rewrite-inplace.c

/*********************************************************************
* Rewrites the contents of the file given on the command line.       *
*                                                                    *
* WARNING:                                                           *
*   This program comes with ABSOLUTELY NO WARRANTY whatsoever, use   *
*   it entirely at your own risk! The author shall never be held     *
*   responsible for loss of your data, ruining your hard drive, PC,  *
*   house, city or planet, including but not limited to wars,        *
*   hurricanes, famines, global warming or alien invasions, arising  *
*   from using it.                                                   *
*                                                                    *
* Author:                                                            *
*    Dmitry Kann, http://yktoo.com/                                  *
*                                                                    *
* License:                                                           *
*    LGPL 3.0                                                        *
*                                                                    *
* Compile with:                                                      *
*    gcc rewrite-inplace.c -o rewrite-inplace                        *
*                                                                    *
*********************************************************************/

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>

volatile sig_atomic_t interrupted = 0;

void handle_sigint(int sig){
    interrupted = 1;
}

int main(int argc, char **argv) {
    int    file_desc;
    char   buf[1000000];
    int    chunk_num = 0;
    size_t read_size;
    size_t write_size;
    size_t buf_size = sizeof(buf);
    off_t  file_pos;
    off_t  file_size;
    char* file_name;

    // Check command-line arguments
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <file_name>\n", argv[0]);
        exit(1);
    }

    // Try to open the file
    file_name = argv[1];
    if ((file_desc = open(file_name, O_RDWR)) == -1) {
        perror("Could not open the file");
        exit(2);
    }

    // Get file length
    if ((file_size = lseek(file_desc, 0, SEEK_END)) == (off_t)-1) {
        perror("Could not get file position");
        exit(3);
    }

    printf("File %s is open, size %zu bytes\n", file_name, file_size);

    // Register the signal
    signal(SIGINT, handle_sigint);

    // Iterate through the file contents
    file_pos = 0;
    while (file_pos<file_size && !interrupted) {

        // Progress display
        if (chunk_num++ % 10 == 0) {
            printf("%zu/%zu bytes written\r", file_pos, file_size);
        }

        // Position the file pointer for reading
        if (lseek(file_desc, file_pos, SEEK_SET) == -1) {
            perror("Reading: lseek() failed");
            exit(4);
        }

        // Fill in the buffer with bytes
        if ((read_size = read(file_desc, buf, buf_size)) < 0) {
            perror("Reading: read() failed");
            exit(5);
        }

        if (read_size == 0)
            break;

        // Position the file pointer for writing
        if (lseek(file_desc, file_pos, SEEK_SET) == -1) {
            perror("Writing: lseek() failed");
            exit(6);
        }

        // Write the bytes
        if ((write_size = write(file_desc, buf, read_size)) == -1) {
            perror("Writing: write() failed");
            exit(7);
        }
        if (write_size < read_size) {
            perror("Writing: write() wrote less bytes than required");
            exit(7);
        }

        // Advance the pointer
        file_pos += read_size;
    }

    // Close the file
    close(file_desc);

    if (interrupted) {
        fprintf(stderr, "File writing has been interrupted; %zu/%zu bytes written\n", file_pos, file_size);
        exit(15);
    } else {
        printf("File has been rewritten successfully; %zu bytes written\n", file_size);
        exit(0);
    }
}