Don't restart scanner renewer on every Next call

Most calls to Next are just reading some buffered results. The scanner
renewer only needs to be stopped and started again when we ask for
more results from HBase. Also, we shouldn't start a renewer if we know
we have already fetched the final results.

integration_test.go

@@ -2690,7 +2690,8 @@ func TestScannerTimeout(t *testing.T) {
 		"org.apache.hadoop.hbase.UnknownScannerException") {
 		fmt.Println("Error matches: UnknownScannerException")
 	} else {
-		t.Fatalf("Error does not match org.apache.hadoop.hbase.UnknownScannerException")
+		t.Fatalf("Error does not match org.apache.hadoop.hbase.UnknownScannerException, "+
+			"got: %v", err)
 	}
 }
 

scanner.go

@@ -75,24 +75,35 @@ func (s *scanner) fetch() ([]*pb.Result, error) {
 }
 
 func (s *scanner) peek() (*pb.Result, error) {
-	if len(s.results) == 0 {
-		var (
-			err error
-			rs  []*pb.Result
-		)
-		if s.closed {
-			// done scanning
-			return nil, io.EOF
-		}
+	if len(s.results) > 0 {
+		return s.results[0], nil
+	}
 
-		rs, err = s.fetch()
-		if err != nil {
-			return nil, err
-		}
+	if s.closed {
+		// done scanning
+		return nil, io.EOF
+	}
 
-		// fetch cannot return zero results
-		s.results = rs
+	if s.renewCancel != nil {
+		// About to send new Scan request to HBase, cancel our
+		// renewer.
+		s.renewCancel()
+		s.renewCancel = nil
+	}
+
+	rs, err := s.fetch()
+	if err != nil {
+		return nil, err
 	}
+	if !s.closed && s.rpc.RenewInterval() > 0 {
+		// Start up a renewer
+		renewCtx, cancel := context.WithCancel(s.rpc.Context())
+		s.renewCancel = cancel
+		go s.renewLoop(renewCtx, s.startRow)
+	}
+
+	// fetch cannot return zero results
+	s.results = rs
 	return s.results[0], nil
 }
 
@@ -154,21 +165,6 @@ func toLocalResult(r *pb.Result) *hrpc.Result {
 }
 
 func (s *scanner) Next() (*hrpc.Result, error) {
-	if s.rpc.RenewInterval() > 0 && s.renewCancel != nil {
-		s.renewCancel()
-	}
-
-	res, err := s.nextInternal()
-
-	if err == nil && s.rpc.RenewInterval() > 0 {
-		renewCtx, cancel := context.WithCancel(s.rpc.Context())
-		s.renewCancel = cancel
-		go s.renewLoop(renewCtx, s.startRow)
-	}
-	return res, err
-}
-
-func (s *scanner) nextInternal() (*hrpc.Result, error) {
 	var (
 		result, partial *pb.Result
 		err             error