Add aspnet-angular NPM package containing HttpWithStateTransfer utility

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/.gitignore

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+/node_modules/
+**/*.js
+**/*.d.ts

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/.npmignore

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+!/*.js
+!/*.d.ts

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/LICENSE.txt

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+Copyright (c) .NET Foundation. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+these files except in compliance with the License. You may obtain a copy of the
+License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software distributed
+under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+CONDITIONS OF ANY KIND, either express or implied. See the License for the
+specific language governing permissions and limitations under the License.

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/package.json

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+{
+  "name": "aspnet-angular",
+  "version": "0.1.0",
+  "description": "Helpers for using Angular in ASP.NET Core projects",
+  "main": "index.js",
+  "scripts": {
+    "prepublish": "rimraf *.d.ts && tsc && echo 'Finished building NPM package \"aspnet-angular\"'",
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/aspnet/JavaScriptServices.git"
+  },
+  "author": "Microsoft",
+  "license": "Apache-2.0",
+  "bugs": {
+    "url": "https://github.com/aspnet/JavaScriptServices/issues"
+  },
+  "devDependencies": {
+    "@angular/common": "^4.3.2",
+    "@angular/core": "^4.3.2",
+    "@angular/http": "^4.3.2",
+    "@angular/platform-browser": "^4.3.2",
+    "rimraf": "^2.6.1",
+    "typescript": "^2.4.2",
+    "rxjs": "^5.4.2",
+    "zone.js": "^0.8.16"
+  },
+  "peerDependencies": {
+    "@angular/core": "^4.2.5 || ^5.0.0-beta"
+  }
+}

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/src/HttpWithStateTransfer.ts

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+import { Provider, NgModule, Inject } from '@angular/core';
+import { Headers, Http, ResponseOptions, RequestOptionsArgs, Response } from '@angular/http';
+import { Observable } from 'rxjs/Observable';
+import 'rxjs/add/observable/of';
+import 'rxjs/add/operator/map';
+const globalSerializedStateKey = 'HTTP_STATE_TRANSFER';
+const backingStoreDIToken = 'HTTP_STATE_BACKING_STORE';
+
+export interface CacheOptions {
+    permanent: boolean;
+}
+
+export interface CachedHttpResponse {
+    headers: { [name: string]: any } | null;
+    status: number;
+    statusText: string | null;
+    text: string;
+    url: string;
+}
+
+export type BackingStore = { [key: string]: CachedHttpResponse };
+
+export class HttpWithStateTransfer {
+    private backingStore: BackingStore;
+    private http: Http;
+
+    constructor(@Inject(Http) http: Http, @Inject(backingStoreDIToken) backingStore: BackingStore) {
+        this.http = http;
+        this.backingStore = backingStore;
+    }
+
+    public stateForTransfer(): any {
+        return { [globalSerializedStateKey]: this.backingStore };
+    }
+
+    public get(url: string, options?: CacheOptions, requestOptions?: RequestOptionsArgs): Observable<Response> {
+        return this.getCachedResponse(/* cacheKey */ url, () => this.http.get(url, requestOptions), options);
+    }
+
+    private getCachedResponse(cacheKey: string, provider: () => Observable<Response>, options?: CacheOptions): Observable<Response> {        
+        // By default, the cache is only used for the *first* client-side read. So, we're only performing
+        // a one-time transfer of server-side response to the client. If you want to keep and reuse cached
+        // responses continually during server-side and client-side execution, set 'permanent' to 'true.
+        const isClient = typeof window !== 'undefined';
+        const isPermanent = options && options.permanent;
+
+        const allowReadFromCache = isClient || isPermanent;
+        if (allowReadFromCache && this.backingStore.hasOwnProperty(cacheKey)) {
+            const cachedValue = this.backingStore[cacheKey];
+            if (!isPermanent) {
+                delete this.backingStore[cacheKey];
+            }
+            return Observable.of(new Response(new ResponseOptions({
+                body: cachedValue.text,
+                headers: new Headers(cachedValue.headers),
+                status: cachedValue.status,
+                url: cachedValue.url
+            })));
+        }
+
+        return provider()
+            .map(response => {
+                const allowWriteToCache = !isClient || isPermanent;
+                if (allowWriteToCache) {
+                    this.backingStore[cacheKey] = {
+                        headers: response.headers ? response.headers.toJSON() : null,
+                        status: response.status,
+                        statusText: response.statusText,
+                        text: response.text(),
+                        url: response.url
+                    };
+                }
+
+                return response;
+            });
+    }
+}
+
+export function defaultBackingStoreFactory() {
+    const transferredData = typeof window !== 'undefined' ? (window as any)[globalSerializedStateKey] : null;
+    return transferredData || {};
+}
+
+@NgModule({
+    providers: [
+        // The backing store is a separate DI service so you could override exactly how it gets
+        // transferred from server to client
+        { provide: backingStoreDIToken, useFactory: defaultBackingStoreFactory },
+
+        { provide: HttpWithStateTransfer, useClass: HttpWithStateTransfer },
+    ]
+})
+export class HttpWithStateTransferModule {
+}

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/src/index.ts

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+export * from './HttpWithStateTransfer';

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-angular/tsconfig.json

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+{
+  "compilerOptions": {
+    "experimentalDecorators": true,
+    "moduleResolution": "node",
+    "module": "commonjs",
+    "target": "es5",
+    "declaration": true,
+    "outDir": ".",
+    "lib": ["es2015", "dom"]
+  },
+  "files": [
+    "src/index.ts"
+  ],
+  "exclude": [
+    "node_modules"
+  ]
+}