Adds -json flag to format output in JSON format.

For compatibility with github.com/echojc/kp

Fixes #7.

README.md

@@ -6,21 +6,23 @@
     Usage of kt:
       -brokers string
             Comma separated list of brokers. (default "localhost:9092")
+      -json
+            Print output in JSON format.
       -offset string
             Colon separated offsets where to start and end reading messages.
       -topic string
             Topic to consume.
     $ kt -topic kt-test
-    Partition=0 Offset=0 Key= Value=Hello, World 0
-    Partition=0 Offset=1 Key= Value=Hallo, Welt
-    Partition=0 Offset=2 Key= Value=Bonjour, monde
+    Partition=0 Offset=0 Key= Message=Hello, World 0
+    Partition=0 Offset=1 Key= Message=Hallo, Welt
+    Partition=0 Offset=2 Key= Message=Bonjour, monde
     ^C2016/01/26 06:29:19 Received interrupt - shutting down...
     $ kt -topic kt-test -offset 1:
-    Partition=0 Offset=1 Key= Value=Hallo, Welt
-    Partition=0 Offset=2 Key= Value=Bonjour, monde
+    Partition=0 Offset=1 Key= Message=Hallo, Welt
+    Partition=0 Offset=2 Key= Message=Bonjour, monde
     ^C2016/01/26 06:29:29 Received interrupt - shutting down...
     $ kt -topic kt-test -offset 1:1
-    Partition=0 Offset=1 Key= Value=Hallo, Welt
+    Partition=0 Offset=1 Key= Message=Hallo, Welt
     $
 
 ## Installation

main.go

@@ -18,6 +18,7 @@ var config struct {
 	brokers     []string
 	startOffset int64
 	endOffset   int64
+	jsonOutput  bool
 }
 
 func listenForInterrupt() chan struct{} {
@@ -34,8 +35,22 @@ func listenForInterrupt() chan struct{} {
 }
 
 func print(msg *sarama.ConsumerMessage) {
+
+	if config.jsonOutput {
+		fmt.Printf(
+			`{"partition":%v,"offset":%v,"key":%#v,"message":%#v}
+`,
+			msg.Partition,
+			msg.Offset,
+			string(msg.Key),
+			string(msg.Value),
+		)
+
+		return
+	}
+
 	fmt.Printf(
-		"Partition=%v Offset=%v Key=%s Value=%s\n",
+		"Partition=%v Offset=%v Key=%s Message=%s\n",
 		msg.Partition,
 		msg.Offset,
 		msg.Key,
@@ -59,6 +74,7 @@ func parseArgs() {
 	flag.StringVar(&config.topic, "topic", "", "Topic to consume.")
 	flag.StringVar(&brokersString, "brokers", "localhost:9092", "Comma separated list of brokers.")
 	flag.StringVar(&offset, "offset", "", "Colon separated offsets where to start and end reading messages.")
+	flag.BoolVar(&config.jsonOutput, "json", false, "Print output in JSON format.")
 
 	flag.Parse()