Technical overview over channels and parameters.
The communication between the comet client and java webapp comet server is asynchronous. The communication is initiated with a call, and returned with a reply (except in the case of notify, which is a special case).
The communication channels are as follows:
| Channel | purpose |
|---|---|
| /semispace/call/read/number | Initiate a read request. |
| /semispace/reply/read/number | Reply of a read, with the payload being the result if it was obtained. |
| /semispace/call/take/number | Initiate a take request. |
| /semispace/reply/take/number | Result of take. |
| /semispace/call/write/number | Insert an object into the space. This is a synchronous operation when using the comet java client. |
| /semispace/reply/write/number | Acknowledge that the element has been written. |
| /semispace/call/notify/number/type | Register a notification. This is a synchronous operation when using the comet java client. |
| /semispace/reply/notify/number/type | Acknowledge that the notification has been registered. |
| /semispace/event/notify/number/type | Attached is a notification event. |
| /semispace/call/leasecancel/number | Cancel lease with callId as mapped parameter. CallId is the number from the notify method |
| /semispace/reply/leasecancel/number | Acknowledge of listener cancellation |
Channel parameters are:
It does not matter if several different clients use the same channel numbers. The communication to the client is based on the client ID, and has nothing to do with the channel number.
The parameters sent over the channel are packed JSON style. Then the control elements are extracted. The following is an overview:
| Operation | Parameter | Significance |
|---|---|---|
| read | duration json | How long to wait for an object if it is not in the space. Payload to match. First level is object type, the second level are elements to match. (I.e. in a person object with firstname, lastname, it would be firstname=xxx). You cannot have 2 levels. |
| take | ... | Same parameters as read |
| write | timeToLiveMs json | How long the object shall live in the space TODO Shall change to duration Payload. This is the String representation of the client side JSON object. |
| notify | duration json | How long the notification registration shall exist. As for read |
| lease cancel | callId | The caller id the notification lease is registered to. |
If you want to exclude either take or write as feature, you can do this in the web.xml file. This is relevant when you have a service which shall provide a read-only interface to the clients, probably due to data entering the space from a backend service.
| Init parameter | Significance |
|---|---|
| disableTake | If disableTake is true, clients will be unable to remove anything from the space |
| disableWrite | If disableWrite is true, clients will not be able to write anything to the space |
