/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef HAVE_OPEN_MEMSTREAM
/*
* Implementation of the POSIX open_memstream() function, which Linux has
* but BSD lacks.
*
* Summary:
* - Works like a file-backed FILE* opened with fopen(name, "w"), but the
* backing is a chunk of memory rather than a file.
* - The buffer expands as you write more data. Seeking past the end
* of the file and then writing to it zero-fills the gap.
* - The values at "*bufp" and "*sizep" should be considered read-only,
* and are only valid immediately after an fflush() or fclose().
* - A '\0' is maintained just past the end of the file. This is not included
* in "*sizep". (The behavior w.r.t. fseek() is not clearly defined.
* The spec says the null byte is written when a write() advances EOF,
* but it looks like glibc ensures the null byte is always found at EOF,
* even if you just seeked backwards. The example on the opengroup.org
* page suggests that this is the expected behavior. The null must be
* present after a no-op fflush(), which we can't see, so we have to save
* and restore it. Annoying, but allows file truncation.)
* - After fclose(), the caller must eventually free(*bufp).
*
* This is built out of funopen(), which BSD has but Linux lacks. There is
* no flush() operator, so we need to keep the user pointers up to date
* after each operation.
*
* I don't think Windows has any of the above, but we don't need to use
* them there, so we just supply a stub.
*/
#include <cutils/open_memstream.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#if 0
# define DBUG(x) printf x
#else
# define DBUG(x) ((void)0)
#endif
#ifdef HAVE_FUNOPEN
/*
* Definition of a seekable, write-only memory stream.
*/
typedef struct {
char** bufp; /* pointer to buffer pointer */
size_t* sizep; /* pointer to eof */
size_t allocSize; /* size of buffer */
size_t eof; /* furthest point we've written to */
size_t offset; /* current write offset */
char saved; /* required by NUL handling */
} MemStream;
#define kInitialSize 1024
/*
* Ensure that we have enough storage to write "size" bytes at the
* current offset. We also have to take into account the extra '\0'
* that we maintain just past EOF.
*
* Returns 0 on success.
*/
static int ensureCapacity(MemStream* stream, int writeSize)
{
DBUG(("+++ ensureCap off=%d size=%d\n", stream->offset, writeSize));
size_t neededSize = stream->offset + writeSize + 1;
if (neededSize <= stream->allocSize)
return 0;
size_t newSize;
if (stream->allocSize == 0) {
newSize = kInitialSize;
} else {
newSize = stream->allocSize;
newSize += newSize / 2; /* expand by 3/2 */
}
if (newSize < neededSize)
newSize = neededSize;
DBUG(("+++ realloc %p->%p to size=%d\n",
stream->bufp, *stream->bufp, newSize));
char* newBuf = (char*) realloc(*stream->bufp, newSize);
if (newBuf == NULL)
return -1;
*stream->bufp = newBuf;
stream->allocSize = newSize;
return 0;
}
/*
* Write data to a memstream, expanding the buffer if necessary.
*
* If we previously seeked beyond EOF, zero-fill the gap.
*
* Returns the number of bytes written.
*/
static int write_memstream(void* cookie, const char* buf, int size)
{
MemStream* stream = (MemStream*) cookie;
if (ensureCapacity(stream, size) < 0)
return -1;
/* seeked past EOF earlier? */
if (stream->eof < stream->offset) {
DBUG(("+++ zero-fill gap from %d to %d\n",
stream->eof, stream->offset-1));
memset(*stream->bufp + stream->eof, '\0',
stream->offset - stream->eof);
}
/* copy data, advance write pointer */
memcpy(*stream->bufp + stream->offset, buf, size);
stream->offset += size;
if (stream->offset > stream->eof) {
/* EOF has advanced, update it and append null byte */
DBUG(("+++ EOF advanced to %d, appending nul\n", stream->offset));
assert(stream->offset < stream->allocSize);
stream->eof = stream->offset;
} else {
/* within previously-written area; save char we're about to stomp */
DBUG(("+++ within written area, saving '%c' at %d\n",
*(*stream->bufp + stream->offset), stream->offset));
stream->saved = *(*stream->bufp + stream->offset);
}
*(*stream->bufp + stream->offset) = '\0';
*stream->sizep = stream->offset;
return size;
}
/*
* Seek within a memstream.
*
* Returns the new offset, or -1 on failure.
*/
static fpos_t seek_memstream(void* cookie, fpos_t offset, int whence)
{
MemStream* stream = (MemStream*) cookie;
off_t newPosn = (off_t) offset;
if (whence == SEEK_CUR) {
newPosn += stream->offset;
} else if (whence == SEEK_END) {
newPosn += stream->eof;
}
if (newPosn < 0 || ((fpos_t)((size_t) newPosn)) != newPosn) {
/* bad offset - negative or huge */
DBUG(("+++ bogus seek offset %ld\n", (long) newPosn));
errno = EINVAL;
return (fpos_t) -1;
}
if (stream->offset < stream->eof) {
/*
* We were pointing to an area we'd already written to, which means
* we stomped on a character and must now restore it.
