Golang TCPConn Gob Communication - go

I'm having issues with the gob protocol (or maybe networking in general, where my knowledge is weak), and I don't understand why the following code does not work properly. It is just supposed to be a simple example of maintaining an open TCP connection, and sending multiple gobs through it. The code will send, and receive, but often corrupts its data.
Thank you in advance.
package main
import (
"encoding/gob"
"fmt"
"net"
"strconv"
"time"
)
type Message struct {
Msg string
}
func main() {
gob.Register(new(Message))
clientAddr, err := net.ResolveTCPAddr("tcp", "localhost:12346")
if err != nil {
fmt.Println(err)
}
serverAddr, err := net.ResolveTCPAddr("tcp", "localhost:12345")
if err != nil {
fmt.Println(err)
}
serverListener, err := net.ListenTCP("tcp", serverAddr)
if err != nil {
fmt.Println(err)
}
conn, err := net.DialTCP("tcp", clientAddr, serverAddr)
if err != nil {
fmt.Println(err)
}
serverConn, err := serverListener.AcceptTCP()
if err != nil {
fmt.Println(err)
}
done := false
go func() {
for !done {
recieveMessage(serverConn)
}
}()
for i := 1; i < 1000; i++ {
sent := Message{strconv.Itoa(i)}
sendMessage(sent, conn)
}
time.Sleep(time.Second)
done = true
}
func sendMessage(msg Message, conn *net.TCPConn) {
enc := gob.NewEncoder(conn)
err := enc.Encode(msg)
if err != nil {
fmt.Println(err)
}
}
func recieveMessage(conn *net.TCPConn) {
msg := new(Message)
dec := gob.NewDecoder(conn) // Will read from network.
err := dec.Decode(msg)
if err != nil {
fmt.Println(err)
}
fmt.Println("Client recieved:", msg.Msg)
}

The problem is that the decoder can buffer data from the next message. When this happens, the next new decoder starts in the middle of a message. The fix is to use a single encoder and decoder.
func main() {
...
dec := gob.NewDecoder(conn) // Will read from network.
enc := gob.NewEncoder(serverConn)
go func() {
for !done {
recieveMessage(dec)
}
}()
for i := 1; i < 1000; i++ {
sent := Message{strconv.Itoa(i)}
sendMessage(sent, enc)
}
...
}
func sendMessage(msg Message, enc *gob.Encoder) {
err := enc.Encode(msg)
if err != nil {
fmt.Println(err)
}
}
func recieveMessage(dec *gob.Decoder) {
msg := new(Message)
err := dec.Decode(msg)
if err != nil {
fmt.Println(err)
}
fmt.Println("Client recieved:", msg.Msg)
}
Run it in the playground

