I have a problem with Golang, what I'm trying to do is open a TCP connection with a transaction server, execute command then get the output.
I'm used to send the command using nc :
printf "COMMAND HERE" | nc HOST PORT
For the golang wrapper in dev, This is my current code :
TransCommand := "printf \"cmd:list_cmds\\ncommit:1\\nend\\n\""
conn, err := net.Dial("tcp", hostName+":"+portNum)
if err != nil {
fmt.Println(err)
return
}
_, err = conn.Write([]byte(TransCommand))
if err != nil {
println("Write to server failed:", err.Error())
os.Exit(1)
}
println("Writing to Trans : ", TransCommand)
reply := make([]byte, 4096)
_, err = conn.Read(reply)
if err != nil {
println("Write to Trans server failed:", err.Error())
os.Exit(1)
}
println("Response from Trans : ", string(reply))
fmt.Println(ioutil.ReadAll(conn))
conn.Close()
It only returns an output saying that TCP connection is open, I use the same logic in a Ruby GEM, and it works great :
def tcp_send_and_receive(native)
socket = TCPSocket.new(#host, #port)
while line = socket.gets
break if line == "220 CONNECTED.\n"
end
socket.write(native)
native_reply = socket.read
native_reply
end
Is there any difference between Golang and the Ruby implementation ? if not can I stimulate the execution of the command using a TCP connection to the server ?
Related
I'm testing a function I have that gets all azure vms under a specific subscription.
It uses azure sdk for go's compute.VirtualMachinesClient to do so.
My problem is with the vm clients ListAllComplete function.
It's not returning an error. The code just doesn't seem to be able to make it passed that line.
Any suggestions on the source of the problem would be appreciated.
This is the code, I've used the fmt package to follow how far it gets:
func GetAllAzureVms() ([]compute.VirtualMachine, error) {
fmt.Printf("In getAllAzureVm\n")
var vmList []compute.VirtualMachine
vmClient, err := GetAzureVmClient()
fmt.Printf("Out of GetAzureVmClient\n")
if err != nil {
return nil, err
}
fmt.Print("No error from getazurevmclient\n")
vmListComplete, err := vmClient.ListAllComplete(context.Background(), "statusOnly=false")
fmt.Print("vmClient.ListAllComplete done")
if err != nil {
fmt.Print("vmClient.ListAllComplete error")
return nil, err
}
fmt.Print("here")
for vmListComplete.NotDone() {
vmList = append(vmList, vmListComplete.Value())
err := vmListComplete.NextWithContext(context.Background())
if err != nil {
return nil, err
}
}
fmt.Print("here2")
return vmList, nil
}
It cant make it passed the line:
vmListComplete, err := vmClient.ListAllComplete(context.Background(), "statusOnly=false")
No error is returned.
I have a similar piece of code, not for vmClient unluckily, but for securityCustomRules.
What I've found useful was to use ListComplete() instead of ListAll() and the print values through JSON marhsalling.
I hope you can find it useful anyway.
import (
"context"
"fmt"
"os"
"testing"
"github.com/gruntwork-io/terratest/modules/azure"
"github.com/gruntwork-io/terratest/modules/terraform"
)
securityCustomRulesList, err := securityCustomRulesClient.ListComplete(context.Background(), tfResourceGroupName, tfVnetName+"-"+fmt.Sprint(vnetIndex)+"-subnet-02-nsg")
// - Scan iterator items [https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/services/network/mgmt/2019-09-01/network#ApplicationGatewayListResultIterator]
if err != nil {
fmt.Fprintf(os.Stderr, ">>>> Error parsing securityCustomRulesClient:: %s", err)
return
}
for securityCustomRulesList.NotDone() {
// securityCustomRulesList.Value() -> securityRule [https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/services/network/mgmt/2019-09-01/network#SecurityRule]
v := securityCustomRulesList.Value()
vJson, _ := v.MarshalJSON()
fmt.Printf(">> Network securityCustomRulesList JSON %s \n", string(vJson))
//fmt.Printf(">> Network securityCustomRulesList %s - %s\n", *v.Name, *v.SecurityRulePropertiesFormat.Description)
securityCustomRulesList.NextWithContext(context.Background())
}
Which gives me an output like:
>> Creating security custom rules list instance 'securityCustomRulesList'..
