HTTP Session Handling

Several Camel components can use HTTP as the underlying transport protocol. In general HTTP calls are stateless in nature, however some servers allow maintaining state via cookies. Cookies are often used to maintain a server session (e.g. via a session cookie called "JSESSIONID" with servers implementing the JEE Servlet specification).

Session Scope

If a Camel route intends to implement some kind of HTTP session handling the scope of this session should be considered.

Independently of the session scope the implementation must honor the domain of the handled cookies.

Route/Context Scope

It might be desirable to have a single session for a route or a CamelContext. This essentially means that all calls to a server issued from a route or CamelContext share a single HTTP session.

Endpoint Scope

It is also possible to have a session on an Endpoint entity. This would mean that all invocations of an HTTP call issued by a single Endpoint share a session, whereas different Endpoints never share sessions, even if the call is sent to the same server.

Exchange Scope

The third option to define a session scope is on Exchange level. This is particularly useful for scenarios where the server session is really maintaining state.

In this case the route could e.g. first do a login call, then some update calls and finally a logout call. If the session handling would be defined on route or CamelContext scopes this would seem to run, however under load parallel invocations of the route would share a single session, which could cause issues. If the session is defined on exchange scope, each invocation of the route will get a separate session, and the server can maintain a separate state for the different parallel invocations.

Usage

If you are a Camel user, you see that several Camel components support the cookieHandler parameter on endpoint level. All you need to do is to instantiate a cookie handler appropriate for your use case and reference it in the cookieHandler parameter for all endpoints that are supposed to participate in the HTTP session.

There are two pre-implemented cookie handlers:

  • org.apache.camel.http.common.cookie.InstanceCookieHandler

  • org.apache.camel.http.common.cookie.ExchangeCookieHandler

The InstanceCookieHandler stores cookies in an instance of itself. You can compare that to a browser instance that is shared between all the endpoints that use it (and will be used for all invocations of these endpoints). If you want to maintain separate sessions for different endpoints or groups of endpoints you may have multiple instances of the InstanceCookieHandler.

The ExchangeCookieHandler stores the session in the exchange. With the browser analogy this means that each Exchange will get its own browser instance (so sessions are separated). As the ExchangeCookieHandler does not store any state it is generally not useful to have multiple ExchangeCookieHandler instances (as they would access the same data, anyway).

Example

The following three routes will each do two invocations of an echo REST service. In the first route (without a cookie handler) each invocation will get a new session. For the second route all invocations will share a session. For the third route the first, and the second invocation within the route share a session, but different (even parallel) invocations of the route will not share a session.

  <cxf:rsClient id="rsClientProxy" address="http://127.0.0.1:8080/CxfRsProducerSessionTest/"
    serviceClass="org.apache.camel.component.cxf.jaxrs.testbean.EchoService"
    loggingFeatureEnabled="true" />

  <camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
    <route>
       <from uri="direct://proxy"/>
       <to uri="cxfrs://bean://rsClientProxy"/>
       <convertBodyTo type="java.lang.String"/>
       <to uri="cxfrs://bean://rsClientProxy"/>
    </route>
    <route>
       <from uri="direct://proxyinstance"/>
       <to uri="cxfrs://bean://rsClientProxy?cookieHandler=#instanceCookieHandler"/>
       <convertBodyTo type="java.lang.String"/>
       <to uri="cxfrs://bean://rsClientProxy?cookieHandler=#instanceCookieHandler"/>
    </route>
    <route>
       <from uri="direct://proxyexchange"/>
       <to uri="cxfrs://bean://rsClientProxy?cookieHandler=#exchangeCookieHandler"/>
       <convertBodyTo type="java.lang.String"/>
       <to uri="cxfrs://bean://rsClientProxy?cookieHandler=#exchangeCookieHandler"/>
    </route>
  </camelContext>

  <bean id="instanceCookieHandler" class="org.apache.camel.http.common.cookie.InstanceCookieHandler"/>
  <bean id="exchangeCookieHandler" class="org.apache.camel.http.common.cookie.ExchangeCookieHandler"/>

Both CookieHandler implementations support setting a CookiePolicy to control the policy for storing cookies. Default is CookiePolicy.ACCEPT_ORIGINAL_SERVER.

Cookies and EIPs

Some EIPs like Multicast or Split create multiple exchanges from a single one. If no org.apache.camel.http.common.cookie.ExchangeCookieHandler is used before this, each multicast or splitter branch will have its own cookie store. This will not be the case if the first invocation of one of the endpoints using the cookie handler is before the multicast, because in this case the cookie store will be attached to the original exchange, and the exchanges created by the multicast will copy the reference to this cookie store (so there is effectively a shared cookie store across branches. As a workaround, you can call a cookieHandler.getCookieStore() e.g. by setting this to some dummy header.

Component Developers

If you want to develop a HTTP based component that is supposed to participate in a session you have to add the following parts to your code:

  1. Include a build reference to camel-http-common (if it is not already there)

  2. Add a cookieHandler parameter to the endpoint class (together with getter and setter)

  3. Before your code does the HTTP call, if a cookie handler is set on the endpoint perform a cookieHandler.loadCookies(exchange, uri) call. It will return a Map<String, List<String>> containing the headers that need to be sent to the server. The details how you need to send these headers to the server depend on the underlying HTTP API you are using.

  4. After your code does receive the HTTP response if a cookie handler is set on the endpoint perform a cookieHandler.storeCookies(exchange, uri, m) call. m is a Map<String, List<String>> containing the HTTP headers returned from the server.

Some APIs provide more direct support for cookie handling. In this case it might be easier to get the underlying java.net.CookieStore with a cookeManager.getCookieStore(exchange) call and handle the cookies using the cookie interface provided by the underlying library.
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