Policy example for Replaying request

Author: sushaanttb

examples/Replaying Request on Error.xml

@@ -0,0 +1,64 @@
+<!--
+    This policy sample demonstrates a pattern of replaying the request.
+    For eg: One scenario could be when we are using quota and rate limit policies,
+    for some special tier consumers, we would still like to serve the request if there
+    was a quota error but this time with a low-end backend.
+    
+    The "example-policy-name" string is in the when condition is just for example 
+    and needs to be replaced with the actual policy name accordingly.
+
+    Important Note: 
+    Altough this pattern works, we would do end up having 2 log entries now 
+    for the same request, since the request is now being replayed.
+-->
+<policies>
+    <inbound>
+        <base />
+    </inbound>
+    <backend>
+        <base />
+    </backend>
+    <outbound>
+        <base />
+    </outbound>
+    <on-error>
+        <base />
+        <choose>
+            <when condition="@(context.LastError.Source == "example-policy-name")">
+                <set-variable name="replay-url" value="@("http://" + context.Request.Headers.GetValueOrDefault("X-Original-Host") + context.Request.Headers.GetValueOrDefault("X-Original-Url"))" />
+                <set-variable name="original-error-source" value="@(context.LastError.Source)" />
+                <set-variable name="original-error-reason" value="@(context.LastError.Reason)" />
+                <!-- We replay the same request again to APIM -->
+                <send-request mode="copy" response-variable-name="replay-response" timeout="60" ignore-error="false">
+                    <set-url>@(context.Variables.GetValueOrDefault<string>("replay-url"))</set-url>
+                    <set-method>POST</set-method>
+                    <!-- While replaying the request this time, we might need to pass some additional information
+                    this time in our request with corresponding logic in the inbound section to process such requests  
+                    The string "skip-example-policy-error" here is just as an example -->
+                    <set-header name="skip-example-policy-error" exists-action="override">
+                        <value>true</value>
+                    </set-header>
+                </send-request>
+                <!-- THIS IS AN IMPORTANT STEP i.e. the response captured in policy variable "response-variable-name" defined above has to be explicity sent back -->
+                <return-response response-variable-name="replay-response">
+                    <!-- Any additional headers like below can further be added as part of response tracking -->
+                    <set-header name="x-request-replayed" exists-action="override">
+                        <value>true</value>
+                    </set-header>
+                    <set-header name="x-original-error-source" exists-action="override">
+                        <value>@(context.Variables.GetValueOrDefault<string>("original-error-source"))</value>
+                    </set-header>
+                    <set-header name="x-original-error-reason" exists-action="override">
+                        <value>@(context.Variables.GetValueOrDefault<string>("original-error-reason"))</value>
+                    </set-header>
+                </return-response>
+            </when>
+            <otherwise>
+                <!-- Any additional headers like below can further be added as part of response tracking -->
+                <set-header name="x-request-replayed" exists-action="override">
+                    <value>"false"</value>
+                </set-header>
+            </otherwise>
+	    </choose>
+    </on-error>
+</policies>