Access the JSON property from JSON Response - Azure APIM Policies

Question

Hi,

If I am getting below JSON response from an API, how can I get the status and code properties in that.

{
  "error": {
    "status": 0,
    "code": "string",
    "message": "string",
    "target": "string",
    "instance": "string",
    "details": [
      "string"
    ]
  }
}

Below is my policy code which is currently in place.

<policies>

<inbound>

    <base />

</inbound>

<backend>

    <base />

</backend>

<outbound>

	<base />

	<set-variable name="errorResponse" value="@(context.Response.Body.As<JObject>()["error"])" />

	<choose>

		<when condition="@(context.Variables["errorResponse"]!=null)">

			<set-variable name="errorStatus" value="@{

				var jsonObject = JObject.Parse(context.Response.Body.As<JObject>()["error"]);

				var value = (string)jsonObject["status"];

				return value;

			}" />

			<set-variable name="errorStatus" value="@{

				var jsonObject = JObject.Parse(context.Response.Body.As<JObject>()["error"]);

				var value = (string)jsonObject["code"];

				return value;

			}" />

			<choose>

				<when condition="@((int)context.Variables["errorStatus"]==404)">

					<return-response>

						<set-status code="200" reason="NotFound" />

						<set-body template="liquid">

							{ 

								"status": "NotFound"

							}

						</set-body>

					</return-response>

				</when>

			</choose>

		</when>

	</choose>

</outbound>

<on-error>

    <base />

</on-error>

</policies>

Answer 1

If the specified JSON is returned from backend service, you can retrieve the code and status in the following way. This is a simple example, and few error handling is implemented. You should care about this.

The following points should be considered.

• Liquid template does not work in set-body of return-response policy.

  https://learn.microsoft.com/en-us/azure/api-management/return-response-policy

• The original message body stream is unavailable after calling context.Response.Body.As<JObject>(). To avoid this, you should set the preserveContent parameter to true.

  https://learn.microsoft.com/en-us/azure/api-management/api-management-policy-expressions#ref-imessagebody

[Response from backend service]

{
  "error": {
    "status": 0,
    "code": "string",
    "message": "string",
    "target": "string",
    "instance": "string",
    "details": [
      "string"
    ]
  }
}

[policy]

...
    <outbound>
        <base />
        <return-response>
            <set-status code="200" />
            <set-body>@{
                var body = context.Response.Body.As<JObject>(true);
                if(body["error"]!= null && body["error"].HasValues ) {
                    return new JObject(
                        new JProperty("code", (string)body["error"]["code"]),
                        new JProperty("status", (int)body["error"]["status"])
                    ).ToString();
                }
            }</set-body>
        </return-response>
    </outbound>
...