| Index: branches/ariel/xmldumps-backup/checkforbz2footer.c |
| — | — | @@ -0,0 +1,156 @@ |
| | 2 | +#include <unistd.h> |
| | 3 | +#include <stdio.h> |
| | 4 | +#include <string.h> |
| | 5 | +#include <sys/types.h> |
| | 6 | +#include <sys/stat.h> |
| | 7 | +#include <fcntl.h> |
| | 8 | +#include <stdlib.h> |
| | 9 | +#include <errno.h> |
| | 10 | + |
| | 11 | +/* |
| | 12 | + Check to see whether a file ends with a bz2 footer or not |
| | 13 | + (i.e. if it is truncated or corrupted). |
| | 14 | + This is a crude but fast test for integrity; we don't |
| | 15 | + check the CRC at the end of fthe stream, nor do we check the |
| | 16 | + bit padding in the last byte of the file. |
| | 17 | + |
| | 18 | + Arguments: the name of the file to check, presumably |
| | 19 | + a bzipped file. |
| | 20 | + Outputs: none. |
| | 21 | + Exits with 1 if the file contains the footer at the end, |
| | 22 | + 0 if the file does not contain the footer, and -1 on error. |
| | 23 | +*/ |
| | 24 | + |
| | 25 | + |
| | 26 | +int read_footer(unsigned char *buffer, int fin) { |
| | 27 | + int res; |
| | 28 | + |
| | 29 | + res = lseek(fin, -11, SEEK_END); |
| | 30 | + if (res < 0) { |
| | 31 | + fprintf(stderr,"lseek of file failed\n"); |
| | 32 | + exit(-1); |
| | 33 | + } |
| | 34 | + res = read(fin, buffer, 11); |
| | 35 | + if (res < 0) { |
| | 36 | + fprintf(stderr,"read of file failed\n"); |
| | 37 | + exit(-1); |
| | 38 | + } |
| | 39 | + return(0); |
| | 40 | +} |
| | 41 | + |
| | 42 | +#define LEFT 0 |
| | 43 | +#define RIGHT 1 |
| | 44 | + |
| | 45 | +/* return n ones either at left or right end */ |
| | 46 | +int bitmask(int numbits, int end) { |
| | 47 | + if (end == RIGHT) { |
| | 48 | + return((1<<numbits)-1); |
| | 49 | + } |
| | 50 | + else { |
| | 51 | + return(((1<<numbits)-1) << (8-numbits)); |
| | 52 | + } |
| | 53 | +} |
| | 54 | + |
| | 55 | +void shiftbytesright(unsigned char *buffer, int buflen, int numbits) { |
| | 56 | + int i; |
| | 57 | + |
| | 58 | + for (i=buflen-1; i>=0; i--) { |
| | 59 | + /* right 1 */ |
| | 60 | + buffer[i] = (unsigned char) ((int) (buffer[i]) >> numbits); |
| | 61 | + |
| | 62 | + /* grab rightmost from prev byte */ |
| | 63 | + if (i > 0) { |
| | 64 | + buffer[i] = ( unsigned char ) ((unsigned int) buffer[i] | ( ((unsigned int) (buffer[i-1])<<(8-numbits)) & bitmask(1,LEFT))); |
| | 65 | + } |
| | 66 | + } |
| | 67 | +} |
| | 68 | + |
| | 69 | +/* buff1 is some random bytes, buff2 is some random bytes which we expect to start with the contents of buff1, |
| | 70 | + both buffers are bit-shifted to the right "bitsrightshifted". this function compares the two and returns 1 if buff2 |
| | 71 | + matches and 0 otherwise. */ |
| | 72 | +int bytescompare(unsigned char *buff1, unsigned char *buff2, int numbytes, int bitsrightshifted) { |
| | 73 | + int i; |
| | 74 | + |
| | 75 | + if (bitsrightshifted == 0) { |
| | 76 | + for (i = 0; i< numbytes; i++) { |
| | 77 | + if (buff1[i] != buff2[i]) { |
