How do I extract and match values inside APIM management policy

Gregory Suvalian 5

Hello,

I have JSON array in form below

[
  {
    "hostname": "hostname1.company.com",
    "value": 28
  },
  {
    "hostname": "hostname2.company.com",
    "value": 55
  }
]

This is stored on external URL and retrieved during policy run and put into cache.

I need to extract value from this array matching to incoming hostheader of request and having trouble writing correct Azure APIM Policy to do that

<inbound>
        <cache-lookup-value key="hostnames" variable-name="hostnames" />
        <choose>
            <when condition="@(!context.Variables.ContainsKey("hostnames"))">
                <send-request mode="new" response-variable-name="response" timeout="20" ignore-error="true">
                <set-url>@($"https://gist.githubusercontent.com/artisticcheese/b72ecad52e5c6804c7f0e81dd0344dc7/raw/908bf7f93891674ca665d3c4982a02de43b6ed6f/gistfile1.txt")</set-url>

                    <set-method>GET</set-method>
                </send-request>
                <set-variable name="hostnames" value="@(((IResponse)context.Variables["response"]).Body.As<JObject>())" />
                <cache-store-value key="hostnames" value="@((string)context.Variables["hostnames"])" duration="100000" />
            </when>
        </choose>
        <set-variable name="requestHostname" value="@(context.Request.Headers["X-Forwarded-Host"].First())" />
        <set-variable name="matching_value" value="@{ 
          var inputJson = context.Variables["hostnames"];
    var incomingHostheader = context.Variables["requestHostname"];  
    var jsonArray = (JArray)inputJson;
 var matchedEntry = jsonArray.FirstOrDefault(entry => 
                (string)entry["hostname"] == incomingHostheader );
                return matchedEntry;
}" />
        <return-response>
            <set-status code="200" reason="OK" />
            <set-header name="Content-Type" exists-action="override">
                <value>application/json</value>
            </set-header>
            <set-body>@{
        var hostnames = (string)context.Variables["hostnames"];
        return hostnames;
    }</set-body>
        </return-response>
        <base />
    </inbound>

Code does not work, it's probably easier to do compared to what I did so far

Loknath Mahali 0 Microsoft Vendor

Hello @Gregory Suvalian,

Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.

I understand that you are trying to extract a value from a JSON array that is stored on an external URL and retrieved during policy run to match with the incoming host header of a request. Based on the code you provided it seems that you are trying to achieve this by using the policy expressions in Azure APIM. However, the code you provided is not working as expected.

<inbound>
    <cache-lookup-value key="hostnames" variable-name="hostnames" />
    <choose>
        <when condition="@(!context.Variables.ContainsKey("hostnames"))">
            <send-request mode="new" response-variable-name="response" timeout="20" ignore-error="true">
                <set-url>@($"https://gist.githubusercontent.com/artisticcheese/b72ecad52e5c6804c7f0e81dd0344dc7/raw/908bf7f93891674ca665d3c4982a02de43b6ed6f/gistfile1.txt")</set-url>
                <set-method>GET</set-method>
            </send-request>
            <set-variable name="hostnames" value="@(((IResponse)context.Variables["response"]).Body.As<JArray>())" />
            <cache-store-value key="hostnames" value="@((string)context.Variables["hostnames"])" duration="100000" />
        </when>
    </choose>
    <set-variable name="requestHostname" value="@(context.Request.Headers.GetValueOrDefault("X-Forwarded-Host", "").Split(':')[0])" />
    <set-variable name="matching_value" value="@{
        var inputJson = context.Variables["hostnames"];
        var incomingHostheader = context.Variables["requestHostname"];  
        var jsonArray = (JArray)inputJson;
        var matchedEntry = jsonArray.FirstOrDefault(entry => (string)entry["hostname"] == incomingHostheader);
        return matchedEntry?["value"];
    }" />
    <return-response>
        <set-status code="200" reason="OK" />
        <set-header name="Content-Type" exists-action="override">
            <value>

As I suggest you to please try using the above code which will extract the value from the JSON array that matches the incoming host header of the request. If there is no match, it will return null.

I hope this helps! Let me know if you have any further questions.

Loknath Mahali 0 Reputation points Microsoft Vendor

2025-01-28T11:19:33.5833333+00:00

Hello @Gregory Suvalian,Greeting for the day.

This is a friendly follow-up to check if the information provided above helped you understand the issue better and addressed your concerns. If you have any further questions or concerns, please feel free to reach out to us.

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