Read whole data with Golang net.Conn.Read - go

Question

So I'm building a network app in Go and I've seen that Conn.Read reads into a limited byte array, which I had created with make([]byte, 2048) and now the problem is that I don't know the exact length of the content, so it could be too much or not enough.
My question is how can I just read the exact amount of data. I think I have to use bufio, but I'm not sure.

Answer 1

It highly depends on what you're trying to do, and what kind of data you're expecting, for example if you just want to read until the EOF you could use something like this:
func main() {
conn, err := net.Dial("tcp", "google.com:80")
if err != nil {
fmt.Println("dial error:", err)
return
}
defer conn.Close()
fmt.Fprintf(conn, "GET / HTTP/1.0\r\n\r\n")
buf := make([]byte, 0, 4096) // big buffer
tmp := make([]byte, 256) // using small tmo buffer for demonstrating
for {
n, err := conn.Read(tmp)
if err != nil {
if err != io.EOF {
fmt.Println("read error:", err)
}
break
}
//fmt.Println("got", n, "bytes.")
buf = append(buf, tmp[:n]...)
}
fmt.Println("total size:", len(buf))
//fmt.Println(string(buf))
}
//edit: for completeness sake and #fabrizioM's great suggestion, which completely skipped my mind:
func main() {
conn, err := net.Dial("tcp", "google.com:80")
if err != nil {
fmt.Println("dial error:", err)
return
}
defer conn.Close()
fmt.Fprintf(conn, "GET / HTTP/1.0\r\n\r\n")
var buf bytes.Buffer
io.Copy(&buf, conn)
fmt.Println("total size:", buf.Len())
}

Answer 2

You can use the ioutil.ReadAll function:
import (
"fmt"
"io/ioutil"
"net"
)
func whois(domain, server string) ([]byte, error) {
conn, err := net.Dial("tcp", server+":43")
if err != nil {
return nil, err
}
defer conn.Close()
fmt.Fprintf(conn, "%s\r\n", domain)
return ioutil.ReadAll(conn)
}

Answer 3

You can read data something like this:
// import net/textproto
import ("net/textproto", ...)
....
reader := bufio.NewReader(Conn)
tp := textproto.NewReader(reader)
defer Conn.Close()
for {
// read one line (ended with \n or \r\n)
line, _ := tp.ReadLine()
// do something with data here, concat, handle and etc...
}
....