WaitFor compatibility with Node watch processes (non-exiting background process)

[tdhatcher]

Background and Motivation

If an Aspire AppHost needs to particular sequence involving a Node script, this can be problematic.

Allow the state of a resource that is effectively a watch process without an exit to be affected by output text. The desired capability is similar to problemMatcher in VS Code tasks that define an "endsPattern"

Today if you run a Node app (eg. ng serve) it seems to prematurely indicate "readiness" while it's still executing. Any output indicating "readiness" is highly variable in nature due to script customizations and frameworks.

Proposed API

IResourceBuilder<T> extension

WaitFor(IResourceBuilder<IResource> dependency, string message)
WaitForWithMessage(IResourceBuilder<IResource> dependency, string message)

Usage Examples

// ng serve / watch
var angularClient = builder.AddNpmApp("client", "./apps/client1", "start");

// something to run only after npm project ready
var otherThing = builder.AddNpmApp("otherThing", "./apps/client2", "start")
    .WaitForWithMessage(angularClient, "bundle generation complete");

Alternative Designs

Risks

[davidfowl]

As an alternative you can add a http health check to your npm app.

[CZEMacLeod]

I am doing something pretty close to this in my testing for DebuggerAttach for Node and refactored it out a bit.
I will probably make a package out of it, if anyone would find it useful.

https://github.com/CZEMacLeod/AspireWaitForConsoleOutput

[tdhatcher]

@davidfowl that would just be too easy 😁. I will give that a try. That probably helped me solve another minor issue as well with a hashicorp/vault container waiting for it to be unsealed before its ready.

[CZEMacLeod]

@tdhatcher I've published C3D.Extensions.Aspire.WaitForOutput which does this for you.

<PackageReference Include="C3D.Extensions.Aspire.WaitForOutput" Version="0.1.6" />

// ng serve / watch
var angularClient = builder.AddNpmApp("client", "./apps/client1", "start");

// something to run only after npm project ready
var otherThing = builder.AddNpmApp("otherThing", "./apps/client2", "start")
    .WaitForOutput(angularClient, "bundle generation complete");