38.4. Handling HTTP Headers
Overview
When building bridge applications using HTTP or HTTP-based components, it is important to be aware of how the HTTP-based endpoints process headers. In many cases, internal headers (prefixed by Camel) or other headers can cause unwanted side-effects on your application. It is often necessary to remove or filter out certain headings or classes of headings in your route, in order to ensure that your application behaves as expected.
HTTP-based components
The behavior described in this section affects not just the Camel HTTP component (
camel-http), but also a number of other HTTP-based components, including:
camel-http camel-http4 camel-jetty camel-restlet camel-cxf
HTTP consumer endpoint
When a HTTP consumer endpoint receives an incoming message, it creates an In message with the following headers:
CamelHttp*headers- Several headers with the
CamelHttpprefix are created, which record the status of the incoming message. For details of these internal headers, see HTTP. - HTTP headers
- All of the HTTP headers from the original incoming message are mapped to headers on the exchange's In message.
- URL options (Jetty only)
- The URL options from the original HTTP request URL are mapped to headers on the exchange's In message. For example, given the client request with the URL,
http://myserver/myserver?orderid=123, a Jetty consumer endpoint creates theorderidheader with value123.
HTTP producer endpoint
When a HTTP producer endoint receives an exchange and converts it to the target message format, it handles the In message headers as follows:
CamelHttp*- Headers prefixed by
CamelHttpare used to control the behavior of the HTTP producer entpoint. Any headers of this kind are consumed by the HTTP producer endpoint and the endpoint behaves as directed. Camel*- All other headers prefixed by
Camelare presumed to be meant for internal use and are not mapped to HTTP headers in the target message (in other words, these headers are ignored). *- All other headers are converted to HTTP headers in the target message, with the exception of the following headers, which are blocked (based on a case-insensitive match):
content-length content-type cache-control connection date pragma trailer transfer-encoding upgrade via warning
Implications for HTTP bridge applications
When defining a HTTP bridge application (that is, a route starting with a HTTP consumer endpoint and ending with a HTTP producer endpoint), the
CamelHttp* headers set by the consumer endpoint at the start of the route can affect the behavior of the producer endpoint. For this reason, in a bridge application it is advisable to remove the CamelHttp* headers, as follows:
from("http://0.0.0.0/context/path")
.removeHeaders("CamelHttp*)
...
.to("http://remoteHost/context/path");Setting a custom header filter
If you want to customize the way that a HTTP producer endpoint processes headers, you can define your own customer header filter by defining the
headerFilterStrategy option on the endpoint URI. For example, to configure a producer endpoint with the myHeaderFilterStrategy filter, you could use a URI like the following:
http://remoteHost/context/path?headerFilterStrategy=#myHeaderFilterStrategy
Where
myHeaderFilterStrategy is the bean ID of your custom filter instance.
