Empty X-Forwarded-Host header

[adriangonz]

Problem

In Go, trying to access the Host header directly of a request object through r.Header.Get("Host") always return an empty string - regardless of whether the header is actually set or not. Instead, you need to use the r.Host field (which under the hood will just read the actual header). This leads to the X-Forwarded-Host header being left empty when requests are proxied to the cluster API Server:

headlamp/backend/cmd/headlamp.go

Line 1010 in d4f7748

r.Header.Set("X-Forwarded-Host", r.Header.Get("Host"))

This can cause problems when the API Server is fronted by some reverse proxies (e.g. NGINX) which do a strict implementation of the HTTP 1.1 protocol - where the Host (or X-Forwarded-Host) has to always be present. Otherwise, every request sends back a 400 response with an error along the following lines:

400 Bad Request: missing required Host header error

Proposed Solution

To work around the above, it should be enough to just read the Host header directly via r.Host, i.e. doing something like (note that r.Host is already set on the line above):

r.Header.Set("X-Forwarded-Host", r.Host)

[joaquimrocha]

Thanks a lot @adriangonz !
@yolossn Can you check this one out? I think this code was last touched by you.