chainntnfs: add multi-client txid support for confirmation notifications

This commit adds multi-client support for confirmation notification of
the same transaction. Within the daemon there might be scenarios where
multiple goroutines are waiting for the same transaction to be
confirmed in order to properly fulfill their tasks. Previously if
multiple clients were registered for the same txid confirmation
notification, then only the client who registered last would receive
the notification.

chainntnfs/interface_test.go

@@ -2,6 +2,7 @@ package chainntnfs_test
 
 import (
 	"bytes"
+	"fmt"
 	"log"
 	"sync"
 	"testing"
@@ -55,7 +56,7 @@ func testSingleConfirmationNotification(miner *rpctest.Harness,
 
 	txid, err := getTestTxId(miner)
 	if err != nil {
-		t.Fatalf("unable to create test addr: %v", err)
+		t.Fatalf("unable to create test tx: %v", err)
 	}
 
 	// Now that we have a txid, register a confirmation notiication with
@@ -331,10 +332,62 @@ func testBlockEpochNotification(miner *rpctest.Harness,
 	}
 }
 
+func testMultiClientConfirmationNotification(miner *rpctest.Harness,
+	notifier chainntnfs.ChainNotifier, t *testing.T) {
+	// TODO(roasbeef): test various conf targets w/ same txid
+
+	// We'd like to test the case of a multiple clients registered to
+	// receive a confirmation notification for the same transaction.
+
+	txid, err := getTestTxId(miner)
+	if err != nil {
+		t.Fatalf("unable to create test tx: %v", err)
+	}
+
+	var wg sync.WaitGroup
+	const numConfsClients = 5
+	const numConfs = 1
+
+	// Register for a conf notification for the above generated txid with
+	// numConfsClients distinct clients.
+	for i := 0; i < numConfsClients; i++ {
+		confClient, err := notifier.RegisterConfirmationsNtfn(txid, numConfs)
+		if err != nil {
+			t.Fatalf("unable to register for confirmation: %v", err)
+		}
+
+		wg.Add(1)
+		go func() {
+			<-confClient.Confirmed
+			fmt.Println(i)
+			wg.Done()
+		}()
+	}
+
+	confsSent := make(chan struct{})
+	go func() {
+		wg.Wait()
+		close(confsSent)
+	}()
+
+	// Finally, generate a single block which should trigger the unblocking
+	// of all numConfsClients blocked on the channel read above.
+	if _, err := miner.Node.Generate(1); err != nil {
+		t.Fatalf("unable to generate block: %v", err)
+	}
+
+	select {
+	case <-confsSent:
+	case <-time.After(2 * time.Second):
+		t.Fatalf("all confirmation notifications not sent")
+	}
+}
+
 var ntfnTests = []func(node *rpctest.Harness, notifier chainntnfs.ChainNotifier, t *testing.T){
 	testSingleConfirmationNotification,
 	testMultiConfirmationNotification,
 	testBatchConfirmationNotification,
+	testMultiClientConfirmationNotification,
 	testSpendNotification,
 	testBlockEpochNotification,
 }