Pet daemon workers should support stepping debuggers (Chrome inspector or VSCode)

[kriskowal]

What is the Problem Being Solved?

At time of writing, there are a number of hurdles to debugging pet dæmon workers, not least of which is documenting the portion of that story that works. That is:

To start your dæmon in debug mode, you need to spawn it from your CLI with the node --inspect flag. Today, that looks like:

$ packages/cli/bin/endo stop
$ node --inspect packages/cli/bin/endo start 

This ought to be a single endo subcommand that unconditionally restarts the daemon in debug mode. All workers currently inherit the debug flags by virtue of child_process.fork.

Once a debugger is attached, we do fine until we discover that the workers are running without Mathieu’s accommodations for async_hook (which is entrained by the debugger). This is simple neglect to use @endo/init. We instead import ses, shims, and @endo/lockdown/commit.js manually, much of which can be simplified.

Description of the Design

Presumably something like endo restart --inspect would start a debugger session. That requires us to figure out how to thread --inspect when using child_process.fork or fall back to child_process.spawn and set up IPC manually. (We currently daemonize the daemon and wait to hear it’s successfully started listening on its designated interfaces.)

Then we just need to use @endo/init instead of rolling our own version of that manually.

Within a VSCode terminal session with the attached debugger, the following should pause on the debugger line in debugme.js.

$ echo debugger > debugme.js
$ endo restart --inspect
$ endo make debugme.js

Furthermore, this should work:

$ echo 'export const make = () => "ok"' > makeme.js
$ endo make makeme.js
ok

As written today, that reports an error since the returned promise has async_hook symbol own properties that the marshaler does not expect.

Security Considerations

None.

Scaling Considerations

None.

Test Plan

TBD.

Compatibility Considerations

None.

Upgrade Considerations

None.