Related

Cannot receive response packets from multicast server in golang

I setup a udp server listening multicast trafic, and create a client to sent test packet. When the server receives the package, it will send a response. Everything is ok, except the client cannot receive the packet from the server. Why?
package main
import (
"log"
"net"
"os"
"time"
"golang.org/x/net/ipv4"
)
func SetupMulticast(ifn, addr string) {
ifi, err := net.InterfaceByName(ifn)
if err != nil {
log.Fatal(err)
}
//server
c, err := net.ListenPacket("udp4", addr)
if err != nil {
log.Fatal(err)
}
log.Printf("listen ad:%s\n", addr)
p := ipv4.NewPacketConn(c)
gAddr, err2 := net.ResolveUDPAddr("udp4", addr)
if err2 != nil {
log.Fatal(err2)
}
if err := p.JoinGroup(ifi, gAddr); err != nil {
log.Fatal(err)
}
if err := p.SetControlMessage(ipv4.FlagDst|ipv4.FlagSrc, true); err != nil {
log.Fatal(err)
}
go func() {
b := make([]byte, 1500)
for {
n, cm, src, err := p.ReadFrom(b)
if err != nil {
break
}
log.Println("receive:", string(b[:n]), cm.Dst.IsMulticast(), cm.Dst)
if n2, err := p.WriteTo([]byte("world!"), nil, src); err != nil {
log.Printf("fail to write back:%v\n", err)
} else {
log.Printf("write back addr: %s length:%d\n", src, n2)
}
}
}()
//client
if conn, err2 := net.DialUDP("udp4", nil /*src*/, gAddr); err2 != nil {
log.Fatal(err)
} else {
go func() {
for {
log.Println("write hello...")
conn.Write([]byte("hello"))
time.Sleep(time.Second * 2)
}
}()
go func() {
b2 := make([]byte, 1500)
for {
n, err := conn.Read(b2)
if err != nil {
log.Panic(err)
}
log.Printf("sender received response:%s\n", string(b2[:n]))
}
}()
}
}
func main() {
If := os.Args[1] //ens33
Addr := os.Args[2] //224.0.0.248:1025
SetupMulticast(If, Addr)
for {
}
}
And the output:
2022/08/17 22:53:53 listen ad:224.0.0.248:1025
2022/08/17 22:53:53 write hello...
2022/08/17 22:53:53 receive: hello true 224.0.0.248
2022/08/17 22:53:53 write back addr: 192.168.19.131:43925 length:6
2022/08/17 22:53:55 write hello...
2022/08/17 22:53:55 receive: hello true 224.0.0.248
2022/08/17 22:53:55 write back addr: 192.168.19.131:43925 length:6
From the logs, there are no any "sender received response" record. I don't know why?

Can we send request form server to client and get response through quic/http3?

