From 3d9133f93fbe267be567506ae16ab63b58b0931c Mon Sep 17 00:00:00 2001
From: "Peter J. Holzer" <hjp@hjp.at>
Date: Sun, 20 Dec 2020 15:23:59 +0100
Subject: [PATCH] Reassemble partial packets on the client

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 | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/tcpdelay.go b/tcpdelay.go
index 3f7a952..3087a37 100644
--- a/tcpdelay.go
+++ b/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"
@@ -16,7 +16,7 @@ var (
 	server        = app.Command("server", "Run as server")
 	listenAddress = server.Arg("address", "Address:port to listen on").String()
 
-	client = app.Command("client", "Request measurement")
+	client        = app.Command("client", "Request measurement")
 	serverAddress = client.Arg("address", "Address:port to connect to").String()
 )
 
@@ -63,12 +63,16 @@ func tcpdelayClient() {
 	o := 0
 	buffer := make([]byte, 1024)
 	for {
-		n, err := conn.Read(buffer)
-		if err != nil {
-			log.Fatal("Cannot read from ", *serverAddress, err)
-		}
-		if n != len(buffer) {
-			log.Fatal("Read ", n, " bytes intead of ", len(buffer))
+		n := 0
+		for n < len(buffer) {
+			nr, err := conn.Read(buffer[n:])
+			if err != nil {
+				log.Fatal("Cannot read from ", *serverAddress, err.Error())
+			}
+			if nr <= 0 {
+				log.Fatal("Read ", n, " bytes intead of ", len(buffer))
+			}
+			n += nr
 		}
 		tr := time.Now().UnixNano()
 		if string(buffer[0:8]) != "tcpdelay" {