busybox/libbb/percent_decode.c

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/* vi: set sw=4 ts=4: */
/*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
//kbuild:lib-y += percent_decode.o
#include "libbb.h"
static unsigned hex_to_bin(unsigned char c)
{
unsigned v;
v = c - '0';
if (v <= 9)
return v;
/* c | 0x20: letters to lower case, non-letters
* to (potentially different) non-letters */
v = (unsigned)(c | 0x20) - 'a';
if (v <= 5)
return v + 10;
return ~0;
/* For testing:
void t(char c) { printf("'%c'(%u) %u\n", c, c, hex_to_bin(c)); }
int main() { t(0x10); t(0x20); t('0'); t('9'); t('A'); t('F'); t('a'); t('f');
t('0'-1); t('9'+1); t('A'-1); t('F'+1); t('a'-1); t('f'+1); return 0; }
*/
}
char* FAST_FUNC percent_decode_in_place(char *str, int strict)
{
/* note that decoded string is always shorter than original */
char *src = str;
char *dst = str;
char c;
while ((c = *src++) != '\0') {
unsigned v;
if (!strict && c == '+') {
*dst++ = ' ';
continue;
}
if (c != '%') {
*dst++ = c;
continue;
}
v = hex_to_bin(src[0]);
if (v > 15) {
bad_hex:
if (strict)
return NULL;
*dst++ = '%';
continue;
}
v = (v * 16) | hex_to_bin(src[1]);
if (v > 255)
goto bad_hex;
if (strict && (v == '/' || v == '\0')) {
/* caller takes it as indication of invalid
* (dangerous wrt exploits) chars */
return str + 1;
}
*dst++ = v;
src += 2;
}
*dst = '\0';
return str;
}