ngx-http-retry

ngx-http-retry

A configurable Angular HTTP interceptor to retry GET requests and respond to errors and flaky connections.

Installation

To install this library, run:

npm install ngx-http-retry --save -or- yarn add ngx-http-retry

and then import and configure it in your Angular AppModule:

import { NgxHttpRetryModule } from 'ngx-http-retry';

@NgModule({
  imports: [
    NgxHttpRetryModule.forRoot()
  ],
  providers: [serverUnavailableRetryStrategyProvider],
  bootstrap: [AppComponent]
})
export class AppModule { }

Usage

You configure ngx-http-retry by providing (via Angular dependency injection) a collection of injectable classes that implement the HttpRequestRetryStrategy interface. These "retry strategies" tell ngx-http-retry which status codes to retry, how many times to retry, and when to stop retrying.

In addition to being thrown by the http request observable like normal, the last HttpErrorResponse received when ngx-http-retry stops retrying a request is passed to the retry strategy's onFailure method and emitted on the NgxHttpRetryService's httpRetryFailures observable.

Implementing HttpRequestRetryStrategy

import { HttpRequestRetryStrategy } from 'ngx-http-retry';

@Injectable()
export class ServerUnavailableRetryStrategy implements HttpRequestRetryStrategy {
  readonly statuses = [503];
  readonly maxCount = 10;

  delayFn() {
    return 100;
  }

  onFailure(error: HttpErrorResponse) {
    console.log('When ngx-http-retry stops retrying a request, the final error is passed back to the retry strategy.', error.status, error.url);
  }
}

export const serverUnavailableRetryStrategyProvider: Provider = {
  provide: HTTP_REQUEST_RETRY_STRATEGIES,
  useClass: ServerUnavailableRetryStrategy,
  multi: true
};

Using NgxHttpRetryService (optional)

import { NgxHttpRetryService } from 'ngx-http-retry';

export class MyComponent implements OnInit {
  constructor(private readonly ngxHttpRetryService: NgxHttpRetryService) { }

  ngOnInit() {
    this.ngxHttpRetryService.httpRetryFailures.subscribe(error => {
      console.log('You can also listen to errors from all retry strategies in one place.', error.status, error.url);
    });
  }
}

Request Headers

ngx-http-retry will add a header named X-Request-Attempt-Number to each request it sends that with the number of the current attempt. This was added primarily for testing. But it's plausible that this could be useful information to track on the server in some scenarios, so this header is added in production. A future version may allow disabling this option if needed.

License

MIT © Kevin Phelps