Forked the emersion/go-imap v1 project.

imapclient/starttls.go

@@ -0,0 +1,83 @@
+package imapclient
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/tls"
+	"io"
+	"net"
+)
+
+// startTLS sends a STARTTLS command.
+//
+// Unlike other commands, this method blocks until the command completes.
+func (c *Client) startTLS(config *tls.Config) error {
+	upgradeDone := make(chan struct{})
+	cmd := &startTLSCommand{
+		tlsConfig:   config,
+		upgradeDone: upgradeDone,
+	}
+	enc := c.beginCommand("STARTTLS", cmd)
+	enc.flush()
+	defer enc.end()
+
+	// Once a client issues a STARTTLS command, it MUST NOT issue further
+	// commands until a server response is seen and the TLS negotiation is
+	// complete
+
+	if err := cmd.wait(); err != nil {
+		return err
+	}
+
+	// The decoder goroutine will invoke Client.upgradeStartTLS
+	<-upgradeDone
+
+	return cmd.tlsConn.Handshake()
+}
+
+// upgradeStartTLS finishes the STARTTLS upgrade after the server has sent an
+// OK response. It runs in the decoder goroutine.
+func (c *Client) upgradeStartTLS(startTLS *startTLSCommand) {
+	defer close(startTLS.upgradeDone)
+
+	// Drain buffered data from our bufio.Reader
+	var buf bytes.Buffer
+	if _, err := io.CopyN(&buf, c.br, int64(c.br.Buffered())); err != nil {
+		panic(err) // unreachable
+	}
+
+	var cleartextConn net.Conn
+	if buf.Len() > 0 {
+		r := io.MultiReader(&buf, c.conn)
+		cleartextConn = startTLSConn{c.conn, r}
+	} else {
+		cleartextConn = c.conn
+	}
+
+	tlsConn := tls.Client(cleartextConn, startTLS.tlsConfig)
+	rw := c.options.wrapReadWriter(tlsConn)
+
+	c.br.Reset(rw)
+	// Unfortunately we can't re-use the bufio.Writer here, it races with
+	// Client.StartTLS
+	c.bw = bufio.NewWriter(rw)
+
+	startTLS.tlsConn = tlsConn
+}
+
+type startTLSCommand struct {
+	commandBase
+	tlsConfig *tls.Config
+
+	upgradeDone chan<- struct{}
+	tlsConn     *tls.Conn
+}
+
+type startTLSConn struct {
+	net.Conn
+	r io.Reader
+}
+
+func (conn startTLSConn) Read(b []byte) (int, error) {
+	return conn.r.Read(b)
+}