优化缩略图

internal/service/image_resize_budget_test.go

@@ -0,0 +1,113 @@
+package service
+
+import (
+	"bytes"
+	"errors"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"testing"
+)
+
+// encodeTestJPEG 生成一张便于压缩的测试用 JPEG（比 PNG 更适合构造大尺寸样本）。
+func encodeTestJPEG(t *testing.T, w, h int) []byte {
+	t.Helper()
+	img := image.NewRGBA(image.Rect(0, 0, w, h))
+	for y := 0; y < h; y++ {
+		for x := 0; x < w; x++ {
+			img.Set(x, y, color.RGBA{R: uint8(x % 32 * 8), G: uint8(y % 32 * 8), B: 150, A: 255})
+		}
+	}
+	var buf bytes.Buffer
+	if err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: 70}); err != nil {
+		t.Fatalf("encode test jpeg: %v", err)
+	}
+	return buf.Bytes()
+}
+
+// TestResizeImageDataRejectsOverPixelBudget 锁定解码像素预算：超过上限的
+// 原图必须放弃缩放（回退原图直出），而不是在小内存主机上尝试解码。
+func TestResizeImageDataRejectsOverPixelBudget(t *testing.T) {
+	// 12_000_000 像素预算之上：3000×5000 = 1500 万。
+	data := encodeTestJPEG(t, 3000, 5000)
+
+	if _, _, _, err := resizeImageData(data, imageResizeOptions{MaxWidth: 400}); !errors.Is(err, errImageResizeTooLarge) {
+		t.Fatalf("expected errImageResizeTooLarge, got %v", err)
+	}
+}
+
+// TestResizeImageDataAcceptsRealisticPoster 常见高清海报（2892×4096，约
+// 1180 万像素）必须仍在预算之内，否则真实海报会退化成直出多兆字节原图。
+func TestResizeImageDataAcceptsRealisticPoster(t *testing.T) {
+	data := encodeTestJPEG(t, 2892, 4096)
+
+	out, ctype, unchanged, err := resizeImageData(data, imageResizeOptions{MaxWidth: 480, MaxHeight: 600})
+	if err != nil {
+		t.Fatalf("resizeImageData failed: %v", err)
+	}
+	if unchanged {
+		t.Fatal("expected a resized result, got the original bytes")
+	}
+	if ctype != "image/jpeg" {
+		t.Fatalf("content type = %q, want image/jpeg", ctype)
+	}
+	cfg, _, err := image.DecodeConfig(bytes.NewReader(out))
+	if err != nil {
+		t.Fatalf("decode resized output: %v", err)
+	}
+	if cfg.Width != 424 || cfg.Height != 600 {
+		t.Fatalf("resized to %dx%d, want 424x600", cfg.Width, cfg.Height)
+	}
+}
+
+// TestUseCheapScaleInterpolator 大比例缩小走低成本插值，轻微缩小仍保持高质量。
+func TestUseCheapScaleInterpolator(t *testing.T) {
+	cases := []struct {
+		name                   string
+		dstW, dstH, srcW, srcH int
+		want                   bool
+	}{
+		{"poster to card", 480, 600, 2892, 4096, true},
+		{"hero to strip", 480, 320, 1920, 1080, true},
+		{"exactly half is cheap", 960, 540, 1920, 1080, true},
+		{"slight shrink", 900, 540, 1000, 600, false},
+		{"upscale", 1200, 800, 600, 400, false},
+		{"zero source", 100, 100, 0, 0, false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := useCheapScaleInterpolator(tc.dstW, tc.dstH, tc.srcW, tc.srcH); got != tc.want {
+				t.Fatalf("useCheapScaleInterpolator(%d,%d,%d,%d) = %v, want %v",
+					tc.dstW, tc.dstH, tc.srcW, tc.srcH, got, tc.want)
+			}
+		})
+	}
+}
+
+// TestIsOpaqueImageDetectsAlpha 透明度检测：全不透明才允许转 JPEG。
+func TestIsOpaqueImageDetectsAlpha(t *testing.T) {
+	opaque := image.NewRGBA(image.Rect(0, 0, 4, 4))
+	for y := 0; y < 4; y++ {
+		for x := 0; x < 4; x++ {
+			opaque.Set(x, y, color.RGBA{R: 10, G: 20, B: 30, A: 255})
+		}
+	}
+	if !isOpaqueImage(opaque) {
+		t.Fatal("expected fully opaque image to be reported opaque")
+	}
+
+	withAlpha := image.NewRGBA(image.Rect(0, 0, 4, 4))
+	for y := 0; y < 4; y++ {
+		for x := 0; x < 4; x++ {
+			withAlpha.Set(x, y, color.RGBA{R: 10, G: 20, B: 30, A: 255})
+		}
+	}
+	withAlpha.Set(2, 2, color.RGBA{R: 10, G: 20, B: 30, A: 128})
+	if isOpaqueImage(withAlpha) {
+		t.Fatal("expected image with a translucent pixel to be reported non-opaque")
+	}
+
+	if isOpaqueImage(nil) {
+		t.Fatal("expected nil image to be reported non-opaque")
+	}
+}