revise fail handling, again

clarify policy on file read errors and warnings:

* if the file format library reports a warning, we log it in vips, but
that's all
* if the file format library reports an error, we log it, but try to
continue
* if the file format library reports an error and fail is set, we log it
and fail

all loaders now implement this

ChangeLog

@@ -1,6 +1,7 @@
 23/4/17 started 8.5.5
 - doc polishing
 - more improvements for truncated PNG files, thanks juyunsang 
+- improve corrupted jpg handling, thanks juyunsang
 
 23/4/17 started 8.5.4
 - don't depend on image width when setting n_lines, thanks kleisauke

libvips/foreign/csvload.c

@@ -193,7 +193,7 @@ vips_foreign_load_csv_init( VipsForeignLoadCsv *csv )
  * * @lines: read this many lines from file
  * * @whitespace: set of whitespace characters
  * * @separator: set of separator characters
- * * @fail: %gboolean, fail on warnings
+ * * @fail: %gboolean, fail on errors
  *
  * Load a CSV (comma-separated values) file. The output image is always 1 
  * band (monochrome), #VIPS_FORMAT_DOUBLE. Use vips_bandfold() to turn
@@ -221,7 +221,7 @@ vips_foreign_load_csv_init( VipsForeignLoadCsv *csv )
  * @separator sets the characters that separate fields. 
  * Default ;,<emphasis>tab</emphasis>. Separators are never run together.
  *
- * Setting @fail to %TRUE makes the reader fail on any warnings. 
+ * Setting @fail to %TRUE makes the reader fail on any errors. 
  *
  * See also: vips_image_new_from_file(), vips_bandfold().
  *

libvips/foreign/foreign.c

@@ -1016,7 +1016,7 @@ vips_foreign_load_class_init( VipsForeignLoadClass *class )
 
 	VIPS_ARG_BOOL( class, "fail", 11, 
 		_( "Fail" ), 
-		_( "Fail on first warning" ),
+		_( "Fail on first error" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsForeignLoad, fail ),
 		FALSE );

libvips/foreign/jpeg2vips.c

@@ -85,6 +85,8 @@
  * 	- don't warn for missing exif res, since we fall back to jfif now
  * 17/1/17
  * 	- invalidate operation on read error
+ * 12/5/17
+ * 	- fail aborts on error, not warning
  */
 
 /*
@@ -148,7 +150,7 @@ typedef struct _ReadJpeg {
 	 */
 	int shrink;
 
-	/* Fail on warnings.
+	/* Fail on errors.
 	 */
 	gboolean fail;
 
@@ -526,10 +528,10 @@ read_jpeg_generate( VipsRegion *or,
 
 	int y;
 
-#ifdef DEBUG
+#ifdef DEBUG_VERBOSE
 	printf( "read_jpeg_generate: %p line %d, %d rows\n", 
 		g_thread_self(), r->top, r->height );
-#endif /*DEBUG*/
+#endif /*DEBUG_VERBOSE*/
 
 	VIPS_GATE_START( "read_jpeg_generate: work" );
 
@@ -565,23 +567,14 @@ read_jpeg_generate( VipsRegion *or,
 	if( setjmp( jpeg->eman.jmp ) ) {
 		VIPS_GATE_STOP( "read_jpeg_generate: work" );
 
-		return( -1 );
-	}
+#ifdef DEBUG
+		printf( "read_jpeg_generate: lonjmp() exit\n" ); 
+#endif /*DEBUG*/
 
-	/* If --fail is set, we make read fail on any warnings. This will stop
-	 * on any errors from the previous jpeg_read_scanlines().
-	 */
-	if( jpeg->eman.pub.num_warnings > 0 &&
-		jpeg->fail ) {
-		VIPS_GATE_STOP( "read_jpeg_generate: work" );
+		if( jpeg->fail ) 
+			return( -1 );
 
-		/* Only fail once.
-		 */
-		jpeg->eman.pub.num_warnings = 0;
-
-		*stop = TRUE;
-
-		return( -1 );
+		return( 0 );
 	}
 
 	for( y = 0; y < r->height; y++ ) {

libvips/foreign/jpegload.c

@@ -328,7 +328,7 @@ vips_foreign_load_jpeg_buffer_init( VipsForeignLoadJpegBuffer *buffer )
  * Optional arguments:
  *
  * * @shrink: %gint, shrink by this much on load
- * * @fail: %gboolean, fail on warnings
+ * * @fail: %gboolean, fail on errors
  * * @autorotate: %gboolean, use exif Orientation tag to rotate the image 
  *   during load
  *
@@ -339,7 +339,7 @@ vips_foreign_load_jpeg_buffer_init( VipsForeignLoadJpegBuffer *buffer )
  * are 1, 2, 4 and 8. Shrinking during read is very much faster than 
  * decompressing the whole image and then shrinking later.
  *
- * Setting @fail to %TRUE makes the JPEG reader fail on any warnings. 
+ * Setting @fail to %TRUE makes the JPEG reader fail on any errors. 
  * This can be useful for detecting truncated files, for example. Normally 
  * reading these produces a warning, but no fatal error.  
  *
@@ -406,7 +406,7 @@ vips_jpegload( const char *filename, VipsImage **out, ... )
  * Optional arguments:
  *
  * * @shrink: %gint, shrink by this much on load
- * * @fail: %gboolean, fail on warnings
+ * * @fail: %gboolean, fail on errors
  * * @autorotate: %gboolean, use exif Orientation tag to rotate the image 
  *   during load
  *

libvips/foreign/webp2vips.c

@@ -38,9 +38,9 @@
  */
 
 /*
- */
 #define DEBUG_VERBOSE
 #define DEBUG
+ */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>