>> Network securityCustomRulesList JSON {"id":"/subscriptions/8f7d6be2/resourceGroups/unit-tests-tfm-azure-network-resource-group/providers/Microsoft.Network/networkSecurityGroups/unit-tests-tfm-azure-network-vnet-0-subnet-02-nsg/securityRules/test-02","name":"test-02","properties":{"access":"Deny","description":"Deny access","destinationAddressPrefix":"10.0.2.1","destinationAddressPrefixes":[],"destinationPortRange":"*","destinationPortRanges":[],"direction":"Inbound","priority":111,"protocol":"*","sourceAddressPrefix":"10.0.1.0/24","sourceAddressPrefixes":[],"sourcePortRange":"*","sourcePortRanges":[]}}
Useful links:
Here you can find a complete usage example from the official terratest/azure module: https://github.com/gruntwork-io/terratest/blob/dae956eb39e91dfb00f3ba85060a6dbf58c6782b/modules/azure/nsg.go
https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/services/network/mgmt/2019-09-01/network#SecurityRule.MarshalJSON
When I try to create more than 99 TCP connections in less than a millisecond from my local computer with a TCP listener running at a DigitalOcean droplet with Ubuntu, only 99 of them works and rest says connectex: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. Sending the same amount of connection requests to multiple ports seem to work okay.
I already tried to increase tcp_max_syn_backlog and somaxconn but it didn't help. I tried to track TcpExtListenOverflows and TcpExtListenDrops but they don't seem to be increasing as well. I tried to do the same thing with another server to make sure the problem is not about my local computer. I also contacted to DigitalOcean support and they told they are not aware of any hard limits placed by their infrastructure.
Can anyone give me any pointers to create more than 99 TCP connections in less than a millisecond with a single port at an Ubuntu server and a single remote IP?
Scripts I'm using:
Listener:
package main
import (
"log"
"net"
)
const port = "1919"
func main() {
listener, err := net.Listen("tcp", ":"+port)
if err != nil {
log.Fatal(err)
}
for {
_, err := listener.Accept()
if err != nil {
log.Fatal(err)
}
}
}
Dialer:
package main
import (
"fmt"
"net"
"sync"
)
const ConnectionCount = 250
const raddr = "<IP_ADDRESS_IS_INSERTED_HERE>:1919"
func main() {
wg := &sync.WaitGroup{}
mu := &sync.Mutex{}
var success, fail int
for i := 0; i < ConnectionCount; i++ {
wg.Add(1)
go func() {
defer wg.Done()
_, err := net.Dial("tcp", raddr)
mu.Lock()
defer mu.Unlock()
if err == nil {
success++
} else {
fail++
}
fmt.Print("\033[2K\rSuccess: ", success, ", Fail: ", fail)
}()
}
wg.Wait()
}
Output is always 99 Success and 151 Fail. Tried to same thing with direct HTTP requests as well, still only 99 of them works if they are sent at the same time.
I have a device with a GPRS onboard. GPRS connects with the third-party application and it works. I need to know the signal strength of the connection, so, I use ATZ, then AT+CSQ commands. When I work using some terminal software it works. Then, I had tried to use https://github.com/ishuah/bifrost soft as a terminal. It works as well. But how can I simply communicate with a device, not using terminal, without re-connection or connection abortion, etc?
