Edit

Route the request based on the size of its body

  • Article

This article shows an Azure API management policy sample that demonstrates how to route requests based on the size of their bodies. To set or edit a policy code, follow the steps described in Set or edit a policy. To see other examples, see policy samples.

Policy

Paste the code into the inbound block.

<!-- The policy defined in this file demonstrates how to route requests based on the size of the message body. -->
<!-- Content-Length header contains the size of the message body. -->

<!--  256 KB, a limitation on message size in the Azure Service Bus.  -->
<!-- The snippet checks if the message is smaller than 256000 bytes. If it's larger, request is routed somewhere else. -->

<!-- Copy the following snippet into the inbound section. -->

<policies>
    <inbound>
        <base/>
            <set-variable name="bodySize" value="@(context.Request.Headers["Content-Length"][0])"/>
            <choose>
                <when condition="@(int.Parse(context.Variables.GetValueOrDefault<string>("bodySize"))<256000)">
                    <!-- let it pass through by doing nothing -->
                </when>
                <otherwise>
                    <rewrite-uri template="{{alternate-path-and-query}}"/>
                    <set-backend-service base-url="{{alternate-host}}"/>
                </otherwise>
            </choose>

            <!-- In rare cases where Content-Length header is not present we'll have to read the body to get its length. -->
            <!--
            <choose>
                <when condition="@(context.Request.Body.As<string>(preserveContent: true).Length<256000)">

                </when>
                <otherwise>
                    <rewrite-uri template=""/>
                    <set-backend-service base-url=""/>
                </otherwise>
            </choose>
            -->
    </inbound>
    <backend>
        <base/>
    </backend>
    <outbound>
        <base/>
    </outbound>
    <on-error>
        <base/>
    </on-error>
</policies>

Next steps

Learn more about APIM policies: