add --follow / -f flag to start consuming from HEAD-1 offset

cmd/kaf/consume.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"os"
 	"sync"
 
 	"github.com/birdayz/sarama"
@@ -11,13 +12,15 @@ import (
 
 var (
 	offsetFlag string
-	prettyPrint     bool
+	raw        bool
+	follow     bool
 )
 
 func init() {
 	rootCmd.AddCommand(consumeCmd)
 	consumeCmd.Flags().StringVar(&offsetFlag, "offset", "oldest", "Offset to start consuming. Possible values: oldest, newest. Default: newest")
-	consumeCmd.Flags().BoolVar(&prettyPrint, "pretty", false, "Pretty print output if possible, e.g. for JSON.")
+	consumeCmd.Flags().BoolVar(&raw, "raw", false, "Print raw output of messages, without key or prettified JSON")
+	consumeCmd.Flags().BoolVarP(&follow, "follow", "f", false, "Shorthand to start consuming with offset HEAD-1 on each partition. Overrides --offset flag")
 }
 
 var consumeCmd = &cobra.Command{
@@ -61,6 +64,25 @@ var consumeCmd = &cobra.Command{
 			wg.Add(1)
 
 			go func(partition int32) {
+				req := &sarama.OffsetRequest{
+					Version: int16(1),
+				}
+				req.AddBlock(topic, partition, int64(-1), int32(0))
+				ldr, err := client.Leader(topic, partition)
+				if err != nil {
+					panic(err)
+				}
+				offsets, err := ldr.GetAvailableOffsets(req)
+				if err != nil {
+					panic(err)
+				}
+				followOffset := offsets.GetBlock(topic, partition).Offset - 1
+
+				if follow && followOffset > 0 {
+					offset = followOffset
+					fmt.Fprintf(os.Stderr, "Starting on partition %v with offet %v\n", partition, offset)
+				}
+
 				pc, err := consumer.ConsumePartition(topic, partition, offset)
 				if err != nil {
 					panic(err)
@@ -70,14 +92,14 @@ var consumeCmd = &cobra.Command{
 
 					dataToDisplay := msg.Value
 
-					if prettyPrint {
+					if !raw {
 						formatted, err := prettyjson.Format(msg.Value)
 						if err == nil {
 							dataToDisplay = formatted
 						}
 					}
 
-					if msg.Key != nil && len(msg.Key) > 0 {
+					if msg.Key != nil && len(msg.Key) > 0 && !raw {
 						fmt.Printf("%v %v\n", string(msg.Key), string(dataToDisplay))
 					} else {
 						fmt.Printf("%v\n", string(dataToDisplay))