Andy McFadden | cf63d5d | 2010-01-22 16:37:25 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2010 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
Elliott Hughes | 3ff8888 | 2014-08-20 16:16:24 -0700 | [diff] [blame] | 17 | #if defined(__APPLE__) |
Andy McFadden | cf63d5d | 2010-01-22 16:37:25 -0800 | [diff] [blame] | 18 | |
| 19 | /* |
| 20 | * Implementation of the POSIX open_memstream() function, which Linux has |
| 21 | * but BSD lacks. |
| 22 | * |
| 23 | * Summary: |
| 24 | * - Works like a file-backed FILE* opened with fopen(name, "w"), but the |
| 25 | * backing is a chunk of memory rather than a file. |
| 26 | * - The buffer expands as you write more data. Seeking past the end |
| 27 | * of the file and then writing to it zero-fills the gap. |
| 28 | * - The values at "*bufp" and "*sizep" should be considered read-only, |
| 29 | * and are only valid immediately after an fflush() or fclose(). |
| 30 | * - A '\0' is maintained just past the end of the file. This is not included |
| 31 | * in "*sizep". (The behavior w.r.t. fseek() is not clearly defined. |
| 32 | * The spec says the null byte is written when a write() advances EOF, |
| 33 | * but it looks like glibc ensures the null byte is always found at EOF, |
| 34 | * even if you just seeked backwards. The example on the opengroup.org |
| 35 | * page suggests that this is the expected behavior. The null must be |
| 36 | * present after a no-op fflush(), which we can't see, so we have to save |
| 37 | * and restore it. Annoying, but allows file truncation.) |
| 38 | * - After fclose(), the caller must eventually free(*bufp). |
| 39 | * |
| 40 | * This is built out of funopen(), which BSD has but Linux lacks. There is |
| 41 | * no flush() operator, so we need to keep the user pointers up to date |
| 42 | * after each operation. |
| 43 | * |
| 44 | * I don't think Windows has any of the above, but we don't need to use |
| 45 | * them there, so we just supply a stub. |
| 46 | */ |
| 47 | #include <cutils/open_memstream.h> |
| 48 | #include <stdlib.h> |
Andy McFadden | fe5684e | 2010-01-26 09:25:53 -0800 | [diff] [blame] | 49 | #include <sys/types.h> |
| 50 | #include <unistd.h> |
Andy McFadden | cf63d5d | 2010-01-22 16:37:25 -0800 | [diff] [blame] | 51 | #include <stdio.h> |
| 52 | #include <string.h> |
| 53 | #include <errno.h> |
| 54 | #include <assert.h> |
| 55 | |
| 56 | #if 0 |
| 57 | # define DBUG(x) printf x |
| 58 | #else |
| 59 | # define DBUG(x) ((void)0) |
| 60 | #endif |
| 61 | |
Andy McFadden | cf63d5d | 2010-01-22 16:37:25 -0800 | [diff] [blame] | 62 | /* |
| 63 | * Definition of a seekable, write-only memory stream. |
| 64 | */ |
| 65 | typedef struct { |
| 66 | char** bufp; /* pointer to buffer pointer */ |
| 67 | size_t* sizep; /* pointer to eof */ |
| 68 | |
| 69 | size_t allocSize; /* size of buffer */ |
| 70 | size_t eof; /* furthest point we've written to */ |
| 71 | size_t offset; /* current write offset */ |
| 72 | char saved; /* required by NUL handling */ |
| 73 | } MemStream; |
| 74 | |
| 75 | #define kInitialSize 1024 |
| 76 | |
| 77 | /* |
| 78 | * Ensure that we have enough storage to write "size" bytes at the |
