main.go

package main

import (
	"bufio"
	"bytes"
	"encoding/json"
	"io"
	"log"
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
)

const (
	statusURL  = "https://duckduckgo.com/duckchat/v1/status"
	chatURL    = "https://duckduckgo.com/duckchat/v1/chat"
	userAgent = "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:123.0) Gecko/20100101 Firefox/123.0"
)

type OpenAIRequest struct {
	Model    string `json:"model"`
	Messages []struct {
		Role    string `json:"role"`
		Content string `json:"content"`
	} `json:"messages"`
	Stream bool `json:"stream"`
}

type OpenAIResponse struct {
	ID      string         `json:"id"`
	Object  string         `json:"object"`
	Created int64          `json:"created"`
	Model   string         `json:"model"`
	Choices []OpenAIChoice `json:"choices"`
}

type OpenAIChoice struct {
	Index        int         `json:"index"`
	Delta        OpenAIDelta `json:"delta"`
	Logprobs     interface{} `json:"logprobs"`
	FinishReason *string     `json:"finish_reason"`
}

type OpenAIDelta struct {
	Role    string `json:"role,omitempty"`
	Content string `json:"content,omitempty"`
}

type OpenAINonStreamResponse struct {
	ID      string                  `json:"id"`
	Object  string                  `json:"object"`
	Created int64                   `json:"created"`
	Model   string                  `json:"model"`
	Choices []OpenAINonStreamChoice `json:"choices"`
}

type OpenAINonStreamChoice struct {
	Index        int         `json:"index"`
	Message      OpenAIDelta `json:"message"`
	FinishReason *string     `json:"finish_reason"`
}

type DuckDuckGoResponse struct {
	Role    string `json:"role"`
	Message string `json:"message"`
	Created int64  `json:"created"`
	ID      string `json:"id"`
	Action  string `json:"action"`
	Model   string `json:"model"`
}

func chatWithDuckDuckGo(c *gin.Context, messages []struct {
	Role    string `json:"role"`
	Content string `json:"content"`
}, stream bool) {
	client := &http.Client{Timeout: 10 * time.Second}

	// Get vqd_4
	req, err := http.NewRequest("GET", statusURL, nil)
	if err != nil {
		log.Println(err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to create request"})
		return
	}
	req.Header.Set("x-vqd-accept", "1")
	setHeaders(req, userAgent)

	resp, err := client.Do(req)
	if err != nil {
		log.Println(err)
	c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to get vqd_4"})
		return
	}
	defer resp.Body.Close()

	vqd4 := resp.Header.Get("x-vqd-4")

	// Send chat request
	payload := map[string]interface{}{
		"model":    "gpt-3.5-turbo-0125",
		"messages": messages,
	}
	payloadBytes, err := json.Marshal(payload)
	if err != nil {
		log.Println(err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to marshal payload"})
		return
	}

	req, err = http.NewRequest("POST", chatURL, bytes.NewBuffer(payloadBytes))
	if err != nil {
		log.Println(err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to create request"})
		return
	}
	req.Header.Set("x-vqd-4", vqd4)
	setHeaders(req, userAgent)

	resp, err = client.Do(req)
	if err != nil {
		log.Println(err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to send chat request"})
		return
	}
	defer resp.Body.Close()

	// Process response
	reader := bufio.NewReader(resp.Body)
	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")
	c.Header("Transfer-Encoding", "chunked")

	flusher, _ := c.Writer.(http.Flusher)

	var response OpenAIResponse
	response.Choices = make([]OpenAIChoice, 1)

	var responseContent string

	for {
		line, err := reader.ReadBytes('\n')
		if err != nil {
			if err == io.EOF {
				break
			}
			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
			return
		}

		if bytes.HasPrefix(line, []byte("data: ")) {
			chunk := line[6:]

			if bytes.HasPrefix(chunk, []byte("[DONE]")) {
				response.Choices[0].Delta.Content = responseContent
				response.Choices[0].Delta.Role = "assistant"
				response.Choices[0].FinishReason = new(string)
				*response.Choices[0].FinishReason = "stop"
				c.JSON(http.StatusOK, response)
				return
			}

			var data DuckDuckGoResponse
			decoder := json.NewDecoder(bytes.NewReader(chunk))
			decoder.UseNumber()
			err = decoder.Decode(&data)
			if err != nil {
				c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
				return
			}

			response.ID = data.ID
			response.Object = "chat.completion"
			response.Created = data.Created
			response.Model = data.Model
			responseContent += data.Message

			if stream {
				response.Choices[0].Delta.Content = data.Message

				responseBytes, err := json.Marshal(response)
				if err != nil {
					c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
					return
				}

				c.Data(http.StatusOK, "application/json", append(append([]byte("data: "), responseBytes...), []byte("\n\n")...))
				flusher.Flush()

				response.Choices[0].Delta.Content = ""
			}

		}
	}
}

func setHeaders(req *http.Request, userAgent string) {
	req.Header.Set("User-Agent", userAgent)
	req.Header.Set("Accept", "text/event-stream")
	req.Header.Set("Accept-Language", "de,en-US;q=0.7,en;q=0.3")
	req.Header.Set("Accept-Encoding", "gzip, deflate, br")
	req.Header.Set("Referer", "https://duckduckgo.com/")
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Origin", "https://duckduckgo.com")
	req.Header.Set("Connection", "keep-alive")
	req.Header.Set("Cookie", "dcm=1")
	req.Header.Set("Sec-Fetch-Dest", "empty")
	req.Header.Set("Sec-Fetch-Mode", "cors")
	req.Header.Set("Sec-Fetch-Site", "same-origin")
	req.Header.Set("Pragma", "no-cache")
	req.Header.Set("TE", "trailers")
}

func main() {
	gin.SetMode(gin.ReleaseMode)
	r := gin.Default()

	r.GET("/", func(c *gin.Context) {
		c.JSON(http.StatusOK, gin.H{
			"message": "Hello! Thank you for using FreeDuckDuckGo. Made by Vincent Yang. Repo: https://github.com/missuo/FreeDuckDuckGo",
		})
	})

	r.OPTIONS("/v1/chat/completions", func(c *gin.Context) {
		c.Header("Access-Control-Allow-Origin", "*")
		c.Header("Access-Control-Allow-Methods", "POST, OPTIONS")
		c.Header("Access-Control-Allow-Headers", "Content-Type, Accept, Origin, X-Requested-With")
		c.Status(http.StatusOK)
	})

	r.POST("/v1/chat/completions", func(c *gin.Context) {
		var req OpenAIRequest
		if err := c.ShouldBindJSON(&req); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		// only support user role
		for i := range req.Messages {
			if req.Messages[i].Role == "system" {
				req.Messages[i].Role = "user"
			}
		}
		// set model to gpt-3.5-turbo-0125
		req.Model = "gpt-3.5-turbo-0125"
		chatWithDuckDuckGo(c, req.Messages, req.Stream)
	})

	r.GET("/v1/models", func(c *gin.Context) {
		c.JSON(http.StatusOK, gin.H{
			"object": "list",
			"data": []gin.H{
				{
					"id":       "gpt-3.5-turbo-0125",
					"object":   "model",
					"created":  1692901427,
					"owned_by": "system",
				},
			},
		})
	})

	r.Run(":3456")
}