model-gateway/service/file_detect.go

package service

import (
	"net/http"
	"strings"
)

// DetectFileType 根据返回的二进制内容推断 contentType + 扩展名（尽量稳定）
func DetectFileType(data []byte) (contentType string, ext string) {
	if len(data) == 0 {
		return "application/octet-stream", ""
	}
	ct := http.DetectContentType(data)
	// http.DetectContentType 可能带 charset 等参数：text/plain; charset=utf-8
	if idx := strings.Index(ct, ";"); idx > 0 {
		ct = strings.TrimSpace(ct[:idx])
	}
	switch ct {
	case "audio/mpeg":
		return ct, ".mp3"
	case "audio/wave", "audio/wav", "audio/x-wav":
		return ct, ".wav"
	case "video/mp4":
		return ct, ".mp4"
	case "image/png":
		return ct, ".png"
	case "image/jpeg":
		return ct, ".jpg"
	case "application/pdf":
		return ct, ".pdf"
	case "text/plain":
		return ct, ".txt"
	case "application/json":
		return ct, ".json"
	default:
		// 兜底：尝试从 ct 截取 subtype 作为后缀（例如 application/json）
		if parts := strings.Split(ct, "/"); len(parts) == 2 {
			sub := parts[1]
			// 避免出现 "plain; charset=utf-8" 之类的后缀
			if idx := strings.Index(sub, ";"); idx > 0 {
				sub = strings.TrimSpace(sub[:idx])
			}
			return ct, "." + sub
		}
		return ct, ""
	}
}