Modify b58tobin to return canonical size

Makefile.am

@@ -27,6 +27,9 @@ TESTS = \
 	tests/decode-b58c.sh \
 	tests/decode-b58c-fail.sh \
 	tests/decode-b58c-null.sh \
+	tests/decode-b58c-toolong.sh \
+	tests/decode-b58c-tooshort.sh \
+	tests/decode-zero.sh \
 	tests/encode.sh \
 	tests/encode-b58c.sh \
 	tests/encode-fail.sh

README

@@ -13,9 +13,12 @@ This is only required if base58check is used. Raw base58 does not need SHA256.
 Decoding Base58
 ---------------
 
-Simply allocate a buffer to store the binary data in, and call the b58tobin
-function:
-	bool b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz)
+Simply allocate a buffer to store the binary data in, and set a variable with
+the buffer size, and call the b58tobin function:
+	bool b58tobin(void *bin, size_t *binsz, const char *b58, size_t b58sz)
+The "canonical" base58 byte length will be assigned to binsz on success, which
+may be larger than the actual buffer if the input has many leading zeros.
+Regardless of the canonical byte length, the full binary buffer will be used.
 If b58sz is zero, it will be initialised with strlen(b58); note that a true
 zero-length base58 string is not supported here.
 

base58.c

@@ -29,8 +29,9 @@ static const int8_t b58digits_map[] = {
 	47,48,49,50,51,52,53,54, 55,56,57,-1,-1,-1,-1,-1,
 };
 
-bool b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz)
+bool b58tobin(void *bin, size_t *binszp, const char *b58, size_t b58sz)
 {
+	size_t binsz = *binszp;
 	const unsigned char *b58u = (void*)b58;
 	unsigned char *binu = bin;
 	size_t outisz = (binsz + 3) / 4;
@@ -40,13 +41,18 @@ bool b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz)
 	size_t i, j;
 	uint8_t bytesleft = binsz % 4;
 	uint32_t zeromask = ~((1 << ((bytesleft) * 8)) - 1);
+	unsigned zerocount = 0;
 	
 	if (!b58sz)
 		b58sz = strlen(b58);
 	
 	memset(outi, 0, outisz * sizeof(*outi));
 	
-	for (i = 0; i < b58sz; ++i)
+	// Leading zeros, just count
+	for (i = 0; i < b58sz && !b58digits_map[b58u[i]]; ++i)
+		++zerocount;
+	
+	for ( ; i < b58sz; ++i)
 	{
 		if (b58u[i] & 0x80)
 			// High-bit set on invalid digit
@@ -87,6 +93,17 @@ bool b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz)
 		*((uint32_t*)binu) = htonl(outi[j]);
 		binu += sizeof(uint32_t);
 	}
+	
+	// Count canonical base58 byte count
+	binu = bin;
+	for (i = 0; i < binsz; ++i)
+	{
+		if (binu[i])
+			break;
+		--*binszp;
+	}
+	*binszp += zerocount;
+	
 	return true;
 }
 

base58.h

@@ -10,7 +10,7 @@ extern "C" {
 
 extern bool (*b58_sha256_impl)(void *, const void *, size_t);
 
-extern bool b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz);
+extern bool b58tobin(void *bin, size_t *binsz, const char *b58, size_t b58sz);
 extern int b58check(const void *bin, size_t binsz, const char *b58, size_t b58sz);
 
 extern bool b58enc(char *b58, size_t *b58sz, const void *bin, size_t binsz);

clitool.c

@@ -71,16 +71,33 @@ int main(int argc, char **argv)
 	if (decode)
 	{
 		uint8_t bin[decode];
-		if (!b58tobin(bin, decode, r, rt))
+		size_t ssz = decode;
+		if (!b58tobin(bin, &ssz, r, rt))
 			return 2;
 		if (b58c)
 		{
 			int chk = b58check(bin, decode, r, rt);
 			if (chk < 0)
 				return chk;
+			if (fwrite(bin, decode, 1, stdout) != 1)
+				return 3;
+		}
+		else
+		{
+			// Raw base58 doesn't check length match
+			uint8_t cbin[ssz];
+			if (ssz > decode)
+			{
+				size_t zeros = ssz - decode;
+				memset(cbin, 0, zeros);
+				memcpy(&cbin[zeros], bin, decode);
+			}
+			else
+				memcpy(cbin, &bin[decode - ssz], ssz);
+			
+			if (fwrite(cbin, ssz, 1, stdout) != 1)
+				return 3;
 		}
-		if (fwrite(bin, decode, 1, stdout) != 1)
-			return 3;
 	}
 	else
 	{

tests/decode-b58c-toolong.sh

@@ -0,0 +1,2 @@
+#!/bin/sh
+! base58 -d 25 -c 1119DXstMaV43WpYg4ceREiiTv2UntmoiA9a >/dev/null

tests/decode-b58c-tooshort.sh

@@ -0,0 +1,2 @@
+#!/bin/sh
+! base58 -d 25 -c 111111111111111111114oLvT2 >/dev/null

tests/decode-zero.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+hex=$(base58 -d 25 111111 | xxd -p)
+test x$hex = x000000000000

tests/decode.sh

@@ -1,3 +1,3 @@
 #!/bin/sh
-hex=$(base58 -d 25 19DXstMaV43WpYg4ceREiiTv2UntmoiA9j | xxd -p)
-test x$hex != x005a1fc5dd9e6f03819fca94a2d89669469667f9a1
+hex=$(base58 -d 50 19DXstMaV43WpYg4ceREiiTv2UntmoiA9j | xxd -p)
+test x$hex = x005a1fc5dd9e6f03819fca94a2d89669469667f9a074655946