This is needed since the recent removal of the TLS-SNI challenge types.
https://community.letsencrypt.org/t/tls-sni-challenges-disabled-for-most-new-issuance/50316
The HTTP-01 challenge type requires an additional listener on port 80.

fmt.Sprintf("%.g", 86400.4) → "9e+04"
fmt.Sprintf("%.f", 86400.4) → "86400"

The time interval was being reset every time a new connection came in.

"net.IPAddr composite literal uses unkeyed fields"

It also expects to be called with a non-empty string, which isn't
the case with this Split which always envokes the loop at least
once.  If -ice was omitted, an error was logged.

This is a sanity check against any catastrophic failure of our parsing
code.

Current versions of tor accept USERADDR with or without a port number,
but future versions may become more strict and require the port number.
https://bugs.torproject.org/23080

Call conn.RemoteAddr() before entering the datachannelHandler goroutine.
This is a workaround for the hang described at
https://bugs.torproject.org/18628#comment:8

 * Since we're now assuming >= 1.8.3

 * Same as currently used in TB,
   https://gitweb.torproject.org/builders/tor-browser-build.git/tree/projects/go/config?id=8c4c05ddcfc30107b967b204d491523685460226

 * Also, necessary for the "context" import in acme/autocert

 * The field was removed in,
   https://github.com/golang/appengine/commit/11ed51af43a1f8a9ce2afc951b10dbb7b87a5e59

 * From https://github.com/keroserene/go-webrtc/pull/59

 * Ran, `go get google.golang.org/appengine/cmd/aefix`
   from https://github.com/golang/appengine

Rather than having it happen as a side effect of flag parsing.

Having it happen as a side effect of flag parsing caused log messages
related to handling the option (e.g. "IceServerList:") to always go to
stderr, despite the presence of a -log option. This is because the
requested log file had not been opened yet.

Had been removed in 2a46db2c and was
erroneously restored in the merge
36debdfd.

Remove global opt struct.

This variable was being written to by multiple goroutines, overwriting
the Path to either "/proxy" or "/answer" as necessary, which was racy.

This prohibits some nonsense like "./proxy-go -capacity -550", which
otherwise results in a panic like:

INFO: configuration.go:174: Created Configuration at  &{[{[stun:stun.l.google.com:19302]  }] All Balanced }
panic: makechan: size out of range

This is a hedge against any bugs that may cause the badge to hang when
left running for a long time, and it also means that badges will
effectively check for updated code once a day.

Doesn't seem to be used anywhere; may have been inherited from flash
proxy.