add stdout write

this now works:

	$ vips invert k2.jpg .jpg | vips invert stdin x.jpg

"stdin" means read from stdin, ".jpg" means write to stdout in JPG
format

libvips/foreign/foreign.c

@@ -1865,6 +1865,58 @@ vips_foreign_save( VipsImage *in, const char *name, ... )
 	return( result );
 }
 
+/* Can thsi class write this filetype to a stream?
+ */
+static void *
+vips_foreign_find_save_stream_sub( VipsForeignSaveClass *save_class, 
+	const char *suffix )
+{
+	VipsObjectClass *object_class = VIPS_OBJECT_CLASS( save_class );
+	VipsForeignClass *class = VIPS_FOREIGN_CLASS( save_class );
+
+	printf( "testing %s for %s\n", object_class->nickname, suffix );
+
+	if( class->suffs &&
+		vips_ispostfix( object_class->nickname, "_stream" ) &&
+		vips_filename_suffix_match( suffix, class->suffs ) )
+		return( save_class );
+
+	return( NULL );
+}
+
+/**
+ * vips_foreign_find_save_stream:
+ * @suffix: format to find a saver for
+ *
+ * Searches for an operation you could use to write to a stream in @suffix
+ * format. 
+ *
+ * See also: vips_image_write_to_buffer().
+ *
+ * Returns: the name of an operation on success, %NULL on error
+ */
+const char *
+vips_foreign_find_save_stream( const char *name )
+{
+	char suffix[VIPS_PATH_MAX];
+	char option_string[VIPS_PATH_MAX];
+	VipsForeignSaveClass *save_class;
+
+	vips__filename_split8( name, suffix, option_string );
+
+	if( !(save_class = (VipsForeignSaveClass *) vips_foreign_map( 
+		"VipsForeignSave",
+		(VipsSListMap2Fn) vips_foreign_find_save_stream_sub, 
+		(void *) suffix, NULL )) ) {
+		vips_error( "VipsForeignSave",
+			_( "\"%s\" is not a known stream format" ), name );
+
+		return( NULL );
+	}
+
+	return( G_OBJECT_CLASS_NAME( save_class ) );
+}
+
 /* Can we write this buffer with this file type?
  */
 static void *
@@ -1946,6 +1998,7 @@ vips_foreign_operation_init( void )
 	extern GType vips_foreign_load_jpeg_stream_get_type( void ); 
 	extern GType vips_foreign_save_jpeg_file_get_type( void ); 
 	extern GType vips_foreign_save_jpeg_buffer_get_type( void ); 
+	extern GType vips_foreign_save_jpeg_stream_get_type( void ); 
 	extern GType vips_foreign_save_jpeg_mime_get_type( void ); 
 	extern GType vips_foreign_load_tiff_file_get_type( void ); 
 	extern GType vips_foreign_load_tiff_buffer_get_type( void ); 
@@ -2058,6 +2111,7 @@ vips_foreign_operation_init( void )
 	vips_foreign_load_jpeg_stream_get_type(); 
 	vips_foreign_save_jpeg_file_get_type(); 
 	vips_foreign_save_jpeg_buffer_get_type(); 
+	vips_foreign_save_jpeg_stream_get_type(); 
 	vips_foreign_save_jpeg_mime_get_type(); 
 #endif /*HAVE_JPEG*/
 

libvips/include/vips/foreign.h

@@ -354,6 +354,7 @@ GType vips_foreign_save_get_type(void);
 const char *vips_foreign_find_save( const char *filename );
 gchar **vips_foreign_get_suffixes( void );
 const char *vips_foreign_find_save_buffer( const char *suffix );
+const char *vips_foreign_find_save_stream( const char *suffix );
 
 int vips_vipsload( const char *filename, VipsImage **out, ... )
 	__attribute__((sentinel));

libvips/include/vips/image.h

@@ -473,6 +473,9 @@ int vips_image_write_to_file( VipsImage *image, const char *name, ... )
 int vips_image_write_to_buffer( VipsImage *in, 
 	const char *suffix, void **buf, size_t *size, ... )
 	__attribute__((sentinel));
+int vips_image_write_to_stream( VipsImage *in, 
+	const char *suffix, VipsStreamOutput *output, ... )
+	__attribute__((sentinel));
 void *vips_image_write_to_memory( VipsImage *in, size_t *size );
 
 int vips_image_decode_predict( VipsImage *in, 

libvips/iofuncs/image.c

@@ -2704,6 +2704,51 @@ vips_image_write_to_buffer( VipsImage *in,
 	return( 0 );
 }
 
