[FAB-2606] Enable deliver_stdout to seek

https://jira.hyperledger.org/browse/FAB-2606

The `deliver_stdout` client is useful for debugging. This changeset
introduces a `seek` flag that allows us to seek to oldest or newest
(using the convention in [1]), or extract a specific block.

[1] https://godoc.org/github.com/Shopify/sarama#pkg-constants

Change-Id: Iaf8d3c596cfc23768d2bfc257ee32ef9a4512c54
Signed-off-by: Kostas Christidis <kostas@christidis.io>

orderer/sample_clients/deliver_stdout/client.go

@@ -30,6 +30,12 @@ import (
 	"google.golang.org/grpc"
 )
 
+var (
+	oldest  = &ab.SeekPosition{Type: &ab.SeekPosition_Oldest{Oldest: &ab.SeekOldest{}}}
+	newest  = &ab.SeekPosition{Type: &ab.SeekPosition_Newest{Newest: &ab.SeekNewest{}}}
+	maxStop = &ab.SeekPosition{Type: &ab.SeekPosition_Specified{Specified: &ab.SeekSpecified{Number: math.MaxUint64}}}
+)
+
 type deliverClient struct {
 	client  ab.AtomicBroadcast_DeliverClient
 	chainID string
@@ -39,7 +45,7 @@ func newDeliverClient(client ab.AtomicBroadcast_DeliverClient, chainID string) *
 	return &deliverClient{client: client, chainID: chainID}
 }
 
-func seekHelper(chainID string, start *ab.SeekPosition) *cb.Envelope {
+func seekHelper(chainID string, start *ab.SeekPosition, stop *ab.SeekPosition) *cb.Envelope {
 	return &cb.Envelope{
 		Payload: utils.MarshalOrPanic(&cb.Payload{
 			Header: &cb.Header{
@@ -51,23 +57,24 @@ func seekHelper(chainID string, start *ab.SeekPosition) *cb.Envelope {
 
 			Data: utils.MarshalOrPanic(&ab.SeekInfo{
 				Start:    start,
-				Stop:     &ab.SeekPosition{Type: &ab.SeekPosition_Specified{Specified: &ab.SeekSpecified{Number: math.MaxUint64}}},
+				Stop:     stop,
 				Behavior: ab.SeekInfo_BLOCK_UNTIL_READY,
 			}),
 		}),
 	}
 }
 
 func (r *deliverClient) seekOldest() error {
-	return r.client.Send(seekHelper(r.chainID, &ab.SeekPosition{Type: &ab.SeekPosition_Oldest{Oldest: &ab.SeekOldest{}}}))
+	return r.client.Send(seekHelper(r.chainID, oldest, maxStop))
 }
 
 func (r *deliverClient) seekNewest() error {
-	return r.client.Send(seekHelper(r.chainID, &ab.SeekPosition{Type: &ab.SeekPosition_Newest{Newest: &ab.SeekNewest{}}}))
+	return r.client.Send(seekHelper(r.chainID, newest, maxStop))
 }
 
-func (r *deliverClient) seek(blockNumber uint64) error {
-	return r.client.Send(seekHelper(r.chainID, &ab.SeekPosition{Type: &ab.SeekPosition_Specified{Specified: &ab.SeekSpecified{Number: blockNumber}}}))
+func (r *deliverClient) seekSingle(blockNumber uint64) error {
+	specific := &ab.SeekPosition{Type: &ab.SeekPosition_Specified{Specified: &ab.SeekSpecified{Number: blockNumber}}}
+	return r.client.Send(seekHelper(r.chainID, specific, specific))
 }
 
 func (r *deliverClient) readUntilClose() {
@@ -93,11 +100,21 @@ func main() {
 
 	var chainID string
 	var serverAddr string
+	var seek int
 
 	flag.StringVar(&serverAddr, "server", fmt.Sprintf("%s:%d", config.General.ListenAddress, config.General.ListenPort), "The RPC server to connect to.")
 	flag.StringVar(&chainID, "chainID", provisional.TestChainID, "The chain ID to deliver from.")
+	flag.IntVar(&seek, "seek", -2, "Specify the range of requested blocks."+
+		"Acceptable values:"+
+		"-2 (or -1) to start from oldest (or newest) and keep at it indefinitely."+
+		"N >= 0 to fetch block N only.")
 	flag.Parse()
 
+	if seek < -2 {
+		fmt.Println("Wrong seek value.")
+		flag.PrintDefaults()
+	}
+
 	conn, err := grpc.Dial(serverAddr, grpc.WithInsecure())
 	if err != nil {
 		fmt.Println("Error connecting:", err)
@@ -110,7 +127,15 @@ func main() {
 	}
 
 	s := newDeliverClient(client, chainID)
-	err = s.seekOldest()
+	switch seek {
+	case -2:
+		err = s.seekOldest()
+	case -1:
+		err = s.seekNewest()
+	default:
+		err = s.seekSingle(uint64(seek))
+	}
+
 	if err != nil {
 		fmt.Println("Received error:", err)
 	}