Sending a CSV file Server to Client - go

Question

I've just recently started trying to learn Go and I'm trying to write a small server/client application for sending a csv file, from a server to a client. I'm running into an invalid type error when trying to encode a struct into BigEndian binary. My struct seems to already be in a binary format, I'm unsure why I get the following error:
Error writing binary buffer to big endian binary.Write: invalid type *main.DataPack
Also, I'd like to keep the TCP connection open after sending the file, that's why I'm not using io.Copy.
Currently I'm triggering the handling of the file upload through by sending a '\x00' byte:
// Server
package main
import (
"path/filepath"
"fmt"
"io/ioutil"
"net"
"os"
"encoding/binary"
"bytes"
)
type DataPack struct {
Length int64
Contents []byte
}
func main() {
absPath, _ := filepath.Abs("./progs.csv")
data, _ := ioutil.ReadFile(absPath)
fmt.Println("%s",data)
tel, err := net.Listen("tcp", "0.0.0.0:23")
if err != nil {
fmt.Println(err)
return
}
for {
conn, err := tel.Accept()
if err != nil {
break
}
fmt.Println("above filehandler")
go fileHandler(conn)
}
}
func fileHandler(conn net.Conn) {
buf := make([]byte, 0)
buf = append(buf, '\x00')
conn.Write(buf)
absPath, _ := filepath.Abs("./progs.csv")
file, err := os.Open(absPath)
defer file.Close()
fi, err := file.Stat()
if err != nil {
fmt.Println("Fatal error reading file: ", err)
}
fmt.Println("This is the length of the file: ", fi.Size())
data := &DataPack{Length: fi.Size()} // , Contents: }
data.Contents = make([]byte, data.Length)
n, err := file.Read(data.Contents)
if err != nil {
fmt.Println("error reading contents into struct: ", err)
}
fmt.Println("tried to read file contents: ", n)
fmt.Println("DataPack: %+v", data)
buf1 := new(bytes.Buffer)
err = binary.Write(buf1, binary.BigEndian, &data)
if err != nil {
fmt.Println("Error writing binary buffer to big endian ", err)
}
conn.Write(buf1.Bytes())
}
Here is the client
package main
import (
"log"
"fmt"
"net"
"strings"
"strconv"
"bufio"
)
const (
host = "127.0.0.1"
port = 23
)
func main() {
addr := strings.Join([]string{host, strconv.Itoa(port)}, ":")
client := NewClient()
var err error
client.socket, err = net.Dial("tcp", addr)
if err != nil {
log.Println("error setting up socket: %s", err)
}
for {
m := bufio.NewReader(client.socket)
b, err := m.ReadByte()
if err != nil {
fmt.Println("here is the error: ", err)
}
if b == '\x00'{
fmt.Println("about to receive a file!!!")
b, _ := m.ReadByte()
fmt.Println("just got another byte ", b )
}
}
log.Printf("Over")
}

Answer 1

why you get the error
Visit https://golang.org/pkg/encoding/binary/#Write
Write writes the binary representation of data into w. Data must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
type DataPack struct {
Length int64
Contents []byte
}
Contents isn't a fixed-size value, so you got the invalid type error.
how to solve it
go binary
json
others