add magic "-" stdin filename

this almost works!

$ vips invert - x.jpg < k2.jpg

libvips/foreign/foreign.c

@@ -621,6 +621,55 @@ vips_foreign_find_load_buffer( const void *data, size_t size )
 	return( G_OBJECT_CLASS_NAME( load_class ) );
 }
 
+/* Can this VipsForeign open this stream?
+ */
+static void *
+vips_foreign_find_load_stream_sub( void *item, void *a, void *b )
+{
+	VipsForeignLoadClass *load_class = VIPS_FOREIGN_LOAD_CLASS( item );
+	VipsStreamInput *input = VIPS_STREAM_INPUT( a );
+
+	if( load_class->is_a_stream &&
+		load_class->is_a_stream( input ) ) 
+		return( load_class );
+
+	return( NULL );
+}
+
+/**
+ * vips_foreign_find_load_stream:
+ * @input: stream to load from
+ *
+ * Searches for an operation you could use to load a stream. To see the
+ * range of buffer loaders supported by your vips, try something like:
+ * 
+ * 	vips -l | grep load_stream
+ *
+ * See also: vips_image_new_from_stream().
+ *
+ * Returns: (transfer none): the name of an operation on success, %NULL on 
+ * error.
+ */
+const char *
+vips_foreign_find_load_stream( VipsStreamInput *input )
+{
+	VipsForeignLoadClass *load_class;
+
+	if( !(load_class = (VipsForeignLoadClass *) vips_foreign_map( 
+		"VipsForeignLoad",
+		vips_foreign_find_load_stream_sub, 
+		input, NULL )) ) {
+		vips_error( "VipsForeignLoad", 
+			"%s", _( "stream is not in a known format" ) ); 
+		(void) vips_stream_input_rewind( input );
+		return( NULL );
+	}
+
+	(void) vips_stream_input_rewind( input );
+
+	return( G_OBJECT_CLASS_NAME( load_class ) );
+}
+
 /**
  * vips_foreign_is_a:
  * @loader: name of loader to use for test

libvips/foreign/jpeg2vips.c

@@ -134,9 +134,9 @@
  */
 
 /*
+ */
 #define DEBUG_VERBOSE
 #define DEBUG
- */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -1216,6 +1216,10 @@ vips__jpeg_read_stream( VipsStreamInput *input, VipsImage *out,
 	if( vips__jpeg_read( jpeg, out, header_only ) ) 
 		return( -1 );
 
+	/* We've read the header ... it's pixel decode from now on.
+	vips_stream_input_decode( input );
+	 */
+
 	return( 0 );
 }
 

libvips/foreign/jpegload.c

@@ -34,9 +34,9 @@
  */
 
 /*
+ */
 #define DEBUG_VERBOSE
 #define DEBUG
- */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -359,6 +359,8 @@ vips_foreign_load_jpeg_stream_load( VipsForeignLoad *load )
 static gboolean
 vips_foreign_load_jpeg_stream_is_a( VipsStreamInput *input )
 {
+	printf( "vips_foreign_load_jpeg_stream_is_a:\n" );
+
 	return( vips__isjpeg_stream( input ) );
 }
 

libvips/include/vips/foreign.h

@@ -240,6 +240,7 @@ GType vips_foreign_load_get_type(void);
 
 const char *vips_foreign_find_load( const char *filename );
 const char *vips_foreign_find_load_buffer( const void *data, size_t size );
+const char *vips_foreign_find_load_stream( VipsStreamInput *stream );
 
 VipsForeignFlags vips_foreign_flags( const char *loader, const char *filename );
 gboolean vips_foreign_is_a( const char *loader, const char *filename );

libvips/include/vips/image.h

@@ -450,13 +450,16 @@ VipsImage *vips_image_new_from_memory_copy( const void *data, size_t size,
 VipsImage *vips_image_new_from_buffer( const void *buf, size_t len, 
 	const char *option_string, ... )
 	__attribute__((sentinel));
+VipsImage *vips_image_new_from_stream( VipsStreamInput *input, 
+	const char *option_string, ... ) __attribute__((sentinel));
 VipsImage *vips_image_new_matrix( int width, int height );
 VipsImage *vips_image_new_matrixv( int width, int height, ... );
 VipsImage *vips_image_new_matrix_from_array( int width, int height, 
 	const double *array, int size );
 VipsImage *vips_image_matrix_from_array( int width, int height, 
 	const double *array, int size );
-VipsImage *vips_image_new_from_image( VipsImage *image, const double *c, int n );
+VipsImage *vips_image_new_from_image( VipsImage *image, 
+	const double *c, int n );
 VipsImage *vips_image_new_from_image1( VipsImage *image, double c );
 
 void vips_image_set_delete_on_close( VipsImage *image, 

libvips/iofuncs/image.c

@@ -2167,6 +2167,48 @@ vips_image_new_from_buffer( const void *buf, size_t len,
 	return( out ); 
 }
 