I tried simply echo ATZ > /dev/ttyX - no answer
// This writes, but reads only zeros (((
package main
import (
"github.com/jacobsa/go-serial/serial"
"io"
"log"
"time"
"fmt"
)
func Sleep(duration int) {
time.Sleep(time.Second * time.Duration(duration))
}
func printBuf(b []byte){
for _, val:=range b {
fmt.Printf("%x ", val)
}
}
func main(){
options := serial.OpenOptions{
PortName: "/dev/ttyX",
BaudRate: 115200,
DataBits: 8,
StopBits: 1,
MinimumReadSize: 0,
InterCharacterTimeout: 50,
}
port, err := serial.Open(options)
if err != nil {
log.Printf("port.Read: %v", err)
return
}
// Make sure to close it later.
defer port.Close()
var s string = `AT+CSQ`
b:=[]byte(s)
n, err := port.Write(b)
if err != nil {
log.Printf("port.Write: %v", err)
}
log.Println("Written bytes: ", n)
//Sleep(1)
res := make([]byte, 64)
n, err = port.Read(res)
if err != nil && err != io.EOF {
log.Printf("port.Read: %v", err)
}
log.Println("READ bytes: ", n)
printBuf(res)
}
/*
I expect (for example):
---------
ATZ
OK
AT+CSQ
+CSQ 22.4
*/
Most serial devices need a termination character to react to the commands they receive.
If you add it, your code should work:
var s string = `AT+CSQ\r`
I don't see any other differences from your code and sending a command using a serial terminal. The same should apply when you echo the command directly onto the port file descriptor.
Recently I have been trying to create a program in golang, which runs on a server, and accepts telnet connections. I would then like to open a TUI (text user interface) such as a curses menu (in the case of golang, something like: termui, gocui, etc) over that telnet connection. My question is, how exactly could I do this and/or would it even be possible? I have played around trying to start TUIs when a connection is accepted, but it just opens it on the server side, not on the telnet client side. From what I can tell, there is no easy way to just send a TUI over a telnet or any other socket IO connection for that matter.
Any help is appreciated in trying to figure this out. Thanks! :D
First, you should note that the example I give is completely insecure (don't expose it over the Internet!) and also doesn't provide for things like signal handling or resizing of the terminal (you may want to consider using SSH instead).
But to answer your question, here is an example of running a TCP server and connecting remote clients to a termui program running in a local PTY (uses both the https://github.com/gizak/termui and https://github.com/kr/pty packages):
package main
import (
"flag"
"io"
"log"
"net"
"os"
"os/exec"
ui "github.com/gizak/termui"
"github.com/kr/pty"
)
var termuiFlag = flag.Bool("termui", false, "run a termui example")
func main() {
flag.Parse()
var err error
if *termuiFlag {
err = runTermui()
} else {
err = runServer()
}
if err != nil {
log.Fatal(err)
}
}
// runTermui runs the termui "Hello World" example.
func runTermui() error {
if err := ui.Init(); err != nil {
return err
}
defer ui.Close()
p := ui.NewParagraph("Hello World!")
p.Width = 25
p.Height = 5
ui.Render(p)
for e := range ui.PollEvents() {
if e.Type == ui.KeyboardEvent {
break
}
}
return nil
}
// runServer listens for TCP connections on a random port and connects
// remote clients to a local PTY running the termui example.
func runServer() error {
ln, err := net.Listen("tcp", "127.0.0.1:0")
if err != nil {
return err
}
defer ln.Close()
log.Printf("Listening for requests on %v", ln.Addr())
for {
conn, err := ln.Accept()
if err != nil {
return err
}
log.Printf("Connecting remote client %v to termui", conn.RemoteAddr())
go connectTermui(conn)
}
}
// connectTermui connects a client connection to a termui process running in a
// PTY.
func connectTermui(conn net.Conn) {
defer func() {
log.Printf("Closing remote client %v", conn.RemoteAddr())
conn.Close()
}()
t, err := pty.StartWithSize(
exec.Command(os.Args[0], "--termui"),
&pty.Winsize{Cols: 80, Rows: 24},
)
if err != nil {
log.Printf("Error starting termui: %v", err)
return
}
defer t.Close()
go io.Copy(t, conn)
io.Copy(conn, t)
}
Example usage is to run this program in one window and connect to it using nc in another:
$ go run server.go
2019/01/18 01:39:37 Listening for requests on 127.0.0.1:56192
$ nc 127.0.0.1 56192
You should see the "Hello world" box (hit enter to disconnect).