| | 78 | + return(0); |
| | 79 | + } |
| | 80 | + } |
| | 81 | + return(1); |
| | 82 | + } |
| | 83 | + else { |
| | 84 | + for (i = 1; i< numbytes-2; i++) { |
| | 85 | + if (buff1[i] != buff2[i]) { |
| | 86 | + return(0); |
| | 87 | + } |
| | 88 | + } |
| | 89 | + /* do leftmost byte */ |
| | 90 | + if ((buff1[0] & bitmask(8-bitsrightshifted,RIGHT)) != (buff2[0] & bitmask(8-bitsrightshifted,RIGHT)) ) { |
| | 91 | + return(0); |
| | 92 | + } |
| | 93 | + /* do rightmost byte */ |
| | 94 | + if ((buff1[numbytes-1] & bitmask(bitsrightshifted,LEFT)) != (buff2[numbytes-1] & bitmask(bitsrightshifted,LEFT)) ) { |
| | 95 | + return(0); |
| | 96 | + } |
| | 97 | + return(1); |
| | 98 | + } |
| | 99 | +} |
| | 100 | + |
| | 101 | +int checkfileforfooter(int fin) { |
| | 102 | + unsigned char buffer[11]; |
| | 103 | + int result, i; |
| | 104 | + unsigned char **footer = malloc(8*sizeof(unsigned char *)); |
| | 105 | + |
| | 106 | + /* set up footer plus its various right-shifted incarnations */ |
| | 107 | + /* dude why couldn't you have 0 padded each bzip2 block? seriously ... */ |
| | 108 | + for (i = 0; i< 8; i++) { |
| | 109 | + footer[i] = malloc(sizeof(unsigned char)*7); |
| | 110 | + } |
| | 111 | + footer[0][0]= (unsigned char) 0x17; |
| | 112 | + footer[0][1]= (unsigned char) 0x72; |
| | 113 | + footer[0][2]= (unsigned char) 0x45; |
| | 114 | + footer[0][3]= (unsigned char) 0x38; |
| | 115 | + footer[0][4]= (unsigned char) 0x50; |
| | 116 | + footer[0][5]= (unsigned char) 0x90; |
| | 117 | + footer[0][6]= (unsigned char) 0x00; |
| | 118 | + for (i = 1; i< 8; i++) { |
| | 119 | + memcpy((char *)(footer[i]), (char *)(footer[i-1]),7); |
| | 120 | + shiftbytesright(footer[i],7,1); |
| | 121 | + } |
| | 122 | + |
| | 123 | + read_footer(buffer,fin); |
| | 124 | + |
| | 125 | + result = bytescompare(footer[0],buffer+1,6,0); |
| | 126 | + if (result) { |
| | 127 | + return(result); |
| | 128 | + } |
| | 129 | + |
| | 130 | + for (i=1; i<8; i++) { |
| | 131 | + result = bytescompare(footer[i],buffer,7,i); |
| | 132 | + if (result) { |
| | 133 | + return(result); |
| | 134 | + } |
| | 135 | + } |
| | 136 | + return(0); |
| | 137 | +} |
| | 138 | + |
| | 139 | +int main(int argc, char **argv) { |
| | 140 | + |
| | 141 | + int fin; |
| | 142 | + int result; |
| | 143 | + |
| | 144 | + if (argc != 2) { |
| | 145 | + fprintf(stderr,"usage: %s infile\n", argv[0]); |
| | 146 | + exit(-1); |
| | 147 | + } |
| | 148 | + fin = open (argv[1], O_RDONLY); |
| | 149 | + if (fin < 0) { |
| | 150 | + fprintf(stderr,"failed to open file %s for read\n", argv[1]); |
| | 151 | + exit(-1); |
| | 152 | + } |
| | 153 | + result = checkfileforfooter(fin); |
| | 154 | + close(fin); |
| | 155 | + exit(result); |
| | 156 | +} |
| | 157 | + |
| Property changes on: branches/ariel/xmldumps-backup/checkforbz2footer.c |
| ___________________________________________________________________ |
| Added: svn:eol-style |
| 1 | 158 | + native |