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 2022, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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Function list (Bold in this list means a function is not static)

/* read_line.c

   Implementation of readLine().
#include <unistd.h>
#include <errno.h>
#include "read_line.h"                  /* Declaration of readLine() */
/* Read characters from 'fd' until a newline is encountered. If a newline
  character is not encountered in the first (n - 1) bytes, then the excess
  characters are discarded. The returned string placed in 'buf' is
  null-terminated and includes the newline character if it was read in the
  first (n - 1) bytes. The function return value is the number of bytes
  placed in buffer (which includes the newline character if encountered,
  but excludes the terminating null byte). */

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() */
                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' */

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

            if (ch == '\n')

    *buf = '\0';
    return totRead;


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