fix: support windows certificate fonts

SDK_USAGE.md

@@ -26,6 +26,7 @@ if err != nil {
 - `COS_PUBLIC_BASE_URL`：证书公开访问基础地址。
 - `COS_SECRET_ID`：COS 访问密钥 ID。
 - `COS_SECRET_KEY`：COS 访问密钥。
+- `ZXCHAIN_CERTIFICATE_FONT_PATH`：可选。证书绘制使用的中文字体路径；Windows 可用 `C:/Windows/Fonts/msyh.ttc`。
 
 ## 存证和生成证书并一起返回
 
@@ -58,6 +59,7 @@ result, err := client.CreateSimpleHashAttestationCertificate(context.Background(
     CompletedAt:    "2026.5.11 15:20:01",
     WorkPreviewURL: "https://your-cdn/path/work-preview.jpg",
     EvidenceHash:   "作品hash",        //可选参数，可以不传
+    FontPath:       "C:/Windows/Fonts/msyh.ttc", // 可选；Windows 推荐微软雅黑，或配置 ZXCHAIN_CERTIFICATE_FONT_PATH
 
     CertificateStorage: &zxchainsdk.COSCertificateStorage{    //可选参数，可以不传
         BucketURL:     os.Getenv("COS_BUCKET_URL"),
@@ -88,6 +90,7 @@ fmt.Println("zxChainCertURL:", result.ZXChainCertURL)
 - `CompletedAt`：作品完成时间。
 - `WorkPreviewURL`：作品图片 URL。
 - `EvidenceHash`：可选。作品文件哈希；不传时 SDK 会从 `WorkPreviewURL` 下载内容并自行计算hash值。
+- `FontPath`：可选。中文字体路径；不传时 SDK 会自动查找 Windows/macOS/Linux 常见中文字体，也可以用 `ZXCHAIN_CERTIFICATE_FONT_PATH` 环境变量指定。Windows 常见可用路径：`C:/Windows/Fonts/msyh.ttc`、`C:/Windows/Fonts/simhei.ttf`、`C:/Windows/Fonts/simsun.ttc`。
 - `CertificateStorage`：可选。COS 上传配置。
 
 返回字段：

pkg/zxchainsdk/certificate.go

@@ -393,16 +393,39 @@ func containImage(src image.Image, boxWidth, boxHeight int) image.Image {
 
 func resolveCertificateFont(explicitPath string) (string, error) {
 	if explicitPath != "" {
-		if _, err := os.Stat(explicitPath); err != nil {
-			return "", err
+		return validateCertificateFont(explicitPath)
+	}
+
+	if envPath := os.Getenv("ZXCHAIN_CERTIFICATE_FONT_PATH"); envPath != "" {
+		return validateCertificateFont(envPath)
+	}
+
+	candidates := certificateFontCandidates()
+	for _, candidate := range candidates {
+		if fontPath, err := validateCertificateFont(candidate); err == nil {
+			return fontPath, nil
+		}
 	}
-		if _, err := gg.LoadFontFace(explicitPath, 25); err != nil {
-			return "", fmt.Errorf("load certificate font %s: %w", explicitPath, err)
+	return "", errors.New("missing certificate font, set HashCertificateRequest.FontPath or ZXCHAIN_CERTIFICATE_FONT_PATH to a Chinese TTF/TTC/OTF font")
+}
+
+func validateCertificateFont(fontPath string) (string, error) {
+	if _, err := os.Stat(fontPath); err != nil {
+		return "", err
 	}
-		return explicitPath, nil
+	if _, err := gg.LoadFontFace(fontPath, 25); err != nil {
+		return "", fmt.Errorf("load certificate font %s: %w", fontPath, err)
 	}
+	return fontPath, nil
+}
 
+func certificateFontCandidates() []string {
 	candidates := []string{
+		"C:/Windows/Fonts/msyh.ttc",
+		"C:/Windows/Fonts/msyhbd.ttc",
+		"C:/Windows/Fonts/simhei.ttf",
+		"C:/Windows/Fonts/simsun.ttc",
+		"C:/Windows/Fonts/simkai.ttf",
 		"/System/Library/Fonts/Supplemental/Arial Unicode.ttf",
 		"/System/Library/Fonts/Supplemental/Arial.ttf",
 		"/System/Library/Fonts/Supplemental/Microsoft Sans Serif.ttf",
@@ -414,15 +437,14 @@ func resolveCertificateFont(explicitPath string) (string, error) {
 		"/usr/share/fonts/opentype/noto/NotoSansCJK-Regular.ttc",
 		"/usr/share/fonts/truetype/noto/NotoSansCJK-Regular.ttc",
 	}
-	for _, candidate := range candidates {
-		if _, err := os.Stat(candidate); err != nil {
-			continue
-		}
-		if _, err := gg.LoadFontFace(candidate, 25); err == nil {
-			return candidate, nil
+
+	if windowsDir := firstNonEmpty(os.Getenv("WINDIR"), os.Getenv("SystemRoot")); windowsDir != "" {
+		windowsDir = strings.TrimRight(windowsDir, `\/`)
+		for _, name := range []string{"msyh.ttc", "msyhbd.ttc", "simhei.ttf", "simsun.ttc", "simkai.ttf"} {
+			candidates = append(candidates, windowsDir+"/Fonts/"+name)
 		}
 	}
-	return "", errors.New("missing certificate font, set HashCertificateRequest.FontPath to a Chinese TTF/TTC font")
+	return candidates
 }
 
 func certificateImageObjectKey(evidenceID, certNo string) string {

pkg/zxchainsdk/certificate_flow.go

@@ -62,6 +62,7 @@ type SimpleHashAttestationCertificateRequest struct {
 	CompletedAt    string `json:"completed_at"`            // CompletedAt 表示作品完成时间
 	WorkPreviewURL string `json:"work_preview_url"`        // WorkPreviewURL 表示作品预览图 URL
 	EvidenceHash   string `json:"evidence_hash,omitempty"` // EvidenceHash 表示作品文件哈希，可选。如果不传，SDK 将从 WorkPreviewURL 下载并计算哈希
+	FontPath       string `json:"font_path,omitempty"`     // FontPath 表示用于绘制证书的中文字体路径，可选
 
 	// 可选：如果不传，将使用内置默认值
 	CertificateStorage *COSCertificateStorage `json:"certificate_storage,omitempty"` // CertificateStorage 表示 COS 上传配置
@@ -204,6 +205,7 @@ func (c *SDKClient) CreateSimpleHashAttestationCertificate(ctx context.Context,
 		CompletedAt:        req.CompletedAt,
 		WorkPreviewURL:     req.WorkPreviewURL,
 		EvidenceHash:       evidenceHash,
+		FontPath:           req.FontPath,
 		CertificateStorage: req.CertificateStorage,
 	}
 
@@ -372,7 +374,7 @@ func UploadCertificatePNGToCOS(ctx context.Context, pngBytes []byte, defaultObje
 	_, err = client.Object.Put(ctx, objectKey, bytes.NewReader(pngBytes), &cos.ObjectPutOptions{
 		ObjectPutHeaderOptions: &cos.ObjectPutHeaderOptions{
 			ContentType:   "image/png",
-			ContentLength: int64(len(pngBytes)),
+			ContentLength: len(pngBytes),
 			CacheControl:  "public, max-age=31536000, immutable",
 		},
 	})