Engine-api built with Go(<=1.4) won't work with Docker daemon built with Go(>=1.6)

[Random-Liu]

When using engine-api built with Go(<=1.4) with Docker daemon built with Go(>=1.6), it keeps complaining "Error response from daemon: 400 Bad Request: malformed Host header".

I think the reason is that:

1. After golang/go@6e11f45, the http server in Go 1.6 will validate the HTTP Host header conforming to HTTP 1.1 (See net/http: HTTP/1.1 requests without Host header should be rejected  golang/go#13624)
2. On the http client side, Go writes the HTTP Host header with request.Host or request.URL.Host(if the former is empty) (See here)
3. When using the default docker endpoint (unix:///var/run/docker.sock), engine-api will set request.Host="", request.URL.Host="/var/run/docker.sock" (See set request.URL.Host and set request.Host)
4. When the engine-api is built with Go >= 1.5, everything goes well, because Go will clean up the Host making both request.Host and request.URL.Host to "". Then the HTTP Host header will be "". (See net/http: does not verify validity of Host header golang/go#11206))
5. But when the engine-api is built with Go<=1.4, Go won't clean up the Host, so the HTTP Host header will be "/var/run/docker.sock". It will break Go 1.6 http server side validation in 1. because '/'is not a valid character, causing 400 Bad Request: malformed Host header.

I could fix this by set some random but valid thing like "docker.sock" in the request.URL.Host. If it is not used for unix endpoint, why don't we just set it to a valid Host?

Hope this could be fixed, thanks! :)

More information kubernetes/kubernetes#23809

[duglin]

See moby/moby#20865

[Random-Liu]

@duglin Yeah, I saw that one. :)

I think in moby/moby#20865, people were mainly talking about the Docker CLI. While this one is just talking about the engine-api, which is a little different:

1. People may use engine-api to build anything, they may need to use Go 1.4 for some reason.
2. This issue is easier to fix because it's only about engine-api, I don't think it will affect too many people.

[vdemeester]

I do agree with @Random-Liu, maybe we should handle this in here too.
/cc @calavera @MHBauer

[Random-Liu]

Thanks, @vdemeester!

BTW, we are switching from go-dockerclient to this official engine-api, :). There is no such problem in go-dockerclient (See here)

[MHBauer]

We have control of the default client, so we should be able to handle it. Is there a way uses of engine-api can work around this by providing a customized client? We should work out both ways, if possible.

[duglin]

Explicitly setting the value to something meaningful and valid should be easy enough to do. A PR would be welcome....

[Random-Liu]

@duglin Thanks, I'll send a PR soon :)

[calavera]

Fixed by #190.