refactor: move tracex outside of engine/netx (#782)

* refactor: move tracex outside of engine/netx

Consistently with https://github.com/ooni/probe/issues/2121 and
https://github.com/ooni/probe/issues/2115, we can now move tracex
outside of engine/netx. The main reason why this makes sense now
is that the package is now changed significantly from the one
that we imported from ooni/probe-engine.

We have improved its implementation, which had not been touched
significantly for quite some time, and converted it to unit
testing. I will document tomorrow some extra work I'd like to
do with this package but likely could not do $soon.

* go fmt

* regen tutorials

internal/engine/netx/tracex/dialer.go

@@ -1,159 +0,0 @@
-package tracex
-
-//
-// TCP and connected UDP sockets
-//
-
-import (
-	"context"
-	"net"
-	"time"
-
-	"github.com/ooni/probe-cli/v3/internal/model"
-)
-
-// DialerSaver saves events occurring during the dial
-type DialerSaver struct {
-	// Dialer is the underlying dialer,
-	Dialer model.Dialer
-
-	// Saver saves events.
-	Saver *Saver
-}
-
-// NewConnectObserver returns a DialerWrapper that observes the
-// connect event. This function will return nil, which is a valid
-// DialerWrapper for netxlite.WrapDialer, if Saver is nil.
-func (s *Saver) NewConnectObserver() model.DialerWrapper {
-	if s == nil {
-		return nil // valid DialerWrapper according to netxlite's docs
-	}
-	return &dialerConnectObserver{
-		saver: s,
-	}
-}
-
-type dialerConnectObserver struct {
-	saver *Saver
-}
-
-var _ model.DialerWrapper = &dialerConnectObserver{}
-
-func (w *dialerConnectObserver) WrapDialer(d model.Dialer) model.Dialer {
-	return &DialerSaver{
-		Dialer: d,
-		Saver:  w.saver,
-	}
-}
-
-// DialContext implements Dialer.DialContext
-func (d *DialerSaver) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
-	start := time.Now()
-	conn, err := d.Dialer.DialContext(ctx, network, address)
-	stop := time.Now()
-	d.Saver.Write(&EventConnectOperation{&EventValue{
-		Address:  address,
-		Duration: stop.Sub(start),
-		Err:      err,
-		Proto:    network,
-		Time:     stop,
-	}})
-	return conn, err
-}
-
-func (d *DialerSaver) CloseIdleConnections() {
-	d.Dialer.CloseIdleConnections()
-}
-
-// DialerConnSaver wraps the returned connection such that we
-// collect all the read/write events that occur.
-type DialerConnSaver struct {
-	// Dialer is the underlying dialer
-	Dialer model.Dialer
-
-	// Saver saves events
-	Saver *Saver
-}
-
-// NewReadWriteObserver returns a DialerWrapper that observes the
-// I/O events. This function will return nil, which is a valid
-// DialerWrapper for netxlite.WrapDialer, if Saver is nil.
-func (s *Saver) NewReadWriteObserver() model.DialerWrapper {
-	if s == nil {
-		return nil // valid DialerWrapper according to netxlite's docs
-	}
-	return &dialerReadWriteObserver{
-		saver: s,
-	}
-}
-
-type dialerReadWriteObserver struct {
-	saver *Saver
-}
-
-var _ model.DialerWrapper = &dialerReadWriteObserver{}
-
-func (w *dialerReadWriteObserver) WrapDialer(d model.Dialer) model.Dialer {
-	return &DialerConnSaver{
-		Dialer: d,
-		Saver:  w.saver,
-	}
-}
-
-// DialContext implements Dialer.DialContext
-func (d *DialerConnSaver) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
-	conn, err := d.Dialer.DialContext(ctx, network, address)
-	if err != nil {
-		return nil, err
-	}
-	return &dialerConnWrapper{saver: d.Saver, Conn: conn}, nil
-}
-
-func (d *DialerConnSaver) CloseIdleConnections() {
-	d.Dialer.CloseIdleConnections()
-}
-
-type dialerConnWrapper struct {
-	net.Conn
-	saver *Saver
-}
-
-func (c *dialerConnWrapper) Read(p []byte) (int, error) {
-	proto := c.Conn.RemoteAddr().Network()
-	remoteAddr := c.Conn.RemoteAddr().String()
-	start := time.Now()
-	count, err := c.Conn.Read(p)
-	stop := time.Now()
-	c.saver.Write(&EventReadOperation{&EventValue{
-		Address:  remoteAddr,
-		Data:     p[:count],
-		Duration: stop.Sub(start),
-		Err:      err,
-		NumBytes: count,
-		Proto:    proto,
-		Time:     stop,
-	}})
-	return count, err
-}
-
-func (c *dialerConnWrapper) Write(p []byte) (int, error) {
-	proto := c.Conn.RemoteAddr().Network()
-	remoteAddr := c.Conn.RemoteAddr().String()
-	start := time.Now()
-	count, err := c.Conn.Write(p)
-	stop := time.Now()
-	c.saver.Write(&EventWriteOperation{&EventValue{
-		Address:  remoteAddr,
-		Data:     p[:count],
-		Duration: stop.Sub(start),
-		Err:      err,
-		NumBytes: count,
-		Proto:    proto,
-		Time:     stop,
-	}})
-	return count, err
-}
-
-var _ model.Dialer = &DialerSaver{}
-var _ model.Dialer = &DialerConnSaver{}
-var _ net.Conn = &dialerConnWrapper{}