| 79 | * current offset. We also have to take into account the extra '\0' |
| 80 | * that we maintain just past EOF. |
| 81 | * |
| 82 | * Returns 0 on success. |
| 83 | */ |
| 84 | static int ensureCapacity(MemStream* stream, int writeSize) |
| 85 | { |
| 86 | DBUG(("+++ ensureCap off=%d size=%d\n", stream->offset, writeSize)); |
| 87 | |
| 88 | size_t neededSize = stream->offset + writeSize + 1; |
| 89 | if (neededSize <= stream->allocSize) |
| 90 | return 0; |
| 91 | |
| 92 | size_t newSize; |
| 93 | |
| 94 | if (stream->allocSize == 0) { |
| 95 | newSize = kInitialSize; |
| 96 | } else { |
| 97 | newSize = stream->allocSize; |
| 98 | newSize += newSize / 2; /* expand by 3/2 */ |
| 99 | } |
| 100 | |
| 101 | if (newSize < neededSize) |
| 102 | newSize = neededSize; |
| 103 | DBUG(("+++ realloc %p->%p to size=%d\n", |
| 104 | stream->bufp, *stream->bufp, newSize)); |
| 105 | char* newBuf = (char*) realloc(*stream->bufp, newSize); |
| 106 | if (newBuf == NULL) |
| 107 | return -1; |
| 108 | |
| 109 | *stream->bufp = newBuf; |
| 110 | stream->allocSize = newSize; |
| 111 | return 0; |
| 112 | } |
| 113 | |
| 114 | /* |
| 115 | * Write data to a memstream, expanding the buffer if necessary. |
| 116 | * |
| 117 | * If we previously seeked beyond EOF, zero-fill the gap. |
| 118 | * |
| 119 | * Returns the number of bytes written. |
| 120 | */ |
| 121 | static int write_memstream(void* cookie, const char* buf, int size) |
| 122 | { |
| 123 | MemStream* stream = (MemStream*) cookie; |
| 124 | |
| 125 | if (ensureCapacity(stream, size) < 0) |
| 126 | return -1; |
| 127 | |
| 128 | /* seeked past EOF earlier? */ |
| 129 | if (stream->eof < stream->offset) { |
| 130 | DBUG(("+++ zero-fill gap from %d to %d\n", |
| 131 | stream->eof, stream->offset-1)); |
| 132 | memset(*stream->bufp + stream->eof, '\0', |
| 133 | stream->offset - stream->eof); |
| 134 | } |
| 135 | |
| 136 | /* copy data, advance write pointer */ |
| 137 | memcpy(*stream->bufp + stream->offset, buf, size); |
| 138 | stream->offset += size; |
| 139 | |
| 140 | if (stream->offset > stream->eof) { |
| 141 | /* EOF has advanced, update it and append null byte */ |
| 142 | DBUG(("+++ EOF advanced to %d, appending nul\n", stream->offset)); |
| 143 | assert(stream->offset < stream->allocSize); |
| 144 | stream->eof = stream->offset; |
| 145 | } else { |
| 146 | /* within previously-written area; save char we're about to stomp */ |
| 147 | DBUG(("+++ within written area, saving '%c' at %d\n", |
| 148 | *(*stream->bufp + stream->offset), stream->offset)); |
| 149 | stream->saved = *(*stream->bufp + stream->offset); |
| 150 | } |
| 151 | *(*stream->bufp + stream->offset) = '\0'; |
| 152 | *stream->sizep = stream->offset; |
| 153 | |
| 154 | return size; |
| 155 | } |
| 156 | |
| 157 | /* |
| 158 | * Seek within a memstream. |
| 159 | * |
| 160 | * Returns the new offset, or -1 on failure. |
| 161 | */ |
| 162 | static fpos_t seek_memstream(void* cookie, fpos_t offset, int whence) |
| 163 | { |
| 164 | MemStream* stream = (MemStream*) cookie; |
| 165 | off_t newPosn = (off_t) offset; |
| 166 | |
| 167 | if (whence == SEEK_CUR) { |
| 168 | newPosn += stream->offset; |
| 169 | } else if (whence == SEEK_END) { |
