add fallbacks to new_from_stream

If the stream-based loaders fail, vips_image_new_from_stream() now falls
back to the old file and buffer loaders.

The file and buffer loaders already try the stream loaders first.

cplusplus/VImage.cpp

@@ -592,7 +592,8 @@ VImage
 VImage::new_from_buffer( const std::string &buf, const char *option_string, 
 	VOption *options )
 {
-	return( new_from_buffer( buf.c_str(), buf.size(), option_string, options ) );
+	return( new_from_buffer( buf.c_str(), buf.size(), 
+		option_string, options ) );
 }
 
 VImage 

libvips/include/vips/stream.h

@@ -214,6 +214,7 @@ int vips_streami_decode( VipsStreami *streami );
 ssize_t vips_streami_read( VipsStreami *streami, void *data, size_t length );
 gboolean vips_streami_is_mappable( VipsStreami *streami );
 const void *vips_streami_map( VipsStreami *streami, size_t *length );
+VipsBlob *vips_streami_map_blob( VipsStreami *streami );
 gint64 vips_streami_seek( VipsStreami *streami, gint64 offset, int whence );
 int vips_streami_rewind( VipsStreami *streami );
 size_t vips_streami_sniff_at_most( VipsStreami *streami, 

libvips/include/vips/type.h

@@ -74,9 +74,12 @@ typedef struct _VipsArea {
 	int count;
 	GMutex *lock;		
 
-	/* Things like ICC profiles need their own free functions.
+	/* Things like ICC profiles need their own free functions. 
+	 *
+	 * Set client to anything you like -- VipsArea doesn't use this.
 	 */
 	VipsCallbackFn free_fn;
+	void *client;
 
 	/* If we are holding an array (for example, an array of double), the
 	 * GType of the elements and their size. 0 for not known.

libvips/iofuncs/image.c

@@ -18,6 +18,8 @@
  * 	- better rules for hasalpha
  * 9/10/18
  * 	- fix up vips_image_dump(), it was still using ints not enums
+ * 10/12/19
+ * 	- add vips_image_new_from_stream() / vips_image_write_to_stream()
  */
 
 /*
@@ -2230,6 +2232,8 @@ VipsImage *
 vips_image_new_from_stream( VipsStreami *streami, 
 	const char *option_string, ... )
 {
+	const char *filename = vips_stream_filename( VIPS_STREAM( streami ) );
+
 	const char *operation_name;
 	va_list ap;
 	int result;
@@ -2237,13 +2241,51 @@ vips_image_new_from_stream( VipsStreami *streami,
 
 	vips_check_init();
 
-        if( !(operation_name = vips_foreign_find_load_stream( streami )) )
-                return( NULL );
+	vips_error_freeze();
+	operation_name = vips_foreign_find_load_stream( streami );
+	vips_error_thaw();
 
-        va_start( ap, option_string );
-        result = vips_call_split_option_string( operation_name,
-                option_string, ap, streami, &out );
-        va_end( ap );
+        if( operation_name ) { 
+		va_start( ap, option_string );
+		result = vips_call_split_option_string( operation_name,
+			option_string, ap, streami, &out );
+		va_end( ap );
+	}
+	else if( filename ) {
+		/* Try with the old file-based loaders.
+		 */
+		if( !(operation_name = vips_foreign_find_load( filename )) )
+			return( NULL );
+
+		va_start( ap, option_string );
+		result = vips_call_split_option_string( operation_name, 
+			option_string, ap, filename, &out );
+		va_end( ap );
+	}
+	else if( vips_streami_is_mappable( streami ) ) {
+		/* Try with the old buffer-based loaders.
+		 */
+		VipsBlob *blob;
+		const void *buf;
+		size_t len;
+
+		if( !(blob = vips_streami_map_blob( streami )) )
+			return( NULL );
+
+		buf = vips_blob_get( blob, &len );
+		if( !(operation_name = 
+			vips_foreign_find_load_buffer( buf, len )) ) {
+			vips_area_unref( VIPS_AREA( blob ) );
+			return( NULL );
+		}
+
+                va_start( ap, option_string );
+                result = vips_call_split_option_string( operation_name,
+                        option_string, ap, blob, &out );
+                va_end( ap );
+
+		vips_area_unref( VIPS_AREA( blob ) );
+	}
 
         if( result )
                 return( NULL );

libvips/iofuncs/streami.c

@@ -873,6 +873,8 @@ vips_streami_is_mappable( VipsStreami *streami )
  * This operation can take a long time. Use vips_streami_is_mappable() to 
  * check if a streami can be mapped efficiently.
  *
+ * The pointer is valid for as long as @streami is alive.
+ *
  * Returns: a pointer to the start of the file contents, or NULL on error.
  */
 const void *
@@ -908,6 +910,45 @@ vips_streami_map( VipsStreami *streami, size_t *length_out )
 	return( streami->data );
 }
 
+static int
+vips_streami_map_cb( void *a, void *b )
+{
+	VipsArea *area = VIPS_AREA( b );
+	GObject *gobject = G_OBJECT( area->client );
+
+	VIPS_UNREF( gobject );
+
+	return( 0 );
+}
+
+/**
+ * vips_streami_map_blob:
+ * @streami: input stream to operate on
+ *
+ * Just like vips_streami_map(), but return a #VipsBlob containing the
+ * pointer. @streami will stay alive as long as the result is alive.
+ *
+ * Returns: a new #VipsBlob containing the data, or NULL on error.
+ */
+VipsBlob *
+vips_streami_map_blob( VipsStreami *streami )
+{
+	const void *buf;
+	size_t len;
+	VipsBlob *blob;
+
+	if( !(buf = vips_streami_map( streami, &len )) ||
+		!(blob = vips_blob_new( vips_streami_map_cb, buf, len )) ) 
+		return( NULL );
+
+	/* The streami must stay alive until the blob is done.
+	 */
+	g_object_ref( streami );
+	VIPS_AREA( blob )->client = streami;
+
+	return( blob );
+}
+
 /**
  * vips_streami_seek:
  * @streami: input stream to operate on

test/test-suite/test_create.py

@@ -121,8 +121,8 @@ class TestCreate:
         sigma = im.deviate()
         mean = im.avg()
 
-        assert sigma == pytest.approx(10, abs=0.2)
-        assert mean == pytest.approx(100, abs=0.2)
+        assert sigma == pytest.approx(10, abs=0.4)
+        assert mean == pytest.approx(100, abs=0.4)
 
     def test_grey(self):
         im = pyvips.Image.grey(100, 90)