Add OpenAI-compatible endpoint to Gemini server (/v1/chat/completions with streaming)

free-gemini-api/main.go

@@ -18,9 +18,54 @@ import (
 
 	"github.com/gofiber/fiber/v3"
 	"github.com/gofiber/fiber/v3/middleware/logger"
+	"github.com/google/uuid"
 	"github.com/joho/godotenv"
 )
 
+type OpenAIChatMessage struct {
+	Role    string `json:"role"`
+	Content string `json:"content"`
+}
+
+type OpenAIChatCompletionRequest struct {
+	Model    string              `json:"model"`
+	Messages []OpenAIChatMessage `json:"messages"`
+	Stream   bool                `json:"stream"`
+}
+
+type OpenAIChoice struct {
+	Index        int               `json:"index"`
+	Message      OpenAIChatMessage `json:"message"`
+	FinishReason string            `json:"finish_reason"`
+}
+
+type OpenAIChatCompletionResponse struct {
+	ID      string         `json:"id"`
+	Object  string         `json:"object"`
+	Created int64          `json:"created"`
+	Model   string         `json:"model"`
+	Choices []OpenAIChoice `json:"choices"`
+}
+
+type OpenAIDelta struct {
+	Role    string `json:"role,omitempty"`
+	Content string `json:"content,omitempty"`
+}
+
+type OpenAIStreamChoice struct {
+	Index        int         `json:"index"`
+	Delta        OpenAIDelta `json:"delta"`
+	FinishReason string      `json:"finish_reason,omitempty"`
+}
+
+type OpenAIChatCompletionChunk struct {
+	ID      string               `json:"id"`
+	Object  string               `json:"object"`
+	Created int64                `json:"created"`
+	Model   string               `json:"model"`
+	Choices []OpenAIStreamChoice `json:"choices"`
+}
+
 var (
 	userSessions sync.Map
 )
@@ -334,6 +379,128 @@ func main() {
 		return c.JSON(resp)
 	})
 
+	// OpenAI-compatible endpoint for drop-in client integrations
+	app.Post("/v1/chat/completions", func(c fiber.Ctx) error {
+		var req OpenAIChatCompletionRequest
+		if err := c.Bind().JSON(&req); err != nil {
+			return c.Status(400).JSON(fiber.Map{"error": "Invalid request"})
+		}
+
+		if len(req.Messages) == 0 {
+			return c.Status(400).JSON(fiber.Map{"error": "Messages array is empty"})
+		}
+
+		// Extract prompt from messages (last user message)
+		var prompt string
+		for i := len(req.Messages) - 1; i >= 0; i-- {
+			if req.Messages[i].Role == "user" {
+				prompt = req.Messages[i].Content
+				break
+			}
+		}
+		if prompt == "" {
+			prompt = req.Messages[len(req.Messages)-1].Content
+		}
+
+		sessionID := c.IP()
+
+		client, err := getOrCreateClient(sessionID)
+		if err != nil {
+			return c.Status(500).JSON(fiber.Map{"error": err.Error()})
+		}
+
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Minute)
+		defer cancel()
+
+		model := req.Model
+		if model == "" {
+			model = "gemini-2.5-flash"
+		}
+
+		if req.Stream {
+			c.Set("Content-Type", "text/event-stream")
+			c.Set("Cache-Control", "no-cache")
+			c.Set("Connection", "keep-alive")
+			c.Set("X-Accel-Buffering", "no")
+
+			return c.SendStreamWriter(func(w *bufio.Writer) {
+				chunkID := "chatcmpl-" + uuid.NewString()[:12]
+				createdTime := time.Now().Unix()
+
+				_, streamErr := client.AskStream(prompt, func(chunk string) {
+					chunkResp := OpenAIChatCompletionChunk{
+						ID:      chunkID,
+						Object:  "chat.completion.chunk",
+						Created: createdTime,
+						Model:   model,
+						Choices: []OpenAIStreamChoice{
+							{
+								Index: 0,
+								Delta: OpenAIDelta{
+									Content: chunk,
+								},
+							},
+						},
+					}
+					data, _ := json.Marshal(chunkResp)
+					fmt.Fprintf(w, "data: %s\n\n", data)
+					w.Flush()
+				})
+
+				if streamErr != nil {
+					log.Printf("❌ Streaming error: %v", streamErr)
+					return
+				}
+
+				// Send final stop chunk
+				finalResp := OpenAIChatCompletionChunk{
+					ID:      chunkID,
+					Object:  "chat.completion.chunk",
+					Created: createdTime,
+					Model:   model,
+					Choices: []OpenAIStreamChoice{
+						{
+							Index:        0,
+							FinishReason: "stop",
+						},
+					},
+				}
+				data, _ := json.Marshal(finalResp)
+				fmt.Fprintf(w, "data: %s\n\n", data)
+				fmt.Fprintf(w, "data: [DONE]\n\n")
+				w.Flush()
+			})
+		}
+
+		resp, err := client.Ask(prompt)
+		if err != nil {
+			if ctx.Err() == context.DeadlineExceeded {
+				userSessions.Delete(sessionID)
+				return c.Status(504).JSON(fiber.Map{"error": "Request timed out. Session reset."})
+			}
+			return c.Status(500).JSON(fiber.Map{"error": err.Error()})
+		}
+
+		openAIResp := OpenAIChatCompletionResponse{
+			ID:      "chatcmpl-" + uuid.NewString()[:12],
+			Object:  "chat.completion",
+			Created: time.Now().Unix(),
+			Model:   model,
+			Choices: []OpenAIChoice{
+				{
+					Index: 0,
+					Message: OpenAIChatMessage{
+						Role:    "assistant",
+						Content: resp.Text,
+					},
+					FinishReason: "stop",
+				},
+			},
+		}
+
+		return c.JSON(openAIResp)
+	})
+
 	// Music generation endpoint (separate because it uses tool="music_gen")
 	app.Post("/music", func(c fiber.Ctx) error {
 		var req gemini.ChatRequest