tree dc5f27e53c5cae7c7328a45d8cc7ec3ee29a0d27
parent 95bf16728de08f1b037df4b736faee2786b35870
author Damjan Georgievski <gdamjan@gmail.com> 1399043081 +0200
committer Klaus Trainer <klaus_trainer@apache.org> 1399985622 +0200

Send a real EventSource event for heartbeat

The EventSource connection can get stuck (in TCP half-open state*) and there's no way
for the client to detect that. This commit changes the way heartbeat is sent, instead of
sending a newline character, it sends an empty event of type heartbeat:

    event: heartbeat
    data:

This event doesn't have an id: field, so the client will retain its latest Last-Event-ID state.

This doesn't change the expectations of clients that used EventSource till now, because they
subscribe to the 'message' event type. To get the 'heartbeat' events a client will need to
explicitly subscribe to it:

    source.addEventListener('heartbeat', function () { /* cancel a timer that would otherwise reconnect the source */ });

* this can happen when you suspend your laptop, on flaky internet connection, ADSL reconnect,
bad wifi signals, bad routers etc. Pretty often in a typical internet usage nowadays.