I'm using quic-go to implement my thought, I need the server to forwardly send request to client to get response, just like we do that client sends request to web server commonly. But with quic-go, after connection is setup, can server initialize streams to send request to client and get responses? I did a trying but haven't made it work. The code below is from the echo.go of example dir, the two parts between comment lines are added by me.
package main
import (
"context"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"encoding/pem"
"fmt"
"io"
"log"
"math/big"
"github.com/lucas-clemente/quic-go"
)
const addr = "localhost:4242"
const message = "foobar"
// We start a server echoing data on the first stream the client opens,
// then connect with a client, send the message, and wait for its receipt.
func main() {
go func() { log.Fatal(echoServer()) }()
err := clientMain()
if err != nil {
panic(err)
}
}
// Start a server that echos all data on the first stream opened by the client
func echoServer() error {
listener, err := quic.ListenAddr(addr, generateTLSConfig(), nil)
if err != nil {
return err
}
conn, err := listener.Accept(context.Background())
if err != nil {
return err
}
stream, err := conn.AcceptStream(context.Background())
if err != nil {
panic(err)
}
// Echo through the loggingWriter
_, err = io.Copy(loggingWriter{stream}, stream)
if err != nil {
panic(err)
}
//------------------------------
stream1, err := conn.OpenStream()
if err != nil {
panic(err)
}
message := "aaaaa"
fmt.Printf("2-Server: Sending '%s'\n", message)
_, err = stream1.Write([]byte(message))
//------------------------------
return err
}
func clientMain() error {
tlsConf := &tls.Config{
InsecureSkipVerify: true,
NextProtos: []string{"quic-echo-example"},
}
conn, err := quic.DialAddr(addr, tlsConf, nil)
if err != nil {
return err
}
stream, err := conn.OpenStreamSync(context.Background())
if err != nil {
return err
}
fmt.Printf("Client: Sending '%s'\n", message)
_, err = stream.Write([]byte(message))
if err != nil {
return err
}
buf := make([]byte, len(message))
_, err = io.ReadFull(stream, buf)
if err != nil {
return err
}
fmt.Printf("Client: Got '%s'\n", buf)
err = stream.Close()
if err != nil {
return err
}
//-------------------------------
for {
stream1, err := conn.AcceptStream(context.Background())
if err != nil {
panic(err)
}
buf1 := make([]byte, len(message))
_, err = io.ReadFull(stream1, buf1)
if err != nil {
panic(err)
}
fmt.Printf("2-Client: Got '%s'\n", buf1)
err = stream1.Close()
if err != nil {
panic(err)
}
}
//-------------------------------
return nil
}
// A wrapper for io.Writer that also logs the message.
type loggingWriter struct{ io.Writer }
func (w loggingWriter) Write(b []byte) (int, error) {
fmt.Printf("Server: Got '%s'\n", string(b))
return w.Writer.Write(b)
}
// Setup a bare-bones TLS config for the server
func generateTLSConfig() *tls.Config {
key, err := rsa.GenerateKey(rand.Reader, 1024)
if err != nil {
panic(err)
}
template := x509.Certificate{SerialNumber: big.NewInt(1)}
certDER, err := x509.CreateCertificate(rand.Reader, &template, &template, &key.PublicKey, key)
if err != nil {
panic(err)
}
keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)})
certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})
tlsCert, err := tls.X509KeyPair(certPEM, keyPEM)
if err != nil {
panic(err)
}
return &tls.Config{
Certificates: []tls.Certificate{tlsCert},
NextProtos: []string{"quic-echo-example"},
}
}
You are close.
Notice how the server writes, then returns, it reaches out to log.Fatal before the client had a chance to read and handle the data.
Take care to the message variable, one is 6 length long, the other one is only 5 length long.
Properly close your stream, the server was not ending it ending before handing over;
package main
import (
"context"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"encoding/pem"
"fmt"
"io"
"log"
"math/big"
"github.com/lucas-clemente/quic-go"
)
const addr = "localhost:4242"
const message = "foobar"
// We start a server echoing data on the first stream the client opens,
// then connect with a client, send the message, and wait for its receipt.
func main() {
go func() {
err := echoServer()
if err != nil {
log.Println(err)
}
}()
err := clientMain()
if err != nil {
panic(err)
}
}
// Start a server that echos all data on the first stream opened by the client
func echoServer() error {
listener, err := quic.ListenAddr(addr, generateTLSConfig(), nil)
if err != nil {
return err
}
conn, err := listener.Accept(context.Background())
if err != nil {
return err
}
stream, err := conn.AcceptStream(context.Background())
if err != nil {
panic(err)
}
// Echo through the loggingWriter
_, err = io.Copy(loggingWriter{stream}, stream)
if err != nil {
log.Println(err)
return err
}
//------------------------------
fmt.Printf("Server: open stream\n")
stream1, err := conn.OpenStream()
if err != nil {
return err
}
fmt.Printf("2-Server: Sending '%s'\n", message)
var n int
n, err = stream1.Write([]byte(message))
fmt.Printf("Server: write %v %v\n", n, err)
stream1.Close()
//------------------------------
return err
}
func clientMain() error {
tlsConf := &tls.Config{
InsecureSkipVerify: true,
NextProtos: []string{"quic-echo-example"},
}
conn, err := quic.DialAddr(addr, tlsConf, nil)
if err != nil {
return err
}
stream, err := conn.OpenStreamSync(context.Background())
if err != nil {
return err
}
fmt.Printf("Client: Sending '%s'\n", message)
_, err = stream.Write([]byte(message))
if err != nil {
return err
}
buf := make([]byte, len(message))
_, err = io.ReadFull(stream, buf)
if err != nil {
return err
}
fmt.Printf("Client: Got '%s'\n", buf)
err = stream.Close()
if err != nil {
return err
}
//-------------------------------
for {
fmt.Printf("Client: accept stream\n")
stream1, err := conn.AcceptStream(context.Background())
if err != nil {
return err
}
fmt.Printf("Client: got stream %v\n", err)
buf1 := make([]byte, len(message))
_, err = io.ReadFull(stream1, buf1)
if err != nil {
return err
}
fmt.Printf("2-Client: Got '%s'\n", buf1)
err = stream1.Close()
if err != nil {
return err
}
break
}
//-------------------------------
return nil
}
// A wrapper for io.Writer that also logs the message.
type loggingWriter struct{ io.Writer }
func (w loggingWriter) Write(b []byte) (int, error) {
fmt.Printf("Server: Got '%s'\n", string(b))
return w.Writer.Write(b)
}
// Setup a bare-bones TLS config for the server
func generateTLSConfig() *tls.Config {
key, err := rsa.GenerateKey(rand.Reader, 1024)
if err != nil {
panic(err)
}
template := x509.Certificate{SerialNumber: big.NewInt(1)}
certDER, err := x509.CreateCertificate(rand.Reader, &template, &template, &key.PublicKey, key)
if err != nil {
panic(err)
}
keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)})
certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})
tlsCert, err := tls.X509KeyPair(certPEM, keyPEM)
if err != nil {
panic(err)
}
return &tls.Config{
Certificates: []tls.Certificate{tlsCert},
NextProtos: []string{"quic-echo-example"},
}
}

