feat(channels/weixin_ilink): 微信 iLink 渠道插件（扫码登录+长轮询+游标+context_token+AES-128-ECB 媒体+24h 主动推送窗口）

plugins/channels/weixin_ilink/aes.go

@@ -0,0 +1,79 @@
+package weixin_ilink
+
+import (
+	"crypto/aes"
+	"errors"
+	"fmt"
+)
+
+// ErrBadCiphertext is returned when ciphertext is not a whole number of AES
+// blocks or its padding is malformed.
+var ErrBadCiphertext = errors.New("weixin_ilink: bad ciphertext or padding")
+
+// pkcs7Pad appends PKCS#7 padding to src so its length becomes a multiple of
+// blockSize. Every appended byte holds the pad length, so it self-describes
+// and Unpad can strip it unambiguously.
+func pkcs7Pad(src []byte, blockSize int) []byte {
+	n := blockSize - len(src)%blockSize
+	out := make([]byte, len(src)+n)
+	copy(out, src)
+	for i := len(src); i < len(out); i++ {
+		out[i] = byte(n)
+	}
+	return out
+}
+
+// pkcs7Unpad strips PKCS#7 padding from src. It returns ErrBadCiphertext when
+// the length is not a block multiple or the final pad byte is inconsistent.
+func pkcs7Unpad(src []byte, blockSize int) ([]byte, error) {
+	if len(src) == 0 || len(src)%blockSize != 0 {
+		return nil, ErrBadCiphertext
+	}
+	n := int(src[len(src)-1])
+	if n < 1 || n > blockSize {
+		return nil, ErrBadCiphertext
+	}
+	for _, b := range src[len(src)-n:] {
+		if int(b) != n {
+			return nil, ErrBadCiphertext
+		}
+	}
+	return src[:len(src)-n], nil
+}
+
+// aesECBEncrypt encrypts src under AES with the supplied key using ECB mode.
+// Go's crypto/cipher package does not ship ECB, so the mode is implemented
+// here: src is padded to a block multiple and every block is encrypted
+// independently with the same key. ECB is deterministic and not semantically
+// secure; it is required here only because the iLink CDN protocol mandates it
+// for media payloads.
+func aesECBEncrypt(key, src []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("weixin_ilink: new aes cipher: %w", err)
+	}
+	padded := pkcs7Pad(src, block.BlockSize())
+	out := make([]byte, len(padded))
+	for i := 0; i < len(padded); i += block.BlockSize() {
+		block.Encrypt(out[i:i+block.BlockSize()], padded[i:i+block.BlockSize()])
+	}
+	return out, nil
+}
+
+// aesECBDecrypt decrypts src under AES with the supplied key and strips the
+// PKCS#7 padding. ECB has no IV, so the first block decrypts directly with the
+// key. It returns ErrBadCiphertext for malformed input.
+func aesECBDecrypt(key, src []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("weixin_ilink: new aes cipher: %w", err)
+	}
+	if len(src) == 0 || len(src)%block.BlockSize() != 0 {
+		return nil, ErrBadCiphertext
+	}
+	out := make([]byte, len(src))
+	for i := 0; i < len(src); i += block.BlockSize() {
+		block.Decrypt(out[i:i+block.BlockSize()], src[i:i+block.BlockSize()])
+	}
+	return pkcs7Unpad(out, block.BlockSize())
+}