*/
DBUG(("+++ restoring char '%c' at %d\n",
stream->saved, stream->offset));
*(*stream->bufp + stream->offset) = stream->saved;
}
stream->offset = (size_t) newPosn;
if (stream->offset < stream->eof) {
/*
* We're seeked backward into the stream. Preserve the character
* at EOF and stomp it with a NUL.
*/
stream->saved = *(*stream->bufp + stream->offset);
*(*stream->bufp + stream->offset) = '\0';
*stream->sizep = stream->offset;
} else {
/*
* We're positioned at, or possibly beyond, the EOF. We want to
* publish the current EOF, not the current position.
*/
*stream->sizep = stream->eof;
}
return newPosn;
}
/*
* Close the memstream. We free everything but the data buffer.
*/
static int close_memstream(void* cookie)
{
free(cookie);
return 0;
}
/*
* Prepare a memstream.
*/
FILE* open_memstream(char** bufp, size_t* sizep)
{
FILE* fp;
MemStream* stream;
if (bufp == NULL || sizep == NULL) {
errno = EINVAL;
return NULL;
}
stream = (MemStream*) calloc(1, sizeof(MemStream));
if (stream == NULL)
return NULL;
fp = funopen(stream,
NULL, write_memstream, seek_memstream, close_memstream);
if (fp == NULL) {
free(stream);
return NULL;
}
*sizep = 0;
*bufp = NULL;
stream->bufp = bufp;
stream->sizep = sizep;
return fp;
}
#else /*not HAVE_FUNOPEN*/
FILE* open_memstream(char** bufp, size_t* sizep)
{
abort();
}
#endif /*HAVE_FUNOPEN*/
#if 0
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
* Simple regression test.
*
* To test on desktop Linux with valgrind, it's possible to make a simple
* change to open_memstream() to use fopencookie instead:
*
* cookie_io_functions_t iofuncs =
* { NULL, write_memstream, seek_memstream, close_memstream };
* fp = fopencookie(stream, "w", iofuncs);
*
* (Some tweaks to seek_memstream are also required, as that takes a
* pointer to an offset rather than an offset, and returns 0 or -1.)
*/
int testMemStream(void)
{
FILE *stream;
char *buf;
size_t len;
off_t eob;
printf("Test1\n");
/* std example */
stream = open_memstream(&buf, &len);
fprintf(stream, "hello my world");
fflush(stream);
printf("buf=%s, len=%zu\n", buf, len);
eob = ftello(stream);
fseeko(stream, 0, SEEK_SET);
fprintf(stream, "good-bye");
fseeko(stream, eob, SEEK_SET);
fclose(stream);
printf("buf=%s, len=%zu\n", buf, len);
free(buf);
printf("Test2\n");
/* std example without final seek-to-end */
stream = open_memstream(&buf, &len);
fprintf(stream, "hello my world");
fflush(stream);
printf("buf=%s, len=%zu\n", buf, len);
eob = ftello(stream);
fseeko(stream, 0, SEEK_SET);
fprintf(stream, "good-bye");
//fseeko(stream, eob, SEEK_SET);
fclose(stream);
printf("buf=%s, len=%zu\n", buf, len);
free(buf);
printf("Test3\n");
/* fancy example; should expand buffer with writes */
static const int kCmpLen = 1024 + 128;
char* cmp = malloc(kCmpLen);
memset(cmp, 0, 1024);
memset(cmp+1024, 0xff, kCmpLen-1024);
sprintf(cmp, "This-is-a-tes1234");
sprintf(cmp + 1022, "abcdef");
stream = open_memstream (&buf, &len);
setvbuf(stream, NULL, _IONBF, 0); /* note: crashes in glibc with this */
fprintf(stream, "This-is-a-test");
fseek(stream, -1, SEEK_CUR); /* broken in glibc; can use {13,SEEK_SET} */
fprintf(stream, "1234");
fseek(stream, 1022, SEEK_SET);
fputc('a', stream);
fputc('b', stream);
fputc('c', stream);
fputc('d', stream);
fputc('e', stream);
fputc('f', stream);
fflush(stream);
if (memcmp(buf, cmp, len+1) != 0) {
printf("mismatch\n");
} else {
printf("match\n");
}
printf("Test4\n");
stream = open_memstream (&buf, &len);
fseek(stream, 5000, SEEK_SET);
fseek(stream, 4096, SEEK_SET);
fseek(stream, -1, SEEK_SET); /* should have no effect */
fputc('x', stream);
if (ftell(stream) == 4097)
printf("good\n");
else
printf("BAD: offset is %ld\n", ftell(stream));
printf("DONE\n");
return 0;
}
/* expected output:
Test1
buf=hello my world, len=14
buf=good-bye world, len=14
Test2
buf=hello my world, len=14
buf=good-bye, len=8
Test3
match
Test4
good
DONE
*/
#endif
#endif /*!HAVE_OPEN_MEMSTREAM*/