golang : network response from ioutil.ReadAll() is empty, connection reset by peer

Question

I'm trying to test out performing a simple TCP MODBUS read of a single register from a device emulator. When running the code it is showing a response of 0 bytes and I get the message "connection reset by peer". Any ideas as to why it's not working?

UPDATE, my request was incorrect, the correct working MODBUS TCP poll code is:

package main

import (
    "fmt"
    "net"
)

// TCP MODBUS client
func main() {
    conn, err := net.Dial("tcp", "192.168.98.114:502")
    if err != nil {
        fmt.Println(err)
    }
    numRegs := 1
    # make a MODBUS TCP request (be careful, the format is different to MODBUS serial)
    request := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x06, 0x01, 0x03, 0x00, 0x01, 0x00, 0x01}
    n, err := conn.Write(request)
    if err != nil {
        fmt.Println(err)
    }
    expectedResponseLen := 5 + 2 * numRegs
    response := make([]byte, expectedResponseLen)
    n, err = conn.Read(response)
    conn.Close()
    if err != nil {
        fmt.Println(err)
    }
    for i := 0; i < n; i++ {
        fmt.Printf("%02x ", response[i])
    }
    fmt.Println("\n")
}

Answer 1

Originally I thought that fmt.Fprintf may be changing the request data on the way out, but this example seems to work OK.

However, I would still recommend using the lower-level Write/Read instead of fmt.Fprintf/ioutil.ReadAll:

req := []byte { 0x01, 0x03, 0x00, 0x01, 0x00, 0x01, 0xd5, 0xca }

n, err := conn.Write(req)

if err != nil {
    fmt.Println("write error:", err)
    return
}

fmt.Printf("wrote %d bytes for request: %#v", n, req)

rsp := make([]byte, 64)

n, err = conn.Read(rsp)

fmt.Printf("received %d bytes in response: %#v", n, rsp[:n])

if err != nil {
    fmt.Println("read error:", err)
}