feat(backend): 公开接口反爬轻量版——per-IP 日配额 + 列表收紧（todo #3）

DailyQuota 二级闸（单品 1000/日、店铺列表 300/日，0=关；出错放行不误伤）；
店铺列表 page_size 上限 50→20（客户端固定传 20 无破坏）；公开响应敏感字段
（cost/purchase_price/profit）零暴露回归测试。
明确不做：签名链接（QR 已印刷+UUIDv4 不可枚举）、滑块（杀零门槛分享）、登录墙。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/internal/handler/public.go

@@ -232,7 +232,8 @@ func (h *PublicHandler) ListShopProducts(c *gin.Context) {
 	if page < 1 {
 		page = 1
 	}
-	if pageSize < 1 || pageSize > 50 {
+	// 上限 20（2026-07 反爬收紧：客户端固定传 20，调大只方便爬全店）
+	if pageSize < 1 || pageSize > 20 {
 		pageSize = 20
 	}
 

backend/internal/handler/public_anticrawl_test.go

@@ -0,0 +1,90 @@
+package handler
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm"
+
+	"github.com/wangjia/jiu/backend/testutil"
+)
+
+// 反爬收紧回归（2026-07）：page_size 上限夹到 20；公开接口响应绝不出现
+// 成本类敏感字段名（白名单 DTO 防未来 Preload 全量 struct 回归泄露）。
+
+func setupPublicFullRouter(db *gorm.DB) *gin.Engine {
+	h := NewPublicHandler(db)
+	r := gin.New()
+	r.Use(gin.Recovery())
+	r.GET("/api/v1/public/shops/:shop_code/products", h.ListShopProducts)
+	r.GET("/api/v1/public/products/:public_id", h.GetProduct)
+	return r
+}
+
+func TestPublicListPageSizeClampedTo20(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PUBPS")
+	wh := testutil.CreateTestWarehouse(db, shop.ID, "仓")
+	r := setupPublicFullRouter(db)
+
+	for i := 0; i < 25; i++ {
+		p := testutil.CreateTestProduct(db, shop.ID, fmt.Sprintf("酒%02d", i))
+		setPublicID(db, p.ID, fmt.Sprintf("pub-ps-%02d", i))
+		addInventory(db, shop.ID, wh.ID, p.ID, 1)
+	}
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/api/v1/public/shops/PUBPS/products?page_size=50", nil)
+	r.ServeHTTP(w, req)
+	require.Equal(t, http.StatusOK, w.Code)
+
+	var resp map[string]interface{}
+	require.NoError(t, json.Unmarshal(w.Body.Bytes(), &resp))
+	assert.Equal(t, float64(25), resp["total"])
+	data := resp["data"].([]interface{})
+	assert.Len(t, data, 20, "page_size=50 应被夹到上限 20")
+	assert.Equal(t, float64(20), resp["page_size"])
+}
+
+// 公开响应不得出现的敏感字段名（成本/利润口径只对管理员，公开面零暴露）。
+var sensitiveFieldNames = []string{"cost", "purchase_price", "profit"}
+
+func assertNoSensitiveFields(t *testing.T, body string) {
+	t.Helper()
+	lower := strings.ToLower(body)
+	for _, f := range sensitiveFieldNames {
+		assert.NotContains(t, lower, f, "公开接口响应不应含敏感字段名 %q", f)
+	}
+}
+
+func TestPublicResponsesExcludeCostFields(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PUBSEC")
+	wh := testutil.CreateTestWarehouse(db, shop.ID, "仓")
+	r := setupPublicFullRouter(db)
+
+	p := testutil.CreateTestProduct(db, shop.ID, "敏感字段酒")
+	setPublicID(db, p.ID, "pub-sec-1")
+	addInventory(db, shop.ID, wh.ID, p.ID, 3)
+
+	// 列表
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/api/v1/public/shops/PUBSEC/products", nil)
+	r.ServeHTTP(w, req)
+	require.Equal(t, http.StatusOK, w.Code)
+	assertNoSensitiveFields(t, w.Body.String())
+
+	// 单品
+	w2 := httptest.NewRecorder()
+	req2, _ := http.NewRequest("GET", "/api/v1/public/products/pub-sec-1", nil)
+	r.ServeHTTP(w2, req2)
+	require.Equal(t, http.StatusOK, w2.Code)
+	assertNoSensitiveFields(t, w2.Body.String())
+}

backend/internal/middleware/dailyquota.go

@@ -0,0 +1,48 @@
+package middleware
+
+import (
+	"fmt"
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/wangjia/jiu/backend/config"
+	"github.com/wangjia/jiu/backend/internal/ratelimit"
+)
+
+// DailyQuota 同一 IP 的自然日累计配额——分钟级限流之上的第二道反爬闸。
+// key = "dq:<scope>:<yyyymmdd>:<ip>"，TTL 26h（跨午夜/时钟偏移裕量，键按日期
+// 自然分片，旧键过期自灭）。limit<=0 或总开关关闭时放行；计数器出错（redis
+// 降级窗口等）也放行——宁可漏限不误伤真实客户。
+func DailyQuota(scope string, limit func() int) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		lim := limit()
+		if !config.C.RateLimit.Enabled || lim <= 0 {
+			c.Next()
+			return
+		}
+		ip := c.ClientIP()
+		if ip == "" {
+			c.Next()
+			return
+		}
+		now := time.Now()
+		key := fmt.Sprintf("dq:%s:%s:%s", scope, now.Format("20060102"), ip)
+		n, err := ratelimit.Default().Counter().Incr(key, 26*time.Hour)
+		if err == nil && n > int64(lim) {
+			c.Header("Retry-After", strconv.Itoa(secondsToMidnight(now)))
+			c.AbortWithStatusJSON(http.StatusTooManyRequests,
+				gin.H{"error": "今日访问次数已达上限，请明日再试"})
+			return
+		}
+		c.Next()
+	}
+}
+
+// secondsToMidnight 距下一个本地零点的秒数（日配额的自然重置时刻）。
+func secondsToMidnight(now time.Time) int {
+	next := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location()).AddDate(0, 0, 1)
+	return int(next.Sub(now).Seconds())
+}

