feat: use handshake context when possible (#199)

This is a port of GoogleCloudPlatform/cloud-sql-go-connector#427.

connect_tls_117.go

@@ -0,0 +1,44 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build go1.17
+// +build go1.17
+
+package alloydbconn
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+
+	"cloud.google.com/go/alloydbconn/errtype"
+	"cloud.google.com/go/alloydbconn/internal/alloydb"
+)
+
+// connectTLS returns a new TLS client side connection
+// using conn as the underlying transport.
+//
+// The returned connection has already completed its TLS handshake.
+func connectTLS(ctx context.Context, conn net.Conn, c *tls.Config, i *alloydb.Instance) (net.Conn, error) {
+	tlsConn := tls.Client(conn, c)
+	// HandshakeContext was introduced in Go 1.17, hence
+	// this file is conditionally compiled on only Go versions >= 1.17.
+	if err := tlsConn.HandshakeContext(ctx); err != nil {
+		// refresh the instance info in case it caused the handshake failure
+		i.ForceRefresh()
+		_ = tlsConn.Close() // best effort close attempt
+		return nil, errtype.NewDialError("handshake failed", i.String(), err)
+	}
+	return tlsConn, nil
+}

connect_tls_other.go

@@ -0,0 +1,42 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !go1.17
+// +build !go1.17
+
+package alloydbconn
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+
+	"cloud.google.com/go/alloydbconn/errtype"
+	"cloud.google.com/go/alloydbconn/internal/alloydb"
+)
+
+// connectTLS returns a new TLS client side connection
+// using conn as the underlying transport.
+//
+// The returned connection has already completed its TLS handshake.
+func connectTLS(_ context.Context, conn net.Conn, c *tls.Config, i *alloydb.Instance) (net.Conn, error) {
+	tlsConn := tls.Client(conn, c)
+	if err := tlsConn.Handshake(); err != nil {
+		// refresh the instance info in case it caused the handshake failure
+		i.ForceRefresh()
+		_ = tlsConn.Close() // best effort close attempt
+		return nil, errtype.NewDialError("handshake failed", i.String(), err)
+	}
+	return tlsConn, nil
+}

dialer.go

@@ -18,7 +18,6 @@ import (
 	"context"
 	"crypto/rand"
 	"crypto/rsa"
-	"crypto/tls"
 	_ "embed"
 	"fmt"
 	"net"
@@ -194,12 +193,9 @@ func (d *Dialer) Dial(ctx context.Context, instance string, opts ...DialOption)
 			return nil, errtype.NewDialError("failed to set keep-alive period", i.String(), err)
 		}
 	}
-	tlsConn := tls.Client(conn, tlsCfg)
-	if err := tlsConn.Handshake(); err != nil {
-		// refresh the instance info in case it caused the handshake failure
-		i.ForceRefresh()
-		_ = tlsConn.Close() // best effort close attempt
-		return nil, errtype.NewDialError("handshake failed", i.String(), err)
+	tlsConn, err := connectTLS(ctx, conn, tlsCfg, i)
+	if err != nil {
+		return nil, err
 	}
 	latency := time.Since(startTime).Milliseconds()
 	go func() {