/* sendfilecp.c - copying a file using sendfile
 */


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

extern int errno;

int main (int argc, char* argv[])
{
  /* check that we have the right number of command line parameters */
  if (argc != 3) {
    fprintf(stderr, "usage: %s <source file> <destination file>\n", 
	argv[0]);
    exit(1);
  }

  int fdin;               /* file descriptor of source file */
  int fdout;              /* file descriptor of destination file */
  struct stat statbuf;    /* metadata for source file */
  int offset = 0;         /* byte offset used by sendfile */
  int rc;                 /* return code from sendfile */

  /* Open source file */
  fdin = open(argv[1], O_RDONLY);
  if (fdin == -1) {
    fprintf(stderr, "unable to open %s - %s\n", argv[1], strerror(errno));
    exit(1);
  }

  /* open destination file */
  fdout = open(argv[2], O_WRONLY|O_CREAT, statbuf.st_mode);
  if (fdout == -1) {
    fprintf(stderr, "unable to open %s -%s\n", argv[2], strerror(errno));
    exit(1);
  }

  /* get metadata of the source file */
  if (fstat(fdin, &statbuf) == -1) {
    fprintf(stderr, "unable to obtain metadata for %s - %s\n", argv[1], 
	    strerror(errno)); 
    exit(1);
  }

 /* copy file */
 rc = sendfile (fdout, fdin, (off_t *)&offset, statbuf.st_size);
 if (rc == -1) {
    fprintf(stderr, "sendfile error - %s\n", strerror(errno));
    exit(1);
 }
 if (rc != statbuf.st_size) {
   fprintf(stderr, "sendfile error - partial transfer: %d of %d bytes\n",
           rc, (int)statbuf.st_size);
   exit(1);
 }

 /* clean up and exit */
 close(fdout);
 close(fdin);

 return 0;
}