Canonical HTTP Header Key Meaning

Canonical form means that first character and after that any character following a hyphen is in uppercase. All other characters will be in lowercase. Example of canonical forms are

Content-Type
Accept-Encoding

All the keys in the headers are represented in the canonical form only. For eg if there are below headers in an incoming http request

content-type: applcation/json
accept-encoding: gzip

Then at server most of the http library in different languages at server will interpret it in the canonical form. For example the above headers will be as below when we print headers at server end.

Content-Type: application/json
Accept-Encoding: gzip

Note that

• content-type is converted to canonical form Content-Type

• accept-encoding is converted to canonical form Accept-Encoding