+/**
+ * vips_image_new_from_stream: (constructor)
+ * @input: (transfer none): stream to fetch image from
+ * @option_string: set of extra options as a string
+ * @...: %NULL-terminated list of optional named arguments
+ *
+ * Loads an image from the formatted stream @input, 
+ * loader recommended by vips_foreign_find_load_stream(). 
+ *
+ * Load options may be given in @option_string 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 string. 
+ *
+ * See also: vips_image_write_to_buffer().
+ *
+ * Returns: (transfer full): the new #VipsImage, or %NULL on error.
+ */
+VipsImage *
+vips_image_new_from_stream( VipsStreamInput *input, 
+	const char *option_string, ... )
+{
+	const char *operation_name;
+	va_list ap;
+	int result;
+	VipsImage *out;
+
+	vips_check_init();
+
+        if( !(operation_name = vips_foreign_find_load_stream( input )) )
+                return( NULL );
+
+        va_start( ap, option_string );
+        result = vips_call_split_option_string( operation_name,
+                option_string, ap, input, &out );
+        va_end( ap );
+
+        if( result )
+                return( NULL );
+
+        return( out );
+}
+
 /**
  * vips_image_new_matrix: (constructor)
  * @width: image width

libvips/iofuncs/object.c

@@ -1899,16 +1899,35 @@ vips_object_set_argument_from_string( VipsObject *object,
 
 		/* Read the filename. 
 		 */
-		if( flags & (VIPS_OPERATION_SEQUENTIAL_UNBUFFERED |
-			     VIPS_OPERATION_SEQUENTIAL) ) 
+		if( flags & 
+			(VIPS_OPERATION_SEQUENTIAL_UNBUFFERED | 
+			 VIPS_OPERATION_SEQUENTIAL) ) 
 			access = VIPS_ACCESS_SEQUENTIAL;
 		else
 			access = VIPS_ACCESS_RANDOM; 
 
-		if( !(out = vips_image_new_from_file( value, 
-			"access", access,
-			NULL )) )
-			return( -1 );
+		/* The special filename "-" means stdin.
+		 */
+		if( strcmp( value, "-" ) == 0 ) {
+			VipsStreamInput *input;
+
+			if( !(input = 
+				vips_stream_input_new_from_descriptor( 0 )) )
+				return( -1 );
+			if( !(out = vips_image_new_from_stream( input, "", 
+				"access", access,
+				NULL )) ) {
+				VIPS_UNREF( input );
+				return( -1 );
+			}
+			VIPS_UNREF( input );
+		}
+		else {
+			if( !(out = vips_image_new_from_file( value, 
+				"access", access,
+				NULL )) )
+				return( -1 );
+		}
 
 		g_value_init( &gvalue, VIPS_TYPE_IMAGE );
 		g_value_set_object( &gvalue, out );

libvips/iofuncs/stream.c

@@ -41,8 +41,8 @@
  */
 
 /*
-#define VIPS_DEBUG
  */
+#define VIPS_DEBUG
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -243,6 +243,8 @@ vips_stream_input_read_real( VipsStreamInput *input,
 {
 	VipsStream *stream = VIPS_STREAM( input );
 
+	VIPS_DEBUG_MSG( "vips_stream_input_read_real:\n" );
+
 	if( input->blob ) {
 		VipsArea *area = (VipsArea *) input->blob;
 		ssize_t available = VIPS_MIN( length,
@@ -255,7 +257,7 @@ vips_stream_input_read_real( VipsStreamInput *input,
 
 		return( available );
 	}
-	else if( stream->descriptor ) {
+	else if( stream->descriptor != -1 ) {
 		return( read( stream->descriptor, buffer, length ) );
 	}
 	else {
@@ -269,6 +271,8 @@ vips_stream_input_rewind_real( VipsStreamInput *input )
 {
 	VipsStream *stream = VIPS_STREAM( input );
 
+	VIPS_DEBUG_MSG( "vips_stream_input_rewind_real:\n" );
+
 	if( input->decode ) {
 		vips_error( STREAM_NAME( stream ),
 			"%s", _( "can't rewind after decode begins" ) );
@@ -279,6 +283,9 @@ vips_stream_input_rewind_real( VipsStreamInput *input )
 		stream->descriptor != -1 ) {
 		off_t new_pos;
 