How do I make it such that a TCP connection will timeout if the connection doesn't receive a response every second?

I'm trying to create a TCP server that will timeout if the client does not respond within the span of every second.
I tried:
func main() {
listener, err := net.Listen("tcp", "localhost:8000")
if err != nil {
log.Fatal(err)
}
for {
conn, err := listener.Accept()
conn.SetDeadline(time.Now().Add(timeout))
if err != nil {
log.Print(err)
}
go handleConn(conn)
}
}
where the timeout is a single second but the disconnects immediately, not even waiting for a reply.
What you want can be achieved by setting socket options on your listener. Tweak the values as per your needs
Note that this is its own KeepAlive and does not depend on incoming/outgoing data by application
func enableTCPKeepAlive(listener *net.TCPListener) error {
rawConn, err := listener.SyscallConn()
if err != nil {
return err
}
cfg := config.TLSServerConfig()
rawConn.Control(
func(fdPtr uintptr) {
// got socket file descriptor. Setting parameters.
fd := int(fdPtr)
//Idle time before sending probe.
err = syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, syscall.TCP_KEEPIDLE, cfg.TCPKAIdleTime)
if err != nil {
return err
}
//Number of probes.
err := syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, syscall.TCP_KEEPCNT, cfg.TCPKANumProbes)
if err != nil {
return err
}
//Wait time after an unsuccessful probe.
err = syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, syscall.TCP_KEEPINTVL, cfg.TCPKAInterval)
if err != nil {
return err
}
// go syscall doesn't have the constant 0x12 (18) for TCP_USER_TIMEOUT.
// 0x12 value referenced from linux kernel source code header:
// include/uapi/linux/tcp.h
err = syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, 0x12, cfg.TCPKAUserTimeout)
if err != nil {
return err
}
})
return nil
}
There are more options available than the ones I have mentioned above.
Call this function on your listener before the for loop.
func main() {
listener, err := net.Listen("tcp", "localhost:8000")
if err != nil {
log.Fatal(err)
}
err = enableTCPKeepAlive(listener)
if err != nil {
log.Fatal(err)
}
for {
conn, err := listener.Accept()
conn.SetDeadline(time.Now().Add(timeout))
if err != nil {
log.Print(err)
}
go handleConn(conn)
}
}
The problem is almost always in code that is not posted here. The function obviously works like a charme:
package main
import (
"crypto/rand"
"log"
"net"
"time"
)
func main() {
listener, err := net.Listen("tcp", "localhost:8000")
if err != nil {
log.Fatal(err)
}
go func() {
for {
conn, err := listener.Accept()
if err != nil {
log.Print(err)
return
}
go func(c net.Conn) {
defer c.Close()
conn.SetDeadline(time.Now().Add(2 * time.Second))
if err != nil {
log.Print(err)
return
}
buf := make([]byte, 1<<19) // 512 KB
for {
_, err := conn.Read(buf)
if err != nil {
log.Print(err)
break
}
}
}(conn)
}
}()
payload := make([]byte, 1<<20)
_, err = rand.Read(payload) // generate a random payload
if err != nil {
log.Print(err)
}
conn, err := net.Dial("tcp", listener.Addr().String())
if err != nil {
log.Fatal(err)
}
log.Println("Connected to server.")
time.Sleep(5 * time.Second)
_, err = conn.Write(payload)
if err != nil {
log.Print(err)
}
listener.Close()
}

