Magisk/native/jni/b64xz.c

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/* b64xz.c - Base64-XZ Extractor
*
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* This program converts data from stdin to stdout.
* The input should be compressed with xz (integrity check only support CRC32 or none) and then
* encoded into base64 format. What b64xz does is basically the reverse of the
* mentioned process: decode base64 to bytes, decompress xz, then dump to stdout
*
* The compiled binary will be hex-dumped into update-binary
* Busybox will be xz-compressed, base64 encoded and dumped into update-binary
* This program is to recover busybox for Magisk installation environment
*/
#include <unistd.h>
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#include <xz.h>
static const char trans_tbl[] =
"|$$$}rstuvwxyz{$$$$$$$>?@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[\\]^_`abcdefghijklmnopq";
static void decodeblock(uint8_t* in, uint8_t* out) {
out[0] = (uint8_t)(in[0] << 2 | in[1] >> 4);
out[1] = (uint8_t)(in[1] << 4 | in[2] >> 2);
out[2] = (uint8_t)(((in[2] << 6) & 0xc0) | in[3]);
}
static int unxz(struct xz_dec *dec, const void *buf, unsigned size) {
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uint8_t out[8192];
struct xz_buf b = {
.in = buf,
.in_pos = 0,
.in_size = size,
.out = out,
.out_pos = 0,
.out_size = sizeof(out)
};
enum xz_ret ret;
do {
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ret = xz_dec_run(dec, &b);
if (ret != XZ_OK && ret != XZ_STREAM_END)
return 1;
write(STDOUT_FILENO, out, b.out_pos);
b.out_pos = 0;
} while (b.in_pos != size);
return 0;
}
int main(int argc, char const* argv[]) {
if (argc > 1)
return 0;
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uint8_t in[4], buf[6144];
unsigned len = 0, pos = 0;
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int8_t c;
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xz_crc32_init();
struct xz_dec *dec = xz_dec_init(XZ_DYNALLOC, 1 << 26);
if (dec == NULL)
return 1;
while (read(STDIN_FILENO, &c, sizeof(c)) == 1) {
c = ((c < 43 || c > 122) ? -1 : (trans_tbl[c - 43] == '$' ? -1 : trans_tbl[c - 43] - 62));
if (c >= 0)
in[len++] = c;
if (len < 4)
continue;
len = 0;
decodeblock(in, buf + pos);
pos += 3;
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if (pos == sizeof(buf)) {
if (unxz(dec, buf, pos))
return 1;
pos = 0;
}
}
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if (pos && unxz(dec, buf, pos))
return 1;
xz_dec_end(dec);
return 0;
}