dnssd Name Conflict Resolution results in HTTP Bad Request

[geekman]

Actually I'm not sure if I should file this in dnssd or hap, but I think the issue is unique to hap, so it's filed here.

When dnssd detects that a hostname is in use, it then tries to pick a different name by appending a space & number "%s %d", which is probably what iOS does too:

https://github.com/brutella/dnssd/blob/8574d113aa9e847409d25d90ac0ba1e0512f601c/probe.go#L76-L86

In doing so, the hostname now contains a space and HomeKit encodes the space as \032 in the Host: header which results in an invalid hostname under HTTP, so the http parser replies with an error. Related issue #9.

There's already an attempt to avoid spaces by replacing the server/accessory name before passing it to dnssd, but in this case the spaces were added by dnssd:

hap/server.go

Lines 509 to 519 in 1a3e48c

	stripped := strings.Replace(s.a.Info.Name.Value(), " ", "_", -1)
	cfg := dnssd.Config{
	Name: removeAccentsFromString(stripped),
	Type: "_hap._tcp",
	Domain: "local",
	Host: strings.Replace(s.uuid, ":", "", -1), // use the id (without the colons) to get unique hostnames
	Text: s.txtRecords(),
	Port: s.port,
	Ifaces: s.Ifaces,
	}

I'm not sure that iOS will fix this issue anytime soon (or at all), so maybe hap/dnssd should try to avoid generating such names. Maybe dnssd could defer to the caller (hap, in this case) for conflict resolution strategies, where it could send back "-" + random_hex_str instead of using " %d".

[bwesterb]

Fixed now? See #57

[geekman]

I think that solves this issue, but it won't fully resolve the fact that Go's HTTP server and Request validates the Host header early during parsing and errors out in cases like non-ASCII names. This issue also served as a note-to-self for me to record the underlying issue.

If only there was some way to prevent the Host header validation, or use our own, without having to rewrite large parts of Go's http library.