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Fix base64 decoding on platforms where char is unsigned #79

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4 changes: 4 additions & 0 deletions Makefile.am
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Original file line number Diff line number Diff line change
Expand Up @@ -252,3 +252,7 @@ t_test_str_to_rrtype_LDADD = wdns/libwdns.la
TESTS += t/test-fast_inet_ntop
check_PROGRAMS += t/test-fast_inet_ntop
t_test_fast_inet_ntop_SOURCES = t/test-fast_inet_ntop.c t/test-common.c

TESTS += t/test-b64_decode
check_PROGRAMS += t/test-b64_decode
t_test_b64_decode_SOURCES = t/test-b64_decode.c t/test-common.c
20 changes: 10 additions & 10 deletions libmy/b64_decode.c
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Expand Up @@ -9,11 +9,11 @@ For details, see http://sourceforge.net/projects/libb64

int base64_decode_value(char value_in)
{
static const char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
static const char decoding_size = sizeof(decoding);
value_in -= 43;
if (value_in < 0 || value_in > decoding_size) return -1;
return decoding[(int)value_in];
static const signed char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
static const int decoding_size = sizeof(decoding);
int offset = (int) (unsigned char) value_in - 43;
if (offset < 0 || offset >= decoding_size) return -1;
return decoding[offset];
}

void base64_init_decodestate(base64_decodestate* state_in)
Expand All @@ -26,7 +26,7 @@ int base64_decode_block(const char* code_in, const int length_in, char* plaintex
{
const char* codechar = code_in;
char* plainchar = plaintext_out;
char fragment;
int fragment;

*plainchar = state_in->plainchar;

Expand All @@ -42,7 +42,7 @@ int base64_decode_block(const char* code_in, const int length_in, char* plaintex
state_in->plainchar = *plainchar;
return plainchar - plaintext_out;
}
fragment = (char)base64_decode_value(*codechar++);
fragment = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar = (fragment & 0x03f) << 2;
case step_b:
Expand All @@ -53,7 +53,7 @@ int base64_decode_block(const char* code_in, const int length_in, char* plaintex
state_in->plainchar = *plainchar;
return plainchar - plaintext_out;
}
fragment = (char)base64_decode_value(*codechar++);
fragment = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar++ |= (fragment & 0x030) >> 4;
*plainchar = (fragment & 0x00f) << 4;
Expand All @@ -65,7 +65,7 @@ int base64_decode_block(const char* code_in, const int length_in, char* plaintex
state_in->plainchar = *plainchar;
return plainchar - plaintext_out;
}
fragment = (char)base64_decode_value(*codechar++);
fragment = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar++ |= (fragment & 0x03c) >> 2;
*plainchar = (fragment & 0x003) << 6;
Expand All @@ -77,7 +77,7 @@ int base64_decode_block(const char* code_in, const int length_in, char* plaintex
state_in->plainchar = *plainchar;
return plainchar - plaintext_out;
}
fragment = (char)base64_decode_value(*codechar++);
fragment = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar++ |= (fragment & 0x03f);
}
Expand Down
140 changes: 140 additions & 0 deletions t/test-b64_decode.c
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@@ -0,0 +1,140 @@
/*
* Copyright (c) 2026 DomainTools LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#include "test-common.h"

#include "libmy/b64_decode.h"
#include "libmy/b64_decode.c"

#include <string.h>

#define NAME "test-b64_decode"

/*
* base64_decode_value() must report every non-alphabet octet as negative,
* whatever the sign of a plain char is on this platform. base64_decode_block()
* relies on that to skip padding and whitespace.
*/
static size_t
test_decode_value(void) {
size_t failures = 0;
size_t i;
static const struct {
char input;
int expected;
} testdata[] = {
{ 'A', 0 },
{ 'Z', 25 },
{ 'a', 26 },
{ 'z', 51 },
{ '0', 52 },
{ '9', 61 },
{ '+', 62 },
{ '/', 63 },
{ '=', -2 },
{ ' ', -1 },
{ '\t', -1 },
{ '\n', -1 },
{ '\r', -1 },
{ '-', -1 },
{ '{', -1 }, /* one past the end of the decoding table */
{ '\x7f', -1 },
{ '\xff', -1 },
};

for (i = 0; i < sizeof(testdata)/sizeof(testdata[0]); i++) {
int res = base64_decode_value(testdata[i].input);

if (res == testdata[i].expected) {
fprintf(stderr, "PASS %zu: base64_decode_value(0x%02x) = %d\n",
i, (unsigned char) testdata[i].input, res);
} else {
fprintf(stderr, "FAIL %zu: base64_decode_value(0x%02x) = %d != %d\n",
i, (unsigned char) testdata[i].input, res,
testdata[i].expected);
failures++;
}
}

return (failures);
}

/*
* Decoding must ignore padding and embedded whitespace. DNSKEY, CDNSKEY,
* RRSIG and OPENPGPKEY presentation format all carry both.
*/
static size_t
test_decode_block(void) {
size_t failures = 0;
size_t i;
static const struct {
const char *input;
const char *expected;
size_t elen;
} testdata[] = {
{ "AQIDBAUGBwg=", "\x01\x02\x03\x04\x05\x06\x07\x08", 8 },
{ "ZGVhZGJlZWY=", "deadbeef", 8 },
{ "ZGVhZGJlZWY==", "deadbeef", 8 },
{ "ZGVh ZGJl ZWY=", "deadbeef", 8 },
{ "ZGVhZGJl\nZWY=", "deadbeef", 8 },
{ "ZGVhZGJl\r\n\tZWY=", "deadbeef", 8 },
{ " ZGVhZGJlZWY= ", "deadbeef", 8 },
{ "AA==", "\x00", 1 },
{ "", "", 0 },
};

for (i = 0; i < sizeof(testdata)/sizeof(testdata[0]); i++) {
base64_decodestate b64;
char buf[64];
int len;

memset(buf, 0, sizeof(buf));
base64_init_decodestate(&b64);
len = base64_decode_block(testdata[i].input,
strlen(testdata[i].input),
buf, &b64);

if (len == (int) testdata[i].elen &&
memcmp(buf, testdata[i].expected, testdata[i].elen) == 0)
{
fprintf(stderr, "PASS %zu: base64_decode_block(\"%s\") len %d\n",
i, testdata[i].input, len);
} else {
ubuf *u = ubuf_init(64);

escape(u, (const uint8_t *) buf, len < 0 ? 0 : (size_t) len);
fprintf(stderr, "FAIL %zu: base64_decode_block(\"%s\") len %d != %zu value=%s\n",
i, testdata[i].input, len, testdata[i].elen,
ubuf_cstr(u));
ubuf_destroy(&u);
failures++;
}
}

return (failures);
}

int main (void) {
int ret = 0;

ret |= check(test_decode_value(), "test_decode_value", NAME);
ret |= check(test_decode_block(), "test_decode_block", NAME);

if (ret)
return (EXIT_FAILURE);

return (EXIT_SUCCESS);
}