[[HTTP-SessionHandling]]
= HTTP Session Handling

*Since Camel 2.19*

Several Camel components can use HTTP as the underlying transport
protocol. In general HTTP calls are stateless in nature, however some
servers allow to maintain 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).

[[HTTP-SessionHandling-SessionScope]]
== Session Scope

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

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

[[HTTP-SessionHandling-RouteContextScope]]
== Route/Context Scope

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

[[HTTP-SessionHandling-EndpointScope]]
== Endpoint Scope

It is also possible to have a session on an xref:endpoint.adoc[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. 
Some components like camel-http, and camel-http support endpoint scoped
sessions even prior to version 2.19.

[[HTTP-SessionHandling-ExchangeScope]]
==  Exchange Scope

The third option to define a session scope is on
xref:exchange.adoc[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.

[[HTTP-SessionHandling-Usage]]
== 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` and
`org.apache.camel.http.common.cookie.ExchangeCookieHandler.`

The `InstanceCookieHandler` stores  cookies in an instance of itself.
You can compare that with 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).

[[HTTP-SessionHandling-Example]]
== 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.

[source,xml]
--------------------------------------------------------------------------------------------------------
 <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"/>  
--------------------------------------------------------------------------------------------------------

[[HTTP-SessionHandling-ComponentDevelopers]]
== 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.

[[HTTP-SessionHandling-MoreInfo]]
== More Info

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.

