Created attachment 1543 [details]
patch

This provides SOCKS4A support, which allows a SOCKS4 client to provide a
host name instead of an IP address. It indicates that it's doing so by
using a known-invalid IP address 0.0.0.x (where x != 0), and then
appending the NUL-terminated hostname to the connection request.

Although we check for the terminating NUL manually and the
'fatal(len %d > have %d)' should never happen, the condition for it (in
the existing processing of the username) seems to have been off-by-one;
not accounting for the terminating NUL. I've fixed that while I'm at it.