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Custom implementation of Base64 decoding function.

Browse Source 
Compared to the previous implementation based on OpenSSL, the new implementation
has these advantages:

 1. Strict and reliable detection of invalid strings, including strings with
    less than 4 bytes of garbage at the end;

 2. Allows to use Base64 strings without '=' padding.
This commit is contained in:
Valentin Bartenev
2021-10-26 15:43:44 +03:00
parent 7503cc96df
commit 7bf6253941
9 changed files with 209 additions and 82 deletions
Download Patch File Download Diff File Expand all files Collapse all files

97
src/nxt_string.c
View File

@@ -745,3 +745,100 @@ nxt_is_complex_uri_encoded(u_char *src, size_t length)
return 1;
}
ssize_t
nxt_base64_decode(u_char *dst, u_char *src, size_t length)
{
u_char *end, *p;
size_t pad;
uint8_t v1, v2, v3, v4;
static const uint8_t decode[] = {
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 62, 77, 77, 77, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 77, 77, 77, 77, 77, 77,
77, 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, 77, 77, 77, 77, 77,
77, 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, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77
};
end = src + length;
pad = (4 - (length % 4)) % 4;
if (dst == NULL) {
if (pad > 2) {
return NXT_ERROR;
}
while (src < end) {
if (decode[*src] != 77) {
src++;
continue;
}
if (pad == 0) {
pad = end - src;
if ((pad == 1 || (pad == 2 && src[1] == '=')) && src[0] == '=')
{
break;
}
}
return NXT_ERROR;
}
return (length + 3) / 4 * 3 - pad;
}
nxt_assert(length != 0);
if (pad == 0) {
pad = (end[-1] == '=') + (end[-2] == '=');
end -= (pad + 3) & 4;
} else {
end -= 4 - pad;
}
p = dst;
while (src < end) {
v1 = decode[src[0]];
v2 = decode[src[1]];
v3 = decode[src[2]];
v4 = decode[src[3]];
*p++ = (v1 << 2 | v2 >> 4);
*p++ = (v2 << 4 | v3 >> 2);
*p++ = (v3 << 6 | v4);
src += 4;
}
if (pad > 0) {
v1 = decode[src[0]];
v2 = decode[src[1]];
*p++ = (v1 << 2 | v2 >> 4);
if (pad == 1) {
v3 = decode[src[2]];
*p++ = (v2 << 4 | v3 >> 2);
}
}
return (p - dst);
}