Add media proxy feature for resource downloading

- Introduced a new API endpoint `GET /api/v1/video/proxy` to facilitate media resource downloads, allowing users to bypass domain restrictions imposed by WeChat.
- Updated configuration to include proxy settings such as `SHORT_VIDEO_PROXY_ENABLED`, `SHORT_VIDEO_PROXY_ALLOWED_DOMAINS`, `SHORT_VIDEO_PROXY_MAX_SIZE_MB`, and `SHORT_VIDEO_PROXY_TIMEOUT_SECONDS`.
- Enhanced the `ShortVideoConfig` struct to accommodate new proxy-related fields.
- Improved error handling for proxy requests, including checks for allowed domains and file size limits.
- Updated documentation to reflect the new proxy functionality and its configuration options, ensuring clarity for users and developers.

internal/remove_watermark/service/video_service.go

@@ -27,6 +27,10 @@ var (
 	ErrURLNotFound        = errors.New("no valid url found in content")
 	ErrShortVideoAPIKey   = errors.New("short video api key is not configured")
 	ErrDailyQuotaExceeded = errors.New("daily free quota exceeded, please watch an ad to continue")
+	ErrProxyDisabled      = errors.New("media proxy is disabled")
+	ErrProxyDomainBlocked = errors.New("domain is not in the allowed list")
+	ErrProxyFileTooLarge  = errors.New("file size exceeds the limit")
+	ErrProxyInvalidURL    = errors.New("invalid proxy url")
 )
 
 type VideoService struct {
@@ -292,3 +296,131 @@ func (s *VideoService) ReportDownloadFailure(ctx context.Context, report Downloa
 	}
 	return nil
 }
+
+// ProxyMediaResult 代理媒体请求的结果
+type ProxyMediaResult struct {
+	Body          io.ReadCloser
+	ContentType   string
+	ContentLength int64
+	StatusCode    int
+}
+
+// ProxyMedia 代理媒体资源下载，用于绕过微信小程序的域名限制
+// 该方法会验证目标URL是否在允许的域名白名单内，并流式转发响应
+func (s *VideoService) ProxyMedia(ctx context.Context, targetURL string) (*ProxyMediaResult, error) {
+	// 检查是否启用代理功能
+	if !s.cfg.ProxyEnabled {
+		return nil, ErrProxyDisabled
+	}
+
+	// 验证并解析 URL
+	parsed, err := url.Parse(targetURL)
+	if err != nil || parsed.Scheme == "" || parsed.Host == "" {
+		return nil, ErrProxyInvalidURL
+	}
+
+	// 只允许 http/https 协议
+	if parsed.Scheme != "http" && parsed.Scheme != "https" {
+		return nil, ErrProxyInvalidURL
+	}
+
+	// 检查域名白名单（如果配置了的话）
+	if len(s.cfg.ProxyAllowedDomains) > 0 {
+		allowed := false
+		for _, domain := range s.cfg.ProxyAllowedDomains {
+			if strings.HasSuffix(parsed.Host, domain) || parsed.Host == domain {
+				allowed = true
+				break
+			}
+		}
+		if !allowed {
+			return nil, ErrProxyDomainBlocked
+		}
+	}
+
+	// 创建带超时的 HTTP 客户端（代理请求可能需要更长时间）
+	proxyTimeout := s.cfg.ProxyTimeout
+	if proxyTimeout <= 0 {
+		proxyTimeout = 60 * time.Second
+	}
+	proxyClient := &http.Client{
+		Timeout: proxyTimeout,
+	}
+
+	// 构建代理请求
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, targetURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("build proxy request: %w", err)
+	}
+
+	// 设置常见的请求头，模拟正常浏览器行为
+	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36")
+	req.Header.Set("Accept", "*/*")
+	req.Header.Set("Accept-Language", "zh-CN,zh;q=0.9,en;q=0.8")
+	req.Header.Set("Referer", fmt.Sprintf("%s://%s/", parsed.Scheme, parsed.Host))
+
+	// 发起请求
+	resp, err := proxyClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("proxy request failed: %w", err)
+	}
+
+	// 检查响应状态
+	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
+		resp.Body.Close()
+		return nil, &ThirdPartyError{
+			StatusCode: resp.StatusCode,
+			Message:    fmt.Sprintf("upstream returned status %d", resp.StatusCode),
+		}
+	}
+
+	// 检查文件大小限制
+	if s.cfg.ProxyMaxSize > 0 && resp.ContentLength > s.cfg.ProxyMaxSize {
+		resp.Body.Close()
+		return nil, ErrProxyFileTooLarge
+	}
+
+	// 获取 Content-Type
+	contentType := resp.Header.Get("Content-Type")
+	if contentType == "" {
+		contentType = "application/octet-stream"
+	}
+
+	return &ProxyMediaResult{
+		Body:          resp.Body,
+		ContentType:   contentType,
+		ContentLength: resp.ContentLength,
+		StatusCode:    resp.StatusCode,
+	}, nil
+}
+
+// ValidateProxyURL 验证代理URL是否有效（不实际请求，只做格式和白名单检查）
+func (s *VideoService) ValidateProxyURL(targetURL string) error {
+	if !s.cfg.ProxyEnabled {
+		return ErrProxyDisabled
+	}
+
+	parsed, err := url.Parse(targetURL)
+	if err != nil || parsed.Scheme == "" || parsed.Host == "" {
+		return ErrProxyInvalidURL
+	}
+
+	if parsed.Scheme != "http" && parsed.Scheme != "https" {
+		return ErrProxyInvalidURL
+	}
+
+	if len(s.cfg.ProxyAllowedDomains) > 0 {
+		allowed := false
+		for _, domain := range s.cfg.ProxyAllowedDomains {
+			if strings.HasSuffix(parsed.Host, domain) || parsed.Host == domain {
+				allowed = true
+				break
+			}
+		}
+		if !allowed {
+			return ErrProxyDomainBlocked
+		}
+	}
+
+	return nil
+}