feat(app): add internal components batch 5

internal/app/media_crypto.go

@@ -0,0 +1,21 @@
+package app
+
+import (
+	"errors"
+)
+
+func pkcs7Unpad(src []byte, blockSize int) ([]byte, error) {
+	if len(src) == 0 || len(src)%blockSize != 0 {
+		return nil, errors.New("invalid pkcs7 length")
+	}
+	pad := int(src[len(src)-1])
+	if pad == 0 || pad > blockSize || pad > len(src) {
+		return nil, errors.New("invalid pkcs7 padding")
+	}
+	for _, v := range src[len(src)-pad:] {
+		if int(v) != pad {
+			return nil, errors.New("invalid pkcs7 padding bytes")
+		}
+	}
+	return src[:len(src)-pad], nil
+}