Remove context support in favor of using a read only channel

Author: jeronimoalbi

README.md

@@ -26,6 +26,37 @@ Getting Started
 
 See the [getting started](http://kusanagi.io/docs/getting-started) tutorial to begin with the **KUSANAGI**™ framework and the **Go** SDK.
 
+### Cancellation Signal
+
+The Go SDK implements support to signal deadlines or cancellation through a read only channel that is available to **Middleware** and **Service** components.
+
+The channel can be read using the `Api.Done()` method. For example, within a service action:
+
+```go
+func handler(action *kusanagi.Action) (*kusanagi.Action, error) {
+    // Create a context for the current service call
+    ctx, cancel := context.WithCancel(context.Background())
+
+    // Create a channel to get the task result
+    result := make(chan int)
+
+    // Run some async task
+    go task(ctx, result)
+
+    // Cancel the context when the service call times out
+    select{
+    case v := <-result:
+       action.Log(v, 6)
+    case <-action.Done():
+        cancel()
+    }
+
+    return action, nil
+}
+```
+
+It is highly recommended to monitor this channel and stop any ongoing task when the channel is closed.
+
 Documentation
 -------------
 

v2/action.go

@@ -548,7 +548,7 @@ func (a *Action) Call(
 	// Make the runtime call
 	callee := []string{service, version, action}
 	c, err := call(
-		a.GetContext(),
+		a.Done(),
 		schema.GetAddress(),
 		a.GetActionName(),
 		callee,

v2/api.go

@@ -9,7 +9,6 @@
 package kusanagi
 
 import (
-	"context"
 	"path"
 
 	"github.com/kusanagi/kusanagi-sdk-go/v2/lib/cli"
@@ -140,12 +139,7 @@ func (a *Api) Log(value interface{}, level int) (*Api, error) {
 	return a, nil
 }
 
-// GetContext return the context for the current request.
-func (a *Api) GetContext() context.Context {
-	return a.state.context
-}
-
-// Done is a dummy method to comply with KUSANAGI SDK specifications.
-func (a *Api) Done() bool {
-	panic("SDK does not support async call to end action: Api.done()")
+// Done returns a channel that signals the deadline or cancellation of the call.
+func (a *Api) Done() <-chan struct{} {
+	return a.state.done
 }

v2/lib/runtime/runtime.go

@@ -9,7 +9,6 @@
 package runtime
 
 import (
-	"context"
 	"fmt"
 	"time"
 
@@ -20,7 +19,7 @@ import (
 )
 
 // Call makes a runtime call to a service.
-func Call(ctx context.Context, address string, message []byte, timeout uint) (*payload.Reply, time.Duration, error) {
+func Call(stop <-chan struct{}, address string, message []byte, timeout uint) (*payload.Reply, time.Duration, error) {
 	var duration time.Duration
 
 	// Define a custom ZMQ context
@@ -36,7 +35,7 @@ func Call(ctx context.Context, address string, message []byte, timeout uint) (*p
 	// When the context is done terminate the ZMQ context to stop the runtime call
 	go func() {
 		select {
-		case <-ctx.Done():
+		case <-stop:
 			if err := zctx.Term(); err != nil {
 				log.Errorf("Failed to terminate runtime call context: %v", err)
 			}

v2/runtime.go

@@ -9,7 +9,6 @@
 package kusanagi
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"time"
@@ -28,7 +27,7 @@ type callResult struct {
 }
 
 func call(
-	ctx context.Context,
+	stop <-chan struct{},
 	address string,
 	action string,
 	callee []string,
@@ -66,7 +65,7 @@ func call(
 		// NOTE: Run-time calls are made to the server address where the caller is runnning
 		//       and NOT directly to the service we wish to call. The KUSANAGI framework
 		//       takes care of the call logic for us to keep consistency between all the SDKs.
-		reply, duration, err := runtime.Call(ctx, protocol.SocketAddress(address, tcp), message, timeout)
+		reply, duration, err := runtime.Call(stop, protocol.SocketAddress(address, tcp), message, timeout)
 		if err != nil {
 			c <- callResult{Duration: duration, Error: err}
 		} else if err := reply.Error; err != nil {

v2/server.go

@@ -33,7 +33,7 @@ type state struct {
 	reply   *payload.Reply
 	payload []byte
 	input   cli.Input
-	context context.Context
+	done    chan struct{}
 	logger  log.RequestLogger
 	request requestMsg
 }
@@ -194,9 +194,11 @@ func (s *server) startMessageListener(msgc <-chan requestMsg) <-chan requestOutp
 					action:  action,
 					schemas: schemas,
 					input:   s.input,
+					done:    make(chan struct{}),
 					logger:  logger,
 					request: msg,
 				}
+				defer close(state.done)
 
 				// Prepare defaults for the request output
 				output := requestOutput{state: &state}
@@ -206,7 +208,6 @@ func (s *server) startMessageListener(msgc <-chan requestMsg) <-chan requestOutp
 					output.err = fmt.Errorf(`Invalid action for component %s: "%s"`, title, action)
 					resc <- output
 					return
-
 				}
 
 				// Try to read the new schemas when present
@@ -227,7 +228,6 @@ func (s *server) startMessageListener(msgc <-chan requestMsg) <-chan requestOutp
 				// Create a child context with the process execution timeout as limit
 				ctx, cancel := context.WithTimeout(ctx, timeout)
 				defer cancel()
-				state.context = ctx
 
 				// Create a channel to wait for the processor output
 				outc := make(chan requestOutput)