1/*
2 * xorimage.c - partially based on OpenWrt's addpattern.c
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
17 */
18
19
20#include <stdio.h>
21#include <stdlib.h>
22#include <string.h>
23#include <stdint.h>
24#include <time.h>
25#include <unistd.h>
26#include <sys/stat.h>
27
28static char default_pattern[] = "12345678";
29
30
31int xor_data(uint8_t *data, size_t len, const uint8_t *pattern, int p_len, int p_off)
32{
33	int offset = p_off;
34	while (len--) {
35		*data ^= pattern[offset];
36		data++;
37		offset = (offset + 1) % p_len;
38	}
39	return offset;
40}
41
42
43void usage(void) __attribute__ (( __noreturn__ ));
44
45void usage(void)
46{
47	fprintf(stderr, "Usage: xorimage [-i infile] [-o outfile] [-p <pattern>]\n");
48	exit(EXIT_FAILURE);
49}
50
51
52int main(int argc, char **argv)
53{
54	char buf[1024];	/* keep this at 1k or adjust garbage calc below */
55	FILE *in = stdin;
56	FILE *out = stdout;
57	char *ifn = NULL;
58	char *ofn = NULL;
59	const char *pattern = default_pattern;
60	int c;
61	int v0, v1, v2;
62	size_t n;
63	int p_len, p_off = 0;
64
65	while ((c = getopt(argc, argv, "i:o:p:h")) != -1) {
66		switch (c) {
67			case 'i':
68				ifn = optarg;
69				break;
70			case 'o':
71				ofn = optarg;
72				break;
73			case 'p':
74				pattern = optarg;
75				break;
76			case 'h':
77			default:
78				usage();
79		}
80	}
81
82	if (optind != argc || optind == 1) {
83		fprintf(stderr, "illegal arg \"%s\"\n", argv[optind]);
84		usage();
85	}
86
87	if (ifn && !(in = fopen(ifn, "r"))) {
88		fprintf(stderr, "can not open \"%s\" for reading\n", ifn);
89		usage();
90	}
91
92	if (ofn && !(out = fopen(ofn, "w"))) {
93		fprintf(stderr, "can not open \"%s\" for writing\n", ofn);
94		usage();
95	}
96
97	p_len = strlen(pattern);
98
99	if (p_len == 0) {
100		fprintf(stderr, "pattern cannot be empty\n");
101		usage();
102	}
103
104
105	while ((n = fread(buf, 1, sizeof(buf), in)) > 0) {
106		if (n < sizeof(buf)) {
107			if (ferror(in)) {
108			FREAD_ERROR:
109				fprintf(stderr, "fread error\n");
110				return EXIT_FAILURE;
111			}
112		}
113
114		p_off = xor_data(buf, n, pattern, p_len, p_off);
115
116		if (!fwrite(buf, n, 1, out)) {
117		FWRITE_ERROR:
118			fprintf(stderr, "fwrite error\n");
119			return EXIT_FAILURE;
120		}
121	}
122
123	if (ferror(in)) {
124		goto FREAD_ERROR;
125	}
126
127	if (fflush(out)) {
128		goto FWRITE_ERROR;
129	}
130
131	fclose(in);
132	fclose(out);
133
134	return EXIT_SUCCESS;
135}
136