fix(types): reply.getHeader can return numbers and arrays

[seanparmelee]

Currently, the type definition for FastifyReply.getHeader has a return type of string | undefined. For a header that's allowed to appear multiple times (such as Server-Timing), one might do something like:

reply.header('server-timing', [
  'miss, db;dur=53, app;dur=47.2',
  'customView, dc;desc=atl',
  'cache;desc="Cache Read";dur=23.2',
]);

for which a call to reply.getHeader('server-timing') would return:

['miss, db;dur=53, app;dur=47.2', 'customView, dc;desc=atl', 'cache;desc="Cache Read";dur=23.2']

Given this, and the type definition for Node's getHeader, I think the the type definition for FastifyReply.getHeader should be updated to be: number | string | string[] | undefined.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[Uzlopak]

I am sorry, that I make this remark now:

I can understand if getHeader can return an array of strings. But numbers would mean, that we actually convert strings to numbers when we parse the headers. And I kind of doubt, that we actually do this in the header parser.

[xtx1130]

Why not use any here? In nodejs doc, it returns is any type

[seanparmelee]

Hi @Uzlopak,

I can understand if getHeader can return an array of strings. But numbers would mean, that we actually convert strings to numbers when we parse the headers. And I kind of doubt, that we actually do this in the header parser.

Correct, this is more for the case where somewhere in the lifecycle a header is set via .header with a value that's a number. I added a unit test in this PR to demonstrate this current functionality.

I was originally going to only add string[], but saw that getHeaders was also allowing for number as is the Node type definition for getHeader (v14, v16, latest) and figured they should be consistent.

Hi @xtx1130 hopefully this also answers your query regarding using any.

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