[[Howtoavoidsendingsomeorallmessageheaders-Howtoavoidsendingsomeorallmessageheaders]]
=== How to avoid sending some or all message headers?

When I send a message to a Camel endpoint such as the
<<mail-component,Mail>> component, then the mail include some message
headers I do not want. How can I avoid this?

[[Howtoavoidsendingsomeorallmessageheaders-UseremoveHeadersintheroute]]
==== Use removeHeaders in the route

This is a gotcha more people encounter. However it's very easy to solve.
To remove all headers use a wildcard expression:

[source,java]
----
from(...).removeHeaders("*").to("smtp://....")
----

Similarly to remove all headers except some of your own (`myheader1` and
`myheader2`) use a wildcard with a vararg:

[source,java]
----
from(...).removeHeaders("*", "myheader1", "myheader2").to("smtp://....")
----

To do (a similar thing) in XML DSL you simply do:

[source,xml]
----
<route>
  <from uri="..."/>
  <removeHeaders pattern="*" excludePattern="header1|header2"/>
  <to uri="smtp://..."/>
</route>
----

At present, the `excludePattern` only supports one header name (which
can be include wild cards or regular expressions). We tackle this
limitation with
https://issues.apache.org/jira/browse/CAMEL-6445[CAMEL-6445].

Again to remove only Camel headers but no other transport headers:

[source,java]
----
from(...).removeHeaders("Camel*").to("smtp://....")
----

To do this in XML DSL you simply do:

[source,xml]
----
<route>
  <from uri="..."/>
  <removeHeaders pattern="Camel*"/>
  <to uri="smtp://..."/>
</route>
----

There is also a removeHeader in the DSL to remove a single header. But
it does not support patterns, so you can only remove a single header by
its name.

[[Howtoavoidsendingsomeorallmessageheaders-UseHeaderFilterStrategy]]
==== Use HeaderFilterStrategy

An alternative is that some of the Camel
link:../component.adoc[Components] supports configuring a custom header
filter strategy.
This allows you to implement the
`org.apache.camel.spi.HeaderFilterStrategy` interface, where one can
filter unwanted headers from the communication while not removing them from the
Exchange. Though it's often easier to use the `removeHeaders` in the Camel route
as shown above.

Camel core offers a default filter strategy implementation, the
DefaultHeaderFilterStrategy class, to which one can provide a regular expression
pattern or a set of header names to be filtered out.

[source,xml]
----
<bean class="org.apache.camel.impl.DefaultHeaderFilterStrategy" id="myFilter">
    <property name="outFilter">
        <set>
            <value>unwantedHeaderName</value>
        </set>
    </property>
</bean>
...
<setHeader headerName="allowedHeaderName"><constant>some metadata</constant></setHeader>
<setHeader headerName="unwantedHeaderName"><constant>some private data</constant></setHeader>
<to id="publish" uri="activemq:queue:destinationName?headerFilterStrategy=#myFilter"/>
<log message="${header.unwantedHeaderName}"/>
----

The destination queue would receive a JMS message with the allowedHeaderName as
JMS property. If the queue messages are consumed by a Camel route, then the
exchange will have the allowedHeaderName as a header. The log would print "some
private data" since the header has only been filtered out from the producer
endpoint, but not removed from the Exchange.

[[Howtoavoidsendingsomeorallmessageheaders-SelectingTheAcceptedHeaders]]
==== Selecting the accepted headers

The more steps a route has, more headers tend to be present in the exchange.
When the number of headers is large, undetermined, or one can't know in advance
which headers must be filtered out, it is desirable not to deliver by default
the headers to the destination endpoint.

In this case, one can filter out everything and selectively send only certain
headers to the destination endpoint. The DefaultHeaderFilterStrategy behavior
can be reversed so only certain headers are accepted through the filterOnMatch
property.

[source,xml]
----
<bean class="org.apache.camel.impl.DefaultHeaderFilterStrategy" id="myFilter">
    <property name="filterOnMatch" value="false" />
    ...
</bean>
----