reading golang websocket returns random bytes

My program:
package main
import (
"fmt"
"io"
"log"
"net"
"github.com/gobwas/ws"
)
func HandleConn(conn net.Conn) {
for {
header, err := ws.ReadHeader(conn)
if err != nil {
log.Fatal(err)
}
buf := make([]byte, header.Length)
_, err = io.ReadFull(conn, buf)
if err != nil {
log.Fatal(err)
}
fmt.Println(buf)
fmt.Println(string(buf))
}
}
func main() {
ln, err := net.Listen("tcp", "localhost:8080")
if err != nil {
log.Fatal(err)
}
for {
conn, err := ln.Accept()
if err != nil {
log.Fatal(err)
}
_, err = ws.Upgrade(conn)
if err != nil {
log.Fatal(err)
}
go HandleConn(conn)
}
}
I do in browser console:
let socket = new WebSocket("ws://127.0.0.1:8080")
socket.send("Hello world")
I see random bytes in the my terminal. Each call to socket.send("Hello world") return different bytes. But the length of the byte array is always equal to the length of the string. Where does golang get these random bytes? How can I fix this? My program is an example from the docs.
If you are going to not use the wsutil you need to unmask the payload:
buff := make([]byte, header.Length)
_, err = io.ReadFull(conn, buff)
if err != nil {
// handle error
}
if header.Masked {
ws.Cipher(buff, header.Mask, 0)
}
fmt.Println(string(buff))

Channels in Golang with TCP/IP socket not working

I just started writting a Golang client for a server that I've made in C with TCP/IP sockets, then I figured out that my channel wasn't working.
Any ideas why ?
func reader(r io.Reader, channel chan<- []byte) {
buf := make([]byte, 2048)
for {
n, err := r.Read(buf[:])
if err != nil {
return
}
channel <- buf[0:n]
}
}
func client(e *gowd.Element) {
f, err := os.Create("/tmp/dat2")
if err != nil {
log.Fatal()
}
read := make(chan []byte)
c, err := net.Dial("tcp", "127.0.0.1:4242")
if err != nil {
log.Fatal(err)
}
go reader(c, read)
for {
buf := <-read
n := strings.Index(string(buf), "\n")
if n == -1 {
continue
}
msg := string(buf[0:n])
if msg == "WELCOME" {
fmt.Fprint(c, "GRAPHIC\n")
}
f.WriteString(msg + "\n")
}
Testing my server with netcat results in the following output :
http://pasted.co/a37b2954
But i only have : http://pasted.co/f13d56b4
I'm new to chan in Golang so maybe I'm wrong (I probably am)
Channel usage looks alright, however retrieving value from channel would overwrite previously read value at buf := <-read since your waiting for newline.
Also you can use bufio.Reader to read string upto newline.
Your code snippet is partial so its not feasible to execute, try and let me know:
func reader(r io.Reader, channel chan<- string) {
bufReader := bufio.NewReader(conn)
for {
msg, err := bufReader.ReadString('\n')
if err != nil { // connection error or connection reset error, etc
break
}
channel <- msg
}
}
func client(e *gowd.Element) {
f, err := os.Create("/tmp/dat2")
if err != nil {
log.Fatal()
}
read := make(chan string)
c, err := net.Dial("tcp", "127.0.0.1:4242")
if err != nil {
log.Fatal(err)
}
go reader(c, read)
for {
msg := <-read
if msg == "WELCOME" {
fmt.Fprint(c, "GRAPHIC\n")
}
f.WriteString(msg + "\n")
}
//...
}
EDIT:
Please find example of generic TCP client to read data. Also I have removed scanner from above code snippet and added buffer reader.
func main() {
conn, err := net.Dial("tcp", "127.0.0.1:4242")
if err != nil {
log.Fatal(err)
}
reader := bufio.NewReader(conn)
for {
msg, err := reader.ReadString('\n')
if err != nil {
break
}
fmt.Println(msg)
}
}

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