clean up allocation/setup logic for open_[w]memstream

bring these functions up to date with the current idioms we use/prefer
in fmemopen and fopencookie.

src/stdio/open_memstream.c

@@ -12,6 +12,12 @@ struct cookie {
 	size_t space;
 };
 
+struct ms_FILE {
+	FILE f;
+	struct cookie c;
+	unsigned char buf[BUFSIZ];
+};
+
 static off_t ms_seek(FILE *f, off_t off, int whence)
 {
 	ssize_t base;
@@ -57,34 +63,34 @@ static int ms_close(FILE *f)
 
 FILE *open_memstream(char **bufp, size_t *sizep)
 {
-	FILE *f;
-	struct cookie *c;
+	struct ms_FILE *f;
 	char *buf;
 
-	if (!(f=malloc(sizeof *f + sizeof *c + BUFSIZ))) return 0;
+	if (!(f=malloc(sizeof *f))) return 0;
 	if (!(buf=malloc(sizeof *buf))) {
 		free(f);
 		return 0;
 	}
-	memset(f, 0, sizeof *f + sizeof *c);
-	f->cookie = c = (void *)(f+1);
+	memset(&f->f, 0, sizeof f->f);
+	memset(&f->c, 0, sizeof f->c);
+	f->f.cookie = &f->c;
 
-	c->bufp = bufp;
-	c->sizep = sizep;
-	c->pos = c->len = c->space = *sizep = 0;
-	c->buf = *bufp = buf;
+	f->c.bufp = bufp;
+	f->c.sizep = sizep;
+	f->c.pos = f->c.len = f->c.space = *sizep = 0;
+	f->c.buf = *bufp = buf;
 	*buf = 0;
 
-	f->flags = F_NORD;
-	f->fd = -1;
-	f->buf = (void *)(c+1);
-	f->buf_size = BUFSIZ;
-	f->lbf = EOF;
-	f->write = ms_write;
-	f->seek = ms_seek;
-	f->close = ms_close;
+	f->f.flags = F_NORD;
+	f->f.fd = -1;
+	f->f.buf = f->buf;
+	f->f.buf_size = sizeof f->buf;
+	f->f.lbf = EOF;
+	f->f.write = ms_write;
+	f->f.seek = ms_seek;
+	f->f.close = ms_close;
 
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) f->f.lock = -1;
 
-	return __ofl_add(f);
+	return __ofl_add(&f->f);
 }

src/stdio/open_wmemstream.c

@@ -14,6 +14,12 @@ struct cookie {
 	mbstate_t mbs;
 };
 
+struct wms_FILE {
+	FILE f;
+	struct cookie c;
+	unsigned char buf[1];
+};
+
 static off_t wms_seek(FILE *f, off_t off, int whence)
 {
 	ssize_t base;
@@ -59,34 +65,34 @@ static int wms_close(FILE *f)
 
 FILE *open_wmemstream(wchar_t **bufp, size_t *sizep)
 {
-	FILE *f;
-	struct cookie *c;
+	struct wms_FILE *f;
 	wchar_t *buf;
 
-	if (!(f=malloc(sizeof *f + sizeof *c))) return 0;
+	if (!(f=malloc(sizeof *f))) return 0;
 	if (!(buf=malloc(sizeof *buf))) {
 		free(f);
 		return 0;
 	}
-	memset(f, 0, sizeof *f + sizeof *c);
-	f->cookie = c = (void *)(f+1);
+	memset(&f->f, 0, sizeof f->f);
+	memset(&f->c, 0, sizeof f->c);
+	f->f.cookie = &f->c;
 
-	c->bufp = bufp;
-	c->sizep = sizep;
-	c->pos = c->len = c->space = *sizep = 0;
-	c->buf = *bufp = buf;
+	f->c.bufp = bufp;
+	f->c.sizep = sizep;
+	f->c.pos = f->c.len = f->c.space = *sizep = 0;
+	f->c.buf = *bufp = buf;
 	*buf = 0;
 
-	f->flags = F_NORD;
-	f->fd = -1;
-	f->buf = (void *)(c+1);
-	f->buf_size = 0;
-	f->lbf = EOF;
-	f->write = wms_write;
-	f->seek = wms_seek;
-	f->close = wms_close;
+	f->f.flags = F_NORD;
+	f->f.fd = -1;
+	f->f.buf = f->buf;
+	f->f.buf_size = 0;
+	f->f.lbf = EOF;
+	f->f.write = wms_write;
+	f->f.seek = wms_seek;
+	f->f.close = wms_close;
 
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) f->f.lock = -1;
 
-	return __ofl_add(f);
+	return __ofl_add(&f->f);
 }