Prerendering imposes its own (overridable) timeout with descriptive error

Author: SteveSandersonMS

src/Microsoft.AspNetCore.SpaServices/Prerendering/PrerenderTagHelper.cs

@@ -18,6 +18,7 @@ public class PrerenderTagHelper : TagHelper
         private const string PrerenderExportAttributeName = "asp-prerender-export";
         private const string PrerenderWebpackConfigAttributeName = "asp-prerender-webpack-config";
         private const string PrerenderDataAttributeName = "asp-prerender-data";
+        private const string PrerenderTimeoutAttributeName = "asp-prerender-timeout";
         private static INodeServices _fallbackNodeServices; // Used only if no INodeServices was registered with DI
 
         private readonly string _applicationBasePath;
@@ -50,6 +51,9 @@ public PrerenderTagHelper(IServiceProvider serviceProvider)
         [HtmlAttributeName(PrerenderDataAttributeName)]
         public object CustomDataParameter { get; set; }
 
+        [HtmlAttributeName(PrerenderTimeoutAttributeName)]
+        public int TimeoutMillisecondsParameter { get; set; }
+
         [HtmlAttributeNotBound]
         [ViewContext]
         public ViewContext ViewContext { get; set; }
@@ -79,7 +83,8 @@ public override async Task ProcessAsync(TagHelperContext context, TagHelperOutpu
                 },
                 unencodedAbsoluteUrl,
                 unencodedPathAndQuery,
-                CustomDataParameter);
+                CustomDataParameter,
+                TimeoutMillisecondsParameter);
             output.Content.SetHtmlContent(result.Html);
 
             // Also attach any specified globals to the 'window' object. This is useful for transferring

src/Microsoft.AspNetCore.SpaServices/Prerendering/Prerenderer.cs

@@ -23,7 +23,8 @@ public static Task<RenderToStringResult> RenderToString(
             JavaScriptModuleExport bootModule,
             string requestAbsoluteUrl,
             string requestPathAndQuery,
-            object customDataParameter)
+            object customDataParameter,
+            int timeoutMilliseconds)
         {
             return nodeServices.InvokeExportAsync<RenderToStringResult>(
                 NodeScript.Value.FileName,
@@ -32,7 +33,8 @@ public static Task<RenderToStringResult> RenderToString(
                 bootModule,
                 requestAbsoluteUrl,
                 requestPathAndQuery,
-                customDataParameter);
+                customDataParameter,
+                timeoutMilliseconds);
         }
     }
 }

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-prerendering/src/Prerendering.ts

@@ -5,6 +5,8 @@ import * as domain from 'domain';
 import { run as domainTaskRun } from 'domain-task/main';
 import { baseUrl } from 'domain-task/fetch';
 
+const defaultTimeoutMilliseconds = 30 * 1000;
+
 export interface RenderToStringCallback {
     (error: any, result: RenderToStringResult): void;
 }
@@ -33,7 +35,7 @@ export interface BootModuleInfo {
     webpackConfig?: string;
 }
 
-export function renderToString(callback: RenderToStringCallback, applicationBasePath: string, bootModule: BootModuleInfo, absoluteRequestUrl: string, requestPathAndQuery: string, customDataParameter: any) {
+export function renderToString(callback: RenderToStringCallback, applicationBasePath: string, bootModule: BootModuleInfo, absoluteRequestUrl: string, requestPathAndQuery: string, customDataParameter: any, overrideTimeoutMilliseconds: number) {
     findBootFunc(applicationBasePath, bootModule, (findBootFuncError, bootFunc) => {
         if (findBootFuncError) {
             callback(findBootFuncError, null);
@@ -66,8 +68,22 @@ export function renderToString(callback: RenderToStringCallback, applicationBase
             // Make the base URL available to the 'domain-tasks/fetch' helper within this execution context
             baseUrl(absoluteRequestUrl);
 
+            // Begin rendering, and apply a timeout
+            const bootFuncPromise = bootFunc(params);
+            if (!bootFuncPromise || typeof bootFuncPromise.then !== 'function') {
+                callback(`Prerendering failed because the boot function in ${bootModule.moduleName} did not return a promise.`, null);
+                return;
+            }
+            const timeoutMilliseconds = overrideTimeoutMilliseconds || defaultTimeoutMilliseconds; // e.g., pass -1 to override as 'never time out'
+            const bootFuncPromiseWithTimeout = timeoutMilliseconds > 0
+                ? wrapWithTimeout(bootFuncPromise, timeoutMilliseconds, 
+                    `Prerendering timed out after ${timeoutMilliseconds}ms because the boot function in '${bootModule.moduleName}' `
+                    + 'returned a promise that did not resolve or reject. Make sure that your boot function always resolves or '
+                    + 'rejects its promise. You can change the timeout value using the \'asp-prerender-timeout\' tag helper.')
+                : bootFuncPromise;
+
             // Actually perform the rendering
-            bootFunc(params).then(successResult => {
+            bootFuncPromiseWithTimeout.then(successResult => {
                 callback(null, { html: successResult.html, globals: successResult.globals });
             }, error => {
                 callback(error, null);
@@ -84,6 +100,25 @@ export function renderToString(callback: RenderToStringCallback, applicationBase
     });
 }
 
+function wrapWithTimeout<T>(promise: Promise<T>, timeoutMilliseconds: number, timeoutRejectionValue: any): Promise<T> {
+    return new Promise<T>((resolve, reject) => {
+        const timeoutTimer = setTimeout(() => {
+            reject(timeoutRejectionValue);
+        }, timeoutMilliseconds);
+
+        promise.then(
+            resolvedValue => {
+                clearTimeout(timeoutTimer);
+                resolve(resolvedValue);
+            },
+            rejectedValue => {
+                clearTimeout(timeoutTimer);
+                reject(rejectedValue);
+            }
+        )
+    });
+}
+
 function findBootModule<T>(applicationBasePath: string, bootModule: BootModuleInfo, callback: (error: any, foundModule: T) => void) {
     const bootModuleNameFullPath = path.resolve(applicationBasePath, bootModule.moduleName);
     if (bootModule.webpackConfig) {