sockets/read_line.c

This is sockets/read_line.c (Listing 59-1, page 1201), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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#include <unistd.h>
#include <errno.h>
#include "read_line.h"                  /* Declaration of readLine() */
ssize_t
readLine(int fd, void *buffer, size_t n)
{
    ssize_t numRead;                    /* # of bytes fetched by last read() */
    size_t totRead;                     /* Total bytes read so far */
    char *buf;
    char ch;

    if (n <= 0 || buffer == NULL) {
        errno = EINVAL;
        return -1;
    }

    buf = buffer;                       /* No pointer arithmetic on "void *" */

    totRead = 0;
    for (;;) {
        numRead = read(fd, &ch, 1);

        if (numRead == -1) {
            if (errno == EINTR)         /* Interrupted --> restart read() */
                continue;
            else
                return -1;              /* Some other error */

        } else if (numRead == 0) {      /* EOF */
            if (totRead == 0)           /* No bytes read; return 0 */
                return 0;
            else                        /* Some bytes read; add '\0' */
                break;

        } else {                        /* 'numRead' must be 1 if we get here */
            if (totRead < n - 1) {      /* Discard > (n - 1) bytes */
                totRead++;
                *buf++ = ch;
            }

            if (ch == '\n')
                break;
        }
    }

    *buf = '\0';
    return totRead;
}

 

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