Add OnStart callback for emulator start

[chasefleming]

Closes #565

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• Targeted PR against master branch
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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7496500) 52.62% compared to head (f2abb88) 53.30%.
Report is 85 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #566      +/-   ##
==========================================
+ Coverage   52.62%   53.30%   +0.68%     
==========================================
  Files          29       29              
  Lines        3795     3876      +81     
==========================================
+ Hits         1997     2066      +69     
- Misses       1646     1652       +6     
- Partials      152      158       +6     

Flag	Coverage Δ
unittests	53.30% <ø> (+0.68%)	⬆️

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[turbolent]

Nice! What is the release/v0 branch?

[chasefleming]

@turbolent we need a way to still release non v1 features now that everything has been merged to master. I cut this branch off of the v0.59.0 commit, so have the ability to do more releases like v0.60.0 if we need a change in the meantime. This means we'll have to cherry pick everything we do over here into a PR for the master branch as well. Don't foresee many changes though.

[turbolent]

Sounds good! 👍 There's a discussion about having such a branch in #564, maybe good to coordinate and document it, so we don't end up with multiple different ones

[chasefleming]

Thanks for the heads up @turbolent . Left a comment on there.

[bluesign]

@chasefleming is this works? afaik start call is blocking (library we used there, graceland is blocking actually)

I think emulator should start after the start call anyway, what was the issue there? Is there something creating delay ?

[chasefleming]

@bluesign you're right. I need to rethink my approach. Moving this to a draft PR. Sorry, what do you mean by "start after start call." If start blocks, what I am trying to do is figure out a way to notify whatever called it that you can continue on a next step. e.g. deploy a contract to the emulator.

[bluesign]

@chasefleming who is the caller here? who is starting emulator I mean. I think if you call Listen before Start, emulator should be ready anyway, OS will make socket wait till it is handled.

[chasefleming]

@bluesign In one use case, the CLI is the caller. I tried this, but unless I put a sleep to delay it the following code fails because it's not actually ready:

err := emulatorServer.Listen()
if err != nil {
	// TODO: handle error
}

go func() {
	emulatorServer.Start()
}()
fmt.Println("Emulator server is ready")

Any ideas or see anything I'm doing wrong?

[chasefleming]

This is addressed by this: onflow/flow-go-sdk#578