Polipo blocks for 60s on startup with dodgy router

I'm just posting this here for the benefit of anyone who may run into a
similar problem in the future.

On startup, polipo tries to determine its own hostname by calling
gethostname, gethostbyname and gethostbyaddr. It uses this for log
messages and the (disabled by default) "Via" http header.

See initHttp() in http.c:
https://github.com/jech/polipo/blob/d0055a6/http.c#L205

and the "proxyName" configuration variable:
http://www.pps.univ-paris-diderot.fr/~jch/software/polipo/polipo.html#Client-connections

On a specific configuration:
* uClibc
* Huawei echolife HG520b router with an old firmware
* A hostname in /etc/hostname that isn't known by the router or
  /etc/hosts (yes, I know; this was on a system beyond my control).

gethostbyname was issuing DNS requests but the router was not issuing
any response. gethostbyname timed out each request after 10s, and
retried 6 times, for a total of 60s. Polipo blocks during this process.

Note that polipo has its own non-blocking DNS implementation in dns.c,
but the "proxyName" lookup in initHttp uses the blocking libc functions.

This was on uClibc -- I don't know how long the timeout will be for
other implementations of gethostbyname.

Cheers,
Dave.


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