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import type { AppRouteHandlerFn, AppRouteHandlers } from '../module'
import { HTTP_METHODS, type HTTP_METHOD } from '../../../web/http'
const AUTOMATIC_ROUTE_METHODS = ['HEAD', 'OPTIONS'] as const
function handleMethodNotAllowedResponse(): Response {
return new Response(null, { status: 405 })
}
export function autoImplementMethods(
handlers: AppRouteHandlers
): Record<HTTP_METHOD, AppRouteHandlerFn> {
// Loop through all the HTTP methods to create the initial methods object.
// Each of the methods will be set to the 405 response handler.
const methods: Record<HTTP_METHOD, AppRouteHandlerFn> = HTTP_METHODS.reduce(
(acc, method) => ({
...acc,
// If the userland module implements the method, then use it. Otherwise,
// use the 405 response handler.
[method]: handlers[method] ?? handleMethodNotAllowedResponse,
}),
{} as Record<HTTP_METHOD, AppRouteHandlerFn>
)
// Get all the methods that could be automatically implemented that were not
// implemented by the userland module.
const implemented = new Set(HTTP_METHODS.filter((method) => handlers[method]))
const missing = AUTOMATIC_ROUTE_METHODS.filter(
(method) => !implemented.has(method)
)
// Loop over the missing methods to automatically implement them if we can.
for (const method of missing) {
// If the userland module doesn't implement the HEAD method, then
// we'll automatically implement it by calling the GET method (if it
// exists).
if (method === 'HEAD') {
if (handlers.GET) {
// Implement the HEAD method by calling the GET method.
methods.HEAD = handlers.GET
// Mark it as implemented.
implemented.add('HEAD')
}
continue
}
// If OPTIONS is not provided then implement it.
if (method === 'OPTIONS') {
// TODO: check if HEAD is implemented, if so, use it to add more headers
// Get all the methods that were implemented by the userland module.
const allow: HTTP_METHOD[] = ['OPTIONS', ...implemented]
// If the list of methods doesn't include HEAD, but it includes GET, then
// add HEAD as it's automatically implemented.
if (!implemented.has('HEAD') && implemented.has('GET')) {
allow.push('HEAD')
}
// Sort and join the list with commas to create the `Allow` header. See:
// https://httpwg.org/specs/rfc9110.html#field.allow
const headers = { Allow: allow.sort().join(', ') }
// Implement the OPTIONS method by returning a 204 response with the
// `Allow` header.
methods.OPTIONS = () => new Response(null, { status: 204, headers })
// Mark this method as implemented.
implemented.add('OPTIONS')
continue
}
throw new Error(
`Invariant: should handle all automatic implementable methods, got method: ${method}`
)
}
return methods
}
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