Pool Manager: limit, pause and cancel requests

[vixez]

This is a PR related to #92

The goal is to limit the amount of simultaneous requests, and pause requests when a token is being updated.
It is also possible to cancel active requests.

PoolManager can handle both of these.
I have added an explanation to README.md and updated CHANGELOG.md as well.

Pool Manager

Using a PoolManager allows you to set the maximum amount of simultaneous requests, and pause
requests during token updates.

Create a PoolManager and assign it to an InterceptedClient:

final PoolManager poolManager = PoolManager(    
  maxActiveConnections: 8, 
);  
  
InterceptedClient.build(    
  poolManager: poolManager, 
);  

In the above example only 8 requests can be active at once. By default this is 32.

Skip the pool

It is possible to skip a pool that is active, on hold, or blocked by a token update.
This can be useful to, for example, update a token in a RetryPolicy while the pool is on hold.
If the InterceptedClient.kSkipPoolHeader header is found in the request the pool will be skipped, so the request is executed immediately.

To your headers, add for example:

headers[InterceptedClient.kSkipPoolHeader] = 'true';

The value of the header does not matter and the InterceptedClient.kSkipPoolHeader is filtered out of the request before being sent to the server.

Refreshing a token

If you use a RetryPolicy you can use the PoolManager to put new requests on hold until
the RetryPolicy has completed. Use requestUpdateToken to let the PoolManager know you want to
update the token and put new requests on hold. Once you have updated the token,
use releaseUpdateToken to resume requests.

Be sure to add logic (through an interceptor) to update queued requests with the new token you got
in the RetryPolicy.

poolManager in the example should be a reference to where you stored the PoolManager you
assigned to InterceptedClient.

class TokenRetryPolicy extends RetryPolicy {  
  @override Future<bool> shouldAttemptRetryOnResponse(ResponseData response) async { 
    if (response.statusCode == 401) { 
     // Need to get a new token 
     await poolManager.requestUpdateToken();  
     
     /*  --- YOUR TOKEN REFRESH LOGIC --- */  
     
     poolManager.releaseUpdateToken(); return true; } 
     return false; 
   }
 }  

Cancel active requests

You can cancel all requests that have not yet returned a response. They will return with RequestCancelledException.
This is done through the PoolManager with cancelRequests (optionally releasing token updates with the forceReleaseUpdateToken) parameter.

[CodingAleCR]

Hey, this looks amazing, I will continue testing it out with the new 2.0.0 APIs, thank you for all the hard work you have put into this!

[vixez]

You're welcome. Let me know if there is anything I need to change/can do.

[vixez]

I have updated this to work with the 2.0.0 beta.

[fnicastri]

Any update on this @CodingAleCR ? Looking forward to use this on my app(almost ready to be released) app!

Thanks for this awesome lib!

[vixez]

Added the ability to cancel all requests that have not yet returned a response

[CodingAleCR]

I really like this, but not entirely sure about the implementation. Lately, I've been thinking about adding a special PooledInterceptor or something that you can implement in order to opt-in for the functionality. What would you think about something like this?

[CodingAleCR]

I really like this, but not entirely sure about the implementation. Lately, I've been thinking about adding a special PooledInterceptor or something that you can implement in order to opt-in for the functionality. What would you think about something like this?

[vixez]

That could be an option as well, yes 🤔

[LucPham]

waiting a release!!

[fnicastri]

🤷‍♂️

[CodingAleCR]

I've explored other options but none that I like as alternatives, this has the most potential and stability. Would you be willing to update the PR with the latest changes?

[CodingAleCR]

I think it's best if we expose http package along with this package so we can avoid having to install manually http when using http_interceptor.

[shinayser]

Is this feature still will be implemented or its abbandoned?

[CodingAleCR]

I asked for a couple of updates. When done it should be good to go

[shinayser]

@vixez Have you quit this implementation or got any update on this?

[vixez]

@shinayser I have rewritten major parts of our API code for the app, making this no longer needed.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.