interop: add canonical type lengths as constants

Contracts need them anyway.

pkg/interop/types.go

@@ -1,5 +1,25 @@
 package interop
 
+const (
+	// Hash160Len is the length of proper Hash160 in bytes, use it to
+	// sanitize input parameters.
+	Hash160Len = 20
+	// Hash256Len is the length of proper Hash256 in bytes, use it to
+	// sanitize input parameters.
+	Hash256Len = 32
+	// PublicKeyCompressedLen is the length of compressed public key (which
+	// is the most common public key type), use it to sanitize input
+	// parameters.
+	PublicKeyCompressedLen = 33
+	// PublicKeyUncompressedLen is the length of uncompressed public key
+	// (but you're not likely to ever encounter that), use it to sanitize
+	// input parameters.
+	PublicKeyUncompressedLen = 65
+	// SignatureLen is the length of standard signature, use it to sanitize
+	// input parameters.
+	SignatureLen = 64
+)
+
 // Signature represents 64-byte signature.
 type Signature []byte