fix: cancel netconn contexts after close handshake

[ethanndickson]

This fixes a failed to get reader: failed to read frame header: EOF error we saw in coder/coder when upgrading to a version of the library where these contexts were cancelled during netConn.Close (>= v1.8.8).

This problem appears to happen when netConn.c.Close(...) is called after context cancellation causes nc.c.close() to be called (via Conn.timeoutLoop).

I really would've liked to fully understand why this problem was occurring on coder/coder, but following our usage of the library in the few testcases that this happens is incredibly difficult (as they're effectively fully end-to-end tests), and I was unable to produce an MRE for this bug despite my best efforts.

[mafredri]

Thanks for the PR @ethanndickson!

I wanted to see if we're potentially causing a regression with this change and it looks like if read or write is open during Close, this change will block those.

Just some fairly simple tests:

	t.Run("netConn2", func(t *testing.T) {
		tt, c1, c2 := newConnTest(t, nil, nil)

		n1 := websocket.NetConn(tt.ctx, c1, websocket.MessageBinary)
		n2 := websocket.NetConn(tt.ctx, c2, websocket.MessageBinary)

		done := make(chan struct{})
		go func() {
			defer close(done)
			_, err := n1.Read(make([]byte, 1))
			assert.Equal(t, "read error", err, io.EOF)
		}()

		time.Sleep(time.Millisecond * 100)
		t.Log("closing n1")
		err := n1.Close()
		t.Log("closed n1")
		assert.Success(t, err)
		err = n2.Close()
		assert.Success(t, err)
		<-done
	})

	t.Run("netConn3", func(t *testing.T) {
		tt, c1, c2 := newConnTest(t, nil, nil)

		n1 := websocket.NetConn(tt.ctx, c1, websocket.MessageBinary)
		n2 := websocket.NetConn(tt.ctx, c2, websocket.MessageBinary)

		done := make(chan struct{})
		go func() {
			defer close(done)
			_, err := n1.Write(bytes.Repeat([]byte("hello"), 32*1024))
			assert.Equal(t, "write error", err, io.EOF)
		}()

		time.Sleep(time.Millisecond * 100)
		t.Log("closing n1")
		err := n1.Close()
		t.Log("closed n1")
		assert.Success(t, err)
		err = n2.Close()
		assert.Success(t, err)
		<-done
	})

Before:

❯ go test . -run=TestConn/netConn'[2-3]'
--- FAIL: TestConn (0.00s)
    --- FAIL: TestConn/netConn2 (0.10s)
        conn_test.go:199: closing n1
        conn_test.go:195: unexpected read error: expected &fmt.wrapError{msg:"failed to get reader: context canceled", err:(*errors.errorString)(0xc0000e62d0)} but got &errors.errorString{s:"EOF"}
        conn_test.go:201: closed n1
        conn_test.go:204: failed to close WebSocket: failed to write control frame opClose: failed to write frame: failed to flush: io: read/write on closed pipe
    --- FAIL: TestConn/netConn3 (0.10s)
        conn_test.go:222: closing n1
        conn_test.go:218: unexpected write error: expected &fmt.wrapError{msg:"failed to write msg: failed to write frame: context canceled", err:(*fmt.wrapError)(0xc0002a4060)} but got &errors.errorString{s:"EOF"}
        conn_test.go:224: closed n1
        conn_test.go:227: failed to close WebSocket: failed to write control frame opClose: failed to write frame: failed to flush: io: read/write on closed pipe
FAIL
FAIL	github.com/coder/websocket	0.107s
FAIL

After:

❯ go test . -run=TestConn/netConn'[2-3]'
--- FAIL: TestConn (0.00s)
    --- FAIL: TestConn/netConn3 (5.11s)
        conn_test.go:222: closing n1
        conn_test.go:218: unexpected write error: expected &fmt.wrapError{msg:"failed to write msg: failed to write frame: use of closed network connection", err:(*fmt.wrapError)(0xc0003b40a0)} but got &errors.errorString{s:"EOF"}
        conn_test.go:224: closed n1
        conn_test.go:225: failed to close WebSocket: failed to write control frame opClose: failed to acquire lock: context deadline exceeded
    --- FAIL: TestConn/netConn2 (5.11s)
        conn_test.go:199: closing n1
        conn_test.go:195: unexpected read error: expected &fmt.wrapError{msg:"failed to get reader: use of closed network connection", err:poll.errNetClosing{}} but got &errors.errorString{s:"EOF"}
        conn_test.go:201: closed n1
        conn_test.go:204: failed to close WebSocket: failed to write control frame opClose: failed to write frame: failed to flush: io: read/write on closed pipe
FAIL
FAIL	github.com/coder/websocket	5.111s
FAIL

Both tests then take 5s (i.e. hitting a context timeout). I don't have any great ideas for an easy fix off the top of my head 😕.