client: implement rudimentary zmq client

client/README.md

@@ -0,0 +1,2 @@
+`# apt-get install libzmq3-dev`
+`$ go get github.com/pebbe/zmq4`

client/zmq_client.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"encoding/binary"
+	"log"
+
+	"github.com/gtank/ctxd/parser"
+	zmq "github.com/pebbe/zmq4"
+	"github.com/pkg/errors"
+)
+
+const (
+	PORT = 28332
+)
+
+func main() {
+	ctx, err := zmq.NewContext()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer ctx.Term()
+
+	// WARNING: The Socket is not thread safe. This means that you cannot
+	// access the same Socket from different goroutines without using something
+	// like a mutex.
+	sock, err := ctx.NewSocket(zmq.SUB)
+	if err != nil {
+		log.Fatal(errors.Wrap(err, "creating socket"))
+	}
+	err = sock.SetSubscribe("rawblock")
+	if err != nil {
+		log.Fatal(errors.Wrap(err, "subscribing"))
+	}
+	err = sock.Connect("tcp://127.0.0.1:28332")
+	if err != nil {
+		log.Fatal(errors.Wrap(err, "connecting"))
+	}
+	defer sock.Close()
+
+	for {
+		msg, err := sock.RecvMessageBytes(0)
+		if err != nil {
+			log.Println(errors.Wrap(err, "on message receipt"))
+			continue
+		}
+
+		if len(msg) < 3 {
+			log.Printf("got unknown msg: %v", msg)
+			continue
+		}
+
+		topic, body := msg[0], msg[1]
+
+		var sequence int
+		if len(msg[2]) == 4 {
+			sequence = int(binary.LittleEndian.Uint32(msg[len(msg)-1]))
+		}
+
+		switch string(topic) {
+		case "rawblock":
+			log.Printf("got block (%d): %x\n", sequence, body[:80])
+			go handleBlock(sequence, body)
+		default:
+			log.Printf("unexpected topic: %s (%d)", topic, sequence)
+		}
+	}
+}
+
+func handleBlock(sequence int, blockData []byte) {
+	block := parser.NewBlock()
+	rest, err := block.ParseFromSlice(blockData)
+	if err != nil {
+		log.Println("Error parsing block (%d): %v", err)
+		return
+	}
+	if len(rest) != 0 {
+		log.Println("Received overlong message:\n%x", rest)
+		return
+	}
+
+	log.Printf("Received a version %d block with %d transactions.", block.GetVersion(), block.GetTxCount())
+}