Add retry handling to base and feed service

src/app/services/base.service.ts

@@ -1,14 +1,38 @@
 import {Injectable} from '@angular/core';
-import {HttpHeaders} from '@angular/common/http';
+import { HttpErrorResponse, HttpHeaders} from '@angular/common/http';
+import {delay, mergeMap, retryWhen} from 'rxjs/operators';
+import {Observable, of, throwError} from 'rxjs';
+
+const httpTooManyCode = 429;
+const httpHeaderRateRetry = 'Retry-After';
 
 @Injectable({
   providedIn: 'root'
 })
 export abstract class BaseService {
   protected headers: HttpHeaders;
-
   protected constructor() {
     this.headers = new HttpHeaders();
     this.headers.set('Content-Type', 'application/json');
   }
+
+  /**
+   * Retries a request according to the rate limit
+   * @param maxRetry
+   */
+  protected retryRated(maxRetry = 3) {
+    let retries = maxRetry;
+    return (src: Observable<any>) => {
+      return src.pipe(retryWhen(errors => errors.pipe(mergeMap(error => {
+          if (error.status === httpTooManyCode) {
+            const retryAfter = Number(error.headers.get(httpHeaderRateRetry) || 1) * 1000;
+            return of(error.status).pipe(delay(retryAfter));
+          } else if (retries-- > 0) {
+            return of(error).pipe(delay(10000));
+          }
+          return throwError(error);
+        }))
+      ));
+    };
+  }
 }

src/app/services/feed/feed.service.ts

@@ -1,5 +1,5 @@
 import {Injectable} from '@angular/core';
-import {HttpClient} from '@angular/common/http';
+import {HttpClient, HttpErrorResponse} from '@angular/common/http';
 import {Post} from 'src/app/models/post';
 import {Author} from 'src/app/models/author';
 import {environment} from 'src/environments/environment';
@@ -180,7 +180,7 @@ export class FeedService extends BaseService {
       }
     };
 
-    return this.http.post(environment.graphQLUrl, body, {headers: this.headers});
+    return this.http.post(environment.graphQLUrl, body, {headers: this.headers}).pipe(this.retryRated());
   }
 
   /**
@@ -194,7 +194,7 @@ export class FeedService extends BaseService {
       }
     };
 
-    return this.http.post(environment.graphQLUrl, body, {headers: this.headers});
+    return this.http.post(environment.graphQLUrl, body, {headers: this.headers}).pipe(this.retryRated());
   }
 
   /**
@@ -209,8 +209,8 @@ export class FeedService extends BaseService {
         postId: pPostID
       }
     };
-
-    return this.http.post(environment.graphQLUrl, body, {headers: this.headers});
+    return this.http.post(environment.graphQLUrl, body, {headers: this.headers})
+      .pipe(this.retryRated());
   }
 
   /**
@@ -222,7 +222,9 @@ export class FeedService extends BaseService {
     this.postsAvailable.next(true);
     this.posts.next([]);
     return this.http.post(environment.graphQLUrl, FeedService.buildGetPostBody(sort, 0),
-      {headers: this.headers}).subscribe(response => {
+      {headers: this.headers})
+      .pipe(this.retryRated())
+      .subscribe(response => {
         this.posts.next(this.constructAllPosts(response));
         this.activePostList = sort;
       });
@@ -235,6 +237,7 @@ export class FeedService extends BaseService {
     this.offset += this.offsetStep;
     const body = FeedService.buildGetPostBody(this.activePostList, this.offset);
     this.http.post(environment.graphQLUrl, body, {headers: this.headers})
+      .pipe(this.retryRated())
       .subscribe(response => {
         const posts = this.constructAllPosts(response);
         const updatedPostList = this.posts.getValue().concat(posts);