+		VIPS_DEBUG_MSG( "   rewinding desriptor %d\n", 
+			stream->descriptor );
+
 		new_pos = lseek( stream->descriptor, 0, SEEK_SET );
 		if( new_pos == -1 ) {
 			vips_error_system( errno, STREAM_NAME( stream ),
@@ -468,12 +475,14 @@ vips_stream_input_read( VipsStreamInput *input,
 
 	ssize_t bytes_read;
 
+	VIPS_DEBUG_MSG( "vips_stream_input_read:\n" );
+
 	bytes_read = 0;
 
 	/* Are we serving from header_bytes? Get what we can from there.
 	 */
 	if( input->header_bytes &&
-		input->header_bytes->len < input->read_position ) {
+		input->read_position < input->header_bytes->len ) {
 		ssize_t available;
 
 		available = VIPS_MIN( length, 
@@ -485,19 +494,21 @@ vips_stream_input_read( VipsStreamInput *input,
 		buffer += available;
 		length -= available;
 		bytes_read += available;
+
+		VIPS_DEBUG_MSG( "    %zd bytes from cache\n", available );
 	}
 
 	/* Any more bytes required? Call the read() method.
 	 */
 	if( length > 0 ) {
-		ssize_t read;
+		ssize_t n;
 
-		if( (read = class->read( input, buffer, length )) == -1 ) {
+		if( (n = class->read( input, buffer, length )) == -1 ) {
 			vips_error_system( errno, STREAM_NAME( input ), 
 				"%s", _( "read error" ) ); 
 			return( -1 );
 		}
-		if( read == 0 )
+		if( n == 0 )
 			input->eof = TRUE;
 
 		/* If we're not rewindable, we need to save header bytes for
@@ -506,14 +517,18 @@ vips_stream_input_read( VipsStreamInput *input,
 		if( input->header_bytes &&
 			!input->rewindable &&
 			!input->decode &&
-			read > 0 ) 
+			n > 0 ) 
 			g_byte_array_append( input->header_bytes, 
-				buffer, read );
+				buffer, n );
 
-		input->read_position += read;
-		bytes_read += read;
+		input->read_position += n;
+		bytes_read += n;
+
+		VIPS_DEBUG_MSG( "    %zd bytes from read()\n", n );
 	}
 
+	VIPS_DEBUG_MSG( "    %zd bytes total\n", bytes_read );
+
 	return( bytes_read );
 }
 
@@ -522,18 +537,24 @@ vips_stream_input_rewind( VipsStreamInput *input )
 {
 	VipsStreamInputClass *class = VIPS_STREAM_INPUT_GET_CLASS( input );
 
+	VIPS_DEBUG_MSG( "vips_stream_input_rewind:\n" );
+
 	return( class->rewind( input ) );
 }
 
 gboolean
 vips_stream_input_eof( VipsStreamInput *input )
 {
+	VIPS_DEBUG_MSG( "vips_stream_input_eof:\n" );
+
 	return( input->eof ); 
 }
 
 void 
 vips_stream_input_decode( VipsStreamInput *input )
 {
+	VIPS_DEBUG_MSG( "vips_stream_input_decode:\n" );
+
 	input->decode = TRUE;
 	VIPS_FREEF( g_byte_array_unref, input->header_bytes ); 
 	VIPS_FREEF( g_byte_array_unref, input->sniff ); 
@@ -548,20 +569,20 @@ vips_stream_input_decode( VipsStreamInput *input )
 unsigned char *
 vips_stream_input_sniff( VipsStreamInput *input, size_t length )
 {
-	ssize_t read;
+	ssize_t n;
 	unsigned char *q;
 
+	VIPS_DEBUG_MSG( "vips_stream_input_sniff: %zd bytes\n", length );
+
 	if( vips_stream_input_rewind( input ) )
 		return( NULL );
 
 	g_byte_array_set_size( input->sniff, length );
 
-	for( q = input->sniff->data; length > 0; length -= read, q += read ) {
-		read = vips_stream_input_read( input, q, length );
-		if( read == -1 ||
-			read == 0 )
+	for( q = input->sniff->data; length > 0; length -= n, q += n )
+		if( (n = vips_stream_input_read( input, q, length )) == -1 ||
+			n == 0 )
 			return( NULL );
-	}
 
 	return( input->sniff->data );
 }