Exception handling changes

In preparation for work on progressive loading, update the exception
handling scheme slightly.

Until now, exceptions (as thrown with fz_throw, and caught with
fz_try/fz_catch) have merely had an informative string. They have
never had anything that can be compared to see if an error is of
a particular type.

We now introduce error codes; when we fz_throw, we now always
give an error code, and can optionally (using fz_throw_message)
give both an error code and an informative string.

When we fz_rethrow from within a fz_catch, both the error code and
the error message is maintained. Using fz_rethrow_message we can
'improve' the error message, but the code is maintained.

The error message can be read out using fz_caught_message() and the
error code can be read as fz_caught().

Currently we only define a 'generic' error. This will expand in future
versions to include other error types that may be tested for.

1 files changed, 9 insertions, 4 deletions

diff --git a/image/muimage.c b/image/muimage.c
index 890457ab..ed3280b2 100644
--- a/image/muimage.c
+++ b/image/muimage.c
@@ -54,13 +54,18 @@ image_open_document(fz_context *ctx, const char *filename)
 
 	file = fz_open_file(ctx, filename);
 	if (!file)
-		fz_throw(ctx, "cannot open file '%s': %s", filename, strerror(errno));
+		fz_throw(ctx, FZ_ERROR_GENERIC, "cannot open file '%s': %s", filename, strerror(errno));
 
-	fz_try(ctx) {
+	fz_try(ctx)
+	{
 		doc = image_open_document_with_stream(ctx, file);
-	} fz_always(ctx) {
+	}
+	fz_always(ctx)
+	{
 		fz_close(file);
-	} fz_catch(ctx) {
+	}
+	fz_catch(ctx)
+	{
 		fz_rethrow(ctx);
 	}