Version: 9.4.12.v20180830 |

Limiting Form Content
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## Limiting Form Content

Form content sent to the server is processed by Jetty into a map of parameters to be used by the web application. This can be vulnerable to denial of service (DOS) attacks since significant memory and CPU can be consumed if a malicious clients sends very large form content or large number of form keys. Thus Jetty limits the amount of data and keys that can be in a form posted to Jetty.

The default maximum size Jetty permits is 200000 bytes and 1000 keys. You can change this default for a particular webapp or for all webapps on a particular Server instance.

### Configuring Form Limits for a Webapp

To configure the form limits for a single web application, the context handler (or webappContext) instance must be configured using the following methods:

    ContextHandler.setMaxFormContentSize(int maxSizeInBytes);
    ContextHandler.setMaxFormKeys(int formKeys);

These methods may be called directly when embedding Jetty, but more commonly are configured from a context XML file or WEB-INF/jetty-web.xml file:

    <Configure class="org.eclipse.jetty.webapp.WebAppContext">

      ...

      <Set name="maxFormContentSize">200000</Set>
      <Set name="maxFormKeys">200</Set>
    </Configure>

### Configuring Form Limits for the Server

If a context does not have specific form limits configured, then the server attributes are inspected to see if a server wide limit has been set on the size or keys. The following XML shows how these attributes can be set in `jetty.xml`:

    <configure class="org.eclipse.jetty.server.Server">

      ...

      <Call name="setAttribute">
        <Arg>org.eclipse.jetty.server.Request.maxFormContentSize</Arg>
        <Arg>100000</Arg>
       </Call>
      <Call name="setAttribute">
        <Arg>org.eclipse.jetty.server.Request.maxFormKeys</Arg>
        <Arg>2000</Arg>
       </Call>
    </configure>

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