From 1509996c093e41a76be6ad5fd9429f100d65f60c Mon Sep 17 00:00:00 2001
From: James Barnett <noreply@jamesbarnett.xyz>
Date: Sun, 23 Dec 2018 20:30:06 +0000
Subject: Add basic TCP proxy with injected latency

---
 slowpoke.go | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 slowpoke.go

(limited to 'slowpoke.go')

diff --git a/slowpoke.go b/slowpoke.go
new file mode 100644
index 0000000..3178196
--- /dev/null
+++ b/slowpoke.go
@@ -0,0 +1,112 @@
+package slowpoke
+
+import (
+	"io"
+	"net"
+	"time"
+
+	"github.com/op/go-logging"
+)
+
+type Slowpoke struct {
+	conn       net.Conn
+	targetAddr string
+	latency    time.Duration
+	isClosed   bool
+	close      chan bool
+	logger     *logging.Logger
+}
+
+func New(conn net.Conn, targetAddr string, latency time.Duration, logger *logging.Logger) *Slowpoke {
+	return &Slowpoke{
+		conn:       conn,
+		targetAddr: targetAddr,
+		latency:    latency,
+		isClosed:   false,
+		close:      make(chan bool),
+		logger:     logger,
+	}
+}
+
+func (s *Slowpoke) StartTransfer() {
+	defer s.conn.Close()
+	target, err := net.Dial("tcp", s.targetAddr)
+	if err != nil {
+		// TODO validate target addr before this point
+		s.logger.Errorf("Failed to connect to target address %s:\n%v", s.targetAddr, err)
+		return
+	}
+	defer target.Close()
+	s.logger.Debugf("Established connection to %s", target.RemoteAddr())
+
+	go s.transferWithLatency(s.conn, target)
+	go s.transferWithLatency(target, s.conn)
+
+	<-s.close
+
+	s.logger.Infof("Connection between client %s and target %s closed", s.conn.RemoteAddr(), target.RemoteAddr())
+}
+
+func createBuffer() []byte {
+	// TODO configurable
+	return make([]byte, 1500)
+}
+
+func (s *Slowpoke) transferWithLatency(source net.Conn, target net.Conn) {
+	byteBuffer := createBuffer()
+
+	var transferDirection string
+	// If the data source is the client then we are sending
+	if source == s.conn {
+		transferDirection = "%d bytes sent"
+	} else {
+		transferDirection = "%d bytes received"
+	}
+
+	for {
+
+		bytesRead, readError := source.Read(byteBuffer)
+
+		if bytesRead > 0 {
+
+			if s.latency != 0 {
+				s.logger.Debugf(transferDirection+" with latency of %s", bytesRead, s.latency)
+				time.Sleep(s.latency)
+			} else {
+				s.logger.Debugf(transferDirection, bytesRead)
+			}
+
+			bytesWritten, writeError := target.Write(byteBuffer[0:bytesRead])
+
+			if writeError != nil {
+				s.handleError("Error during write: %v", writeError)
+				break
+			}
+			if bytesRead != bytesWritten {
+				s.logger.Warningf("Read %d bytes but could only write %d bytes", bytesRead, bytesWritten)
+			}
+		}
+		if readError != nil {
+			s.handleError("Error during read: %v", readError)
+			break
+		}
+	}
+
+}
+
+func (s *Slowpoke) handleError(msg string, err error) {
+	if s.isClosed {
+		// One of the send/receive streams was already closed. Nothing to do.
+		return
+	}
+
+	s.isClosed = true
+	s.close <- true
+
+	if err == io.EOF {
+		// EOF is expected and not really an error
+		s.logger.Debug("Received EOF")
+	} else {
+		s.logger.Errorf(msg, err)
+	}
+}
-- 
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