load and save XMP metadata in tiff

see https://github.com/jcupitt/libvips/issues/198

ChangeLog

@@ -4,6 +4,7 @@
 - added pbm (one bit) save
 - changed vips_gaussblur() parameters, sorry
 - add .szi as a dzsave zip synonym
+- support tiff XMP metadata
 
 25/7/14 started 7.41.0
 - start working on --disable-deprecated

libvips/foreign/foreign.c

@@ -1679,7 +1679,8 @@ vips_magickload( const char *filename, VipsImage **out, ... )
  * @page means load this page from the file. By default the first page (page
  * 0) is read.
  *
- * Any ICC profile is read and attached to the VIPS image.
+ * Any ICC profile is read and attached to the VIPS image. Any XMP metadata is
+ * read and attached to the image. 
  *
  * See also: vips_image_new_from_file().
  *
@@ -1811,6 +1812,9 @@ vips_tiffload_buffer( void *buf, size_t len, VipsImage **out, ... )
  * Bigtiff is a variant of the TIFF
  * format that allows more than 4GB in a file.
  *
+ * If @in has a field called VIPS_META_XMP_NAME ("xmp-data") it is written to
+ * the tiff image. 
+ *
  * See also: vips_tiffload(), vips_image_write_to_file().
  *
  * Returns: 0 on success, -1 on error.

libvips/foreign/tiff2vips.c

@@ -150,6 +150,8 @@
  * 	- 1/2/4 bit palette images can have alpha
  * 27/10/14 Lovell
  * 	- better istiff detector spots bigtiff
+ * 3/12/14
+ * 	- read any XMP metadata
  */
 
 /*
@@ -1141,6 +1143,19 @@ parse_header( ReadTiff *rtiff, VipsImage *out )
 			(VipsCallbackFn) vips_free, data_copy, data_length );
 	}
 
+	/* Read any XMP metadata.
+	 */
+	if( TIFFGetField( rtiff->tiff, 
+		TIFFTAG_XMLPACKET, &data_length, &data ) ) {
+		void *data_copy;
+
+		if( !(data_copy = vips_malloc( NULL, data_length )) ) 
+			return( -1 );
+		memcpy( data_copy, data, data_length );
+		vips_image_set_blob( out, VIPS_META_XMP_NAME, 
+			(VipsCallbackFn) vips_free, data_copy, data_length );
+	}
+
 	return( 0 );
 }
 

libvips/foreign/vips2tiff.c

@@ -139,7 +139,9 @@
  * 26/1/14
  * 	- add RGB as well as YCbCr write
  * 20/11/14
- * 	- cache input in tile write mode to keep us seqential
+ * 	- cache input in tile write mode to keep us sequential
+ * 3/12/14
+ * 	- embed XMP in output
  */
 
 /*
@@ -455,6 +457,28 @@ embed_profile( TiffWrite *tw, TIFF *tif )
 	return( 0 );
 }
 
+/* Embed any XMP metadata. 
+ */
+static int
+embed_xmp( TiffWrite *tw, TIFF *tif )
+{
+	void *data;
+	size_t data_length;
+
+	if( !vips_image_get_typeof( tw->im, VIPS_META_XMP_NAME ) )
+		return( 0 );
+	if( vips_image_get_blob( tw->im, VIPS_META_XMP_NAME, 
+		&data, &data_length ) )
+		return( -1 );
+	TIFFSetField( tif, TIFFTAG_XMLPACKET, data_length, data );
+
+#ifdef DEBUG
+	printf( "vips2tiff: attached XMP from meta\n" );
+#endif /*DEBUG*/
+
+	return( 0 );
+}
+
 /* Write a TIFF header. width and height are the size of the VipsImage we are
  * writing (may have been shrunk!).
  */
@@ -486,10 +510,10 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
 	TIFFSetField( tif, TIFFTAG_YRESOLUTION, 
 		VIPS_CLIP( 0.01, tw->yres, 10000 ) );
 
-	/* Attach ICC profile.
-	 */
 	if( embed_profile( tw, tif ) )
 		return( -1 );
+	if( embed_xmp( tw, tif ) )
+		return( -1 );
 
 	/* And colour fields.
 	 */
@@ -1466,10 +1490,12 @@ tiff_copy( TiffWrite *tw, TIFF *out, TIFF *in )
 		}
 	}
 
-	/* We can't copy profiles :( Set again from TiffWrite.
+	/* We can't copy profiles or xmp :( Set again from TiffWrite.
 	 */
 	if( embed_profile( tw, out ) )
 		return( -1 );
+	if( embed_xmp( tw, out ) )
+		return( -1 );
 
 	buf = vips_malloc( NULL, TIFFTileSize( in ) );
 	n = TIFFNumberOfTiles( in );