.NET Core 3.0 + Angular 9 cli application called via the SpaServices extensions hangs in common configuration

[miguellira]

Describe the bug

Running a .NET Core 3.0 + Angular 9 cli (version 9.0.0-rc.2 as of this post) with the angular cli build option progress set to false will hang until the StartupTimeout expires (default: 120 seconds)

To Reproduce

I created a repo with a bare bones .NET Core 3.0 + Angular 9 cli application to demo the bug. Simply clone, npm build the ClientApp folder, and dotnet run. Or you can follow the steps below to do this from scratch:

1. Ensure you have .NET Core 3.0 installed
2. Create a .NET Core application with the current Angular templates by typing: dotnet new angular -n HelloWorld
3. Navigate to the ClientApp folder and install the Typescript helper functions required for Angular 9 by typing: npm install tslib@latest
4. Update to Angular 9 by typing: ng update @angular/core @angular/cli --next
5. Ensure the progress build option in the angular.json file is set to false
6. Run the application by navigating back to the root folder and typing: dotnet run
7. Launch a browser and navigate to: https://localhost:5001

The application will hang and eventually timeout.

Further technical details

This appears to be caused by a change in how ng serve outputs to the console in the new Angular 9 CLI. The AngularCliMiddleware makes a WaitForMatch() method call against the standard output to signify when the Angular assets have been generated and the web server is ready to receive requests (Line 84). However, unless the progress option is set to true in the angular.json file you never see the expected line.

UPDATE: Updated to .NET Core 3.1 and Angular 9.0.0-rc.5. Same issue. New, simpler workaround is to modify your npm start script to perform a simple echo prior to ng serve (see comment below)

UPDATE (6/5/2020): Lots of recent comments so I figured I'd share exactly what has worked for me with every release of .NET and Angular since my original post. Update your package.json like so:

  "scripts": {
    "ng": "ng",
    "start": "echo hello && ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  }

[benelliott]

I also have this issue, but don't want to have to re-enable progress as webpack's build progress output is routed to stderr, and this makes log4net go a bit nuts. If this could be solved in a different way it would be great - especially since listening for the dev server to spit out a specific string always felt a bit fragile.

[benelliott]

Actually, I don't think it's quite as simple as that - when I run ng serve --progress=false from my App directory, I still see the listening on... message.

I think the problem is that the message will only show on the first log output from the CLI (https://github.com/angular/angular-cli/blob/2c0efd834b08ac5ea166d88c0ff57cc35df19421/packages/angular_devkit/build_angular/src/dev-server/index.ts#L361) and this often takes longer than the five second default timeout after which .NET assumes that the CLI has died (https://github.com/aspnet/AspNetCore/blob/master/src/Middleware/SpaServices.Extensions/src/AngularCli/AngularCliMiddleware.cs#L22).

[elianora]

I am using .NET Core 3.1 and am encountering the same issue using @angular/cli@~9.0.0-rc.5. I never get the line expected by the AngularCliMiddleware from the Angular CLI. I have had it work correctly intermittently with both --progress=true and --progress=false.

I have zero clue as to why the following workaround works, but I consistently get the expected behavior if I add any statement that outputs to stdout prior to ng serve . My package.json script is echo hello && npm serve --progress=false, and I get the following reliably:

EDIT: Adding environment info:

• Windows 10 build 18363
• Node.js 12.13.0
• Visual Studio Code 1.40.2
• dotnet CLI 3.1.100
• @angular/cli 9.0.0-rc.5

[benelliott]

@elianora I spent some time digging around today and found this bug: #6146

Basically, the wrapper around StdOut might miss the listening on... message if it's at the end of a block with lots of newlines. As of Angular 9 this is a problem because the message is more likely to be printed in the same block as the webpack chunk output.

Could you check that you're referencing the latest version of the SpaServices packages? I think this fix (ab02951) is only present in 3.0.0 onwards.

[elianora]

I am currently referencing 3.1.0 and my TargetFramework is set to netcoreapp3.1.

[benelliott]

I've made a shamelessly hacky workaround which will do for now. Basically, I wrap the call to the Angular CLI in another Node script, and spoof the "open your browser on" message so that dotnet notices it.

You can try the workaround yourself:

1. Edit your package.json to rename your start script to start:ng
2. Add a new start script: "start": "node start-dotnet.js". Your package.json should look like

        "start":  "node start-for-dotnet.js",
        "start:ng": "ng serve [or whatever you had before]",

3. Next to your package.json, add a file called start-dotnet.js with contents

// Hack to work around https://github.com/aspnet/AspNetCore/issues/17277

const { spawn } = require('child_process');

const portArgIndex = process.argv.indexOf('--port');

if (portArgIndex === -1) {
    throw new Error('Could not detect port number');
}

const port = process.argv[portArgIndex + 1];

console.log(`open your browser on http://localhost:${port}`);

const child = spawn(`cmd`, ['/c', `npm.cmd run start:ng -- --port ${port}`]);

console.log('Angular CLI started on PID', child.pid);

child.stdout.on('data', x => console.log(x && x.toString()));

child.stderr.on('data', x => console.error(x && x.toString()));

const sleep = () => {
    console.log('[Node.js keepalive]');
    setTimeout(sleep, 10000);
}

sleep();

[benelliott]

const child = spawn(`cmd`, ['/c', `npm.cmd run start:ng -- --port ${port}`]);

This line is Windows-specific, the Linux equivalent would be something along the lines of (but possibly not exactly)

const child = spawn(`npm`, ['run', `start:ng -- --port ${port}`]);

[elianora]

I run into no issues just using echo something && ng serve, but certainly will keep this in mind if I or anyone else I'm working with run into this issue again; when I get home I will see what the behavior on other operating systems looks like.

[benelliott]

Do you still have dotnet randomly choosing a CLI port when you do that?

[elianora]

I do, yes.

[miguellira]

@elianora suggestion of modifying the npm start script in your package.json by adding an echo statement prior to ng serve is enough to notify the AngularCliMiddleware the angular dev server is running. This is a better workaround than setting the progress flag to true.

BTW, can't see how it would matter but I did notice a subtle difference in how the Angular CLI outputs build info between Angular 8 and 9. Specifically, the Date and Hash information comes after the chunk information in Angular 9, where as it is the first line in Angular 8.

info: Microsoft.AspNetCore.SpaServices[0]

chunk {main} main.js, main.js.map (main) 60.7 kB [initial] [rendered]

chunk {polyfills} polyfills.js, polyfills.js.map (polyfills) 140 kB [initial] [rendered]

chunk {runtime} runtime.js, runtime.js.map (runtime) 6.15 kB [entry] [rendered]

chunk {styles} styles.js, styles.js.map (styles) 9.94 kB [initial] [rendered]

chunk {vendor} vendor.js, vendor.js.map (vendor) 2.99 MB [initial] [rendered]

Date: 2019-12-06T04:20:45.321Z - Hash: 6ee5d8996273b040afe7 - Time: 5917ms <-- This is now on one line and in a new location in Angular 9

...

Of course the actual string the AngularCliMiddleware is searching for: "open your browser on" is still being emitted by the angular_devkit package (Line 303).

[benelliott]

The echo workaround works for me too... so my workaround might be slight overkill :)

I don't fully get why it fixes it though...

EDIT: it seems that when I add the --aot flag, the echo workaround no longer helps. I have to use the NodeJS workaround in this case.