Is safe to use "X-..." header in a HTTP response?

Question

I have to pass a meta-information in my HTTP response so I figured out that I could use the response header, for instance "X-MyData: 123456". Is that safe? I mean, there is a possibility that a client proxy remove this header?

Thanks!

Answer 1

For reference, X- headers are also referred to as x-token in the BNF of RFC 2045, as user-defined ("X-") in section 5 of RFC 2047 and as Experimental headers in section 4.2.2.1 of the News Article Format draft.

Deprecating Use of the "X-" Prefix in Application Protocols (BCP, June 2012):

deprecates the "X-" convention for most application protocols and makes specific recommendations about how to proceed in a world without the distinction between standard and non-standard parameters

Answer 2

A client proxy could do anything it wanted, but in general would not strip any headers.

Headers starting with an X- are typically reserved for nonstandard usage (i.e. no future standard will introduce a header starting X-) but a proxy may understand them and choose to modify them as it wants.