| 170 | newPosn += stream->eof; |
| 171 | } |
| 172 | |
| 173 | if (newPosn < 0 || ((fpos_t)((size_t) newPosn)) != newPosn) { |
| 174 | /* bad offset - negative or huge */ |
| 175 | DBUG(("+++ bogus seek offset %ld\n", (long) newPosn)); |
| 176 | errno = EINVAL; |
| 177 | return (fpos_t) -1; |
| 178 | } |
| 179 | |
| 180 | if (stream->offset < stream->eof) { |
| 181 | /* |
| 182 | * We were pointing to an area we'd already written to, which means |
| 183 | * we stomped on a character and must now restore it. |
| 184 | */ |
| 185 | DBUG(("+++ restoring char '%c' at %d\n", |
| 186 | stream->saved, stream->offset)); |
| 187 | *(*stream->bufp + stream->offset) = stream->saved; |
| 188 | } |
| 189 | |
| 190 | stream->offset = (size_t) newPosn; |
| 191 | |
| 192 | if (stream->offset < stream->eof) { |
| 193 | /* |
| 194 | * We're seeked backward into the stream. Preserve the character |
| 195 | * at EOF and stomp it with a NUL. |
| 196 | */ |
| 197 | stream->saved = *(*stream->bufp + stream->offset); |
| 198 | *(*stream->bufp + stream->offset) = '\0'; |
| 199 | *stream->sizep = stream->offset; |
| 200 | } else { |
| 201 | /* |
| 202 | * We're positioned at, or possibly beyond, the EOF. We want to |
| 203 | * publish the current EOF, not the current position. |
| 204 | */ |
| 205 | *stream->sizep = stream->eof; |
| 206 | } |
| 207 | |
| 208 | return newPosn; |
| 209 | } |
| 210 | |
| 211 | /* |
| 212 | * Close the memstream. We free everything but the data buffer. |
| 213 | */ |
| 214 | static int close_memstream(void* cookie) |
| 215 | { |
| 216 | free(cookie); |
| 217 | return 0; |
| 218 | } |
| 219 | |
| 220 | /* |
| 221 | * Prepare a memstream. |
| 222 | */ |
| 223 | FILE* open_memstream(char** bufp, size_t* sizep) |
| 224 | { |
| 225 | FILE* fp; |
| 226 | MemStream* stream; |
| 227 | |
| 228 | if (bufp == NULL || sizep == NULL) { |
| 229 | errno = EINVAL; |
| 230 | return NULL; |
| 231 | } |
| 232 | |
| 233 | stream = (MemStream*) calloc(1, sizeof(MemStream)); |
| 234 | if (stream == NULL) |
| 235 | return NULL; |
| 236 | |
| 237 | fp = funopen(stream, |
| 238 | NULL, write_memstream, seek_memstream, close_memstream); |
| 239 | if (fp == NULL) { |
| 240 | free(stream); |
| 241 | return NULL; |
| 242 | } |
| 243 | |
| 244 | *sizep = 0; |
| 245 | *bufp = NULL; |
| 246 | stream->bufp = bufp; |
| 247 | stream->sizep = sizep; |
| 248 | |
| 249 | return fp; |
| 250 | } |
| 251 | |
Andy McFadden | cf63d5d | 2010-01-22 16:37:25 -0800 | [diff] [blame] | 252 | |
| 253 | |
| 254 | |
| 255 | #if 0 |
| 256 | #define _GNU_SOURCE |
| 257 | #include <stdio.h> |
| 258 | #include <stdlib.h> |
| 259 | #include <string.h> |
| 260 | |
| 261 | /* |
| 262 | * Simple regression test. |
| 263 | * |
| 264 | * To test on desktop Linux with valgrind, it's possible to make a simple |
| 265 | * change to open_memstream() to use fopencookie instead: |
| 266 | * |
| 267 | * cookie_io_functions_t iofuncs = |
| 268 | * { NULL, write_memstream, seek_memstream, close_memstream }; |
| 269 | * fp = fopencookie(stream, "w", iofuncs); |
| 270 | * |
| 271 | * (Some tweaks to seek_memstream are also required, as that takes a |
| 272 | * pointer to an offset rather than an offset, and returns 0 or -1.) |
