light version of HttpClient

[fafhrd91]

i removed HttpClient from 0.12, but i think we need some lightweight version of it,
something like

    client = aiohttp.HttpClient('http://...', keep_alive=True)
    yield from client.request('GET', '/path1')
    yield from client.request('POST', '/path2')

@asvetlov @kxepal @popravich ?

[asvetlov]

I think we need http session object for processing keep-alive and cookies updating.
Something that behaves like-a-browser-page.
IIRC @kxepal had shared the idea.
keep-alive and cookies should be enabled by default (I doubt we need to disable those at all for high-level-client).

Another question: should client/session be constructed on top of connection pool like request library does?
My opinion is NO, we can add connection_pool abstraction on top of session:

with (yield from pool) as conn:
    yield from conn.get()

[fafhrd91]

what is the reason for keep alive and cookies? we already have both in connector. same for connection pool

[kxepal]

Hm..personally, I didn't found HttpClient useful: it's quite primitive while for mature setups you'll already have some load balancer like haproxy in front of your nodes making HttpClient pool feature not actual.

May be it's good to have poorman's client with the connection pool. However, then it should be more featured to not just round robin all the hosts until first success, but pick the best according connection time, load, responsibility and other metrics. What I support is a good topic for new project outside aiohttp domain.

As about lightweight http client, I think it should be also more human-friendly: having always to pass request method as a string doesn't make it so.

    client = aiohttp.HttpClient('http://...', keep_alive=True)
    yield from client.get('/path1')
    yield from client.post('/path2')

As about having http session object +1. However, it shouldn't be a hardly embed into the client: http session (cookie, auth headers, whatever) is just a request context which should be switched with easy without creating another HttpClient instance.

[asvetlov]

Fixed by introducing ClientSession #328

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