[for discussion] asyncio.client: move cache access out of ClientIO into Protocol

[navytux]

to ensure that we do not store the same information twice into the cache; this may or may not be important

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kirr:

for discussion

Extracted from #195

[navytux]

See "a) moving cache access out of ClientIO into Protocol ..." in #195 (comment) .

[d-maurer]

#195 does not try to move the cache access out of ClientIO to the protocol but have it in the protocol as well.

The cache access in ClientIO is there to be able to deliver cached data even when the server connection is down (i.e. we do not have a protocol instance). In real life, this is likely not necessary because ClientStorage has already tried a cache access and will only use lower level calls when this has failed. However, there is a test which verifies the behavior.

The cache access in ClientIO usually makes the one in Protocol.load_before redundant, unless the client has not been "operational" (i.e. did not have an associated protocol). In the latter case, the ClientIO cache access and the one in load_before do not happen in the same coroutine step and therefore, the cache might have been modified in the meantime.

I do not know what happens when information is stored in the cache which is already there. The original code tried hard to avoid this - maybe, it is important.