I'm trying to make a simple command forwarder to connect my home computer to a server I own, so that I can push commands to my server and my home pc gets it. Those commands are simple pause/resume for my downloader. My design is, that on a server, I run a hub instance, which creates a window for passing commands and a window for backend to pass those commands to my pc. I'm bounding those two "windows" with a channel, they run a server. When a client connects and sends a message to the hub, it gets streamed through a channel to backend window and then to the real backend (on my home pc). When backend responds to the backend window on the hub, the hub prints the result back to the client.
With this approach, only the first message passes and works with my downloader. I have to reconnect the backend from my home pc with the hub each time I get a message to get this working properly. I don't think that's the proper way with websockets, so here I am. After one successful request (when the backend finishes it's work and replies the result), it gets looped forever with EOF error.
The important parts of the code are:
main executable
hub handlers
backend connector
If you put the source in your GOPATH (i'm developing it for the tip version of go to support modern websockets), to compile it:
go build gosab/cmd, to run it:
./cmd -mode="hub" hub
./cmd -mode="backend" --address="localhost:8082" backend
To pass messages to the hub, use this javascript:
var s = new WebSocket("ws://localhost:8082")
s.send("1 5")
So how do I handle it? Are channels a good way to communicate between two different requests?
I'm surprised you haven't received an answer to this.
What you need to do is something like the code below. When you receive an incoming websocket connection, a new goroutine is spawned for that connection. If you let that goroutine end, it'll disconnect the websocket client.
I'm making an assumption that you're not necessarily going to be running the client and server on the same computer. If you always are, then it'd be better to do the communication internally via channels or such instead of using websockets or a network port. I only mention this because I'm not completely sure what you're using this for. I just hope I answered the right part of your question.
package main
import (
"code.google.com/p/go.net/websocket"
"flag"
"fmt"
"net/http"
"os"
"time"
)
type Message struct {
RequestID int
Command string
SomeOtherThing string
Success bool
}
var mode *string = flag.String("mode", "<nil>", "Mode: server or client")
var address *string = flag.String("address", "localhost:8080", "Bind address:port")
func main() {
flag.Parse()
switch *mode {
case "server":
RunServer()
case "client":
RunClient()
default:
flag.Usage()
}
}
func RunServer() {
http.Handle("/", http.FileServer(http.Dir("www")))
http.Handle("/server", websocket.Handler(WSHandler))
fmt.Println("Starting Server")
err := http.ListenAndServe(*address, nil)
if err != nil {
fmt.Printf("HTTP failed: %s\n", err.Error())
os.Exit(1)
}
}
func WSHandler(ws *websocket.Conn) {
defer ws.Close()
fmt.Println("Client Connected")
for {
var message Message
err := websocket.JSON.Receive(ws, &message)
if err != nil {
fmt.Printf("Error: %s\n", err.Error())
return
}
fmt.Println(message)
// do something useful here...
response := new(Message)
response.RequestID = message.RequestID
response.Success = true
response.SomeOtherThing = "The hot dog left the castle as requested."
err = websocket.JSON.Send(ws, response)
if err != nil {
fmt.Printf("Send failed: %s\n", err.Error())
os.Exit(1)
}
}
}
func RunClient() {
fmt.Println("Starting Client")
ws, err := websocket.Dial(fmt.Sprintf("ws://%s/server", *address), "", fmt.Sprintf("http://%s/", *address))
if err != nil {
fmt.Printf("Dial failed: %s\n", err.Error())
os.Exit(1)
}
incomingMessages := make(chan Message)
go readClientMessages(ws, incomingMessages)
i := 0
for {
select {
case <-time.After(time.Duration(2e9)):
i++
response := new(Message)
response.RequestID = i
response.Command = "Eject the hot dog."
err = websocket.JSON.Send(ws, response)
if err != nil {
fmt.Printf("Send failed: %s\n", err.Error())
os.Exit(1)
}
case message := <-incomingMessages:
fmt.Println(message)
}
}
}
func readClientMessages(ws *websocket.Conn, incomingMessages chan Message) {
for {
var message Message
err := websocket.JSON.Receive(ws, &message)
if err != nil {
fmt.Printf("Error: %s\n", err.Error())
return
}
incomingMessages <- message
}
}