crypto.md5: fix calculating the same hash values, when .sum() is called several times (#19703)

vlib/crypto/md5/md5.v

@@ -58,6 +58,14 @@ pub fn (mut d Digest) reset() {
 	d.len = 0
 }
 
+fn (d &Digest) clone() &Digest {
+	return &Digest{
+		...d
+		s: d.s.clone()
+		x: d.x.clone()
+	}
+}
+
 // new returns a new Digest (implementing hash.Hash) computing the MD5 checksum.
 pub fn new() &Digest {
 	mut d := &Digest{}
@@ -103,7 +111,7 @@ pub fn (mut d Digest) write(p_ []u8) !int {
 // sum returns the md5 sum of the bytes in `b_in`.
 pub fn (d &Digest) sum(b_in []u8) []u8 {
 	// Make a copy of d so that caller can keep writing and summing.
-	mut d0 := *d
+	mut d0 := d.clone()
 	hash := d0.checksum()
 	mut b_out := b_in.clone()
 	for b in hash {
@@ -112,7 +120,10 @@ pub fn (d &Digest) sum(b_in []u8) []u8 {
 	return b_out
 }
 
-// checksum returns the byte checksum of the `Digest`.
+// checksum returns the byte checksum of the `Digest`,
+// it is an internal method and is not recommended because its results are not idempotent.
+[deprecated: 'checksum() will be changed to a private method, use sum() instead']
+[deprecated_after: '2024-04-30']
 pub fn (mut d Digest) checksum() []u8 {
 	// Append 0x80 to the end of the message and then append zeros
 	// until the length is a multiple of 56 bytes. Finally append

vlib/crypto/md5/md5_test.v

@@ -11,7 +11,9 @@ fn test_crypto_md5_writer() {
 	mut digest := md5.new()
 	digest.write('this is a'.bytes()) or { assert false }
 	digest.write(' md5 checksum.'.bytes()) or { assert false }
-	sum := digest.sum([])
+	mut sum := digest.sum([])
+	assert sum.hex() == '6fb421ff99036547655984da12973431'
+	sum = digest.sum([])
 	assert sum.hex() == '6fb421ff99036547655984da12973431'
 }
 

vlib/crypto/sha1/sha1.v

@@ -127,7 +127,10 @@ pub fn (d &Digest) sum(b_in []u8) []u8 {
 	return b_out
 }
 
-// checksum returns the current byte checksum of the `Digest`.
+// checksum returns the current byte checksum of the `Digest`,
+// it is an internal method and is not recommended because its results are not idempotent.
+[deprecated: 'checksum() will be changed to a private method, use sum() instead']
+[deprecated_after: '2024-04-30']
 pub fn (mut d Digest) checksum() []u8 {
 	mut len := d.len
 	// Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.

vlib/crypto/sha256/sha256.v

@@ -167,7 +167,10 @@ pub fn (d &Digest) sum(b_in []u8) []u8 {
 	return b_out
 }
 
-// checksum returns the current byte checksum of the Digest.
+// checksum returns the current byte checksum of the Digest,
+// it is an internal method and is not recommended because its results are not idempotent.
+[deprecated: 'checksum() will be changed to a private method, use sum() instead']
+[deprecated_after: '2024-04-30']
 pub fn (mut d Digest) checksum() []u8 {
 	mut len := d.len
 	// Padding. Add a 1 bit and 0 bits until 56 bytes mod 64.

vlib/crypto/sha512/sha512.v

@@ -239,7 +239,10 @@ pub fn (d &Digest) sum(b_in []u8) []u8 {
 	return b_out
 }
 
-// checksum returns the current byte checksum of the Digest.
+// checksum returns the current byte checksum of the Digest,
+// it is an internal method and is not recommended because its results are not idempotent.
+[deprecated: 'checksum() will be changed to a private method, use sum() instead']
+[deprecated_after: '2024-04-30']
 pub fn (mut d Digest) checksum() []u8 {
 	// Padding. Add a 1 bit and 0 bits until 112 bytes mod 128.
 	mut len := d.len