import "github.com/go-gost/gosocks4"

func handleConnection(conn net.Conn) {
    req, err := gosocks4.ReadRequest(conn)
    if err != nil {
        // handle error
    }

    if req.Cmd == gosocks4.CmdConnect {
        // Dial the target
        target, _ := net.Dial("tcp", req.Addr.String())

        // Reply granted with the bound address
        reply := gosocks4.NewReply(gosocks4.Granted, &gosocks4.Addr{
            Type: gosocks4.AddrIPv4,
            Host: "0.0.0.0",
            Port: 0,
        })
        reply.Write(conn)

        // Relay traffic
        // ...
    }
}

req := gosocks4.NewRequest(gosocks4.CmdConnect, &gosocks4.Addr{
    Type: gosocks4.AddrIPv4,
    Host: "93.184.216.34",
    Port: 80,
}, []byte("userid"))

err := req.Write(conn)

req := gosocks4.NewRequest(gosocks4.CmdConnect, &gosocks4.Addr{
    Type: gosocks4.AddrDomain,
    Host: "example.com",
    Port: 443,
}, []byte("userid"))

err := req.Write(conn)

reply, err := gosocks4.ReadReply(conn)
switch reply.Code {
case gosocks4.Granted:
    // Connection granted
case gosocks4.Failed, gosocks4.Rejected:
    // Request rejected
case gosocks4.RejectedUserid:
    // Auth failure
}

type Addr struct {
    Type int      // AddrIPv4 or AddrDomain
    Host string   // IPv4 address or hostname
    Port uint16   // Destination port
}

type Request struct {
    Cmd    uint8   // CmdConnect or CmdBind
    Addr   *Addr   // Destination address
    Userid []byte  // User identifier
}

type Reply struct {
    Code uint8   // Granted, Failed, Rejected, RejectedUserid
    Addr *Addr   // Bound address
}