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Some notes on the error handling introduced after 0.7.3
- there are four domains for errors:
- CORE: core GStreamer errors
- LIBRARY: supporting library errors
- RESOURCE: errors accessing resources (files, network, memory, ...)
- STREAM: errors in the data stream
- Each error in GStreamer or plug-ins can be put under one of these four.
- the enum is called Gst(Domain)Error and has GST_(DOMAIN)_ERROR_(CODE) members
(see GError API docs for rationale)
- each of the enums starts with _FAILED at 1 (with FAILED being the generic
error if none of the others applies)
- second in the enum is TOO_LAZY, which allows us to keep track of those errors
that we haven't categorized yet. This means they really should either move
to another one, or a new one ought to be created.
- each enum ends with NUM_ERRORS
- elements call gst_element_error to signal an error:
gst_element_error (element, domain, code, message, debug);
With :
- element being the one signalling the error
- domain one of CORE, LIBRARY, RESOURCE, STREAM
- code one of the suffixes in the Gst(Domain)Error enum
- message is either NULL (to signal the standard error message for the
given domain and code), or a printf-like set with the format being
marked for translation.
The string should start with a capital and end in a period so it forms
a complete sentence.
The string can/should be shown to the user of an application.
- debug is either NULL or a non-translated debug string, which can be used
to diagnose errors after they've happened.
The string can be shown to the user when he asks for additional debug info.
A useful macro is GST_ERROR_SYSTEM, which prints out the system error
that explains the failure by using g_strerror.
- Some example calls:
gst_element_error (src, RESOURCE, OPEN_READ,
(_("Could not open file \"%s\" for reading"), src->filename),
GST_ERROR_SYSTEM);
The message is specified since we have more information:
- the resource is a file
- we know the file name
gst_element_error (element, CORE, NEGOTIATION, NULL, NULL);
This is a simple negotiation error. The default message will be
signaled, telling the user that GStreamer had an internal error.
gst_element_error (ebml, RESOURCE, READ, NULL,
("Read error at position %llu (0x%llx)",
pos, pos));
The plugin asked to read on the underlying resource (using bytestream),
but failed. The user will get a generic read error. The debug info
will contain the exact position in the stream at which the read error
occured.
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