libcutils/open_memstream.c - android_system_core - Gitiles

 /*
  * 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.
  */

 #if defined(__APPLE__)

 /*
  * 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

 /*
  * 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;
 }


 #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 /* __APPLE__ */
	/*
	* 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.
	*/

	#if defined(__APPLE__)

	/*
	* 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

	/*
	* 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;
	}




	#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 /* __APPLE__ */