// Package socks contains protocol definition and io lib for SOCKS5 protocol
package socks

import (
  "fmt"
  "io"
)

const (
  socksVersion = uint8(5)
)

// Authentication request header of Socks5 protocol
type Socks5AuthenticationRequest struct {
  version byte
  authMethods [256]byte
}

func ReadAuthentication(reader io.Reader) (auth Socks5AuthenticationRequest, err error) {
  buffer := make([]byte, 2)
  nBytes, err := reader.Read(buffer)
  if err != nil {
    return
  }
  if nBytes < 2 {
    err = fmt.Errorf("Expected 2 bytes read, but actaully %d bytes read", nBytes)
    return
  }
  
  auth.version = buffer[0]
  if auth.version != socksVersion {
    err = fmt.Errorf("Unknown SOCKS version %d", auth.version)
    return
  }
  
  nMethods := buffer[1]
  if nMethods <= 0 {
    err = fmt.Errorf("Zero length of authentication methods")
    return
  }
  
  buffer = make([]byte, nMethods)
  nBytes, err = reader.Read(buffer)
  copy(auth.authMethods[:nBytes], buffer)
  return
}

type Socks5AuthenticationResponse struct {
  version byte
  authMethod byte
}

func (r *Socks5AuthenticationResponse) ToBytes() []byte {
  buffer := make([]byte, 2 /* size of Socks5AuthenticationResponse */)
  buffer[0] = r.version
  buffer[1] = r.authMethod
  return buffer
}

func WriteAuthentication(writer io.Writer, response Socks5AuthenticationResponse) error {
  _, err := writer.Write(response.ToBytes())
  if err != nil {
    return err
  }
  return nil
}