Implement circuit breaker

[MitulShah1]

This PR contains Circuit Breaker Middleware

@aldas @jrhrmsll @lammel Would appreciate it if you can review this PR.

[MitulShah1]

@aldas I've made changes and make it more advance and optimize, can you please check again?

[aldas]

this does not seem to be used.

[aldas]

why not use atomic.uint to count requests in flight? At instead of that openTimer *time.Timer just have atomic uint64 (timestamp nano) that is checked if halfstate has been expired.

or atleast move this semaphore specific logic to own struct + methods that are similar to https://pkg.go.dev/golang.org/x/sync/semaphore API - this would be easier to read.

or very least - all places where there is select { in this code. it must have comment what it does. You do not see often people doing semaphores with chans and it takes too much processing/mental power to understand what the codes does. Especially when it comes to maintaining. For example we Echo maintainers have to read this code in 6, 12, 24 months and understand what it does with minimal effort. I can not expect you to be around then to explain.

[aldas]

Usually Go does not use getter naming. So State() would be more idiomatic.

[aldas]

I think guarding this small block with read lock makes little difference. This whole method should be behind read lock if it is necessary that limits are honored/guarded against races during extreme peaks.

[aldas]

these stats should have their own struct with field and their types. returning map of interfaces looks like something that belongs to javascript world.

[aldas]

I think this is little bit overthinking - if there is a method that returns stats when everyone can easily build their own handlers. assume that there will be people that want to have their own structure for output.

[aldas]

this could be if cb.state == StateOpen { return} to get rid of 1 level of indentation

[MitulShah1]

@aldas Thanks for detail review, I made below changes

1. Removed Unused context
2. Instead of a channel-based semaphore, Added atomic counter operations
3. Timestamp-based state transition instead of using timers.
4. Updated the locking strategy in AllowRequest()
5. Simplified resource management
6. Updated README File

Please review now.

[MitulShah1]

@aldas Can you please review?