dissertation-2-code/tcp/flow.go

package tcp

import (
	"bufio"
	"encoding/binary"
	"fmt"
	"io"
	"mpbl3p/proxy"
	"mpbl3p/shared"
	"net"
	"sync"
	"time"
)

type Conn interface {
	Read(b []byte) (n int, err error)
	Write(b []byte) (n int, err error)
	SetWriteDeadline(time.Time) error

	// For printing
	LocalAddr() net.Addr
	RemoteAddr() net.Addr
}

type InitiatedFlow struct {
	Local  func() string
	Remote string

	mu sync.RWMutex

	Flow
}

func (f *InitiatedFlow) String() string {
	return fmt.Sprintf("TcpOutbound{%v -> %v}", f.Local(), f.Remote)
}

type Flow struct {
	conn    Conn
	isAlive bool

	toConsume, produced          chan []byte
	consumeErrors, produceErrors chan error
}

func NewFlow() Flow {
	return Flow{
		toConsume:     make(chan []byte),
		produced:      make(chan []byte),
		consumeErrors: make(chan error),
		produceErrors: make(chan error),
	}
}

func NewFlowConn(conn Conn) Flow {
	f := Flow{
		conn:    conn,
		isAlive: true,

		toConsume:     make(chan []byte),
		produced:      make(chan []byte),
		consumeErrors: make(chan error),
		produceErrors: make(chan error),
	}

	go f.produceMarshalled()
	go f.consumeMarshalled()

	return f
}

func (f Flow) String() string {
	return fmt.Sprintf("TcpInbound{%v -> %v}", f.conn.RemoteAddr(), f.conn.LocalAddr())
}

func (f *Flow) IsAlive() bool {
	return f.isAlive
}

func InitiateFlow(local func() string, remote string) (*InitiatedFlow, error) {
	f := InitiatedFlow{
		Local:  local,
		Remote: remote,

		Flow: NewFlow(),
	}

	return &f, nil
}

func (f *InitiatedFlow) Reconnect() error {
	f.mu.Lock()
	defer f.mu.Unlock()

	if f.isAlive {
		return nil
	}

	localAddr, err := net.ResolveTCPAddr("tcp", f.Local())
	if err != nil {
		return err
	}

	remoteAddr, err := net.ResolveTCPAddr("tcp", f.Remote)
	if err != nil {
		return err
	}

	conn, err := net.DialTCP("tcp", localAddr, remoteAddr)
	if err != nil {
		return err
	}

	if err := conn.SetWriteBuffer(0); err != nil {
		return err
	}

	f.conn = conn
	f.isAlive = true

	go f.produceMarshalled()
	go f.consumeMarshalled()

	return nil
}

func (f *InitiatedFlow) Consume(p proxy.Packet, g proxy.MacGenerator) error {
	f.mu.RLock()
	defer f.mu.RUnlock()

	return f.Flow.Consume(p, g)
}

func (f *InitiatedFlow) Produce(v proxy.MacVerifier) (proxy.Packet, error) {
	f.mu.RLock()
	defer f.mu.RUnlock()

	return f.Flow.Produce(v)
}

func (f *Flow) Consume(p proxy.Packet, g proxy.MacGenerator) error {
	if !f.isAlive {
		return shared.ErrDeadConnection
	}

	select {
	case err := <-f.consumeErrors:
		f.isAlive = false
		return err
	default:
	}

	marshalled := p.Marshal()
	data := proxy.AppendMac(marshalled, g)

	prefixedData := make([]byte, len(data)+4)
	binary.LittleEndian.PutUint32(prefixedData, uint32(len(data)))
	copy(prefixedData[4:], data)

	f.toConsume <- prefixedData
	return nil
}

func (f *Flow) Produce(v proxy.MacVerifier) (proxy.Packet, error) {
	if !f.isAlive {
		return nil, shared.ErrDeadConnection
	}

	var data []byte

	select {
	case data = <-f.produced:
	case err := <-f.produceErrors:
		f.isAlive = false
		return nil, err
	}

	b, err := proxy.StripMac(data, v)
	if err != nil {
		return nil, err
	}

	return proxy.SimplePacket(b), nil
}

func (f *Flow) consumeMarshalled() {
	for {
		data := <-f.toConsume

		err := f.conn.SetWriteDeadline(time.Now().Add(5 * time.Second))
		if err != nil {
			f.consumeErrors <- err
			return
		}
		_, err = f.conn.Write(data)
		if err != nil {
			f.consumeErrors <- err
			return
		}
	}
}

func (f *Flow) produceMarshalled() {
	buf := bufio.NewReader(f.conn)

	for {
		lengthBytes := make([]byte, 4)
		if n, err := io.LimitReader(buf, 4).Read(lengthBytes); err != nil {
			f.produceErrors <- err
			return
		} else if n != 4 {
			f.produceErrors <- shared.ErrNotEnoughBytes
			return
		}

		length := binary.LittleEndian.Uint32(lengthBytes)
		dataBytes := make([]byte, length)

		var read uint32
		for read < length {
			if n, err := io.LimitReader(buf, int64(length-read)).Read(dataBytes[read:]); err != nil {
				f.produceErrors <- err
				return
			} else {
				read += uint32(n)
			}
		}

		f.produced <- dataBytes
	}
}