update crc-32 of ldif files

update-ldif-cs.c

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <zlib.h>

#define BUFSIZE 256

int update_checksum(const char *filename);

int main(int ac, char *as[]) {
    if(ac<2) {
        fprintf(stderr, "Usage: %s [file.ldif]\n", as[0]);
        return EXIT_FAILURE;
    }


    return update_checksum(as[1]);
}

int update_checksum(const char *filename) {
    FILE *f=NULL;
    int tf=-1;
    if((f=fopen(filename, "r"))==NULL)
        return 1;

    long int start_pos=0;

    for(int c=fgetc(f), i=0; i<2; c=fgetc(f)) {
        switch(c) {
        case '\n':
            ++i;
            break;
        case -1:
            return 1;
            break;
        default:
            break;
        }
        ++start_pos;
    }

	char buf[BUFSIZE];

    unsigned long crc = crc32_z(0L, Z_NULL, 0);
    size_t read_b=0;

    fseek(f, start_pos, SEEK_SET);

	do {
        read_b=fread(buf, 1, BUFSIZE, f);
        crc=crc32_z(crc, (const Bytef *) buf, read_b);
	} while(read_b==BUFSIZE);

	fseek(f, start_pos, SEEK_SET);

    char tempf[]="/tmp/fileXXXXXX";

    if((tf=mkstemp(tempf))==-1)
        goto error;

    dprintf(tf, "# AUTO-GENERATED FILE - DO NOT EDIT!! Use ldapmodify.\n"
            "# CRC32 %lx\n", crc);

    do {
        read_b=fread(buf, 1, BUFSIZE, f);
        dprintf(tf, "%.*s", (int) read_b, buf);
    } while(read_b==BUFSIZE);

    fclose(f);
    close(tf);

    struct stat f_stats;
    memset(&f_stats, 0, sizeof(struct stat));
    stat(filename, &f_stats);

    rename(tempf, filename);
    chown(filename, f_stats.st_uid, f_stats.st_gid);
    chmod(filename, f_stats.st_mode);

    return 0;

error:
    if(f!=NULL) fclose(f);
    if(tf!=-1) close(tf);
    return 1;
}