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Datadog RUM Interceptor

A lightweight request/response interceptor for Datadog RUM, providing enhanced payload visibility for debugging and monitoring.

Features

  • Intercepts Fetch & XHR requests
  • Captures request & response payloads
  • Seamlessly integrates with Datadog RUM
  • Uses Trace ID if available, falls back to fingerprinting
  • Automatically evicts unmatched requests after 5 seconds
  • Users can modify the payload data as needed to remove or redact sensitive information.

Installation

Install via NPM

npm install @kyletaylored/datadog-rum-interceptor

Load via CDN

For direct use in the browser:

<script src="https://www.unpkg.com/@kyletaylored/datadog-rum-interceptor/dist/umd/index.js"></script>

Usage

In a Browser

const DRI = window.DD_RUM_INTERCEPTOR.init({ debug: true });

window.DD_RUM.init({
  applicationId: "YOUR_APP_ID",
  clientToken: "YOUR_CLIENT_TOKEN",
  beforeSend: (event, context) => {
    if (
      event.type === "resource" &&
      ["xhr", "fetch"].includes(event.resource.type)
    ) {
      const payload = DRI.getPayload({ event, context });
      if (payload) {
        event.context.payload = payload;
      }
    }
    return true;
  },
});

In a Node.js Environment

import datadogRumInterceptor from "@kyletaylored/datadog-rum-interceptor";
import { datadogRum } from '@datadog/browser-rum'

const DRI = datadogRumInterceptor.init({ debug: true });

datadogRum.init({
  applicationId: '<DATADOG_APPLICATION_ID>',
  clientToken: '<DATADOG_CLIENT_TOKEN>',
  ...
  beforeSend: (event, context) => {
    if (event.type === 'resource' && ['xhr', 'fetch'].includes(event.resource.type)) {
      const payload = DRI.getPayload({ event, context });
      if (payload) {
        event.context.payload = payload;
      }
    }
    return true;
  },
})

How It Works

graph TD;
  A[Intercept HTTP Requests] -->|Fetch & XHR| B[Listen using @mswjs/interceptors];
  B --> C{Trace ID Exists?};
  C -->|Yes| D[Use Trace ID for tracking];
  C -->|No| E[Generate fingerprint from resource attributes];

  D --> F[Store Request Data Temporarily];
  E --> F;

  F -->|Store using requestId| G[Wait for response];
  G -->|Response received| H[Retrieve request-response pair];
  G -->|No response within 5s| I[Evict unmatched requests];

  H --> J[Call getPayload in beforeSend];
  J --> K[Attach payload to context or log];

  style A fill:#f9f,stroke:#333,stroke-width:2px,color:#000;
  style J fill:#ff9,stroke:#333,stroke-width:2px,color:#000;
  style K fill:#9f9,stroke:#333,stroke-width:2px,color:#000;
Loading
  1. Intercepts HTTP requests
    • Uses @mswjs/interceptors to listen for Fetch & XHR requests.
  2. Links Requests & Responses
    • If Trace ID exists, it’s used for tracking.
    • If Trace ID is missing, a fingerprint is generated from resource attributes (best effort).
  3. Stores data temporarily
    • Request data is stored using requestId until the response is received.
    • Unmatched requests are automatically evicted after 5 seconds.
  4. Retrieves payload in beforeSend
    • The getPayload({ event, context }) method automatically finds and attaches the payload.

API Reference

init(config: object)

Initializes the interceptor.

const DRI = window.DD_RUM_INTERCEPTOR.init({ debug: true });
Option Type Default Description
debug bool false Enable logging for debugging

getPayload({ event, context }): object | null

Retrieves the request/response payload for a given Datadog RUM event.

const data = DRI.getPayload({ event, context });
console.log(data);
Parameter Type Description
event object The Datadog RUM event object.
context object The Datadog RUM context object.
Returns object | null The extracted payload data or null if not found.

stop()

Stops the interceptor and cleans up resources.

DRI.stop();

Troubleshooting

No request data is being captured

  • Ensure interceptor is initialized before Datadog RUM.
  • Verify beforeSend is correctly configured.

Requests with Trace ID are not matching

  • Check if Datadog injects trace headers (x-datadog-trace-id).
  • If missing, the fingerprinting fallback will be used.

Disclaimer

This software is provided "as is," without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose, and non-infringement. In no event shall the authors, contributors, or their employers be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the software or the use or other dealings in the software.

By using this software, you acknowledge and agree that you assume all risks and liabilities associated with its use, and you waive any and all claims against the authors, contributors, and their employers.