Program Statement

A file-transfer pair: the client asks for a filename, the server streams it back. The read-loop handles short counts — Unit 1's readn/writen lesson in practice.

/* server fragment: send any requested file */
int n; char name[256], buf[4096];
n = read(cfd, name, sizeof(name)-1); name[strcspn(name, "\r\n")] = 0;
FILE *fp = fopen(name, "rb");
if (!fp) { write(cfd, "ERR no such file\n", 17); }
else {
    write(cfd, "OK\n", 3);
    while ((n = fread(buf, 1, sizeof(buf), fp)) > 0)
        writen(cfd, buf, n);                 /* loop until all sent */
    fclose(fp);
}
shutdown(cfd, SHUT_WR);                      /* half-close = EOF    */

/* client fragment */
write(fd, argv[2], strlen(argv[2])); write(fd, "\n", 1);
FILE *out = fopen("download.out", "wb");
while ((n = read(fd, buf, sizeof(buf))) > 0) fwrite(buf, 1, n, out);

Record Task

Verify with md5sum that the downloaded copy is byte-identical to the original.

Theory Link

Unit 2 "shutdown vs close" — the half-close (shutdown(fd, SHUT_WR)) is what signals end-of-file to the client cleanly while still allowing the server to read any remaining data.