net/smtp: ignore HELO error in QUIT

Fixes #70011

Change-Id: I9d8b3ffbd66561eee0efffd54038960acd5fcf64
Reviewed-on: https://go-review.googlesource.com/c/go/+/622476
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/net/smtp/smtp.go

@@ -413,9 +413,7 @@ func (c *Client) Noop() error {
 
 // Quit sends the QUIT command and closes the connection to the server.
 func (c *Client) Quit() error {
-	if err := c.hello(); err != nil {
+	c.hello() // ignore error; we're quitting anyhow
-		return err
-	}
 	_, _, err := c.cmd(221, "QUIT")
 	if err != nil {
 		return err

src/net/smtp/smtp_test.go

@@ -288,6 +288,37 @@ Goodbye.
 QUIT
 `
 
+func TestHELOFailed(t *testing.T) {
+	serverLines := `502 EH?
+502 EH?
+221 OK
+`
+	clientLines := `EHLO localhost
+HELO localhost
+QUIT
+`
+
+	server := strings.Join(strings.Split(serverLines, "\n"), "\r\n")
+	client := strings.Join(strings.Split(clientLines, "\n"), "\r\n")
+	var cmdbuf strings.Builder
+	bcmdbuf := bufio.NewWriter(&cmdbuf)
+	var fake faker
+	fake.ReadWriter = bufio.NewReadWriter(bufio.NewReader(strings.NewReader(server)), bcmdbuf)
+	c := &Client{Text: textproto.NewConn(fake), localName: "localhost"}
+
+	if err := c.Hello("localhost"); err == nil {
+		t.Fatal("expected EHLO to fail")
+	}
+	if err := c.Quit(); err != nil {
+		t.Errorf("QUIT failed: %s", err)
+	}
+	bcmdbuf.Flush()
+	actual := cmdbuf.String()
+	if client != actual {
+		t.Errorf("Got:\n%s\nWant:\n%s", actual, client)
+	}
+}
+
 func TestExtensions(t *testing.T) {
 	fake := func(server string) (c *Client, bcmdbuf *bufio.Writer, cmdbuf *strings.Builder) {
 		server = strings.Join(strings.Split(server, "\n"), "\r\n")