tiny cleanup

make the code for error during jpeg buffer write a little cleaner --
rather than calling the jpeg term method ourselves, have a separate
destroy function for the write buffer

ChangeLog

@@ -2,8 +2,9 @@
 - stop window new/free cycling .. faster zoom out on large images in nip2
 - fix some compiler warnings
 - remove the 64-image limit on bandary operations
-- better version date, thanks bmwiedemann
-- bump wrapper script version, thanks bgilbert
+- better version date [bmwiedemann]
+- bump wrapper script version [bgilbert]
+- fix a memleak with an error during jpeg buffer write [lovell]
 
 15/4/17 started 8.6.0
 - supports fits images with leading non-image HDUs, thanks benepo

libvips/foreign/vips2jpeg.c

@@ -84,6 +84,8 @@
  * 	- move exif handling out to exif.c
  * 27/2/17
  * 	- use dbuf for memory output
+ * 19/12/17 Lovell
+ * 	- fix a leak with an error during buffer output
  */
 
 /*
@@ -618,6 +620,8 @@ write_vips( Write *write, int qfac, const char *profile,
 	if( setjmp( write->eman.jmp ) ) 
 		return( -1 );
 
+	/* This should obly be called on a successful write.
+	 */
 	jpeg_finish_compress( &write->cinfo );
 
 	return( 0 );
@@ -725,7 +729,21 @@ init_destination( j_compress_ptr cinfo )
 	empty_output_buffer( cinfo ); 
 }
 
-/* Cleanup. Copy the set of blocks out as a big lump.
+/* Free the buffer writer.
+ */
+static void
+buf_destroy( j_compress_ptr cinfo )
+{
+	if( cinfo->dest ) {
+		OutputBuffer *buf = (OutputBuffer *) cinfo->dest;
+
+		vips_dbuf_destroy( &buf->dbuf );
+	}
+}
+
+/* Cleanup. Copy the set of blocks out as a big lump. This is only called by
+ * libjpeg on successful write --- you must call buf_destroy() explicitly to 
+ * release resources.
  */
 METHODDEF(void)
 term_destination( j_compress_ptr cinfo )
@@ -798,7 +816,7 @@ vips__jpeg_write_buffer( VipsImage *in,
 	/* Make jpeg compression object.
  	 */
 	if( setjmp( write->eman.jmp ) ) {
-		/* Here for longjmp() from new_error_exit().
+		/* Here for longjmp() from new_error_exit() during setup.
 		 */
 		write_destroy( write );
 
@@ -810,19 +828,18 @@ vips__jpeg_write_buffer( VipsImage *in,
 	 */
         buf_dest( &write->cinfo, obuf, olen );
 
-	/* Convert!
+	/* Convert! Write errors come back here as an error return.
 	 */
 	if( write_vips( write, 
 		Q, profile, optimize_coding, progressive, strip, no_subsample,
 		trellis_quant, overshoot_deringing, optimize_scans, 
 		quant_table ) ) {
-		term_destination( &write->cinfo );
-		VIPS_FREE( *obuf );
-		*olen = 0;
+		buf_destroy( &write->cinfo );
 		write_destroy( write );
 
 		return( -1 );
 	}
+	buf_destroy( &write->cinfo );
 	write_destroy( write );
 
 	return( 0 );