Conten-Length header in response is not present

Question

I have noticed that my yesod site does not respond with Content-Length header.

I have tried to add it with addHeader (in the Handler) with no result.

I am sure that I am missing something very fundamental, but do not see it.

My handlers are Handler Html handlers. I have suceeded adding a custom header using addHeader right before defaultLayout...

Answer 1

Content-Length is a special header, in the sense that its presence when incorrect will mess up your response. A number of different components will end up stripping it out. My guess in this case is that your response is being GZIP compressed, which necessarily removes the content-length header.