123 lines
2.4 KiB
C
Executable File
123 lines
2.4 KiB
C
Executable File
#include <stdio.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#include <sys/uio.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <string.h>
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#include "tar.h"
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int fileexists(char *fname);
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int main(int argc, char *argv[])
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{
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char *name = argv[1]; // name of archive
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char buffer[300]; // character buffer for sprintf
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int fp, r, i, j, p, w; // counters and pointers
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if (argc != 2)
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{
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fprintf(stderr, "%s:\n Usage: utar filename \n", strerror(5));
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exit(EXIT_FAILURE);
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}
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if (fileexists(name) == 0)
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{
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fprintf(stderr, "archive doesnt exist%s\n", strerror(2));
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exit(EXIT_FAILURE);
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}
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fp = open(name, O_RDONLY, 0644); // opens file; creates it if it does not exist;
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if (fp < 0)
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{
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fprintf(stderr, "cannot open %s because of %s\n", argv[2], strerror(5));
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exit(EXIT_FAILURE);
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}
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hdr header;
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int tempfp;
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char byte;
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char f_name[sizeof(short int)];
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short int l;
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while (true)
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{
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r = read(fp, &header, sizeof(hdr));
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if (r != sizeof(hdr))
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{
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fprintf(stderr, "%s: file is not the size of a header object\n", strerror(5));
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exit(EXIT_FAILURE);
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}
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else if (header.magic != 0x63746172)
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{
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fprintf(stderr, "%s: header does not include the magic number [magic number is: %x]\n", strerror(5), header.magic);
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exit(EXIT_FAILURE);
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}
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for (i = 0; i < header.block_count; i++)
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{
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if (header.deleted[i] == 1)
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{
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// skip it
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}
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else
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{
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lseek(fp, header.file_name[i], SEEK_SET);
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read(fp, (char *)&l, sizeof(short int));
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read(fp, f_name, l);
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if (fileexists(f_name))
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{
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fprintf(stderr, "%s\n", strerror(17));
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exit(EXIT_FAILURE);
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}
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tempfp = open(f_name, O_RDWR | O_CREAT, 0644); // creates the new file;
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for (j = 0; j < header.file_size[i]; j++)
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{
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r = read(fp, &byte, sizeof(byte));
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if (r < 0)
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{
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fprintf(stderr, "%s: file %s could not be read from archive\n", f_name, strerror(5));
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exit(EXIT_FAILURE);
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}
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w = write(tempfp, &byte, sizeof(byte));
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if (w < 0)
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{
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fprintf(stderr, "%s: file %s could not be written to file\n", f_name, strerror(5));
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exit(EXIT_FAILURE);
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}
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}
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}
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}
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if (header.next < 0)
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{
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printf("Untared Successfully\n");
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exit(EXIT_SUCCESS);
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}
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else
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{
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p = header.next;
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lseek(fp, header.next, SEEK_SET);
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}
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}
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return EXIT_SUCCESS;
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}
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int fileexists(char *fname)
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{
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if (open(fname, O_RDONLY, 0644) < 0)
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{
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return false; // file doesn't exist
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}
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else
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{
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return true; // file exists
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}
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}
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