2.6. Stomp Heartbeats
Abstract
The Stomp 1.1 protocol support a heartbeat policy that allows clients to send keepalive messages to the broker.
Stomp 1.1 heartbeats
Stomp 1.1 adds support for heartbeats (keepalive messages) on Stomp connections. Negotiation of a heartbeat policy is normally initiated by the client (Stomp 1.1 clients only) and the client must be configured to enable heartbeats. No broker settings are required to enable support for heartbeats, however.
At the level of the Stomp wire protocol, heartbeats are negotiated when the client establishes the Stomp connection and the following messages are exchanged between client and server:
CONNECT heart-beat:CltSend,CltRecv CONNECTED: heart-beat:SrvSend,SrvRecv
The CltSend, CltRecv, SrvSend, and SrvRecv fields are interpreted as follows:
- CltSend
- Indicates the minimum frequency of messages sent from the client, expressed as the maximum time between messages in units of milliseconds. If the client does not send a regular Stomp message within this time limit, it must send a special heartbeat message, in order to keep the connection alive.A value of zero indicates that the client does not send heartbeats.
- CltRecv
- Indicates how often the client expects to receive message from the server, expressed as the maximum time between messages in units of milliseconds. If the client does not receive any messages from the server within this time limit, it would time out the connection.A value of zero indicates that the client does not expect heartbeats and will not time out the connection.
- SrvSend
- Indicates the minimum frequency of messages sent from the server, expressed as the maximum time between messages in units of milliseconds. If the server does not send a regular Stomp message within this time limit, it must send a special heartbeat message, in order to keep the connection alive.A value of zero indicates that the server does not send heartbeats.
- SrvRecv
- Indicates how often the server expects to receive message from the client, expressed as the maximum time between messages in units of milliseconds. If the server does not receive any messages from the client within this time limit, it would time out the connection.A value of zero indicates that the server does not expect heartbeats and will not time out the connection.
In order to ensure that the rates of sending and receiving required by the client and the server are mutually compatible, the client and the server negotiate the heartbeat policy, adjusting their sending and receiving rates as needed.
Stomp 1.0 heartbeat compatibility
A difficulty arises, if you want to support an inactivity timeout on your Stomp connections when legacy Stomp 1.0 clients are connected to your broker. The Stomp 1.0 protocol does not support heartbeats, so Stomp 1.0 clients are not capable of negotiating a heartbeat policy.
To get around this limitation, you can specify the
transport.defaultHeartBeat option in the broker's transportConnector element, as follows:
<transportConnector name="stomp" uri="stomp://0.0.0.0:0?transport.defaultHeartBeat=5000,0" />
The effect of this setting is that the broker now behaves as if the Stomp 1.0 client had sent the following Stomp frame when it connected:
CONNECT heart-beat:5000,0
This means that the broker will expect the client to send a message at least once every 5000 milliseconds (5 seconds). The second integer value,
0, indicates that the client does not expect to receive any heartbeats from the server (which makes sense, because Stomp 1.0 clients do not understand heartbeats).
Now, if the Stomp 1.0 client does not send a regular message after 5 seconds, the connection will time out, because the Stomp 1.0 client is not capable of sending out a heartbeat message to keep the connection alive. Hence, you should choose the value of the timeout in
transport.defaultHeartBeat such that the connection will stay alive, as long as the Stomp 1.0 clients are sending messages at their normal rate.
