crypto.hmac: optimize hmac.new, support calculations with a blocksize > 256 (#25686)

Author: CryingN

vlib/crypto/hmac/hmac.v

@@ -4,32 +4,26 @@ module hmac
 
 import crypto.internal.subtle
 
-const ipad = []u8{len: 256, init: 0x36} // TODO: is 256 enough??
-
-const opad = []u8{len: 256, init: 0x5C}
-const npad = []u8{len: 256, init: 0}
-
 // new returns a HMAC byte array, depending on the hash algorithm used.
 pub fn new(key []u8, data []u8, hash_func fn ([]u8) []u8, blocksize int) []u8 {
+	mut inner := []u8{len: blocksize, init: 0x36}
+	mut outer := []u8{len: blocksize, init: 0x5C}
+
 	mut b_key := []u8{}
 	if key.len <= blocksize {
 		b_key = key.clone() // TODO: remove .clone() once https://github.com/vlang/v/issues/6604 gets fixed
 	} else {
 		b_key = hash_func(key)
 	}
-	if b_key.len < blocksize {
-		b_key << npad[..blocksize - b_key.len]
+	if b_key.len > blocksize {
+		b_key = b_key[..blocksize].clone()
 	}
-	mut inner := []u8{}
-	for i, b in ipad[..blocksize] {
-		inner << b_key[i] ^ b
+	for i, b in b_key {
+		inner[i] = b ^ 0x36
+		outer[i] = b ^ 0x5c
 	}
 	inner << data
 	inner_hash := hash_func(inner)
-	mut outer := []u8{cap: b_key.len}
-	for i, b in opad[..blocksize] {
-		outer << b_key[i] ^ b
-	}
 	outer << inner_hash
 	digest := hash_func(outer)
 	return digest