c-ares/ares__read_line.c

/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "setup.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "ares.h"
#include "ares_private.h"

/* This is an internal function.  Its contract is to read a line from
 * a file into a dynamically allocated buffer, zeroing the trailing
 * newline if there is one.  The calling routine may call
 * ares__read_line multiple times with the same buf and bufsize
 * pointers; *buf will be reallocated and *bufsize adjusted as
 * appropriate.  The initial value of *buf should be NULL.  After the
 * calling routine is done reading lines, it should free *buf.
 */
int ares__read_line(FILE *fp, char **buf, int *bufsize)
{
  char *newbuf;
  size_t offset = 0;
  size_t len;

  if (*buf == NULL)
    {
      *buf = malloc(128);
      if (!*buf)
        return ARES_ENOMEM;
      *bufsize = 128;
    }

  while (1)
    {
      if (!fgets(*buf + offset, *bufsize - (int)offset, fp))
        return (offset != 0) ? 0 : (ferror(fp)) ? ARES_EFILE : ARES_EOF;
      len = offset + strlen(*buf + offset);
      if ((*buf)[len - 1] == '\n')
        {
          (*buf)[len - 1] = 0;
          return ARES_SUCCESS;
        }
      offset = len;

      /* Allocate more space. */
      newbuf = realloc(*buf, *bufsize * 2);
      if (!newbuf)
        return ARES_ENOMEM;
      *buf = newbuf;
      *bufsize *= 2;
    }
}