Configure a maximum lifetime for pooled connections

[jhominal]

I think it would be nice for httpx (and httpcore) if it were possible to set the maximum lifetime of a keepalive connection.

This is different from the keepalive_expiry parameter, in that:

• keepalive_expiry: starts once a given connection becomes idle, corresponds to libcurl's CURLOPT_MAXAGE_CONN;
• keepalive_max_lifetime (name to be workshopped): starts as soon as the connection is created, corresponds to libcurl's CURLOPT_MAXLIFETIME_CONN;

This would probably be modeled as a new field in httpx.Limits and httpcore.ConnectionPool.

[tomchristie]

That's neatly coherent with the rest of the API there, yup.
Any pointers on default behaviors from other agents here?
Eg. Do browsers have a max age on persistence for HTTP connections?

[jhominal]

From what I can see:

• libcurl disables maximum lifetime by default;
• from chromium source code, I think that there are idle timeouts (equivalent to keepalive_expiry), but there does not seem to be a total lifetime timeout;
• gecko seems also to only have a keep alive with an idle timeout mechanism, mostly set (on HTTP 1.1) by parsing a timeout parameter in Keep-Alive;
• urllib3 does not seem to have mechanisms to limit connection reuse after they are open;

In short:

• Most networking libraries do not support such a feature (mostly, I have only seen it in libcurl);
• Even for libcurl, this mechanism is disabled by default;