Queuing messages before attach can lead to out-of-order publishing

[tcard]

As expected, before we get the CONNECTED protocol message, published messages get enqueued. When CONNECTED arrives, all pending messages are supposed to be published right away.

But we have a bug: a publish can happen after the CONNECTED arrives and before the pending messages are publishes and that new message will be published right at that moment (since we're CONNECTED), but before the pending messages are published.

2019-12-05 17:10:39.770991+0100 xctest[55987:2631276] DEBUG: (ARTRealtimeChannel.m:577) R:0x7fa3fe95bcf0 C:0x7fa3fe96ce90 (test-3-testing) protocol message 0x7fa3fe970b20 has been queued and merged in an existing message
2019-12-05 17:10:39.771279+0100 xctest[55987:2631276] DEBUG: (ARTRealtimeChannel.m:577) R:0x7fa3fe95bcf0 C:0x7fa3fe96ce90 (test-3-testing) protocol message 0x7fa3fce12c70 has been queued and merged in an existing message
2019-12-05 17:10:39.771599+0100 xctest[55987:2631276] DEBUG: (ARTRealtimeChannel.m:577) R:0x7fa3fe95bcf0 C:0x7fa3fe96ce90 (test-3-testing) protocol message 0x7fa3fce13940 has been queued and merged in an existing message
2019-12-05 17:10:39.771886+0100 xctest[55987:2631276] DEBUG: (ARTRealtimeChannel.m:577) R:0x7fa3fe95bcf0 C:0x7fa3fe96ce90 (test-3-testing) protocol message 0x7fa3fce143f0 has been queued and merged in an existing message
2019-12-05 17:10:39.772236+0100 xctest[55987:2631276] DEBUG: (ARTRealtimeChannel.m:577) R:0x7fa3fe95bcf0 C:0x7fa3fe96ce90 (test-3-testing) protocol message 0x7fa3fe968d70 has been queued and merged in an existing message

...

2019-12-05 17:10:39.779660+0100 xctest[55987:2631518] DEBUG: R:0x7fa3fe95bcf0 realtime is transitioning from 1 - Connecting to 2 - Connected

Now look how the message with name 41 sneaks in:

2019-12-05 17:10:39.781121+0100 xctest[55987:2631276] DEBUG: RS:0x7fa3fe95a160 ARTJsonLikeEncoder<msgpack> encoding '{
    action = 15;
    channel = "test-3-testing";
    messages =     (
                {
            connectionId = "z62Z13c-EJ";
            name = 41;
        }
    );
    msgSerial = 0;
}'; got: {length = 86, bytes = 0x84a96d73 67536572 69616c00 a86d6573 ... a6616374 696f6e0f }

And only later the big message with the enqueued messages is sent:

2019-12-05 17:10:39.798636+0100 xctest[55987:2631518] VERBOSE: RS:0x7fa3fe95a160 ARTJsonLikeEncoder<msgpack>: protocolMessageToDictionary {
    action = 15;
    channel = "test-3-testing";
    messages =     (
                {
            connectionId = "z62Z13c-EJ";
            name = 1;
        },
                {
            connectionId = "z62Z13c-EJ";
            name = 2;
        },
                {
            connectionId = "z62Z13c-EJ";
            name = 3;
        },
                {
            connectionId = "z62Z13c-EJ";
            name = 4;
        },
...