improve file open error handling

better behaviour if you try to open a directory as an image

libvips/foreign/foreign.c

@@ -535,7 +535,7 @@ vips_foreign_find_load( const char *name )
 	 */
 	if( !vips_existsf( "%s", filename ) ) {
 		vips_error( "VipsForeignLoad", 
-			_( "file \"%s\" not found" ), name );
+			_( "file \"%s\" not readable" ), name );
 		return( NULL );
 	}
 

libvips/include/vips/connection.h

@@ -222,7 +222,7 @@ const void *vips_source_map( VipsSource *source, size_t *length );
 VipsBlob *vips_source_map_blob( VipsSource *source );
 gint64 vips_source_seek( VipsSource *source, gint64 offset, int whence );
 int vips_source_rewind( VipsSource *source );
-size_t vips_source_sniff_at_most( VipsSource *source, 
+gint64 vips_source_sniff_at_most( VipsSource *source, 
 	unsigned char **data, size_t length );
 unsigned char *vips_source_sniff( VipsSource *source, size_t length );
 gint64 vips_source_length( VipsSource *source ); 

libvips/iofuncs/memory.c

@@ -358,7 +358,7 @@ vips_tracked_malloc( size_t size )
  * @flags: flags for open()
  * @...: open mode
  *
- * Exactly as open(2), but the number of files current open via
+ * Exactly as open(2), but the number of files currently open via
  * vips_tracked_open() is available via vips_tracked_get_files(). This is used
  * by the vips operation cache to drop cache when the number of files
  * available is low.

libvips/iofuncs/source.c

@@ -1203,7 +1203,7 @@ vips_source_length( VipsSource *source )
  *
  * Returns: number of bytes read, or -1 on error.
  */
-size_t
+gint64
 vips_source_sniff_at_most( VipsSource *source, 
 	unsigned char **data, size_t length )
 {
@@ -1263,7 +1263,9 @@ vips_source_sniff( VipsSource *source, size_t length )
 		return( NULL );
 
 	bytes_read = vips_source_sniff_at_most( source, &data, length );
-	if( bytes_read < (gint64) length )
+	if( bytes_read == -1 )
+		return( NULL );
+	if( bytes_read < length )
 		return( NULL );
 
 	return( data );

libvips/iofuncs/util.c

@@ -634,6 +634,14 @@ vips__open( const char *filename, int flags, ... )
 	mode = va_arg( ap, int );
 	va_end( ap );
 
+	/* Various bad things happen if you accidentally open a directory as a
+	 * file.
+	 */
+	if( g_file_test( filename, G_FILE_TEST_IS_DIR ) ) {
+		errno = EISDIR;
+		return( -1 );
+	}
+
 	fd = g_open( filename, flags, mode );
 
 #ifdef OS_WIN32
@@ -1149,29 +1157,26 @@ vips__ftruncate( int fd, gint64 pos )
 	return( 0 );
 }
 
-/* TRUE if file exists.
+/* TRUE if file exists and is not a directory.
  */
 gboolean
 vips_existsf( const char *name, ... )
 {
         va_list ap;
 	char *path; 
-        int result; 
+        gboolean result; 
 
         va_start( ap, name );
 	path = g_strdup_vprintf( name, ap ); 
         va_end( ap );
 
-        result = g_access( path, R_OK );
+	/* A regular (not a directory) file.
+	 */
+	result = g_file_test( path, G_FILE_TEST_IS_REGULAR );
 
 	g_free( path ); 
 
-	/* access() can fail for various reasons, especially under things 
-	 * like selinux. Only return FALSE if we are certain the file does not
-	 * exist.
-	 */
-	return( result == 0 || 
-		errno != ENOENT );
+	return( result ); 
 }
 
 #ifdef OS_WIN32