libio/fmemopen.c

   1 /* fmemopen implementation.
   2    Copyright (C) 2015-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /* fmemopen() from 2.22 and forward works as defined by POSIX.  It also
  20    provides an older symbol, version 2.2.5, that behaves different regarding
  21    SEEK_END (libio/oldfmemopen.c).  */
  22
  23
  24 #include <errno.h>
  25 #include <libio.h>
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <stdint.h>
  29 #include <string.h>
  30 #include <sys/types.h>
  31 #include "libioP.h"
  32
  33
  34 typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
  35 struct fmemopen_cookie_struct
  36 {
  37   char        *buffer;   /* memory buffer.  */
  38   int         mybuffer;  /* allocated my buffer?  */
  39   int         append;    /* buffer open for append?  */
  40   size_t      size;      /* buffer length in bytes.  */
  41   _IO_off64_t pos;       /* current position at the buffer.  */
  42   size_t      maxpos;    /* max position in buffer.  */
  43 };
  44
  45
  46 static ssize_t
  47 fmemopen_read (void *cookie, char *b, size_t s)
  48 {
  49   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;
  50
  51   if (c->pos + s > c->maxpos)
  52     {
  53       s = c->maxpos - c->pos;
  54       if ((size_t) c->pos > c->maxpos)
  55         s = 0;
  56     }
  57
  58   memcpy (b, &(c->buffer[c->pos]), s);
  59
  60   c->pos += s;
  61
  62   return s;
  63 }
  64
  65
  66 static ssize_t
  67 fmemopen_write (void *cookie, const char *b, size_t s)
  68 {
  69   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;;
  70   _IO_off64_t pos = c->append ? c->maxpos : c->pos;
  71   int addnullc = (s == 0 || b[s - 1] != '\0');
  72
  73   if (pos + s > c->size)
  74     {
  75       if ((size_t) (c->pos + addnullc) >= c->size)
  76         {
  77           __set_errno (ENOSPC);
  78           return 0;
  79         }
  80       s = c->size - pos;
  81     }
  82
  83   memcpy (&(c->buffer[pos]), b, s);
  84
  85   c->pos = pos + s;
  86   if ((size_t) c->pos > c->maxpos)
  87     {
  88       c->maxpos = c->pos;
  89       if (c->maxpos < c->size && addnullc)
  90         c->buffer[c->maxpos] = '\0';
  91       /* A null byte is written in a stream open for update iff it fits.  */
  92       else if (c->append == 0 && addnullc != 0)
  93         c->buffer[c->size-1] = '\0';
  94     }
  95
  96   return s;
  97 }
  98
  99
 100 static int
 101 fmemopen_seek (void *cookie, _IO_off64_t *p, int w)
 102 {
 103   _IO_off64_t np;
 104   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;
 105
 106   switch (w)
 107     {
 108     case SEEK_SET:
 109       np = *p;
 110       break;
 111
 112     case SEEK_CUR:
 113       np = c->pos + *p;
 114       break;
 115
 116     case SEEK_END:
 117       np = c->maxpos + *p;
 118       break;
 119
 120     default:
 121       return -1;
 122     }
 123
 124   if (np < 0 || (size_t) np > c->size)
 125     {
 126       __set_errno (EINVAL);
 127       return -1;
 128     }
 129
 130   *p = c->pos = np;
 131
 132   return 0;
 133 }
 134
 135
 136 static int
 137 fmemopen_close (void *cookie)
 138 {
 139   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;
 140
 141   if (c->mybuffer)
 142     free (c->buffer);
 143   free (c);
 144
 145   return 0;
 146 }
 147
 148
 149 FILE *
 150 __fmemopen (void *buf, size_t len, const char *mode)
 151 {
 152   cookie_io_functions_t iof;
 153   fmemopen_cookie_t *c;
 154   FILE *result;
 155
 156   c = (fmemopen_cookie_t *) calloc (sizeof (fmemopen_cookie_t), 1);
 157   if (c == NULL)
 158     return NULL;
 159
 160   c->mybuffer = (buf == NULL);
 161
 162   if (c->mybuffer)
 163     {
 164       c->buffer = (char *) malloc (len);
 165       if (c->buffer == NULL)
 166         {
 167           free (c);
 168           return NULL;
 169         }
 170       c->buffer[0] = '\0';
 171     }
 172   else
 173     {
 174       if (__glibc_unlikely ((uintptr_t) len > -(uintptr_t) buf))
 175         {
 176           free (c);
 177           __set_errno (EINVAL);
 178           return NULL;
 179         }
 180
 181       c->buffer = buf;
 182
 183       /* POSIX states that w+ mode should truncate the buffer.  */
 184       if (mode[0] == 'w' && mode[1] == '+')
 185         c->buffer[0] = '\0';
 186
 187       if (mode[0] == 'a')
 188         c->maxpos = strnlen (c->buffer, len);
 189     }
 190
 191
 192   /* Mode   |  starting position (cookie::pos) |          size (cookie::size)
 193      ------ |----------------------------------|-----------------------------
 194      read   |          beginning of the buffer |                size argument
 195      write  |          beginning of the buffer |                         zero
 196      append |    first null or size buffer + 1 |  first null or size argument
 197    */
 198
 199   c->size = len;
 200
 201   if (mode[0] == 'r')
 202     c->maxpos = len;
 203
 204   c->append = mode[0] == 'a';
 205   if (c->append)
 206     c->pos = c->maxpos;
 207   else
 208     c->pos = 0;
 209
 210   iof.read = fmemopen_read;
 211   iof.write = fmemopen_write;
 212   iof.seek = fmemopen_seek;
 213   iof.close = fmemopen_close;
 214
 215   result = _IO_fopencookie (c, mode, iof);
 216   if (__glibc_unlikely (result == NULL))
 217     {
 218       if (c->mybuffer)
 219         free (c->buffer);
 220
 221       free (c);
 222     }
 223
 224   return result;
 225 }
 226 libc_hidden_def (__fmemopen)
 227 versioned_symbol (libc, __fmemopen, fmemopen, GLIBC_2_22);