accepts() matches media types and language tags case-sensitively

accepts() compares the accept header entry and the supported value as raw strings, so a client that varies the case gets the default instead of a match.

const app = new Hono()
app.get('/', (c) =>
  c.text(accepts(c, { header: 'Accept', supports: ['text/html'], default: 'application/json' }))
)

// Accept: text/html  -> text/html
// Accept: TEXT/HTML  -> application/json

Both are case-insensitive. Media types by RFC 9110 §8.3.1, language tags by RFC 4647 §2.1. en-us is the one I would expect in the wild, since the uppercase region subtag is only a convention.

Cause

// src/helper/accepts/accepts.ts
const matchType = (acceptType: string, supportedType: string): boolean => {
  if (acceptType === supportedType) {
    return true
  }
  ...
  return acceptMain === supportedMain
}

Nothing case-folds. The subtype wildcard path has the same problem, so TEXT/* does not match text/html either.

This is the same bug #5060 reported for Content-Type. #5064 fixed it for parseBody() and validator(), but accepts() was not part of that change.

PR is up. defaultMatch() returns the caller's own supports entry, so the casing an application registered is preserved.