header parameter name changed from underscore ('_') to hyphen ('-')

[kchsieh]

When I send a header parameter with a name contain underscore, for example:

curl --header "my_var_name: testing" https://httpbin.org/headers

I see in the response, my_var_name got changed to My-Var-Name.
I see two issues with this:

• the underscore got changed to hyphen,
• the all lower-case name was capitalized.

[joshuaflanagan]

I also just ran into this issue, which was especially confusing because I was working on making sure an HTTP client stopped mangling the headers (httprb/http#576). I expect a tool like httpbin to echo back the values as they were sent to it. I understand that different server software may choose to treat underscores and hyphens the same, and ignore case, but that is up to the server to implement. A trace tool should let you confirm what you are sending, not how it is being interpreted.