drain: refactor batch_future into its own file

aka What If structs.go Wasn't So Big?

nomad/structs/batch_future.go

@@ -0,0 +1,43 @@
+package structs
+
+// BatchFuture is used to wait on a batch update to complete
+type BatchFuture struct {
+	doneCh chan struct{}
+	err    error
+	index  uint64
+}
+
+// NewBatchFuture creates a new batch future
+func NewBatchFuture() *BatchFuture {
+	return &BatchFuture{
+		doneCh: make(chan struct{}),
+	}
+}
+
+// Wait is used to block for the future to complete and returns the error
+func (b *BatchFuture) Wait() error {
+	<-b.doneCh
+	return b.err
+}
+
+// WaitCh is used to block for the future to complete
+func (b *BatchFuture) WaitCh() <-chan struct{} {
+	return b.doneCh
+}
+
+// Error is used to return the error of the batch, only after Wait()
+func (b *BatchFuture) Error() error {
+	return b.err
+}
+
+// Index is used to return the index of the batch, only after Wait()
+func (b *BatchFuture) Index() uint64 {
+	return b.index
+}
+
+// Respond is used to unblock the future
+func (b *BatchFuture) Respond(index uint64, err error) {
+	b.index = index
+	b.err = err
+	close(b.doneCh)
+}

nomad/structs/batch_future_test.go

@@ -0,0 +1,35 @@
+package structs
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestBatchFuture(t *testing.T) {
+	t.Parallel()
+	bf := NewBatchFuture()
+
+	// Async respond to the future
+	expect := fmt.Errorf("testing")
+	go func() {
+		time.Sleep(10 * time.Millisecond)
+		bf.Respond(1000, expect)
+	}()
+
+	// Block for the result
+	start := time.Now()
+	err := bf.Wait()
+	diff := time.Since(start)
+	if diff < 5*time.Millisecond {
+		t.Fatalf("too fast")
+	}
+
+	// Check the results
+	if err != expect {
+		t.Fatalf("bad: %s", err)
+	}
+	if bf.Index() != 1000 {
+		t.Fatalf("bad: %d", bf.Index())
+	}
+}

nomad/structs/structs.go

@@ -7101,45 +7101,3 @@ type ACLTokenUpsertResponse struct {
 	Tokens []*ACLToken
 	WriteMeta
 }
-
-// BatchFuture is used to wait on a batch update to complete
-type BatchFuture struct {
-	doneCh chan struct{}
-	err    error
-	index  uint64
-}
-
-// NewBatchFuture creates a new batch future
-func NewBatchFuture() *BatchFuture {
-	return &BatchFuture{
-		doneCh: make(chan struct{}),
-	}
-}
-
-// Wait is used to block for the future to complete and returns the error
-func (b *BatchFuture) Wait() error {
-	<-b.doneCh
-	return b.err
-}
-
-// WaitCh is used to block for the future to complete
-func (b *BatchFuture) WaitCh() <-chan struct{} {
-	return b.doneCh
-}
-
-// Error is used to return the error of the batch, only after Wait()
-func (b *BatchFuture) Error() error {
-	return b.err
-}
-
-// Index is used to return the index of the batch, only after Wait()
-func (b *BatchFuture) Index() uint64 {
-	return b.index
-}
-
-// Respond is used to unblock the future
-func (b *BatchFuture) Respond(index uint64, err error) {
-	b.index = index
-	b.err = err
-	close(b.doneCh)
-}

nomad/structs/structs_test.go

@@ -3652,34 +3652,6 @@ func TestNetworkResourcesEquals(t *testing.T) {
 	}
 }
 
-func TestBatchFuture(t *testing.T) {
-	t.Parallel()
-	bf := NewBatchFuture()
-
-	// Async respond to the future
-	expect := fmt.Errorf("testing")
-	go func() {
-		time.Sleep(10 * time.Millisecond)
-		bf.Respond(1000, expect)
-	}()
-
-	// Block for the result
-	start := time.Now()
-	err := bf.Wait()
-	diff := time.Since(start)
-	if diff < 5*time.Millisecond {
-		t.Fatalf("too fast")
-	}
-
-	// Check the results
-	if err != expect {
-		t.Fatalf("bad: %s", err)
-	}
-	if bf.Index() != 1000 {
-		t.Fatalf("bad: %d", bf.Index())
-	}
-}
-
 func TestNode_Canonicalize(t *testing.T) {
 	t.Parallel()
 	require := require.New(t)