Header returned from headers function within a route doesn't override same-name header in entry.server

[eugeniobet]

Reproduction

Define an header in entry.server.tsx file with the name "X-Test" and give it a value,
visit a route which exports an headers function which returns an object with the same "X-Test" and a different value.
Watch the value returned being the one originally defined in entry.server.tsx

System Info

System:
    OS: Linux 6.2 Ubuntu 23.04 23.04 (Lunar Lobster)
    CPU: (12) x64 12th Gen Intel(R) Core(TM) i5-1235U
    Memory: 7.89 GB / 15.34 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 22.14.0 - ~/.nvm/versions/node/v22.14.0/bin/node
    npm: 10.9.2 - ~/.nvm/versions/node/v22.14.0/bin/npm
    Watchman: 4.9.0 - /usr/bin/watchman
  Browsers:
    Chrome: 129.0.6668.100
  npmPackages:
    @react-router/dev: 7.8.2 => 7.8.2 
    @react-router/express: 7.8.2 => 7.8.2 
    @react-router/node: 7.8.2 => 7.8.2 
    @react-router/remix-config-routes-adapter: 0.0.0-nightly-bf7ecb711-20240911 => 0.0.0-nightly-bf7ecb711-20240911 
    @react-router/serve: 7.8.2 => 7.8.2 
    react-router: 7.8.2 => 7.8.2 
    vite: 5.4.2 => 5.4.2

Used Package Manager

npm

Expected Behavior

The route header to have priority over the entry.server.tsx one

Actual Behavior

The opposite of the expected behaviour

[timdorr]

Can you please give a reproduction with actual code?

[eugeniobet]

I surely can, just tell me if based on the description this is expected behaviour? I think it shouldn't?
Should route header replace entry.server same-name header or is it the other way around?

[eugeniobet]

https://stackblitz.com/edit/github-xysokqvg?file=app%2Froutes%2Fhome.tsx

please check the X-Test value in the network tab

[sergiodxa]

This is expected, entry.server function to SSR your page runs after your route loaders, as you need the loader data to do the SSR, so entry.server will always override headers from loaders

[timdorr]

Correct. This is expected behavior.