Why do headers convert into lowercase automatically?

[theblackfort]

What are you trying to achieve or the steps to reproduce?

I would like to know how to capitalize headers when sending the response. Looks like Fastify converts the headers to lowercase while sending the response.

reply.header(`X-Robots-Tag`, `noindex`);

What was the result you received?

x-robots-tag: noindex

What did you expect?

X-Robots-Tag: noindex

Context

• node version: v10.15.3
• fastify version: 2.1.0
• os: Mac
• any other relevant information: None

[jsumners]

The HTTP spec defines header names as case insensitive. Fastify, and require('http'), translates header names to lowercase for consistency and ease of use. Implementations that expect headers to be case sensitive are broken per https://tools.ietf.org/html/rfc2616#section-4.2:

Each header field consists
of a name followed by a colon (":") and the field value. Field names
are case-insensitive.

[theblackfort]

Fair point but I ask this from an aesthetic point of view. Headers from helmet (https://github.com/fastify/fastify-helmet) are all capitalized and look much better.

Any way to achieve the same?

X-Content-Type-Options: nosniff
X-DNS-Prefetch-Control: off
X-Download-Options: noopen
X-Frame-Options: SAMEORIGIN

[nwoltman]

Fastify handles headers this way as a performance optimization. By only handling headers in a lowercased format, Fastify has better performance and uses less memory.

Also, the Internet will eventually move to HTTP/2, which only supports lowercase headers, so it's not worth getting attached to the aesthetic look of HTTP/1-style headers.

[theblackfort]

“Life can only be understood backwards; but it must be lived forwards.”

[onluiz]

No workaround?

[StingyJack]

HTTP/2, which only supports lowercase headers

That is an incorrect statement. https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2

[nwoltman]

@StingyJack Semantics ¯\_(ツ)_/¯

While uppercase headers can be used at the application level, they will always be sent as lowercase.

However, header field names MUST be converted to lowercase prior to their encoding in HTTP/2. A request or response containing uppercase header field names MUST be treated as malformed (Section 8.1.2.6).

[wongsean]

Fair point, but it would be better to mention it here https://fastify.dev/docs/latest/Reference/Request/#headers.

[Uzlopak]

@wongsean

Feel invited to provide a PR to improve the documentation. ;)