Add open_memstream(3).

libc/Makefile

@@ -132,6 +132,7 @@ stdio/fwrite.o \
 stdio/fwrite_unlocked.o \
 stdio/getdelim.o \
 stdio/getline.o \
+stdio/open_memstream.o \
 stdio/rewind.o \
 stdio/setbuf.o \
 stdio/setvbuf.o \

libc/include/stdio.h

@@ -242,7 +242,7 @@ int dprintf(int fildes, const char* __restrict format, ...)
 	__attribute__((__format__ (printf, 2, 3)));
 FILE* fmemopen(void* __restrict, size_t, const char* __restrict);
 ssize_t getdelim(char** __restrict lineptr, size_t* __restrict n, int delimiter, FILE* __restrict stream);
-/* TODO: open_memstream */
+FILE* open_memstream(char**, size_t*);
 ssize_t getline(char** __restrict lineptr, size_t* __restrict n, FILE* __restrict stream);
 int renameat(int oldfd, const char* oldname, int newfd, const char* newname);
 int vdprintf(int fildes, const char* __restrict format, __gnuc_va_list ap)

libc/stdio/open_memstream.cpp

@@ -0,0 +1,122 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2015.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    libc/stdio/open_memstream.cpp
+    Open a memory stream.
+
+*******************************************************************************/
+
+#include <sys/types.h>
+
+#include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct memstream
+{
+	char** string_out;
+	size_t* used_out;
+	char* string;
+	size_t offset;
+	size_t used;
+	size_t size;
+};
+
+static ssize_t memstream_write(void* ms_ptr, const void* src, size_t count)
+{
+	struct memstream* ms = (struct memstream*) ms_ptr;
+	if ( (size_t) SSIZE_MAX < count )
+		count = SSIZE_MAX;
+	if ( ms->offset == SIZE_MAX && 1 <= count )
+		return errno = EOVERFLOW, -1;
+	if ( (size_t) SSIZE_MAX - ms->offset < count )
+		count = SIZE_MAX - ms->offset;
+	size_t required_size = ms->offset + count;
+	if ( ms->size < required_size )
+	{
+		// TODO: Multiplication overflow.
+		size_t new_size = 2 * ms->size;
+		if ( new_size < 16 )
+			new_size = 16;
+		if ( new_size < required_size )
+			new_size = required_size;
+		if ( SIZE_MAX - new_size < 1 )
+			return errno = EOVERFLOW, -1;
+		char* new_string = (char*) realloc(ms->string, new_size + 1);
+		if ( !new_string )
+			return -1;
+		ms->string = new_string;
+		ms->size = new_size;
+	}
+	memcpy(ms->string + ms->offset, src, count);
+	ms->offset += count;
+	if ( ms->used < required_size )
+	{
+		ms->used = required_size;
+		ms->string[ms->used] = '\0';
+	}
+	*ms->string_out = ms->string;
+	*ms->used_out = ms->used;
+	return count;
+}
+
+static off_t memstream_seek(void* ms_ptr, off_t offset, int whence)
+{
+	struct memstream* ms = (struct memstream*) ms_ptr;
+	off_t base;
+	switch ( whence )
+	{
+	case SEEK_SET: base = 0; break;
+	case SEEK_CUR: base = (off_t) ms->offset; break;
+	case SEEK_END: base = (off_t) ms->used; break;
+	default: return errno = EINVAL, -1;
+	}
+	if ( offset < -base || base - SSIZE_MAX < offset )
+		return errno = EOVERFLOW, -1;
+	return (off_t) (ms->offset = (size_t) (base + offset));
+}
+
+extern "C" FILE* open_memstream(char** string_out, size_t* used_out)
+{
+	char* string = (char*) malloc(1);
+	if ( !string )
+		return NULL;
+	string[0] = '\0';
+	struct memstream* ms = (struct memstream*) malloc(sizeof(struct memstream));
+	if ( !ms )
+		return free(string), (FILE*) NULL;
+	FILE* fp = fnewfile();
+	if ( !fp )
+		return free(ms), free(string), (FILE*) NULL;
+	ms->string_out = string_out;
+	ms->used_out = used_out;
+	ms->string= string;
+	ms->offset = 0;
+	ms->used = 0;
+	ms->size = 0;
+	fp->flags |= _FILE_WRITABLE;
+	fp->user = ms;
+	fp->write_func = memstream_write;
+	fp->seek_func = memstream_seek;
+	*string_out = ms->string;
+	*used_out = ms->used;
+	return fp;
+}