tracked: add connection tracker wrapper based on connfu

Use builder pattern to return implementation with only required features.
Use connfu to handle CloseWrite() and ReadFrom() propagation.

go.mod

@@ -1,6 +1,6 @@
 module github.com/saucelabs/forwarder
 
-go 1.23
+go 1.23.1
 
 require (
 	github.com/dop251/goja v0.0.0-20231027120936-b396bb4c349d
@@ -11,6 +11,7 @@ require (
 	github.com/kevinburke/hostsfile v0.0.0-20220522040509-e5e984885321
 	github.com/mitchellh/go-wordwrap v1.0.1
 	github.com/mmatczuk/anyflag v0.0.0-20240709090339-eb9e24cd1b44
+	github.com/mmatczuk/connfu v0.0.0-20241015064402-db8989f89d8c
 	github.com/prometheus/client_golang v1.20.5
 	github.com/prometheus/client_model v0.6.1
 	github.com/prometheus/common v0.60.0

go.sum

@@ -67,6 +67,8 @@ github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyua
 github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
 github.com/mmatczuk/anyflag v0.0.0-20240709090339-eb9e24cd1b44 h1:Ds9W8Yj5ti4kQXITpCozfNNibS1fUA8+aK2T5th0vXE=
 github.com/mmatczuk/anyflag v0.0.0-20240709090339-eb9e24cd1b44/go.mod h1:PT22bA6vWBzPL8tAeK2XCMvWOQ4e19yY3MJIgnTZRaE=
+github.com/mmatczuk/connfu v0.0.0-20241015064402-db8989f89d8c h1:1CC7JKZjrhe2AQh2T0Tay4j9Pp7HQl3WYpQvZr/ceA0=
+github.com/mmatczuk/connfu v0.0.0-20241015064402-db8989f89d8c/go.mod h1:atoMPmvjynZBBUEoYWCM/ZnXAzZ9RoAnihm7YKXK/nY=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/pelletier/go-toml/v2 v2.2.2 h1:aYUidT7k73Pcl9nb2gScu7NSrKCSHIDE89b3+6Wq+LM=

tracked/tracked.go

@@ -0,0 +1,142 @@
+// Copyright 2022-2024 Sauce Labs Inc., all rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package tracked
+
+import (
+	"io"
+	"net"
+	"sync"
+	"sync/atomic"
+
+	"github.com/mmatczuk/connfu"
+)
+
+// ConnObserver allows to observe the number of bytes read and written from a connection.
+type ConnObserver struct {
+	rx atomic.Uint64
+	tx atomic.Uint64
+}
+
+// Rx returns the number of bytes read from the connection.
+// It requires TrackTraffic to be set to true, otherwise it returns 0.
+func (o *ConnObserver) Rx() uint64 {
+	return o.rx.Load()
+}
+
+// Tx returns the number of bytes written to the connection.
+// It requires TrackTraffic to be set to true, otherwise it returns 0.
+func (o *ConnObserver) Tx() uint64 {
+	return o.tx.Load()
+}
+
+func (o *ConnObserver) addRx(n uint64) {
+	o.rx.Add(n)
+}
+
+func (o *ConnObserver) addTx(n uint64) {
+	o.tx.Add(n)
+}
+
+type closeConn struct {
+	net.Conn
+	l closeListener // this is a field to avoid ambiguous selector error on Close method
+}
+
+func (c *closeConn) Close() error {
+	return c.l.Close()
+}
+
+type closeListener struct {
+	close   func() error
+	once    sync.Once
+	onClose func()
+}
+
+func (c *closeListener) Close() error {
+	err := c.close()
+	c.once.Do(c.onClose)
+	return err
+}
+
+// conn is a net.Conn that tracks the number of bytes read and written.
+// It needs to be configured before first use by setting TrackTraffic and onClose if needed.
+type conn struct {
+	net.Conn
+	o ConnObserver
+}
+
+func (c *conn) Read(p []byte) (n int, err error) {
+	n, err = c.Conn.Read(p)
+	c.o.addRx(uint64(n))
+	return
+}
+
+func (c *conn) Write(p []byte) (n int, err error) {
+	n, err = c.Conn.Write(p)
+	c.o.addTx(uint64(n))
+	return
+}
+
+func (c *conn) ReadFrom(r io.Reader) (n int64, err error) {
+	n, err = c.Conn.(io.ReaderFrom).ReadFrom(r)
+	c.o.addTx(uint64(n))
+	return
+}
+
+type Builder struct {
+	// TrackTraffic enables counting of bytes read and written by the connection.
+	// Use Rx and Tx to get the number of bytes read and written.
+	TrackTraffic bool
+
+	// OnClose is called after the underlying connection is closed and before the Close method returns.
+	// OnClose is called at most once.
+	OnClose func()
+}
+
+func (b Builder) Build(c net.Conn) (net.Conn, *ConnObserver) {
+	var (
+		wc net.Conn
+		co *ConnObserver
+	)
+
+	if b.TrackTraffic {
+		if b.OnClose != nil {
+			cc := &struct {
+				conn
+				closeListener
+			}{
+				conn: conn{Conn: c},
+				closeListener: closeListener{
+					close:   c.Close,
+					onClose: b.OnClose,
+				},
+			}
+			wc = cc
+			co = &cc.conn.o
+		} else {
+			cc := &conn{
+				Conn: c,
+			}
+			wc = cc
+			co = &cc.o
+		}
+	} else {
+		if b.OnClose == nil {
+			wc = c
+		} else {
+			wc = &closeConn{
+				Conn: c,
+				l: closeListener{
+					close:   c.Close,
+					onClose: b.OnClose,
+				},
+			}
+		}
+	}
+
+	return connfu.Combine(wc, c), co
+}

