator.unmarshalError(); errRes != nil {
+			err = fmt.Errorf("error, %w", errRes.Error)
+		}
+		return
+	}
+
+	var headerData = []byte("data: ")
+	line = bytes.TrimSpace(line)
+	if !bytes.HasPrefix(line, headerData) {
+		if writeErr := stream.errAccumulator.write(line); writeErr != nil {
+			err = writeErr
+			return
+		}
+		emptyMessagesCount++
+		if emptyMessagesCount > stream.emptyMessagesLimit {
+			err = ErrTooManyEmptyStreamMessages
+			return
+		}
+
+		goto waitForData
+	}
+
+	line = bytes.TrimPrefix(line, headerData)
+	if string(line) == "[DONE]" {
+		stream.isFinished = true
+		err = io.EOF
+		return
+	}
+
+	err = stream.unmarshaler.unmarshal(line, &response)
+	return
+}
+
+func (stream *streamReader[T]) Close() {
+	stream.response.Body.Close()
+}