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| <h1 title="Package" class="title">Package org.apache.axis2.transport.udp</h1> |
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| <div class="block">Transport implementation for the UDP protocol.</div> |
| </div> |
| <p>See: <a href="#package_description">Description</a></p> |
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| <th class="colLast" scope="col">Description</th> |
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| <td class="colFirst"><a href="../../../../../org/apache/axis2/transport/udp/Endpoint.html" title="class in org.apache.axis2.transport.udp">Endpoint</a></td> |
| <td class="colLast"> |
| <div class="block">UDP endpoint description.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><a href="../../../../../org/apache/axis2/transport/udp/IODispatcher.html" title="class in org.apache.axis2.transport.udp">IODispatcher</a></td> |
| <td class="colLast"> |
| <div class="block">I/O dispatcher for incoming UDP packets.</div> |
| </td> |
| </tr> |
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| <td class="colFirst"><a href="../../../../../org/apache/axis2/transport/udp/UDPConstants.html" title="class in org.apache.axis2.transport.udp">UDPConstants</a></td> |
| <td class="colLast"> |
| <div class="block">Utility class defining constants used by the UDP transport.</div> |
| </td> |
| </tr> |
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| <td class="colFirst"><a href="../../../../../org/apache/axis2/transport/udp/UDPListener.html" title="class in org.apache.axis2.transport.udp">UDPListener</a></td> |
| <td class="colLast"> |
| <div class="block">Transport listener for the UDP protocol.</div> |
| </td> |
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| <td class="colFirst"><a href="../../../../../org/apache/axis2/transport/udp/UDPOutTransportInfo.html" title="class in org.apache.axis2.transport.udp">UDPOutTransportInfo</a></td> |
| <td class="colLast"> |
| <div class="block">Holder of information to send an outgoing message to a UDP destination.</div> |
| </td> |
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| <td class="colFirst"><a href="../../../../../org/apache/axis2/transport/udp/UDPSender.html" title="class in org.apache.axis2.transport.udp">UDPSender</a></td> |
| <td class="colLast"> |
| <div class="block">Transport sender for the UDP protocol.</div> |
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| <h2 title="Package org.apache.axis2.transport.udp Description">Package org.apache.axis2.transport.udp Description</h2> |
| <div class="block">Transport implementation for the UDP protocol. |
| <p> |
| This package contains a transport implementation allowing Axis to |
| send and receive UDP packets. It is an implementation of "raw" UDP in the |
| sense that the message is directly extracted from the UDP payload without |
| any intermediate application protocol. This has several important implications: |
| <ul> |
| <li>The only way to route the incoming message to the appropriate Axis service |
| is to bind the service a specific UDP port. The port number must be |
| explicitly defined in the service configuration. This is different |
| from protocols such as HTTP where the message can be routed |
| based on the URL in the request.</li> |
| <li>The transport has no way to detect the content type of an incoming |
| message. Indeed, there is no equivalent to HTTP's |
| <tt>Content-Type</tt> header. Again the expected content type must be |
| configured explicitly for the service.</li> |
| <li>Since UDP doesn't provide any mean to correlate responses to requests, |
| the transport can only be used for asynchronous communication.</li> |
| </ul> |
| See the documentation of <code>org.apache.synapse.transport.udp.UDPListener</code> |
| for more information about how to configure a service to accept UDP packets. |
| Endpoint references for the UDP transport are assumed to follow the following |
| syntax: |
| <pre> |
| udp://<em>host</em>:<em>port</em>?contentType=...</pre> |
| <p> |
| The UDP transport can be enabled in the Axis configuration as follows: |
| <pre> |
| <transportReceiver name="udp" class="org.apache.synapse.transport.udp.UDPListener"/> |
| <transportSender name="udp" class="org.apache.synapse.transport.udp.UDPSender"/></pre> |
| It should be noted that given its characteristics, UDP is not a |
| suitable transport protocol for SOAP, except maybe in very particular |
| circumstances. Indeed, UDP is an unreliable protocol: |
| <ul> |
| <li>There is no delivery guarantee, i.e. packets may be lost.</li> |
| <li>Messages may arrive out of order.</li> |
| <li>Messages may be duplicated, i.e. delivered twice.</li> |
| </ul> |
| However the unit tests show an example of how to use this transport with SOAP |
| and WS-Addressing to achieve two-way asynchronous communication. |
| Note that the transport has not been designed to implement the |
| <a href="http://specs.xmlsoap.org/ws/2004/09/soap-over-udp/soap-over-udp.pdf">SOAP |
| over UDP specification</a> and will probably not be interoperable. |
| <p> |
| The main purpose of this transport implementation is to integrate Axis (and in |
| particular Synapse) with existing UDP based protocols. See |
| <code>org.apache.synapse.format.syslog</code> for an example of this kind |
| of protocol. |
| |
| <h4>Known issues and limitations</h4> |
| |
| <ul> |
| <li>Packets longer than the configured maximum packet size |
| are silently truncated. Packet truncation should be detected |
| and trigger an error.</li> |
| <li>The listener doesn't implement all management operations |
| specified by |
| <code>org.apache.synapse.transport.base.ManagementSupport</code>.</li> |
| <li>The listener assumes that services are bound to unique UDP ports |
| and predispatches incoming requests based on port numbers. |
| When SOAP with WS-Addressing is used, the packets could be |
| received on a single port and dispatched based on the <tt>To</tt> |
| header. This is not supported.</li> |
| <li>It might be useful to allow configuration of the content type at the |
| transport level rather than the service level. In this case, the |
| <tt>contentType</tt> parameter would not be included in the endpoint |
| reference. This is necessary for interoperability with the SOAP over UDP |
| standard.</li> |
| <li>Technically, it would be quite easy to support binding several UDP ports |
| to the same service. However, the way endpoints are configured |
| at the service level doesn't allow this for the moment. Indeed, |
| using simple text properties only allows to specify the configuration |
| of a single endpoint.</li> |
| <li>The transport sender uses a randomly chosen UDP source port. Some |
| UDP based services may check the source port and discard the packet. |
| Also, in two-way communication scenarios, stateful firewalls will |
| not be able to correlate the exchanged packets and may drop |
| some of them.</li> |
| </ul></div> |
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