catch all unhandled promise rejection for http browser io handler

src/io/browser_http.ts

@@ -145,72 +145,100 @@ export class BrowserHTTPRequest implements IOHandler {
    */
   private async loadBinaryTopology(): Promise<ArrayBuffer> {
     try {
-      const response =
-          await this.getFetchFunc()(this.path[0], this.requestInit);
+      const response = await this.getFetchFunc()(
+          this.path[0], this.addAcceptHeader('application/octet-stream'));
+      this.verifyContentType(response, 'application/octet-stream');
+
       if (!response.ok) {
-        throw new Error(
-            `BrowserHTTPRequest.load() failed due to HTTP response: ${
-                response.statusText}`);
+        throw new Error(`Request to ${this.path[0]} failed with error: ${
+            response.statusText}`);
       }
       return await response.arrayBuffer();
     } catch (error) {
-      throw new Error(`${this.path[0]} not found. ${error}`);
+      throw new Error(`Failed to load ${this.path[0]}. ${error}`);
     }
   }
 
-  protected async loadBinaryModel(): Promise<ModelArtifacts> {
-    const graphPromise = this.loadBinaryTopology();
-    const manifestPromise =
-        await this.getFetchFunc()(this.path[1], this.requestInit);
-    if (!manifestPromise.ok) {
-      throw new Error(`BrowserHTTPRequest.load() failed due to HTTP response: ${
-          manifestPromise.statusText}`);
+  private addAcceptHeader(mimeType: string): RequestInit {
+    const requestOptions = Object.assign({}, this.requestInit || {});
+    const headers = new Headers(requestOptions.headers);
+    headers.append('Accept', mimeType);
+    requestOptions.headers = headers;
+    return requestOptions;
+  }
+
+  private verifyContentType(response: Response, target: string) {
+    const contentType = response.headers.get('content-type');
+    if (!contentType || contentType.indexOf(target) === -1) {
+      throw new Error(`Wrong content type (${contentType}) for ${
+          response.url}, should be (${target}).`);
     }
+  }
+
+  protected async loadBinaryModel(): Promise<ModelArtifacts> {
+    try {
+      const graphPromise = this.loadBinaryTopology();
+      const manifestPromise = await this.getFetchFunc()(
+          this.path[1], this.addAcceptHeader('application/json'));
+      this.verifyContentType(manifestPromise, 'application/json');
+      if (!manifestPromise.ok) {
+        throw new Error(`Request to ${this.path[1]} failed with error: ${
+            manifestPromise.statusText}`);
+      }
 
-    const results = await Promise.all([graphPromise, manifestPromise]);
-    const [modelTopology, weightsManifestResponse] = results;
+      const results = await Promise.all([graphPromise, manifestPromise]);
+      const [modelTopology, weightsManifestResponse] = results;
 
-    const weightsManifest =
-        await weightsManifestResponse.json() as WeightsManifestConfig;
+      const weightsManifest =
+          await weightsManifestResponse.json() as WeightsManifestConfig;
 
-    let weightSpecs: WeightsManifestEntry[];
-    let weightData: ArrayBuffer;
-    if (weightsManifest != null) {
-      const results = await this.loadWeights(weightsManifest);
-      [weightSpecs, weightData] = results;
-    }
+      let weightSpecs: WeightsManifestEntry[];
+      let weightData: ArrayBuffer;
+      if (weightsManifest != null) {
+        const results = await this.loadWeights(weightsManifest);
+        [weightSpecs, weightData] = results;
+      }
 
-    return {modelTopology, weightSpecs, weightData};
+      return {modelTopology, weightSpecs, weightData};
+    } catch (error) {
+      throw new Error(`Request to ${this.path[1]} failed with error: ${error}`);
+    }
   }
 
   protected async loadJSONModel(): Promise<ModelArtifacts> {
-    const modelConfigRequest =
-        await this.getFetchFunc()(this.path as string, this.requestInit);
-    if (!modelConfigRequest.ok) {
-      throw new Error(`BrowserHTTPRequest.load() failed due to HTTP response: ${
-          modelConfigRequest.statusText}`);
-    }
-    const modelConfig = await modelConfigRequest.json();
-    const modelTopology = modelConfig['modelTopology'];
-    const weightsManifest = modelConfig['weightsManifest'];
+    try {
+      const modelConfigRequest = await this.getFetchFunc()(
+          this.path as string, this.addAcceptHeader('application/json'));
+      this.verifyContentType(modelConfigRequest, 'application/json');
 
-    // We do not allow both modelTopology and weightsManifest to be missing.
-    if (modelTopology == null && weightsManifest == null) {
-      throw new Error(
-          `The JSON from HTTP path ${this.path} contains neither model ` +
-          `topology or manifest for weights.`);
-    }
+      if (!modelConfigRequest.ok) {
+        throw new Error(`Request to ${this.path} failed with error: ${
+            modelConfigRequest.statusText}`);
+      }
+      const modelConfig = await modelConfigRequest.json();
+      const modelTopology = modelConfig['modelTopology'];
+      const weightsManifest = modelConfig['weightsManifest'];
 
-    let weightSpecs: WeightsManifestEntry[];
-    let weightData: ArrayBuffer;
-    if (weightsManifest != null) {
-      const weightsManifest =
-          modelConfig['weightsManifest'] as WeightsManifestConfig;
-      const results = await this.loadWeights(weightsManifest);
-      [weightSpecs, weightData] = results;
-    }
+      // We do not allow both modelTopology and weightsManifest to be missing.
+      if (modelTopology == null && weightsManifest == null) {
+        throw new Error(
+            `The JSON from HTTP path ${this.path} contains neither model ` +
+            `topology or manifest for weights.`);
+      }
 
-    return {modelTopology, weightSpecs, weightData};
+      let weightSpecs: WeightsManifestEntry[];
+      let weightData: ArrayBuffer;
+      if (weightsManifest != null) {
+        const weightsManifest =
+            modelConfig['weightsManifest'] as WeightsManifestConfig;
+        const results = await this.loadWeights(weightsManifest);
+        [weightSpecs, weightData] = results;
+      }
+
+      return {modelTopology, weightSpecs, weightData};
+    } catch (error) {
+      throw new Error(`Request to ${this.path} failed with error: ${error}`);
+    }
   }
 
   private async loadWeights(weightsManifest: WeightsManifestConfig):
@@ -230,12 +258,15 @@ export class BrowserHTTPRequest implements IOHandler {
         fetchURLs.push(pathPrefix + path + suffix);
       });
     });
-
-    return [
-      weightSpecs,
-      concatenateArrayBuffers(await loadWeightsAsArrayBuffer(
-          fetchURLs, this.requestInit, this.getFetchFunc()))
-    ];
+    try {
+      return [
+        weightSpecs,
+        concatenateArrayBuffers(await loadWeightsAsArrayBuffer(
+            fetchURLs, this.requestInit, this.getFetchFunc()))
+      ];
+    } catch (error) {
+      throw new Error(`Failed to load weights: ${error}`);
+    }
   }
 
   /**