init: web_hgcg_server 初始化提交

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pub/common/imgutil/decrypt.go

@@ -0,0 +1,74 @@
+package imgutil
+
+import "bytes"
+
+// 与管理后台 ShowImg / imgCode.js 保持一致。
+var (
+	encryptMagicNumber = []byte{0x88, 0xA8, 0x30, 0xCB, 0x10, 0x76}
+	decryptKey         = []byte{50, 48, 49, 57, 121, 115, 97, 112, 112, 55, 53, 50, 55} // 2019ysapp7527
+	plainImageHeaders  = [][]byte{
+		{0xFF, 0xD8, 0xFF}, // jpeg
+		{0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A}, // png
+		{0x47, 0x49, 0x46}, // gif
+	}
+)
+
+const (
+	encryptedPrefixLen = 100
+	encryptXORAllKey   = 0xA3
+)
+
+// DecryptImage 按后台 handleVerAutoImg 的规则解密图床图片。
+// 已是 jpg/png/gif 则原样返回。
+func DecryptImage(data []byte) []byte {
+	if len(data) == 0 {
+		return data
+	}
+	out := append([]byte(nil), data...)
+	if hasEncryptMagic(out) {
+		return xorAllLength(out)
+	}
+	if !isPlainImage(out) {
+		xorPrefix(out, decryptKey, encryptedPrefixLen)
+	}
+	return out
+}
+
+func hasEncryptMagic(data []byte) bool {
+	return len(data) >= len(encryptMagicNumber) && bytes.Equal(data[:len(encryptMagicNumber)], encryptMagicNumber)
+}
+
+func isPlainImage(data []byte) bool {
+	for _, header := range plainImageHeaders {
+		if len(data) >= len(header) && bytes.Equal(data[:len(header)], header) {
+			return true
+		}
+	}
+	return false
+}
+
+func xorPrefix(src, key []byte, length int) {
+	if len(key) == 0 || len(src) == 0 {
+		return
+	}
+	if length <= 0 || length > len(src) {
+		length = len(src)
+	}
+	for i := 0; i < length; {
+		for j := 0; j < len(key) && i < length; j++ {
+			src[i] ^= key[j]
+			i++
+		}
+	}
+}
+
+func xorAllLength(src []byte) []byte {
+	out := make([]byte, 0, len(src))
+	for i, b := range src {
+		if i < len(encryptMagicNumber) && b == encryptMagicNumber[i] {
+			continue
+		}
+		out = append(out, b^encryptXORAllKey)
+	}
+	return out
+}