17.6.2.Traversing Message Paths
The initial WS-Routing sender generates a WS-Routing "path" header that indicates the route. The path can indicate a route via one or more intermediaries using the "via" elements as sub-elements of the "fwd" element. The initial sender indicates the ultimate destination by using a "to" element. In the absence of a "to" element the ultimate destination is deduced by the last "via" in the "fwd" element. The second option occurs most commonly when an ultimate destination reverses roles, becomes an initial sender, and uses the reverse path in a received message as a forward path to send a response to the original sender.
In addition, the initial WS-Routing sender inserts a reverse path for indicating where the initial sender can receive reverse path messages. The initial sender sets the ultimate destination in the reverse path using a "via" element as a sub-element of the "rev" element.
A WS-Routing receiver receiving a WS-Routing message inspects the SOAP header and performs the following operations:
-
If no "fwd" element is present or if the "fwd" element does not contain any "via" elements then inspect the "to" element and verify that the value identifies itself. If this is the case then THIS receiver is the ultimate destination. If there is no "to" element or if the value of the "to" element does not identify THIS WS-Routing receiver then generate a fault.
-
If the "fwd" element is present and contains one or more "via" element(s) then remove the top "via" element listed in the "fwd" element and verify that the value of that "via" element is either empty or identifies THIS WS-Routing receiver. Failing that generate an appropriate WS-Routing fault
If, after removing the top "via" element there are no remaining "via" element(s) listed in the "fwd" element, and there is no "to" element, then THIS WS-Routing receiver is the ultimate destination.
A WS-Routing intermediary MUST follow these additional rules:
-
If a "rev" element is present then add a "via" element as the first "via" element listed in the "rev" element with a value indicating the reverse path endpoint. If a reverse path endpoint cannot be provided then generate a 751 "Reverse Path Unavailable" WS-Routing fault.
-
If one or more "via" element(s) remain in the "fwd" element then forward the WS-Routing message to the endpoint identified by the new top "via" element listed in the "fwd" element.
-
If there are no remaining "via" element(s) listed in the "fwd" element but there is a "to" element then forward the WS-Routing message to the endpoint identified by the "to" element.
-
In the last two cases if the forwarding does not succeed then generate the appropriate WS-Routing fault.
Example17.29.WS Routing Example
Here is an example SOAP call from a client to an endpoint D.com via intermediaries B.com and C.com:
+------------+ +------------+ +------------+ +-------------+
| Initial | | WS-Routing | | WS-Routing | | Ultimate |
| WS-Routing |-->
|Intermediary|-->
|Intermediary|-->
| WS-Routing |
| Sender A |<--| B |<--| C |<--| Receiver D |
+------------+ +------------+ +------------+ +-------------+
HTTP HTTP HTTP
Request from client to intermediary B
<S:Envelope>
<S:Header>
<m:path
xmlns:m="http://schemas.xmlsoap.org/rp/"
S:actor="http://schemas.xmlsoap.org/soap/actor/next"
S:mustUnderstand="1">
<m:action>http://soapinterop.org/</m:action>
<m:to>http://D.com/router</m:to>
<m:id>uuid:09233523-345b-4351-b623-5dsf35sgs5d6</m:id>
<m:fwd>
<m:via>http://B.com/router</m:via>
<m:via>http://C.com/router</m:via>
</m:fwd>
<m:rev />
</m:path>
</S:Header>
<S:Body>
...
</S:Body>
</S:Envelope>
Request from intermediary B to intermediary C
<n0:Envelope>
<n0:Header>
<n2:path
xmlns:n2="http://schemas.xmlsoap.org/rp/"
n0:actor="http://schemas.xmlsoap.org/soap/actor/next"
n0:mustUnderstand="1">
<n2:action>http://soapinterop.org/</n2:action>
<n2:to>http://D.com/router</n2:to>
<n2:id>uuid:09233523-345b-4351-b623-5dsf35sgs5d6</n2:id>
<n2:fwd>
<n2:via>http://C.com/router</n2:via>
</n2:fwd>
<n2:rev>
<n2:via />
</n2:rev>
</n2:path>
</n0:Header>
<n0:Body>
...
</n0:Body>
</n0:Envelope>
Request from intermediary C to endpoint D
<n0:Envelope>
<n0:Header>
<n2:path
xmlns:n2="http://schemas.xmlsoap.org/rp/"
n0:actor="http://schemas.xmlsoap.org/soap/actor/next"
n0:mustUnderstand="1">
<n2:action>http://soapinterop.org/</n2:action>
<n2:to>http://D.com/router</n2:to>
<n2:id>uuid:09233523-345b-4351-b623-5dsf35sgs5d6</n2:id>
<n2:fwd />
<n2:rev>
<n2:via />
<n2:via />
</n2:rev>
</n2:path>
</n0:Header>
<n0:Body>
...
</n0:Body>
</n0:Envelope>
Response from endpoint to C
<n0:Envelope>
<n0:Header>
<n2:path xmlns:n2="http://schemas.xmlsoap.org/rp/"
n0:actor="http://schemas.xmlsoap.org/soap/actor/next"
n0:mustUnderstand="1">
<n2:action>http://soapinterop.org/</n2:action>
<n2:id>uuid:2b2d09ec-a93a-11d6-be21-c9f55c969fe7</n2:id>
<n2:relatesTo>uuid:09233523-345b-4351-b623-5dsf35sgs5d6</n2:relatesTo>
<n2:fwd>
<n2:via />
<n2:via />
</n2:fwd>
<n2:rev>
<n2:via>http://D.com/router</n2:via>
</n2:rev>
<n2:from />
</n2:path>
</n0:Header>
<n0:Body>
...
</n0:Body>
</n0:Envelope>
Response from intermediary C to B
<n0:Envelope>
<n0:Header>
<n2:path xmlns:n2="http://schemas.xmlsoap.org/rp/"
n0:actor="http://schemas.xmlsoap.org/soap/actor/next"
n0:mustUnderstand="1">
<n2:action>http://soapinterop.org/</n2:action>
<n2:id>uuid:2b2d09ec-a93a-11d6-be21-c9f55c969fe7</n2:id>
<n2:relatesTo>uuid:09233523-345b-4351-b623-5dsf35sgs5d6</n2:relatesTo>
<n2:fwd>
<n2:via />
</n2:fwd>
<n2:rev>
<n2:via>http://C.com/router</n2:via>
<n2:via>http://D.com/router</n2:via>
</n2:rev>
<n2:from />
</n2:path>
</n0:Header>
<n0:Body>
...
</n0:Body>
</n0:Envelope>
Response from intermediary B to client
<n0:Envelope>
<n0:Header>
<n2:path xmlns:n2="http://schemas.xmlsoap.org/rp/"
n0:actor="http://schemas.xmlsoap.org/soap/actor/next"
n0:mustUnderstand="1">
<n2:action>http://soapinterop.org/</n2:action>
<n2:id>uuid:2b2d09ec-a93a-11d6-be21-c9f55c969fe7</n2:id>
<n2:relatesTo>uuid:09233523-345b-4351-b623-5dsf35sgs5d6</n2:relatesTo>
<n2:fwd />
<n2:rev>
<n2:via>http://B.com/router</n2:via>
<n2:via>http://C.com/router</n2:via>
<n2:via>http://D.com/router</n2:via>
</n2:rev>
<n2:from />
</n2:path>
</n0:Header>
<n0:Body>
...
</n0:Body>
</n0:Envelope>