Use TailIterator in forwarder

This fixes a weird bug where the iterator couldn't access logs that were
written before it was created.

internals/overlord/logstate/forwarder.go

@@ -46,7 +46,7 @@ func newLogForwarder(serviceName string) *logForwarder {
 }
 
 func (f *logForwarder) forward(buffer *servicelog.RingBuffer) {
-	iterator := buffer.HeadIterator(0)
+	iterator := buffer.TailIterator()
 	// TODO: don't use the parser, just pull/write bytes from iterator
 	parser := servicelog.NewParser(iterator, 1024 /* TODO*/)
 

internals/overlord/logstate/forwarder_test.go

@@ -33,7 +33,9 @@ func (s *forwarderSuite) TestForwarder(c *C) {
 
 	recv1, recv2 := make(chan []servicelog.Entry), make(chan []servicelog.Entry)
 	gatherer1 := newLogGathererForTest(nil, 1*time.Microsecond, 5, recv1)
+	go gatherer1.loop()
 	gatherer2 := newLogGathererForTest(nil, 1*time.Microsecond, 5, recv2)
+	go gatherer2.loop()
 
 	forwarder := newLogForwarder(serviceName)
 	go forwarder.forward(ringBuffer)
@@ -50,7 +52,7 @@ func (s *forwarderSuite) TestForwarder(c *C) {
 	case entries := <-recv1:
 		c.Assert(entries, HasLen, 1)
 		c.Check(entries[0].Service, Equals, serviceName)
-		c.Check(entries[0].Message, Equals, message)
+		c.Check(entries[0].Message, Equals, message+"\n")
 	case <-time.After(10 * time.Millisecond):
 		c.Fatal("timeout waiting to receive logs from gatherer1")
 	}
@@ -59,7 +61,7 @@ func (s *forwarderSuite) TestForwarder(c *C) {
 	case entries := <-recv2:
 		c.Assert(entries, HasLen, 1)
 		c.Check(entries[0].Service, Equals, serviceName)
-		c.Check(entries[0].Message, Equals, message)
+		c.Check(entries[0].Message, Equals, message+"\n")
 	case <-time.After(10 * time.Millisecond):
 		c.Fatal("timeout waiting to receive logs from gatherer2")
 	}