backend/internal/middleware/dailyquota_test.go

@@ -0,0 +1,75 @@
+package middleware
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/wangjia/jiu/backend/config"
+)
+
+func newQuotaRouter(scope string, limit int) *gin.Engine {
+	r := gin.New()
+	r.GET("/", DailyQuota(scope, func() int { return limit }), func(c *gin.Context) {
+		c.String(http.StatusOK, "ok")
+	})
+	return r
+}
+
+func TestDailyQuotaExceeded429(t *testing.T) {
+	enableRateLimit(t)
+	r := newQuotaRouter("tq1", 3)
+	for i := 0; i < 3; i++ {
+		if w := hit(r, "7.7.7.7"); w.Code != http.StatusOK {
+			t.Fatalf("配额内第 %d 发应放行，得到 %d", i+1, w.Code)
+		}
+	}
+	w := hit(r, "7.7.7.7")
+	if w.Code != http.StatusTooManyRequests {
+		t.Fatalf("超日配额应 429，得到 %d", w.Code)
+	}
+	if w.Header().Get("Retry-After") == "" {
+		t.Fatal("429 应带 Retry-After（到午夜秒数）")
+	}
+	// 不同 IP 独立
+	if w := hit(r, "8.8.8.8"); w.Code != http.StatusOK {
+		t.Fatalf("其他 IP 应不受影响，得到 %d", w.Code)
+	}
+}
+
+func TestDailyQuotaScopesIndependent(t *testing.T) {
+	enableRateLimit(t)
+	a := newQuotaRouter("tq2a", 1)
+	b := newQuotaRouter("tq2b", 1)
+	if w := hit(a, "9.9.9.9"); w.Code != http.StatusOK {
+		t.Fatalf("scope a 首发应放行，得到 %d", w.Code)
+	}
+	if w := hit(b, "9.9.9.9"); w.Code != http.StatusOK {
+		t.Fatalf("scope b 有独立配额池，应放行，得到 %d", w.Code)
+	}
+	if w := hit(a, "9.9.9.9"); w.Code != http.StatusTooManyRequests {
+		t.Fatalf("scope a 第二发应 429，得到 %d", w.Code)
+	}
+}
+
+func TestDailyQuotaDisabledOrZeroPassthrough(t *testing.T) {
+	// limit=0 → 该闸关闭
+	enableRateLimit(t)
+	r := newQuotaRouter("tq3", 0)
+	for i := 0; i < 5; i++ {
+		if w := hit(r, "10.0.0.1"); w.Code != http.StatusOK {
+			t.Fatalf("limit=0 第 %d 发应放行，得到 %d", i+1, w.Code)
+		}
+	}
+	// 总开关关闭 → 放行
+	prev := config.C.RateLimit.Enabled
+	config.C.RateLimit.Enabled = false
+	defer func() { config.C.RateLimit.Enabled = prev }()
+	r2 := newQuotaRouter("tq4", 1)
+	for i := 0; i < 5; i++ {
+		if w := hit(r2, "10.0.0.2"); w.Code != http.StatusOK {
+			t.Fatalf("总开关关闭第 %d 发应放行，得到 %d", i+1, w.Code)
+		}
+	}
+}

backend/internal/router/router.go

@@ -59,9 +59,12 @@ func Setup(r *gin.Engine, db *gorm.DB) {
 	refreshIP := middleware.RateLimitByIP(middleware.PerMinute(rl.RefreshPerMin), rl.RefreshPerMin)
 	registerIP := middleware.RateLimitByIP(middleware.PerMinute(rl.RegisterPerMin), rl.RegisterPerMin)
 	errorsIP := middleware.RateLimitByIP(middleware.PerMinute(rl.ErrorsPerMin), rl.ErrorsPerMin)
+	// 日配额二级闸（同一 IP 自然日累计，反爬）：单品 API 与 OG 页同一配额池
+	dqProduct := middleware.DailyQuota("product", func() int { return config.C.RateLimit.DailyProductPerIP })
+	dqShopList := middleware.DailyQuota("shoplist", func() int { return config.C.RateLimit.DailyShopListPerIP })
 
 	// 公开商品详情页（注入 OG 标签的 Flutter index.html，供社交分享爬虫读取）
-	r.GET("/product/:public_id", publicReadIP, publicH.ProductPage)
+	r.GET("/product/:public_id", publicReadIP, dqProduct, publicH.ProductPage)
 
 	v1 := r.Group("/api/v1")
 
@@ -77,8 +80,8 @@ func Setup(r *gin.Engine, db *gorm.DB) {
 	// 公开接口（无需登录）：读接口防爬、写接口防刷
 	public := v1.Group("/public")
 	{
-		public.GET("/products/:public_id", publicReadIP, publicH.GetProduct)
+		public.GET("/products/:public_id", publicReadIP, dqProduct, publicH.GetProduct)
-		public.GET("/shops/:shop_code/products", shopListIP, publicH.ListShopProducts)
+		public.GET("/shops/:shop_code/products", shopListIP, dqShopList, publicH.ListShopProducts)
 		public.GET("/release", publicReadIP, publicH.GetRelease)
 		public.POST("/errors", errorsIP, errorReportH.Submit)
 		public.POST("/register", registerIP, authH.Register)