geo/server/internal/tenant/transport/asset_handler.go

package transport

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"image"
	"image/jpeg"
	"image/png"
	"net/http"
	"strconv"
	"strings"

	"github.com/gin-gonic/gin"
	_ "golang.org/x/image/webp"

	"github.com/geo-platform/tenant-api/internal/bootstrap"
)

type AssetHandler struct {
	secret string
	app    *bootstrap.App
}

func NewAssetHandler(app *bootstrap.App) *AssetHandler {
	return &AssetHandler{
		secret: strings.TrimSpace(app.Config.JWT.Secret),
		app:    app,
	}
}

func (h *AssetHandler) BuildArticleImageURL(objectKey string) string {
	token := h.signObjectKey(objectKey)
	return "/api/public/assets/" + token
}

func (h *AssetHandler) Serve(c *gin.Context) {
	objectKey, ok := h.parseToken(c.Param("token"))
	if !ok {
		c.AbortWithStatus(http.StatusNotFound)
		return
	}

	h.serveObject(c, objectKey)
}

func (h *AssetHandler) ServeDesktop(c *gin.Context) {
	client := MustDesktopClient(c.Request.Context())
	objectKey, ok := objectKeyFromAssetToken(c.Param("token"))
	if !ok || !isDesktopClientAssetKey(objectKey, client.TenantID) {
		c.AbortWithStatus(http.StatusNotFound)
		return
	}

	h.serveObject(c, objectKey)
}

func (h *AssetHandler) serveObject(c *gin.Context, objectKey string) {
	content, err := h.app.ObjectStorage.GetBytes(c.Request.Context(), objectKey)
	if err != nil || len(content) == 0 {
		c.AbortWithStatus(http.StatusNotFound)
		return
	}

	if converted, contentType, ok := convertPublicAssetFormat(content, c.Query("format")); ok {
		c.Header("Cache-Control", "public, max-age=31536000, immutable")
		c.Header("Content-Type", contentType)
		c.Writer.WriteHeader(http.StatusOK)
		_, _ = c.Writer.Write(converted)
		return
	}

	contentType := http.DetectContentType(content)
	c.Header("Cache-Control", "public, max-age=31536000, immutable")
	c.Header("Content-Type", contentType)
	c.Writer.WriteHeader(http.StatusOK)
	_, _ = c.Writer.Write(content)
}

func convertPublicAssetFormat(content []byte, format string) ([]byte, string, bool) {
	normalized := strings.ToLower(strings.TrimSpace(format))
	if normalized == "" {
		return nil, "", false
	}
	if normalized != "png" && normalized != "jpg" && normalized != "jpeg" {
		return nil, "", false
	}

	decoded, _, err := image.Decode(bytes.NewReader(content))
	if err != nil {
		return nil, "", false
	}

	var output bytes.Buffer
	if normalized == "png" {
		if err := png.Encode(&output, decoded); err != nil {
			return nil, "", false
		}
		return output.Bytes(), "image/png", true
	}

	if err := jpeg.Encode(&output, decoded, &jpeg.Options{Quality: 92}); err != nil {
		return nil, "", false
	}
	return output.Bytes(), "image/jpeg", true
}

func (h *AssetHandler) signObjectKey(objectKey string) string {
	encodedKey := base64.RawURLEncoding.EncodeToString([]byte(objectKey))
	mac := hmac.New(sha256.New, []byte(h.secret))
	_, _ = mac.Write([]byte(objectKey))
	signature := base64.RawURLEncoding.EncodeToString(mac.Sum(nil))
	return fmt.Sprintf("%s.%s", encodedKey, signature)
}

func (h *AssetHandler) parseToken(token string) (string, bool) {
	parts := strings.Split(token, ".")
	if len(parts) != 2 {
		return "", false
	}

	objectKeyBytes, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return "", false
	}
	objectKey := string(objectKeyBytes)
	if strings.TrimSpace(objectKey) == "" {
		return "", false
	}

	expected := h.signObjectKey(objectKey)
	if !hmac.Equal([]byte(expected), []byte(token)) {
		return "", false
	}

	return objectKey, true
}

func objectKeyFromAssetToken(token string) (string, bool) {
	parts := strings.Split(token, ".")
	if len(parts) != 2 {
		return "", false
	}

	objectKeyBytes, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return "", false
	}
	objectKey := strings.TrimSpace(string(objectKeyBytes))
	if objectKey == "" {
		return "", false
	}
	return objectKey, true
}

func isDesktopClientAssetKey(objectKey string, tenantID int64) bool {
	if tenantID <= 0 {
		return false
	}
	tenantPrefix := "tenants/" + strconv.FormatInt(tenantID, 10) + "/"
	return strings.HasPrefix(objectKey, tenantPrefix+"images/") ||
		strings.HasPrefix(objectKey, tenantPrefix+"articles/")
}