Monetization Programmatic Quotas

When adding monetization to your API, you would usually set the number of meters a request will consume in the settings of the Monetization Policy. For example, the policy below specifies that each request will consume 1 requests meter and 5 computeUnits meters.

{
  "export": "MonetizationInboundPolicy",
  "module": "$import(@zuplo/runtime)",
  "options": {
    "allowRequestsOverQuota": false,
    "allowedSubscriptionStatuses": ["active", "incomplete"],
    "meterOnStatusCodes": "200-399",
    "meters": {
      "requests": 1,
      "computeUnits": 5
    }
  }
}

However, in some cases, you may not know up front how many units of a particular meter will be consumed until after the response is sent. For example, maybe your backend is responsible for computing the computeUnits on a request and send the result in the response in the compute-units header.

In Zuplo, you can support these dynamic meters by writing a little code. To make the computeUnits meter dynamic, first update the policy by setting the computeUnits meter to 0 as shown below.

{
  "export": "MonetizationInboundPolicy",
  "module": "$import(@zuplo/runtime)",
  "options": {
    "allowRequestsOverQuota": false,
    "allowedSubscriptionStatuses": ["active", "incomplete"],
    "meterOnStatusCodes": "200-399",
    "meters": {
      "requests": 1,
      "computeUnits": 0
    }
  }
}

Next you can create a custom code outbound policy that reads data from the Response (in this case the compute-units header) and sets the meter programmatically.

/modules/set-compute-units-outbound.ts

import {
  MonetizationInboundPolicy,
  ZuploRequest,
  ZuploContext,
} from "@zuplo/runtime";
 
export default async function (
  response: Response,
  request: ZuploRequest,
  context: ZuploContext,
  options: any,
  policyName: string,
) {
  const headerValue = response.headers.get("compute-units");
  let computeUnitsValue;
  if (headerValue && typeof headerValue === "string") {
    computeUnitsValue = parseInt(headerValue);
  }
 
  // Throw an error if the server doesn't send compute units
  // Alternatively, you could have a default value
  if (!computeUnitsValue) {
    throw new Error("Invalid response, no compute units sent.");
  }
 
  // Set the compute units for the request
  MonetizationInboundPolicy.setMeters(context, {
    computeUnits: computeUnitsValue,
  });
 
  return response;
}