ftp: attempt to fix zero length files with TLS - FIXME DO NOT MERGE DIRECTLY

In https://github.com/jlaffaye/ftp/commit/212daf295f the upstream FTP
library changed the way adding your own dialer works which meant that
connections when using explicit FTP were failing.

This patch reworks our connection code to bring it into the
expectations of the library.

backend/ftp/ftp.go

@@ -336,14 +336,44 @@ func (f *Fs) ftpConnection(ctx context.Context) (c *ftp.ServerConn, err error) {
 	fs.Debugf(f, "Connecting to FTP server")
 
 	// Make ftp library dial with fshttp dialer optionally using TLS
+	initialConnection := true
 	dial := func(network, address string) (conn net.Conn, err error) {
+		fs.Debugf(f, "dial(%q,%q)", network, address)
+		defer func() {
+			fs.Debugf(f, "> dial: conn=%T, err=%v", conn, err)
+		}()
 		conn, err = fshttp.NewDialer(ctx).Dial(network, address)
-		if f.tlsConf != nil && err == nil {
-			conn = tls.Client(conn, f.tlsConf)
+		if err != nil {
+			return nil, err
 		}
-		return
+		// Connect using cleartext only for non TLS
+		if f.tlsConf == nil {
+			return conn, nil
+		}
+		// Initial connection only needs to be cleartext for explicit TLS
+		if f.opt.ExplicitTLS && initialConnection {
+			initialConnection = false
+			return conn, nil
+		}
+		// Upgrade connection to TLS
+		tlsConn := tls.Client(conn, f.tlsConf)
+		// Do the initial handshake - tls.Client doesn't do it for us
+		// If we do this then connections to proftpd/pureftpd lock up
+		// See: https://github.com/rclone/rclone/issues/6426
+		// See: https://github.com/jlaffaye/ftp/issues/282
+		if false {
+			err = tlsConn.HandshakeContext(ctx)
+			if err != nil {
+				_ = conn.Close()
+				return nil, err
+			}
+		}
+		return tlsConn, nil
+	}
+	ftpConfig := []ftp.DialOption{
+		ftp.DialWithContext(ctx),
+		ftp.DialWithDialFunc(dial),
 	}
-	ftpConfig := []ftp.DialOption{ftp.DialWithDialFunc(dial)}
 
 	if f.opt.TLS {
 		// Our dialer takes care of TLS but ftp library also needs tlsConf
@@ -351,12 +381,6 @@ func (f *Fs) ftpConnection(ctx context.Context) (c *ftp.ServerConn, err error) {
 		ftpConfig = append(ftpConfig, ftp.DialWithTLS(f.tlsConf))
 	} else if f.opt.ExplicitTLS {
 		ftpConfig = append(ftpConfig, ftp.DialWithExplicitTLS(f.tlsConf))
-		// Initial connection needs to be cleartext for explicit TLS
-		conn, err := fshttp.NewDialer(ctx).Dial("tcp", f.dialAddr)
-		if err != nil {
-			return nil, err
-		}
-		ftpConfig = append(ftpConfig, ftp.DialWithNetConn(conn))
 	}
 	if f.opt.DisableEPSV {
 		ftpConfig = append(ftpConfig, ftp.DialWithDisabledEPSV(true))

go.mod

@@ -2,6 +2,8 @@ module github.com/rclone/rclone
 
 go 1.17
 
+replace github.com/jlaffaye/ftp v0.0.0-20220904184306-99be0634ab9a => github.com/ncw/ftp v0.0.0-20220916150959-909597844e2a
+
 require (
 	bazil.org/fuse v0.0.0-20200524192727-fb710f7dfd05
 	github.com/Azure/azure-pipeline-go v0.2.3

go.sum

@@ -378,10 +378,6 @@ github.com/jcmturner/rpc/v2 v2.0.3 h1:7FXXj8Ti1IaVFpSAziCZWNzbNuZmnvw/i6CqLNdWfZ
 github.com/jcmturner/rpc/v2 v2.0.3/go.mod h1:VUJYCIDm3PVOEHw8sgt091/20OJjskO/YJki3ELg/Hc=
 github.com/jellevandenhooff/dkim v0.0.0-20150330215556-f50fe3d243e1/go.mod h1:E0B/fFc00Y+Rasa88328GlI/XbtyysCtTHZS8h7IrBU=
 github.com/jlaffaye/ftp v0.0.0-20190624084859-c1312a7102bf/go.mod h1:lli8NYPQOFy3O++YmYbqVgOcQ1JPCwdOy+5zSjKJ9qY=
-github.com/jlaffaye/ftp v0.0.0-20220630165035-11536801d1ff h1:tN6UCYCBFNrPwvKf4RP9cIhGo6GcZ/IQTN8nqD7eCok=
-github.com/jlaffaye/ftp v0.0.0-20220630165035-11536801d1ff/go.mod h1:hhq4G4crv+nW2qXtNYcuzLeOudG92Ps37HEKeg2e3lE=
-github.com/jlaffaye/ftp v0.0.0-20220904184306-99be0634ab9a h1:s4ryRQyC5HKZh6qkjNAFcvmD7gImK5bZuj/YZkXy1vw=
-github.com/jlaffaye/ftp v0.0.0-20220904184306-99be0634ab9a/go.mod h1:hhq4G4crv+nW2qXtNYcuzLeOudG92Ps37HEKeg2e3lE=
 github.com/jmespath/go-jmespath v0.4.0 h1:BEgLn5cpjn8UN1mAw4NjwDrS35OdebyEtFe+9YPoQUg=
 github.com/jmespath/go-jmespath v0.4.0/go.mod h1:T8mJZnbsbmF+m6zOOFylbeCJqk5+pHWvzYPziyZiYoo=
 github.com/jmespath/go-jmespath/internal/testify v1.5.1 h1:shLQSRRSCCPj3f2gpwzGwWFoC7ycTf1rcQZHOlsJ6N8=
@@ -460,6 +456,8 @@ github.com/modern-go/reflect2 v1.0.2/go.mod h1:yWuevngMOJpCy52FWWMvUC8ws7m/LJsjY
 github.com/mschoch/smat v0.0.0-20160514031455-90eadee771ae/go.mod h1:qAyveg+e4CE+eKJXWVjKXM4ck2QobLqTDytGJbLLhJg=
 github.com/mwitkow/go-conntrack v0.0.0-20161129095857-cc309e4a2223/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
 github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
+github.com/ncw/ftp v0.0.0-20220916150959-909597844e2a h1:BglfrImWBkK0SyMLSsKmAgutB0rzkoLzt5j5Sjn+heg=
+github.com/ncw/ftp v0.0.0-20220916150959-909597844e2a/go.mod h1:hhq4G4crv+nW2qXtNYcuzLeOudG92Ps37HEKeg2e3lE=
 github.com/ncw/go-acd v0.0.0-20201019170801-fe55f33415b1 h1:nAjWYc03awJAjsozNehdGZsm5LP7AhLOvjgbS8zN1tk=
 github.com/ncw/go-acd v0.0.0-20201019170801-fe55f33415b1/go.mod h1:MLIrzg7gp/kzVBxRE1olT7CWYMCklcUWU+ekoxOD9x0=
 github.com/ncw/swift/v2 v2.0.1 h1:q1IN8hNViXEv8Zvg3Xdis4a3c4IlIGezkYz09zQL5J0=