@helia/verified-fetch/src/utils/get-resolved-accept-header.ts

A fetch-like API for obtaining verified & trustless IPFS content on the web

import { isExplicitAcceptHeader, isExplicitFormatQuery, isExplicitIpldAcceptRequest } from './is-accept-explicit.js'
import { queryFormatToAcceptHeader } from './select-output-type.js'
import type { ParsedUrlStringResults } from './parse-url-string.js'
import type { ComponentLogger } from '@libp2p/interface'

export interface ResolvedAcceptHeaderOptions {
  query?: ParsedUrlStringResults['query']
  headers?: RequestInit['headers']
  logger: ComponentLogger
}

export function getResolvedAcceptHeader ({ query, headers, logger }: ResolvedAcceptHeaderOptions): string | undefined {
  const log = logger.forComponent('helia:verified-fetch:get-resolved-accept-header')
  const requestHeaders = new Headers(headers)
  const incomingAcceptHeader = requestHeaders.get('accept') ?? undefined

  if (incomingAcceptHeader != null) {
    log('incoming accept header "%s"', incomingAcceptHeader)
  }

  if (!isExplicitIpldAcceptRequest({ query, headers: requestHeaders })) {
    log('no explicit IPLD content-type requested, returning incoming accept header %s', incomingAcceptHeader)
    return incomingAcceptHeader
  }

  const queryFormatMapping = queryFormatToAcceptHeader(query?.format)

  if (query?.format != null) {
    log('incoming query format "%s", mapped to %s', query.format, queryFormatMapping)
  }

  let acceptHeader = incomingAcceptHeader
  // if the incomingAcceptHeader is autogenerated by the requesting client (browser/curl/fetch/etc) then we may need to override it if query.format is specified
  if (!isExplicitAcceptHeader(requestHeaders) && isExplicitFormatQuery(query)) {
    log('accept header not recognized, but query format provided, setting accept header to %s', queryFormatMapping)
    acceptHeader = queryFormatMapping
  }

  log('resolved accept header to "%s"', acceptHeader)

  return acceptHeader
}