Implement chat completion streaming (#101)

* Implement chat completion streaming

* Optimize the implementation of chat completion stream

* Fix linter error

chat_stream.go

@@ -0,0 +1,110 @@
+package gogpt
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+)
+
+type ChatCompletionStreamChoiceDelta struct {
+	Content string `json:"content"`
+}
+
+type ChatCompletionStreamChoice struct {
+	Index        int                             `json:"index"`
+	Delta        ChatCompletionStreamChoiceDelta `json:"delta"`
+	FinishReason string                          `json:"finish_reason"`
+}
+
+type ChatCompletionStreamResponse struct {
+	ID      string                       `json:"id"`
+	Object  string                       `json:"object"`
+	Created int64                        `json:"created"`
+	Model   string                       `json:"model"`
+	Choices []ChatCompletionStreamChoice `json:"choices"`
+}
+
+// ChatCompletionStream
+// Note: Perhaps it is more elegant to abstract Stream using generics.
+type ChatCompletionStream struct {
+	emptyMessagesLimit uint
+	isFinished         bool
+
+	reader   *bufio.Reader
+	response *http.Response
+}
+
+func (stream *ChatCompletionStream) Recv() (response ChatCompletionStreamResponse, err error) {
+	if stream.isFinished {
+		err = io.EOF
+		return
+	}
+
+	var emptyMessagesCount uint
+
+waitForData:
+	line, err := stream.reader.ReadBytes('\n')
+	if err != nil {
+		return
+	}
+
+	var headerData = []byte("data: ")
+	line = bytes.TrimSpace(line)
+	if !bytes.HasPrefix(line, headerData) {
+		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 = json.Unmarshal(line, &response)
+	return
+}
+
+func (stream *ChatCompletionStream) Close() {
+	stream.response.Body.Close()
+}
+
+func (stream *ChatCompletionStream) GetResponse() *http.Response {
+	return stream.response
+}
+
+// CreateChatCompletionStream — API call to create a chat completion w/ streaming
+// support. It sets whether to stream back partial progress. If set, tokens will be
+// sent as data-only server-sent events as they become available, with the
+// stream terminated by a data: [DONE] message.
+func (c *Client) CreateChatCompletionStream(
+	ctx context.Context,
+	request ChatCompletionRequest,
+) (stream *ChatCompletionStream, err error) {
+	request.Stream = true
+	req, err := c.newStreamRequest(ctx, "POST", "/chat/completions", request)
+	if err != nil {
+		return
+	}
+
+	resp, err := c.config.HTTPClient.Do(req) //nolint:bodyclose // body is closed in stream.Close()
+	if err != nil {
+		return
+	}
+
+	stream = &ChatCompletionStream{
+		emptyMessagesLimit: c.config.EmptyMessagesLimit,
+		reader:             bufio.NewReader(resp.Body),
+		response:           resp,
+	}
+	return
+}