Magisk/jni/b64xz.c

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/* b64xz.c - Base64-XZ Extractor
*
* This program expects data from stdin. The data should be compressed with xz and
* then encoded into base64 format. What b64xz does is basically the reverse of the
* mentioned process: decode base64 to uint8_ts, 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
*
* I intentionally removed stdio. This will result in a smaller binary size because
* all I/O are handled by system calls (read/write) instead of libc wrappers
*/
#include <unistd.h>
#include <lzma.h>
#define BUFSIZE 8192
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(lzma_stream *strm, void *buf, size_t size) {
lzma_ret ret = 0;
uint8_t out[BUFSIZE];
strm->next_in = buf;
strm->avail_in = size;
do {
strm->next_out = out;
strm->avail_out = sizeof(out);
ret = lzma_code(strm, LZMA_RUN);
write(STDOUT_FILENO, out, sizeof(out) - strm->avail_out);
} while (strm->avail_out == 0 && ret == LZMA_OK);
if (ret != LZMA_OK && ret != LZMA_STREAM_END)
write(STDERR_FILENO, "LZMA error!\n", 13);
return ret;
}
int main(int argc, char const* argv[]) {
if (argc > 1)
return 0;
uint8_t in[4], buf[BUFSIZE];
int len = 0, pos = 0;
char c;
// Setup lzma stream
lzma_stream strm = LZMA_STREAM_INIT;
if (lzma_auto_decoder(&strm, UINT64_MAX, 0) != LZMA_OK) {
write(STDERR_FILENO, "Unable to init lzma stream\n", 28);
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;
if (pos > sizeof(buf) - 3) {
// Buffer is full, unxz
if (unxz(&strm, buf, pos))
return 1;
pos = 0;
}
}
if (pos) {
if (unxz(&strm, buf, pos))
return 1;
}
lzma_end(&strm);
return 0;
}