tracked/tracked_test.go

@@ -0,0 +1,73 @@
+// Copyright 2022-2024 Sauce Labs Inc., all rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package tracked
+
+import (
+	"crypto/tls"
+	"io"
+	"net"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+type closeWriter interface {
+	CloseWrite() error
+}
+
+func TestBuildTCP(t *testing.T) {
+	wc, co := Builder{TrackTraffic: true}.Build(new(net.TCPConn))
+	if co == nil {
+		t.Error("Expected a connection observer")
+	}
+	if _, ok := wc.(io.ReaderFrom); ok != (strings.HasPrefix(runtime.GOOS, "linux")) {
+		t.Error("ReaderFrom missmatch")
+	}
+	if _, ok := wc.(io.WriterTo); ok {
+		t.Error("Unexpected WriterTo")
+	}
+	if _, ok := wc.(closeWriter); !ok {
+		t.Error("Missing CloseWrite")
+	}
+}
+
+func TestBuildTLS(t *testing.T) {
+	wc, co := Builder{TrackTraffic: true}.Build(new(tls.Conn))
+	if co == nil {
+		t.Error("Expected a connection observer")
+	}
+	if _, ok := wc.(io.ReaderFrom); ok {
+		t.Error("Unexpected ReaderFrom")
+	}
+	if _, ok := wc.(io.WriterTo); ok {
+		t.Error("Unexpected WriterTo")
+	}
+	if _, ok := wc.(closeWriter); !ok {
+		t.Error("Missing CloseWrite")
+	}
+}
+
+func TestBuildOnClose(t *testing.T) {
+	var closed bool
+	wc, co := Builder{OnClose: func() { closed = true }}.Build(new(net.TCPConn))
+	if co != nil {
+		t.Error("Unexpected connection observer")
+	}
+	if _, ok := wc.(io.ReaderFrom); ok {
+		t.Error("Unexpected ReaderFrom")
+	}
+	if _, ok := wc.(io.WriterTo); ok {
+		t.Error("Unexpected WriterTo")
+	}
+	if _, ok := wc.(closeWriter); !ok {
+		t.Error("Missing CloseWrite")
+	}
+	wc.Close()
+	if !closed {
+		t.Error("OnClose not called")
+	}
+}