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