Streaming support (#61)

* Add streaming support feature (#54)

* Add streaming support feature

removes golangci linting deprecation warnings
See: [Issue #49](https://github.com/sashabaranov/go-gpt3/issues/49)

* remove dead token

* Remove the goroutines from previous implementation

Set up separate test and file for streaming support
Add client code under cmd dir

* Supress CI errors

Need to update import path to test under feature/streaming-support
branch

* suppress linting errors

---------

Co-authored-by: sashabaranov <677093+sashabaranov@users.noreply.github.com>

* remove main.go

* remove code duplication

* use int64

* finalize streaming support

* lint

* fix tests

---------

Co-authored-by: e. alvarez <55966724+ealvar3z@users.noreply.github.com>

stream.go

@@ -0,0 +1,83 @@
+package gogpt
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+type CompletionStream struct {
+	reader   *bufio.Reader
+	response *http.Response
+}
+
+func (stream *CompletionStream) Recv() (response CompletionResponse, err error) {
+waitForData:
+	line, err := stream.reader.ReadBytes('\n')
+	if err != nil {
+		if errors.Is(err, io.EOF) {
+			return
+		}
+	}
+
+	var headerData = []byte("data: ")
+	line = bytes.TrimSpace(line)
+	if !bytes.HasPrefix(line, headerData) {
+		goto waitForData
+	}
+
+	line = bytes.TrimPrefix(line, headerData)
+	if string(line) == "[DONE]" {
+		return
+	}
+
+	err = json.Unmarshal(line, &response)
+	return
+}
+
+func (stream *CompletionStream) Close() {
+	stream.response.Body.Close()
+}
+
+// CreateCompletionStream — API call to create a 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) CreateCompletionStream(
+	ctx context.Context,
+	request CompletionRequest,
+) (stream *CompletionStream, err error) {
+	request.Stream = true
+	reqBytes, err := json.Marshal(request)
+	if err != nil {
+		return
+	}
+
+	urlSuffix := "/completions"
+	req, err := http.NewRequest("POST", c.fullURL(urlSuffix), bytes.NewBuffer(reqBytes))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "text/event-stream")
+	req.Header.Set("Cache-Control", "no-cache")
+	req.Header.Set("Connection", "keep-alive")
+	req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", c.authToken))
+	if err != nil {
+		return
+	}
+
+	req = req.WithContext(ctx)
+	resp, err := c.HTTPClient.Do(req) //nolint:bodyclose // body is closed in stream.Close()
+	if err != nil {
+		return
+	}
+
+	stream = &CompletionStream{
+		reader:   bufio.NewReader(resp.Body),
+		response: resp,
+	}
+	return
+}