Implementation of open_memstream().
POSIX seems to have chosen open_memstream() over the BSD variant. We
want something for Dalvik that will work on both GNU/Linux and Android,
so this is open_memstream() implemented in terms of BSD funopen().
For Windows there's just a stub that calls abort().
I'm putting this in libcutils since it seems inappropriate for bionic
(which provides the BSD alternatives) but isn't Dalvik-specific.
diff --git a/libcutils/Android.mk b/libcutils/Android.mk
index b219473..93933e2 100644
--- a/libcutils/Android.mk
+++ b/libcutils/Android.mk
@@ -31,6 +31,7 @@
config_utils.c \
cpu_info.c \
load_file.c \
+ open_memstream.c \
strdup16to8.c \
strdup8to16.c \
record_stream.c \
diff --git a/libcutils/open_memstream.c b/libcutils/open_memstream.c
new file mode 100644
index 0000000..b49ef9b
--- /dev/null
+++ b/libcutils/open_memstream.c
@@ -0,0 +1,379 @@
+/*
+ * 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 <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*/