1 /* Fmemopen implementation. 2 Copyright (C) 2000, 2002 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 Contributed by Hanno Mueller, kontakt@hanno.de, 2000. 5 6 The GNU C Library is free software; you can redistribute it and/or 7 modify it under the terms of the GNU Lesser General Public 8 License as published by the Free Software Foundation; either 9 version 2.1 of the License, or (at your option) any later version. 10 11 The GNU C Library is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 Lesser General Public License for more details. 15 16 You should have received a copy of the GNU Lesser General Public 17 License along with the GNU C Library; if not, write to the Free 18 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 19 02111-1307 USA. */ 20 21 /* 22 * fmemopen() - "my" version of a string stream 23 * Hanno Mueller, kontakt@hanno.de 24 * 25 * 26 * I needed fmemopen() for an application that I currently work on, 27 * but couldn't find it in libio. The following snippet of code is an 28 * attempt to implement what glibc's documentation describes. 29 * 30 * No, it isn't really tested yet. :-) 31 * 32 * 33 * 34 * I already see some potential problems: 35 * 36 * - I never used the "original" fmemopen(). I am sure that "my" 37 * fmemopen() behaves differently than the original version. 38 * 39 * - The documentation doesn't say wether a string stream allows 40 * seeks. I checked the old fmemopen implementation in glibc's stdio 41 * directory, wasn't quite able to see what is going on in that 42 * source, but as far as I understand there was no seek there. For 43 * my application, I needed fseek() and ftell(), so it's here. 44 * 45 * - "append" mode and fseek(p, SEEK_END) have two different ideas 46 * about the "end" of the stream. 47 * 48 * As described in the documentation, when opening the file in 49 * "append" mode, the position pointer will be set to the first null 50 * character of the string buffer (yet the buffer may already 51 * contain more data). For fseek(), the last byte of the buffer is 52 * used as the end of the stream. 53 * 54 * - It is unclear to me what the documentation tries to say when it 55 * explains what happens when you use fmemopen with a NULL 56 * buffer. 57 * 58 * Quote: "fmemopen [then] allocates an array SIZE bytes long. This 59 * is really only useful if you are going to write things to the 60 * buffer and then read them back in again." 61 * 62 * What does that mean if the original fmemopen() did not allow 63 * seeking? How do you read what you just wrote without seeking back 64 * to the beginning of the stream? 65 * 66 * - I think there should be a second version of fmemopen() that does 67 * not add null characters for each write. (At least in my 68 * application, I am not actually using strings but binary data and 69 * so I don't need the stream to add null characters on its own.) 70 */ 71 72 #include <errno.h> 73 #include <libio.h> 74 #include <stdio.h> 75 #include <stdlib.h> 76 #include <string.h> 77 #include <sys/types.h> 78 #include "libioP.h" 79 80 81 typedef struct fmemopen_cookie_struct fmemopen_cookie_t; 82 struct fmemopen_cookie_struct 83 { 84 char *buffer; 85 int mybuffer; 86 size_t size; 87 _IO_off64_t pos; 88 size_t maxpos; 89 }; 90 91 92 static ssize_t 93 fmemopen_read (void *cookie, char *b, size_t s) 94 { 95 fmemopen_cookie_t *c; 96 97 c = (fmemopen_cookie_t *) cookie; 98 99 if (c->pos + s > c->size) 100 { 101 if ((size_t) c->pos == c->size) 102 return 0; 103 s = c->size - c->pos; 104 } 105 106 memcpy (b, &(c->buffer[c->pos]), s); 107 108 c->pos += s; 109 if ((size_t) c->pos > c->maxpos) 110 c->maxpos = c->pos; 111 112 return s; 113 } 114 115 116 static ssize_t 117 fmemopen_write (void *cookie, const char *b, size_t s) 118 { 119 fmemopen_cookie_t *c; 120 int addnullc; 121 122 c = (fmemopen_cookie_t *) cookie; 123 124 addnullc = s == 0 || b[s - 1] != '\0'; 125 126 if (c->pos + s + addnullc > c->size) 127 { 128 if ((size_t) (c->pos + addnullc) == c->size) 129 { 130 __set_errno (ENOSPC); 131 return -1; 132 } 133 s = c->size - c->pos - addnullc; 134 } 135 136 memcpy (&(c->buffer[c->pos]), b, s); 137 138 c->pos += s; 139 if ((size_t) c->pos > c->maxpos) 140 { 141 c->maxpos = c->pos; 142 if (addnullc) 143 c->buffer[c->maxpos] = '\0'; 144 } 145 146 return s; 147 } 148 149 150 static int 151 fmemopen_seek (void *cookie, _IO_off64_t *p, int w) 152 { 153 _IO_off64_t np; 154 fmemopen_cookie_t *c; 155 156 c = (fmemopen_cookie_t *) cookie; 157 158 switch (w) 159 { 160 case SEEK_SET: 161 np = *p; 162 break; 163 164 case SEEK_CUR: 165 np = c->pos + *p; 166 break; 167 168 case SEEK_END: 169 np = c->size - *p; 170 break; 171 172 default: 173 return -1; 174 } 175 176 if (np < 0 || (size_t) np > c->size) 177 return -1; 178 179 c->pos = np; 180 181 return np; 182 } 183 184 185 static int 186 fmemopen_close (void *cookie) 187 { 188 fmemopen_cookie_t *c; 189 190 c = (fmemopen_cookie_t *) cookie; 191 192 if (c->mybuffer) 193 free (c->buffer); 194 free (c); 195 196 return 0; 197 } 198 199 200 FILE * 201 fmemopen (void *buf, size_t len, const char *mode) 202 { 203 cookie_io_functions_t iof; 204 fmemopen_cookie_t *c; 205 206 c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t)); 207 if (c == NULL) 208 return NULL; 209 210 c->mybuffer = (buf == NULL); 211 212 if (c->mybuffer) 213 { 214 c->buffer = (char *) malloc (len); 215 if (c->buffer == NULL) 216 { 217 free (c); 218 return NULL; 219 } 220 c->buffer[0] = '\0'; 221 } 222 else 223 c->buffer = buf; 224 225 c->size = len; 226 227 if (mode[0] == 'w') 228 c->buffer[0] = '\0'; 229 230 c->maxpos = strlen (c->buffer); 231 232 if (mode[0] == 'a') 233 c->pos = c->maxpos; 234 else 235 c->pos = 0; 236 237 iof.read = fmemopen_read; 238 iof.write = fmemopen_write; 239 iof.seek = fmemopen_seek; 240 iof.close = fmemopen_close; 241 242 return _IO_fopencookie (c, mode, iof); 243 } 244