net: Conn.Close() does not error on double close on wasm

[johanbrandhorst]

Does this issue reproduce with the latest release?

Yes

What did you do?

Tried to write a test that checks whether a net.Conn is already closed by checking that calling Close returns an error and run it on wasm. See

go/src/crypto/tls/handshake_server_test.go

Lines 1980 to 1982 in 5d5f779

	if runtime.GOARCH == "wasm" {
	t.Skip("conn.Close does not error as expected when called multiple times on WASM")
	}

for the current workaround.

What did you expect to see?

An error suggesting that the connection has already been closed, as is consistent with all other architectures tested.

What did you see instead?

No error.

Discussion

I think the offending code is here:

go/src/net/net_fake.go

Lines 110 to 115 in 5d5f779

	func (fd *netFD) Close() error {
	fd.closedMu.Lock()
	if fd.closed {
	fd.closedMu.Unlock()
	return nil
	}

On unix platforms the behaviour is to return internal/poll.ErrNetClosing or internal/pool.ErrFileClosing:

go/src/internal/poll/fd_unix.go

Lines 93 to 96 in 5d5f779

	func (fd *FD) Close() error {
	if !fd.fdmu.increfAndClose() {
	return errClosing(fd.isFile)
	}

go/src/internal/poll/fd.go

Lines 42 to 47 in 5d5f779

	func errClosing(isFile bool) error {
	if isFile {
	return ErrFileClosing
	}
	return ErrNetClosing
	}

[johanbrandhorst]

@neelance