Hi all,
Having had no objections to anything in the first draft, I have posted
draft 2 of the 1.6 spec:
http://www.ebi.ac.uk/~aj/1.6_draft2/documents/spec.html
Mostly this comprises clarifications and fixes (e.g. a diagram for
exception handling) but there is one clarification I would like
feedback on - HTTP status codes. Apologies for the lengthy explanation
below...
DAS 1.53 already specifies the X-DAS-Status header to describe DAS
error conditions, but does not say how these relate to HTTP status
codes. The issue is confused because some of the X-DAS-Status codes
chosen match "equivalent" HTTP statuses (e.g. 400 bad request == 400
bad DAS command) while others do not (401 unauthorized == 401 bad
dsn). Until fairly recently ProServer actually put the X-DAS-Status
codes as HTTP status codes, but I changed this behaviour as it can
result in misleading error reporting by clients.
When I came to clarify how DAS status co-exists with HTTP status for
1.6, I realised that it is open to interpretation. One view is that
HTTP statuses describe -only- the transport layer, and as such you
always use HTTP 200 OK unless there is a problem in the transport
layer. The HTTP spec thus retains its meaning. A second view is that
the meaning of the HTTP codes can be changed as we don't use the HTTP
features that rely on them (mainly authentication). A third view is
that DAS statuses should be seen as more descriptive versions of
existing HTTP statuses (e.g. 401 bad dsn is a more descriptive version
of 400 bad request). The 400 and 500 statuses as described in the HTTP
spec do not preclude this interpretation.
To speak for what ProServer does, it used to take the second view, and
now takes the first view. I am wondering whether a middle-ground (the
third view) strikes a better balance between compatibility with old
DAS clients (which don't check X-DAS-Status) and HTTP (which requires
401 unauthorized etc).
Please let me know what you think about the approach taken in the draft.
Cheers,
Andy
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