@worker-tools/middleware/esm/context.js

A suite of standalone HTTP server middlewares for Worker Runtimes.

// deno-lint-ignore-file no-explicit-any
export { pipe as combine } from 'ts-functional-pipe';
import { ResolvablePromise } from '@worker-tools/resolvable-promise';
import { AppendOnlyList } from "./utils/append-only-list.js";
export class EffectsList extends AppendOnlyList {
}
/**
 * @deprecated Function might change name
 */
export function executeEffects(effects, response) {
    var _a;
    // TODO: to reduce or reduceRight, that is the question...
    // reduceRight matches the behavior of my initial, non-compose friendly middleware model 
    // which was just increasingly deep levels of wrapped function calls.
    // In that model, the effects (post-processes) of the last applied middleware were executed first.
    // Regular reduce matches the order in which middlewares are applied, 
    // which probably is close what users expect to happen, anyway...
    return (_a = [...effects].reduceRight(async (response, effect) => { var _a; return (_a = effect(await response)) !== null && _a !== void 0 ? _a : response; }, response)) !== null && _a !== void 0 ? _a : response;
}
/**
 * A helper function to create user-defined middleware.
 *
 * Its main purpose is to allow developers to create correctly typed middleware without dealing with generics.
 * This is achieved via the `_defaultExt` parameter, which is used to infer the types of the *extension* added to the *context*.
 * As the `_` prefix implies, it is not actually used.
 * The purpose of the default extension object is solely to tell the type checker which additional keys to expect on the context object after this middleware is applied.
 * The job of adding (default) values to the context belongs to the middleware function.
 *
 * Here are some example usages. All are valid in JavaScript and TypeScript:
 *
 * ```ts
 * const fn = createMiddleware({}, _ => _)
 * const gn = createMiddleware({}, async ax => ({ ...await ax }))
 * const hn = createMiddleware({ foo: '' }, async ax => ({ ...await ax, foo: 'star' }))
 * const jn = createMiddleware({ bar: '' }, async ax => {
 *   const x = await ax;
 *   x.effects.push(resp => {
 *     resp.headers.set('x-middleware', 'jn')
 *   })
 *   return { ...x, bar: 'star' }
 * })
 * const myMW = combine(fn, hn, jn, gn)
 * //=> Context & { foo: string } & { bar: string }
 * ```
 *
 * @param _defaultExt The default extension to the current context. Can also be a function that returns the extension object, to avoid unnecessary memory allocation.
 * @param middlewareFn A middleware functions: Adds the keys listed in `defaultExt` to the context
 * @returns The provided `middlewareFn` with type annotations inferred based on `defaultExt`
 */
export function createMiddleware(_defaultExt, middlewareFn) {
    return middlewareFn;
}
/**
 * Takes a handler function of the form `(x: Request, ctx: Context) => Awaitable<Response>` and applies middleware to it.
 * @deprecated Name might change, errorHandler not implemented
 */
export function withMiddleware(middleware, handler, _errorHandler) {
    return async (request, ...args) => {
        const handle = new ResolvablePromise();
        const handled = Promise.resolve(handle);
        const effects = new EffectsList();
        const ctx = { request, effects, handled, args: [request, ...args], waitUntil: () => { } };
        try {
            const userCtx = await middleware(ctx);
            const userRes = await handler(request, userCtx);
            const response = await executeEffects(effects, userRes);
            handle.resolve(response);
            return response;
        }
        catch (err) {
            throw err;
            // TODO
            // if (fallback && err instanceof Response) {
            //    fallback(request, Object.assign(ctx, { response: err }))
            // }
        }
    };
}
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