+/**
+ * vips_image_write_to_stream: (method)
+ * @in: image to write
+ * @suffix: format to write 
+ * @output: stream to write to
+ * @...: %NULL-terminated list of optional named arguments
+ *
+ * Writes @in to @output in format @suffix.
+ *
+ * Save options may be appended to @suffix as "[name=value,...]" or given as
+ * a NULL-terminated list of name-value pairs at the end of the arguments.
+ * Options given in the function call override options given in the filename. 
+ *
+ * You can call the various save operations directly if you wish, see
+ * vips_jpegsave_stream(), for example. 
+ *
+ * See also: vips_image_write_to_file().
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int
+vips_image_write_to_stream( VipsImage *in, 
+	const char *suffix, VipsStreamOutput *output, ... )
+{
+	char filename[VIPS_PATH_MAX];
+	char option_string[VIPS_PATH_MAX];
+	const char *operation_name;
+	va_list ap;
+	int result;
+
+	vips__filename_split8( suffix, filename, option_string );
+	if( !(operation_name = vips_foreign_find_save_stream( filename )) )
+		return( -1 );
+
+	va_start( ap, output );
+	result = vips_call_split_option_string( operation_name, option_string, 
+		ap, in, output );
+	va_end( ap );
+
+	if( result )
+		return( -1 );
+
+	return( 0 );
+}
+
 /**
  * vips_image_write_to_memory: (method)
  * @in: image to write

libvips/iofuncs/object.c

@@ -1886,6 +1886,8 @@ vips_object_set_argument_from_string( VipsObject *object,
 		VipsImage *out;
 		VipsOperationFlags flags;
 		VipsAccess access;
+		char filename[VIPS_PATH_MAX];
+		char option_string[VIPS_PATH_MAX];
 
 		if( !value ) {
 			vips_object_no_value( object, name );
@@ -1906,15 +1908,16 @@ vips_object_set_argument_from_string( VipsObject *object,
 		else
 			access = VIPS_ACCESS_RANDOM; 
 
-		/* The special filename "-" means stdin.
-		 */
-		if( strcmp( value, "-" ) == 0 ) {
+		vips__filename_split8( value, filename, option_string );
+
+		if( strcmp( "stdin", filename ) == 0 ) {
 			VipsStreamInput *input;
 
 			if( !(input = 
 				vips_stream_input_new_from_descriptor( 0 )) )
 				return( -1 );
-			if( !(out = vips_image_new_from_stream( input, "", 
+			if( !(out = vips_image_new_from_stream( input, 
+				option_string, 
 				"access", access,
 				NULL )) ) {
 				VIPS_UNREF( input );
@@ -2185,14 +2188,37 @@ vips_object_get_argument_to_string( VipsObject *object,
 
 	if( g_type_is_a( otype, VIPS_TYPE_IMAGE ) ) { 
 		VipsImage *in;
-/* Pull out the image and write it.
-		 */
-		g_object_get( object, name, &in, NULL );
-		if( vips_image_write_to_file( in, arg, NULL ) ) {
-			g_object_unref( in );
-			return( -1 );
+		char filename[VIPS_PATH_MAX];
+		char option_string[VIPS_PATH_MAX];
+
+		vips__filename_split8( arg, filename, option_string );
+
+		if( vips_isprefix( ".", filename ) ) {
+			VipsStreamOutput *output;
+
+			if( !(output = 
+				vips_stream_output_new_from_descriptor( 1 )) )
+				return( -1 );
+			g_object_get( object, name, &in, NULL );
+			if( vips_image_write_to_stream( in, 
+				arg, output, NULL ) ) {
+				VIPS_UNREF( in );
+				VIPS_UNREF( output );
+				return( -1 );
+			}
+			VIPS_UNREF( in );
+			VIPS_UNREF( output );
+		}
+		else {
+			/* Pull out the image and write it.
+			 */
+			g_object_get( object, name, &in, NULL );
+			if( vips_image_write_to_file( in, arg, NULL ) ) {
+				VIPS_UNREF( in );
+				return( -1 );
+			}
+			VIPS_UNREF( in );
 		}
-		g_object_unref( in );
 	}
 	else if( g_type_is_a( otype, VIPS_TYPE_OBJECT ) &&
 		(oclass = g_type_class_ref( otype )) &&

libvips/iofuncs/stream.c

@@ -744,7 +744,6 @@ vips_stream_output_new_from_descriptor( int descriptor )
 	stream = VIPS_STREAM_OUTPUT( 
 		g_object_new( VIPS_TYPE_STREAM_OUTPUT, 
 			"descriptor", descriptor,
-			"filename", "descriptor",
 			NULL ) );
 
 	if( vips_object_build( VIPS_OBJECT( stream ) ) ) {