🚀 go-pugleaf

guido@cwi.nl (Guido van Rossum) writes:

>Is there an expert on Sun RPC in this group?

>I am in the process of re-implementing Sun RPC.  All the documentation
>I have are RFC1014 (XDR) and RFC1057 (RPC), and RFC1094 (NFS).  I have
>a question that isn't answered by these documents:

I'm wondering why you do that, given that Sun's implementation is
publicxly available in source.

>When using the UDP version, how does the client recover from lost
>packets?  When the call packet is lost, a simple retransmission is
>enough, however, when a reply packet is lost, a retransmission can
>cause the request to be executed twice.  How does e.g. an NFS client
>handle this if the request is not idempotent (like RENAME)?  Is there
>a way for the client to tell from the failing reply from the second
>try that the first try must have succeeded even though the response
>got lost?

A client cannot know if his request got lost, or the response. Both
result in a timeout. The client will retransmit or give up, depending
on circumstance.

>Note that I need to know how the existing Sun RPC implementation
>handles this situation, not how it could be done in a hypothetical
>system (I know all about Amoeba's RPC, for instance).

If the request is not idempotent, you need to activate the server
cache with svcudp_enablecache(). Note that is an undocumented
function. Get the 4.0 rpcxdr source and look there for details.

>Pointers to sources or documents are welcome!

Sources: see above, docs: RTFS ;-)
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