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HttpBackend

Abstract base class for all HTTP backends. A backend receives a prepared request and returns an Observable<HttpEvent>. Swapping the backend changes the transport layer without touching the client or any application code.

@opra/client ships with FetchBackend. @opra/angular provides AngularBackend. Extend HttpBackend to build your own.

Class​

abstract class HttpBackend extends Backend {
  readonly serviceUrl: string;
  interceptors?: HttpInterceptor<any>[];

  abstract handle(init: HttpBackend.RequestInit): Observable<HttpEvent>;
}

Constructor​

protected constructor(serviceUrl: string, options?: HttpBackend.Options)

The serviceUrl is normalized: trailing slash is added if missing, query string and fragment are stripped.

Properties​

PropertyTypeDescription
serviceUrlstringNormalized base URL
interceptorsHttpInterceptor[]Interceptors applied before the request reaches the transport

Abstract method: handle(init)​

Implement this to define the transport. Emit events as the request progresses and complete the observable when done.

abstract handle(init: HttpBackend.RequestInit): Observable<HttpEvent>

Custom backend example​

import { HttpBackend, HttpClientBase, HttpEventType, HttpResponse } from '@opra/client';
import { Observable } from 'rxjs';

class MockBackend extends HttpBackend {
  private fixtures = new Map<string, any>();

  fixture(path: string, body: any) {
    this.fixtures.set(path, body);
    return this;
  }

  handle(init: HttpBackend.RequestInit): Observable<HttpEvent> {
    return new Observable(subscriber => {
      const url = new URL(init.url, this.serviceUrl);
      const body = this.fixtures.get(url.pathname) ?? null;
      subscriber.next({
        type: HttpEventType.Response,
        request: init,
        response: new HttpResponse({ status: body ? 200 : 404, body }),
      });
      subscriber.complete();
    });
  }
}

class MockClient extends HttpClientBase {
  readonly backend: MockBackend;

  constructor(serviceUrl = 'http://localhost') {
    const backend = new MockBackend(serviceUrl);
    super(backend);
    this.backend = backend;
  }
}

Interfaces​

HttpBackend.Options​

interface Options extends Backend.Options {
  document?: ApiDocument;
}

HttpBackend.RequestInit​

interface RequestInit extends Backend.RequestInit {
  method: string;
  url: string | URL;
  headers?: Headers;
  body?: any;
}

See also​