upper case converted to lower case when reading response HEADER in node/express js with httpclients axios and request-promise

Question

In my application(node/express), I have to call a third party server to read some data. The response of the third party server will have custom header sessionId - Id being capitalized as per the document. But in my application, the custom header key is changed to sessionid - id in lowercase. I tested this behaviour in axios and request-promise http client.

Why upper case in header key is converted to lowercase in node/express?

Feral

Answer 1

Express's Request object has a case-insensitive .get('header-name') method to look up headers. The way the Express team implemented the case-insensitivity is apparently to downcase the header names in when they store them.

Express does case-insensitive matching here to comply with RFC2616's specification that header names are to be case-insensitive. That means your third party server is free to return a header named sessionId, sessionid, SeSsIoNiD or whatever, and it still means sessionid to your own app. (RFC2616 is the formal specification for the HTTP protocol.)

Columbine

Did you mean res.get() for testing a response? Otherwise, not understanding the use-case for getting the Request Headers, which should have been added via req.set() – Uturn