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[Braindump] Proposal for redesigning the client interface #607

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[Braindump] Proposal for redesigning the client interface #607

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172e853
Proposal for redesigning the client interface
slinkydeveloper Nov 9, 2020
43b2e85
Now It's more clean
slinkydeveloper Nov 9, 2020
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44 changes: 26 additions & 18 deletions v2/client/client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,24 +25,32 @@ type Client interface {
// transport and return any response event.
Request(ctx context.Context, event event.Event) (*event.Event, protocol.Result)

// StartReceiver will register the provided function for callback on receipt
// of a cloudevent. It will also start the underlying protocol as it has
// been configured.
// This call is blocking.
// Valid fn signatures are:
// * func()
// * func() error
// * func(context.Context)
// * func(context.Context) protocol.Result
// * func(event.Event)
// * func(event.Event) protocol.Result
// * func(context.Context, event.Event)
// * func(context.Context, event.Event) protocol.Result
// * func(event.Event) *event.Event
// * func(event.Event) (*event.Event, protocol.Result)
// * func(context.Context, event.Event) *event.Event
// * func(context.Context, event.Event) (*event.Event, protocol.Result)
StartReceiver(ctx context.Context, fn interface{}) error
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how about leaving StartReceiver and also add the blocking single pulling functions?

you still need a hook on client to give it a thread, I am not seeing how that is happening without dramatically changing the contract.

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how about leaving StartReceiver and also add the blocking single pulling functions?

So one of the points with this proposal is that I would love to relax this assumption on the protocol side https://github.com/cloudevents/sdk-go/pull/606/files#diff-484d929efc01852c00d94e8e519500757204bacd6a67224c50db3c805eabc8f5R12 and enforce only in StartReceiver, where it really matters. Nor StartReceiver or invoking from multiple threads Receive makes sense in the context of Websockets.

My worry is that, If we put everything in Client, we'll have races everywhere, because we need to handle a lot of different cases:

  • user invokes Receive, it's blocked on Receive but then invokes StartReceiver
  • user invokes StartReceiver, then invokes Receive
  • OpenInbound for StartReceiver, then user invokes Receive too
  • StartReceiver context is canceled, but then user invokes Receive

While, if we make it clear that StartReceiver is like one level up/different to the client, e.g. accepting directly the Protocol in StartReceiver, then we have a clean implementation, both for StartReceiver and for Client.Receive. And also makes pretty clear to the user the usage aka don't mess up with Receive and StartReceiver at the same time.

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Maybe want you are saying is we need a new implementation for a stream based client. Client is for more like pub/sub style apis, and we can create a new one specific for streams like WS provides?

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Pretty much, but in particular my point is that I see the pub/sub APIs as a layer on top of a stream API (in fact, protocol APIs are already stream apis)

Receive(ctx context.Context) (event.Event, error)

Respond(ctx context.Context) (event.Event, ResponseFn, error)
}

type ResponseFn func(ctx context.Context, e *event.Event, r protocol.Result) error

// StartEventHandler will register the provided function for callback on receipt
// of a cloudevent. It will also start the underlying protocol as it has
// been configured.
// This call is blocking.
// Valid fn signatures are:
// * func()
// * func() error
// * func(context.Context)
// * func(context.Context) protocol.Result
// * func(event.Event)
// * func(event.Event) protocol.Result
// * func(context.Context, event.Event)
// * func(context.Context, event.Event) protocol.Result
// * func(event.Event) *event.Event
// * func(event.Event) (*event.Event, protocol.Result)
// * func(context.Context, event.Event) *event.Event
// * func(context.Context, event.Event) (*event.Event, protocol.Result)
func StartEventHandler(ctx context.Context, fn interface{}) error {

}

// New produces a new client with the provided transport object and applied
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