event: add new Subscription type and related utilities

This commit introduces a new Subscription type, which is synonymous with
ethereum.Subscription. It also adds a couple of utilities that make
working with Subscriptions easier. The mot complex utility is Feed, a
synchronisation device that implements broadcast subscriptions. Feed is
slightly faster than TypeMux and will replace uses of TypeMux across the
go-ethereum codebase in the future.

event/subscription_test.go

@@ -0,0 +1,121 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package event
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"golang.org/x/net/context"
+)
+
+var errInts = errors.New("error in subscribeInts")
+
+func subscribeInts(max, fail int, c chan<- int) Subscription {
+	return NewSubscription(func(quit <-chan struct{}) error {
+		for i := 0; i < max; i++ {
+			if i >= fail {
+				return errInts
+			}
+			select {
+			case c <- i:
+			case <-quit:
+				return nil
+			}
+		}
+		return nil
+	})
+}
+
+func TestNewSubscriptionError(t *testing.T) {
+	t.Parallel()
+
+	channel := make(chan int)
+	sub := subscribeInts(10, 2, channel)
+loop:
+	for want := 0; want < 10; want++ {
+		select {
+		case got := <-channel:
+			if got != want {
+				t.Fatalf("wrong int %d, want %d", got, want)
+			}
+		case err := <-sub.Err():
+			if err != errInts {
+				t.Fatalf("wrong error: got %q, want %q", err, errInts)
+			}
+			if want != 2 {
+				t.Fatalf("got errInts at int %d, should be received at 2", want)
+			}
+			break loop
+		}
+	}
+	sub.Unsubscribe()
+
+	err, ok := <-sub.Err()
+	if err != nil {
+		t.Fatal("got non-nil error after Unsubscribe")
+	}
+	if ok {
+		t.Fatal("channel still open after Unsubscribe")
+	}
+}
+
+func TestResubscribe(t *testing.T) {
+	t.Parallel()
+
+	var i int
+	nfails := 6
+	sub := Resubscribe(100*time.Millisecond, func(ctx context.Context) (Subscription, error) {
+		// fmt.Printf("call #%d @ %v\n", i, time.Now())
+		i++
+		if i == 2 {
+			// Delay the second failure a bit to reset the resubscribe interval.
+			time.Sleep(200 * time.Millisecond)
+		}
+		if i < nfails {
+			return nil, errors.New("oops")
+		}
+		sub := NewSubscription(func(unsubscribed <-chan struct{}) error { return nil })
+		return sub, nil
+	})
+
+	<-sub.Err()
+	if i != nfails {
+		t.Fatalf("resubscribe function called %d times, want %d times", i, nfails)
+	}
+}
+
+func TestResubscribeAbort(t *testing.T) {
+	t.Parallel()
+
+	done := make(chan error)
+	sub := Resubscribe(0, func(ctx context.Context) (Subscription, error) {
+		select {
+		case <-ctx.Done():
+			done <- nil
+		case <-time.After(2 * time.Second):
+			done <- errors.New("context given to resubscribe function not canceled within 2s")
+		}
+		return nil, nil
+	})
+
+	sub.Unsubscribe()
+	if err := <-done; err != nil {
+		t.Fatal(err)
+	}
+}