http://www.mediawiki.org/wiki/Special:Code/MediaWiki/90870
Revision: 90870
Author: ariel
Date: 2011-06-27 08:02:06 +0000 (Mon, 27 Jun 2011)
Log Message:
-----------
quick checker for truncated bz2 files
Added Paths:
-----------
branches/ariel/xmldumps-backup/checkforbz2footer.c
Added: branches/ariel/xmldumps-backup/checkforbz2footer.c
===================================================================
--- branches/ariel/xmldumps-backup/checkforbz2footer.c
(rev 0)
+++ branches/ariel/xmldumps-backup/checkforbz2footer.c 2011-06-27 08:02:06 UTC
(rev 90870)
@@ -0,0 +1,156 @@
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <errno.h>
+
+/*
+ Check to see whether a file ends with a bz2 footer or not
+ (i.e. if it is truncated or corrupted).
+ This is a crude but fast test for integrity; we don't
+ check the CRC at the end of fthe stream, nor do we check the
+ bit padding in the last byte of the file.
+
+ Arguments: the name of the file to check, presumably
+ a bzipped file.
+ Outputs: none.
+ Exits with 1 if the file contains the footer at the end,
+ 0 if the file does not contain the footer, and -1 on error.
+*/
+
+
+int read_footer(unsigned char *buffer, int fin) {
+ int res;
+
+ res = lseek(fin, -11, SEEK_END);
+ if (res < 0) {
+ fprintf(stderr,"lseek of file failed\n");
+ exit(-1);
+ }
+ res = read(fin, buffer, 11);
+ if (res < 0) {
+ fprintf(stderr,"read of file failed\n");
+ exit(-1);
+ }
+ return(0);
+}
+
+#define LEFT 0
+#define RIGHT 1
+
+/* return n ones either at left or right end */
+int bitmask(int numbits, int end) {
+ if (end == RIGHT) {
+ return((1<<numbits)-1);
+ }
+ else {
+ return(((1<<numbits)-1) << (8-numbits));
+ }
+}
+
+void shiftbytesright(unsigned char *buffer, int buflen, int numbits) {
+ int i;
+
+ for (i=buflen-1; i>=0; i--) {
+ /* right 1 */
+ buffer[i] = (unsigned char) ((int) (buffer[i]) >> numbits);
+
+ /* grab rightmost from prev byte */
+ if (i > 0) {
+ buffer[i] = ( unsigned char ) ((unsigned int) buffer[i] | ( ((unsigned
int) (buffer[i-1])<<(8-numbits)) & bitmask(1,LEFT)));
+ }
+ }
+}
+
+/* buff1 is some random bytes, buff2 is some random bytes which we expect to
start with the contents of buff1,
+ both buffers are bit-shifted to the right "bitsrightshifted". this function
compares the two and returns 1 if buff2
+ matches and 0 otherwise. */
+int bytescompare(unsigned char *buff1, unsigned char *buff2, int numbytes, int
bitsrightshifted) {
+ int i;
+
+ if (bitsrightshifted == 0) {
+ for (i = 0; i< numbytes; i++) {
+ if (buff1[i] != buff2[i]) {
+ return(0);
+ }
+ }
+ return(1);
+ }
+ else {
+ for (i = 1; i< numbytes-2; i++) {
+ if (buff1[i] != buff2[i]) {
+ return(0);
+ }
+ }
+ /* do leftmost byte */
+ if ((buff1[0] & bitmask(8-bitsrightshifted,RIGHT)) != (buff2[0] &
bitmask(8-bitsrightshifted,RIGHT)) ) {
+ return(0);
+ }
+ /* do rightmost byte */
+ if ((buff1[numbytes-1] & bitmask(bitsrightshifted,LEFT)) !=
(buff2[numbytes-1] & bitmask(bitsrightshifted,LEFT)) ) {
+ return(0);
+ }
+ return(1);
+ }
+}
+
+int checkfileforfooter(int fin) {
+ unsigned char buffer[11];
+ int result, i;
+ unsigned char **footer = malloc(8*sizeof(unsigned char *));
+
+ /* set up footer plus its various right-shifted incarnations */
+ /* dude why couldn't you have 0 padded each bzip2 block? seriously ... */
+ for (i = 0; i< 8; i++) {
+ footer[i] = malloc(sizeof(unsigned char)*7);
+ }
+ footer[0][0]= (unsigned char) 0x17;
+ footer[0][1]= (unsigned char) 0x72;
+ footer[0][2]= (unsigned char) 0x45;
+ footer[0][3]= (unsigned char) 0x38;
+ footer[0][4]= (unsigned char) 0x50;
+ footer[0][5]= (unsigned char) 0x90;
+ footer[0][6]= (unsigned char) 0x00;
+ for (i = 1; i< 8; i++) {
+ memcpy((char *)(footer[i]), (char *)(footer[i-1]),7);
+ shiftbytesright(footer[i],7,1);
+ }
+
+ read_footer(buffer,fin);
+
+ result = bytescompare(footer[0],buffer+1,6,0);
+ if (result) {
+ return(result);
+ }
+
+ for (i=1; i<8; i++) {
+ result = bytescompare(footer[i],buffer,7,i);
+ if (result) {
+ return(result);
+ }
+ }
+ return(0);
+}
+
+int main(int argc, char **argv) {
+
+ int fin;
+ int result;
+
+ if (argc != 2) {
+ fprintf(stderr,"usage: %s infile\n", argv[0]);
+ exit(-1);
+ }
+ fin = open (argv[1], O_RDONLY);
+ if (fin < 0) {
+ fprintf(stderr,"failed to open file %s for read\n", argv[1]);
+ exit(-1);
+ }
+ result = checkfileforfooter(fin);
+ close(fin);
+ exit(result);
+}
+
Property changes on: branches/ariel/xmldumps-backup/checkforbz2footer.c
___________________________________________________________________
Added: svn:eol-style
+ native
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