imapserver: Prevent spurious test failures due to compression layer being closed and TLS close-writes failing

imapclient/client.go

@@ -170,10 +170,20 @@ func (c *Conn) xflush() {
 	}
 }
 
+// SetPanic sets whether errors cause a panic instead of returning errors.
+func (c *Conn) SetPanic(panic bool) {
+	c.panic = panic
+}
+
 // Close closes the connection, flushing and closing any compression and TLS layer.
 //
 // You may want to call Logout first. Closing a connection with a mailbox with
 // deleted messages not yet expunged will not expunge those messages.
+//
+// Closing a TLS connection that is logged out, or closing a TLS connection with
+// compression enabled (i.e. two layered streams), may cause spurious errors
+// because the server may immediate close the underlying connection when it sees
+// the connection is being closed.
 func (c *Conn) Close() (rerr error) {
 	defer c.recover(&rerr)
 

imapserver/compress_test.go

@@ -40,6 +40,11 @@ func TestCompressStartTLS(t *testing.T) {
 	tc.transactf("ok", "append inbox (\\seen) {%d+}\r\n%s", len(exampleMsg), exampleMsg)
 	tc.transactf("ok", "noop")
 	tc.transactf("ok", "fetch 1 body.peek[1]")
+
+	// Prevent client.Close from failing the test. The client first closes the
+	// compression stream, which causes the server to close the connection, after which
+	// the messages to close the TLS connection are written to a closed socket.
+	tc.client.SetPanic(false)
 }
 
 func TestCompressBreak(t *testing.T) {