Add option --relative

The sender's network stack assembles tcp packets without regard for
write boundaries, so the receiver has to be prepared for partial reads.

tcpdelay.go

@@ -2,8 +2,8 @@ package main
 
 import (
 	"encoding/binary"
-	"gopkg.in/alecthomas/kingpin.v2"
 	"fmt"
+	"gopkg.in/alecthomas/kingpin.v2"
 	"log"
 	"net"
 	"os"
@@ -18,6 +18,7 @@ var (
 
 	client        = app.Command("client", "Request measurement")
 	serverAddress = client.Arg("address", "Address:port to connect to").String()
+	relativeTimes = client.Flag("relative", "Print times relative to start").Bool()
 )
 
 func tcpdelayServer() {
@@ -56,6 +57,7 @@ func tcpdelayServer() {
 }
 
 func tcpdelayClient() {
+	t0 := time.Now().UnixNano()
 	conn, err := net.Dial("tcp", *serverAddress)
 	if err != nil {
 		log.Fatal("Cannot connect to ", *serverAddress, err)
@@ -63,13 +65,17 @@ func tcpdelayClient() {
 	o := 0
 	buffer := make([]byte, 1024)
 	for {
-		n, err := conn.Read(buffer)
+		n := 0
+		for n < len(buffer) {
+			nr, err := conn.Read(buffer[n:])
 			if err != nil {
-			log.Fatal("Cannot read from ", *serverAddress, err)
+				log.Fatal("Cannot read from ", *serverAddress, err.Error())
 			}
-		if n != len(buffer) {
+			if nr <= 0 {
 				log.Fatal("Read ", n, " bytes intead of ", len(buffer))
 			}
+			n += nr
+		}
 		tr := time.Now().UnixNano()
 		if string(buffer[0:8]) != "tcpdelay" {
 			log.Fatal("Unexpected magic ", buffer[0:8])
@@ -79,7 +85,11 @@ func tcpdelayClient() {
 			log.Fatal("Unexpected offset ", oSent, " instead of ", o)
 		}
 		ts := binary.BigEndian.Uint64(buffer[16:])
-		fmt.Println(o, ts, tr) // XXX - buffer for performance
+		if *relativeTimes {
+			fmt.Println(o, int64(ts)-t0, tr-t0)
+		} else {
+			fmt.Println(o, ts, tr)
+		}
 		o += n
 	}