Empty host header on http 1.1 results in invalid host header logging in error.log

[Maxim Dounin]

Hello!

On Wed, Jul 22, 2015 at 06:53:13AM +0200, Bart Warmerdam wrote:

> Why does nginx logs an info log a message like ...client sent invalid host
> header while reading client request headers... request: "GET /keepalive.html
> HTTP/1.1", host: ""
> if the host header is empty. According to the http 1.1 specification it is
> legal to send an empty host header so it should not log this message since
> the header is not invalid. So the requests contains the host header but
> without a value. The call also results in a 400 instead of a 2xx or 3xx
> response.

Empty host names are illegal as per RFC 2616 and RFC 2396 it uses 
to define URIs.

http://tools.ietf.org/html/rfc2616#section-14.23:

      Host = "Host" ":" host [ ":" port ] ; Section 3.2.2

http://tools.ietf.org/html/rfc2396#section-3.2.2:

      host          = hostname | IPv4address
      hostname      = *( domainlabel "." ) toplabel [ "." ]
      domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
      toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
      IPv4address   = 1*digit "." 1*digit "." 1*digit "." 1*digit

Empty host names are only allowed as per newer RFC 3986.  This is 
not something nginx was adapted to allow though.  May be it 
should.

-- 
Maxim Dounin
http://nginx.org/