util: convenience function to create gmime stream for stdout

It turns out that our use of GMimeStreamPipe has only succeeded
because gmime has been ignoring some seek failures; this will no
longer be the case in gmime 3.0, so we use a GMimeStreamPipe, which
does not assume seekability, wrapped in a buffering stream.

util/Makefile.local

@@ -5,7 +5,7 @@ extra_cflags += -I$(srcdir)/$(dir)
 
 libnotmuch_util_c_srcs := $(dir)/xutil.c $(dir)/error_util.c $(dir)/hex-escape.c \
 		  $(dir)/string-util.c $(dir)/talloc-extra.c $(dir)/zlib-extra.c \
-		$(dir)/util.c
+		$(dir)/util.c $(dir)/gmime-extra.c
 
 libnotmuch_util_modules := $(libnotmuch_util_c_srcs:.c=.o)
 

util/gmime-extra.c

@@ -0,0 +1,20 @@
+#include "gmime-extra.h"
+
+GMimeStream *
+g_mime_stream_stdout_new()
+{
+    GMimeStream *stream_stdout = NULL;
+    GMimeStream *stream_buffered = NULL;
+
+    stream_stdout = g_mime_stream_pipe_new (STDOUT_FILENO);
+    if (!stream_stdout)
+	return NULL;
+
+    g_mime_stream_pipe_set_owner (GMIME_STREAM_PIPE (stream_stdout), FALSE);
+
+    stream_buffered = g_mime_stream_buffer_new (stream_stdout, GMIME_STREAM_BUFFER_BLOCK_WRITE);
+
+    g_object_unref (stream_stdout);
+
+    return stream_buffered;
+}

util/gmime-extra.h

@@ -0,0 +1,6 @@
+#ifndef _GMIME_EXTRA_H
+#define _GMIME_EXTRA_H
+#include <gmime/gmime.h>
+
+GMimeStream *g_mime_stream_stdout_new(void);
+#endif