| 273 | */ |
| 274 | int testMemStream(void) |
| 275 | { |
| 276 | FILE *stream; |
| 277 | char *buf; |
| 278 | size_t len; |
| 279 | off_t eob; |
| 280 | |
| 281 | printf("Test1\n"); |
| 282 | |
| 283 | /* std example */ |
| 284 | stream = open_memstream(&buf, &len); |
| 285 | fprintf(stream, "hello my world"); |
| 286 | fflush(stream); |
| 287 | printf("buf=%s, len=%zu\n", buf, len); |
| 288 | eob = ftello(stream); |
| 289 | fseeko(stream, 0, SEEK_SET); |
| 290 | fprintf(stream, "good-bye"); |
| 291 | fseeko(stream, eob, SEEK_SET); |
| 292 | fclose(stream); |
| 293 | printf("buf=%s, len=%zu\n", buf, len); |
| 294 | free(buf); |
| 295 | |
| 296 | printf("Test2\n"); |
| 297 | |
| 298 | /* std example without final seek-to-end */ |
| 299 | stream = open_memstream(&buf, &len); |
| 300 | fprintf(stream, "hello my world"); |
| 301 | fflush(stream); |
| 302 | printf("buf=%s, len=%zu\n", buf, len); |
| 303 | eob = ftello(stream); |
| 304 | fseeko(stream, 0, SEEK_SET); |
| 305 | fprintf(stream, "good-bye"); |
| 306 | //fseeko(stream, eob, SEEK_SET); |
| 307 | fclose(stream); |
| 308 | printf("buf=%s, len=%zu\n", buf, len); |
| 309 | free(buf); |
| 310 | |
| 311 | printf("Test3\n"); |
| 312 | |
| 313 | /* fancy example; should expand buffer with writes */ |
| 314 | static const int kCmpLen = 1024 + 128; |
| 315 | char* cmp = malloc(kCmpLen); |
| 316 | memset(cmp, 0, 1024); |
| 317 | memset(cmp+1024, 0xff, kCmpLen-1024); |
| 318 | sprintf(cmp, "This-is-a-tes1234"); |
| 319 | sprintf(cmp + 1022, "abcdef"); |
| 320 | |
| 321 | stream = open_memstream (&buf, &len); |
| 322 | setvbuf(stream, NULL, _IONBF, 0); /* note: crashes in glibc with this */ |
| 323 | fprintf(stream, "This-is-a-test"); |
| 324 | fseek(stream, -1, SEEK_CUR); /* broken in glibc; can use {13,SEEK_SET} */ |
| 325 | fprintf(stream, "1234"); |
| 326 | fseek(stream, 1022, SEEK_SET); |
| 327 | fputc('a', stream); |
| 328 | fputc('b', stream); |
| 329 | fputc('c', stream); |
| 330 | fputc('d', stream); |
| 331 | fputc('e', stream); |
| 332 | fputc('f', stream); |
| 333 | fflush(stream); |
| 334 | |
| 335 | if (memcmp(buf, cmp, len+1) != 0) { |
| 336 | printf("mismatch\n"); |
| 337 | } else { |
| 338 | printf("match\n"); |
| 339 | } |
| 340 | |
| 341 | printf("Test4\n"); |
| 342 | stream = open_memstream (&buf, &len); |
| 343 | fseek(stream, 5000, SEEK_SET); |
| 344 | fseek(stream, 4096, SEEK_SET); |
| 345 | fseek(stream, -1, SEEK_SET); /* should have no effect */ |
| 346 | fputc('x', stream); |
| 347 | if (ftell(stream) == 4097) |
| 348 | printf("good\n"); |
| 349 | else |
| 350 | printf("BAD: offset is %ld\n", ftell(stream)); |
| 351 | |
| 352 | printf("DONE\n"); |
| 353 | |
| 354 | return 0; |
| 355 | } |
| 356 | |
| 357 | /* expected output: |
| 358 | Test1 |
| 359 | buf=hello my world, len=14 |
| 360 | buf=good-bye world, len=14 |
| 361 | Test2 |
| 362 | buf=hello my world, len=14 |
| 363 | buf=good-bye, len=8 |
| 364 | Test3 |
| 365 | match |
| 366 | Test4 |
| 367 | good |
| 368 | DONE |
| 369 | */ |
| 370 | |
| 371 | #endif |
| 372 | |
Elliott Hughes | 3ff8888 | 2014-08-20 16:16:24 -0700 | [diff] [blame] | 373 | #endif /* __APPLE__ */ |