Improve xsnap-worker's reaction to EOF/SIGPIPE by explicit logging to stderr (#4103)

[siarhei-agoric]

closes: #4103
refs: agoric-labs/xsnap-pub PR #53

Description

This is the agoric-sdk side of the changes for xsnap-worker, containing updating the git subproject and adding new tests.

Security Considerations

New version of xsnap-worker explicitly exits and logs clear text errors to stderr when it detects an unexpected EOF or SIGPIPE condition, which does disclose some information regarding its internal state.

Scaling Considerations

Overall behavior is the same as xsnap-worker dies/exits just as before.

Documentation Considerations

none for agoric-sdk.

Testing Considerations

a new test had been added.

Upgrade Considerations

none.

[mhofman]

Quick preliminary feedback.

Dealing with streams and child processes in node is probably one of the most difficult thing to do cleanly and robustly. Let's pair at some point to try an make this test logic a little more idiomatic.

[gibson042]

I agree with @mhofman's comments as well.

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[mhofman]

I think we're missing a crucial test: pipe closed while trying to write a query (worker JS doing issueCommand).

We can probably do that by having the handleCommand in the worker do 2 issueCommand in a row, or close the "from xsnap" stream immediately after issuing the command.

[gibson042]

Style suggestions only; I like the new tests!

[mhofman]

The new structure of the test looks great. Once the few nits are addressed, we'll be almost ready for merging (I assume as a squash merge in this case, unless you plan on doing a local rebase to fixup commits)

Before merging this PR, we'll want to first merge agoric-labs/xsnap-pub#53, and use the outcome commit from the Agoric branch there as the new submodule commit here (and reflected in the build.env file)

Approving assuming this is done before merging.