Added new command message: Cancel

[ahitacat]

Proposal

Add a new control message of type command that can be used to cancel a work that is already in progress in a worker. yggd will receive this command and forward it to the appropriate worker. If this worker implements the cancellation feature it will stop or cancel its work. But it is up to the worker to implement this functionality.

This PR also provides an example of how the cancellation message can be implemented in the echo worker. It uses a map of synchronized channels to manage the current work, and to send the cancellation message to the goroutines that are handle it.

This commit adds:

• A new command message that can be use to cancel work in progress that is done in the workers.Is send as a command to yggdrasil client. Yggdrasil will send this message to the workers Cancel method.

• A new function to the worker, CancelRX. This function will handle the cancel signal in workers side. If it is null the worker doesn't support cancellation of messages.

• echo worker implements this cancel function to handle cancellation when it runs in slow mode.

How to test it

Follow the Quickstart steps to set the environment. With the following changes:

Terminal 2 Run the worker with the loop and sleep parameters, this will allow some time to launch the cancel message.

go run ./worker/echo --log-level trace --loop 10 --sleep 10s

Terminal 4 Run the hello world, that will send a new job to the worker.

echo "hello world"| \
go run ./cmd/yggctl generate data-message --directive echo - | \
pub -broker tcp://localhost:1883 -topic yggdrasil/$(hostname)/data/in

In the worker it will appear the id of that message:

2023/10/06 12:21:58 addr = echo
2023/10/06 12:21:58 id = 67c40762-2343-48ad-9bf1-23a9b98bdacb
2023/10/06 12:21:58 responseTo = 
2023/10/06 12:21:58 metadata = map[string]string{}
2023/10/06 12:21:58 data = [104 101 108 108 111 32 119 111 114 108 100 10]
2023/10/06 12:21:58 emitting event BEGIN

Use the id 67c40762-2343-48ad-9bf1-23a9b98bdacb to send the cancellation message:

echo '{"command":"cancel", "arguments":{"directive":"echo","messageID":"67c40762-2343-48ad-9bf1-23a9b98bdacb"}}' |\
go run ./cmd/yggctl generate control-message --type command - |\
pub -broker tcp://test.mosquitto.org:1883 -topic yggdrasil/$(hostname)/control/in

[ahitacat]

Summary of changes made from reviews:

• fix typos in code and comments
• fix logs to follow the conventions on this project and set better debug levels
• echo worker use RWMutexMap from internal/sync to create a table of channels to handle current pending work.
  • Those pending works are related to sent echo message through yggdrasil, echo worker running in sleep mode will have the opportunity to cancel that work that has not being finished.
• add doc-string comments

[ahitacat]

Sumary of changes

Addressed all the change from @jirihnidek comments:

• Improve the description of CancelMessage function.
• Check that directive is not empty

[subpop]

worker/echo/main.go has changed; could you resolve those conflicts and we'll see if we can revisit this PR again.

[ahitacat]

Changelog

• Minor fixed spoted by @subpop
• Reformulate CancelMessage signature. I have move the handle of the parameters into the client, so this function needs to recieve CancelMessage(directive string, message_id string, cancel_id string)
• Open a new discussion about move some internal modules to other path and allow them to be imported into new projects.
• Added a DBus Error and open a new discussion. [TODO: Open a discussion on how to treat better DBUs API errors]
• Added a new example, using the loop functionality of the worker (added in this PR).
• Provide some steps on the description of this PR on how it can be tested.
• Rebased and resolve conflicts.

[ahitacat]

@subpop @jirihnidek I have fixed the typos and include your suggestions :smile: