libio/fmemopen.c

   1 /* fmemopen implementation.
   2    Copyright (C) 2015-2023 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    <https://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 <stdio.h>
  26 #include <stdlib.h>
  27 #include <stdint.h>
  28 #include <string.h>
  29 #include <sys/types.h>
  30 #include "libioP.h"
  31
  32
  33 typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
  34 struct fmemopen_cookie_struct
  35 {
  36   char        *buffer;   /* memory buffer.  */
  37   int         mybuffer;  /* allocated my buffer?  */
  38   int         append;    /* buffer open for append?  */
  39   size_t      size;      /* buffer length in bytes.  */
  40   off64_t     pos;       /* current position at the buffer.  */
  41   size_t      maxpos;    /* max position in buffer.  */
  42 };
  43
  44
  45 static ssize_t
  46 fmemopen_read (void *cookie, char *b, size_t s)
  47 {
  48   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;
  49
  50   if (c->pos + s > c->maxpos)
  51     {
  52       s = c->maxpos - c->pos;
  53       if ((size_t) c->pos > c->maxpos)
  54         s = 0;
  55     }
  56
  57   memcpy (b, &(c->buffer[c->pos]), s);
  58
  59   c->pos += s;
  60
  61   return s;
  62 }
  63
  64
  65 static ssize_t
  66 fmemopen_write (void *cookie, const char *b, size_t s)
  67 {
  68   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;;
  69   off64_t pos = c->append ? c->maxpos : c->pos;
  70   int addnullc = (s == 0 || b[s - 1] != '\0');
  71
  72   if (pos + s > c->size)
  73     {
  74       if ((size_t) (c->pos + addnullc) >= c->size)
  75         {
  76           __set_errno (ENOSPC);
  77           return 0;
  78         }
  79       s = c->size - pos;
  80     }
  81
  82   memcpy (&(c->buffer[pos]), b, s);
  83
  84   c->pos = pos + s;
  85   if ((size_t) c->pos > c->maxpos)
  86     {
  87       c->maxpos = c->pos;
  88       if (c->maxpos < c->size && addnullc)
  89         c->buffer[c->maxpos] = '\0';
  90       /* A null byte is written in a stream open for update iff it fits.  */
  91       else if (c->append == 0 && addnullc != 0)
  92         c->buffer[c->size-1] = '\0';
  93     }
  94
  95   return s;
  96 }
  97
  98
  99 static int
 100 fmemopen_seek (void *cookie, off64_t *p, int w)
 101 {
 102   off64_t np;
 103   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;
 104
 105   switch (w)
 106     {
 107     case SEEK_SET:
 108       np = *p;
 109       break;
 110
 111     case SEEK_CUR:
 112       np = c->pos + *p;
 113       break;
 114
 115     case SEEK_END:
 116       np = c->maxpos + *p;
 117       break;
 118
 119     default:
 120       return -1;
 121     }
 122
 123   if (np < 0 || (size_t) np > c->size)
 124     {
 125       __set_errno (EINVAL);
 126       return -1;
 127     }
 128
 129   *p = c->pos = np;
 130
 131   return 0;
 132 }
 133
 134
 135 static int
 136 fmemopen_close (void *cookie)
 137 {
 138   fmemopen_cookie_t *c = (fmemopen_cookie_t *) cookie;
 139
 140   if (c->mybuffer)
 141     free (c->buffer);
 142   free (c);
 143
 144   return 0;
 145 }
 146
 147
 148 FILE *
 149 __fmemopen (void *buf, size_t len, const char *mode)
 150 {
 151   cookie_io_functions_t iof;
 152   fmemopen_cookie_t *c;
 153   FILE *result;
 154
 155   c = (fmemopen_cookie_t *) calloc (sizeof (fmemopen_cookie_t), 1);
 156   if (c == NULL)
 157     return NULL;
 158
 159   c->mybuffer = (buf == NULL);
 160
 161   if (c->mybuffer)
 162     {
 163       c->buffer = (char *) malloc (len);
 164       if (c->buffer == NULL)
 165         {
 166           free (c);
 167           return NULL;
 168         }
 169       c->buffer[0] = '\0';
 170     }
 171   else
 172     {
 173       if (__glibc_unlikely ((uintptr_t) len > -(uintptr_t) buf))
 174         {
 175           free (c);
 176           __set_errno (EINVAL);
 177           return NULL;
 178         }
 179
 180       c->buffer = buf;
 181
 182       /* POSIX states that w+ mode should truncate the buffer.  */
 183       if (mode[0] == 'w' && mode[1] == '+')
 184         c->buffer[0] = '\0';
 185
 186       if (mode[0] == 'a')
 187         c->maxpos = strnlen (c->buffer, len);
 188     }
 189
 190
 191   /* Mode   |  starting position (cookie::pos) |          size (cookie::size)
 192      ------ |----------------------------------|-----------------------------
 193      read   |          beginning of the buffer |                size argument
 194      write  |          beginning of the buffer |                         zero
 195      append |    first null or size buffer + 1 |  first null or size argument
 196    */
 197
 198   c->size = len;
 199
 200   if (mode[0] == 'r')
 201     c->maxpos = len;
 202
 203   c->append = mode[0] == 'a';
 204   if (c->append)
 205     c->pos = c->maxpos;
 206   else
 207     c->pos = 0;
 208
 209   iof.read = fmemopen_read;
 210   iof.write = fmemopen_write;
 211   iof.seek = fmemopen_seek;
 212   iof.close = fmemopen_close;
 213
 214   result = _IO_fopencookie (c, mode, iof);
 215   if (__glibc_unlikely (result == NULL))
 216     {
 217       if (c->mybuffer)
 218         free (c->buffer);
 219
 220       free (c);
 221     }
 222
 223   return result;
 224 }
 225 libc_hidden_def (__fmemopen)
 226 versioned_symbol (libc, __fmemopen, fmemopen, GLIBC_2_22);