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.

10 files changed, 486 insertions, 0 deletions

diff --git a/include/arch/darwin-x86/AndroidConfig.h b/include/arch/darwin-x86/AndroidConfig.h
index 20e0000..1f7545e 100644
--- a/include/arch/darwin-x86/AndroidConfig.h
+++ b/include/arch/darwin-x86/AndroidConfig.h
@@ -256,6 +256,16 @@
 #define HAVE_STRLCPY 1
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+/* #define HAVE_OPEN_MEMSTREAM 1 */
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+#define HAVE_FUNOPEN 1
+
+/*
  * Define if writev() exists
  */
 #define HAVE_WRITEV 1
diff --git a/include/arch/freebsd-x86/AndroidConfig.h b/include/arch/freebsd-x86/AndroidConfig.h
index b01a854..57d5024 100644
--- a/include/arch/freebsd-x86/AndroidConfig.h
+++ b/include/arch/freebsd-x86/AndroidConfig.h
@@ -295,6 +295,16 @@
 #define HAVE_STRLCPY 1
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+/* #define HAVE_OPEN_MEMSTREAM 1 */
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+#define HAVE_FUNOPEN 1
+
+/*
  * Define if prctl() exists
  */
 /* #define HAVE_PRCTL 1 */
diff --git a/include/arch/linux-arm/AndroidConfig.h b/include/arch/linux-arm/AndroidConfig.h
index 26547a2..f51ddb1 100644
--- a/include/arch/linux-arm/AndroidConfig.h
+++ b/include/arch/linux-arm/AndroidConfig.h
@@ -298,6 +298,16 @@
 #define HAVE_STRLCPY 1
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+/* #define HAVE_OPEN_MEMSTREAM 1 */
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+#define HAVE_FUNOPEN 1
+
+/*
  * Define if prctl() exists
  */
 #define HAVE_PRCTL 1
diff --git a/include/arch/linux-sh/AndroidConfig.h b/include/arch/linux-sh/AndroidConfig.h
index 67ac277..5e93990 100644
--- a/include/arch/linux-sh/AndroidConfig.h
+++ b/include/arch/linux-sh/AndroidConfig.h
@@ -303,6 +303,16 @@
 #define HAVE_STRLCPY 1
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+/* #define HAVE_OPEN_MEMSTREAM 1 */
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+#define HAVE_FUNOPEN 1
+
+/*
  * Define if prctl() exists
  */
 #define HAVE_PRCTL 1
diff --git a/include/arch/linux-x86/AndroidConfig.h b/include/arch/linux-x86/AndroidConfig.h
index 31bdb5f..b0fe90a 100644
--- a/include/arch/linux-x86/AndroidConfig.h
+++ b/include/arch/linux-x86/AndroidConfig.h
@@ -279,6 +279,16 @@
 /* #define HAVE_STRLCPY 1 */
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+#define HAVE_OPEN_MEMSTREAM 1
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+/* #define HAVE_FUNOPEN 1 */
+
+/*
  * Define if prctl() exists
  */
 #define HAVE_PRCTL 1
diff --git a/include/arch/target_linux-x86/AndroidConfig.h b/include/arch/target_linux-x86/AndroidConfig.h
index d89d054..4db3e72 100644
--- a/include/arch/target_linux-x86/AndroidConfig.h
+++ b/include/arch/target_linux-x86/AndroidConfig.h
@@ -289,6 +289,16 @@
 #define HAVE_STRLCPY 1
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+/* #define HAVE_OPEN_MEMSTREAM 1 */
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+#define HAVE_FUNOPEN 1
+
+/*
  * Define if prctl() exists
  */
 #define HAVE_PRCTL 1
diff --git a/include/arch/windows/AndroidConfig.h b/include/arch/windows/AndroidConfig.h
index 0fc4955..1b6ece1 100644
--- a/include/arch/windows/AndroidConfig.h
+++ b/include/arch/windows/AndroidConfig.h
@@ -272,6 +272,16 @@
 /* #define HAVE_STRLCPY 1 */
 
 /*
+ * Define if the open_memstream() function exists on the system.
+ */
+/* #define HAVE_OPEN_MEMSTREAM 1 */
+
+/*
+ * Define if the BSD funopen() function exists on the system.
+ */
+/* #define HAVE_FUNOPEN 1 */
+
+/*
  * Define if <winsock2.h> exists.
  * Only MinGW has it.
  */
diff --git a/include/cutils/open_memstream.h b/include/cutils/open_memstream.h
new file mode 100644
index 0000000..b7998be
--- /dev/null
+++ b/include/cutils/open_memstream.h
@@ -0,0 +1,36 @@
+/*
+ * 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 __CUTILS_OPEN_MEMSTREAM_H__
+#define __CUTILS_OPEN_MEMSTREAM_H__
+
+#include <stdio.h>
+
+#ifndef HAVE_OPEN_MEMSTREAM
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+FILE* open_memstream(char** bufp, size_t* sizep);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /*!HAVE_OPEN_MEMSTREAM*/
+
+#endif /*__CUTILS_OPEN_MEMSTREAM_H__*/
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 @@ commonSources := \
 	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*/