javascript 以 6 角重试 HTTP 请求
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Retry HTTP requests in angular 6
提问by Amir Khademi
I use an interceptor to show error messages on display based on the HTTP response for every request.
我使用拦截器根据每个请求的 HTTP 响应在显示器上显示错误消息。
intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
const customReq = request.clone({
//headers: request.headers.set('app-language', 'en')
});
return next
.handle(customReq).pipe(
tap((ev: HttpEvent<any>) => {
if (ev instanceof HttpResponse) {
// processing request
}
}),
catchError(response => {
if (response instanceof HttpErrorResponse) {
switch (response.status) {
case 0:
// server API connection error show
break;
case 403:
// error Token Invalid and Redirect to logout
break;
case 401:
// error Token Invalid and Redirect to logout
break;
case 502:
// Bad gateway error
break;
case 500:
// internal server error
break;
}
}
// return next.handle(request);
return observableThrowError(response);
})
);
}
In my project, the web server could be unavailable for a second in some case and reply a 500 error code. I don't want my web app to show an error message immediately after receiving an error and I want it to retry the request for a couple of times with a delay like one second.
在我的项目中，Web 服务器在某些情况下可能会暂时不可用并回复 500 错误代码。我不希望我的 Web 应用程序在收到错误后立即显示错误消息，我希望它重试请求几次，延迟时间为一秒钟。
I already tried rxjs retry :
我已经尝试过 rxjs 重试：
...
.handle(customReq).pipe(retry(5),
...
it's not useful since it has no delay. based on this answer How to create an RXjs RetryWhen with delay and limit on tries
它没有用，因为它没有延迟。基于此答案 如何创建具有延迟和限制尝试的 RXjs RetryWhen
I tried retryWhen like:
我试过 retryWhen 喜欢：
.handle(customReq).pipe(
tap((ev: HttpEvent<any>) => {
if (ev instanceof HttpResponse) {
console.log('###processing response', ev, this.location);
}
}),
retryWhen(error => {
return error
.flatMap((error: any) => {
if (error.status == 400) {
return Observable.of(error.status).delay(1000);
}
if (error.status == 0) {
return observableThrowError(error).delay(1000);
}
return observableThrowError(error);
})
.take(5)
.concat(observableThrowError(error));
}),
but it doesn't work as expected and it doens't go inside the if conditions.
但它没有按预期工作，并且不会进入 if 条件。
回答by m1ch4ls
There are several errors in your code:
您的代码中有几个错误：
- You are shadowing
errorvariable - first it's an error stream and then it's an error object. - Using
observableThrowErrorwithdelayhas no effect. Error will bypass every operator except those dealing with error. - You are mixing "
pipe(operator())" style operators and prototype style operators.operator().
- 您正在隐藏
error变量 - 首先它是一个错误流，然后它是一个错误对象。 - 使用
observableThrowErrorwithdelay没有效果。除了处理错误的操作符之外，错误将绕过所有操作符。 - 您正在混合“
pipe(operator())”样式运算符和原型样式运算符.operator()。
I have suggested some changes:
我提出了一些改变：
.handle(customReq).pipe(
tap((ev: HttpEvent<any>) => {
if (ev instanceof HttpResponse) {
console.log('###processing response', ev, this.location);
}
}),
retryWhen(errors => errors
.pipe(
concatMap((error, count) => {
if (count < 5 && (error.status == 400 || error.status == 0)) {
return Observable.of(error.status);
}
return observableThrowError(error);
}),
delay(1000)
)
),
Main change is tracking error count through second argument of concatMapinstead of using takeopeator which is mainly useful for unsubscribing the observable and I think you want throw an error instead.
主要变化是通过第二个参数concatMap而不是使用take运算符来跟踪错误计数，这主要用于取消订阅可观察对象，我认为您想要抛出错误。
回答by Santiago Ceron
You could use retry operator, better to use it on an interceptor
您可以使用重试运算符，最好在拦截器上使用它
intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
return next.handle(request)
.pipe(retry(RETRY_NUMBER))
It will only retry when the request fails, then to identify errors you could throw an error and then catch it
它只会在请求失败时重试，然后为了识别错误，您可以抛出错误然后捕获它
.pipe(tap(event => {
// tipo http
if (event instanceof HttpResponse) {
if (event.body && event.body.error === true && event.body.errorMessage) {
throw new Error(event.body.errorMessage);
}
}
}))
.pipe(catchError((err) => {
if (err.status === 0) {
//do something
}
// other conditions ...
return EMPTY;
}));
Don't forget t return EMPTYbecause the interceptor needs to return an observable
不要忘记 t returnEMPTY因为拦截器需要返回一个 observable
