Request Interception — Block and Modify HTTP Requests

Foxbridge implements the CDP Fetch domain for request interception, translating to Juggler’s Browser.setRequestInterception API.

Enabling Interception


// Via Puppeteer
await page.setRequestInterception(true);
 
page.on('request', request => {
  if (request.url().includes('ads'))
    request.abort();
  else
    request.continue();
});

Under the hood, Puppeteer calls Fetch.enable which foxbridge translates to:


Fetch.enable → Browser.setRequestInterception({enabled: true})

The browserContextId is automatically resolved from the CDP session.

Supported Methods

CDP Method	Juggler Method	Description
`Fetch.enable`	`Browser.setRequestInterception`	Start intercepting requests
`Fetch.disable`	`Browser.setRequestInterception(false)`	Stop intercepting
`Fetch.continueRequest`	`Browser.continueInterceptedRequest`	Continue with optional URL/header modifications
`Fetch.fulfillRequest`	`Browser.fulfillInterceptedRequest`	Respond with custom status/headers/body
`Fetch.failRequest`	`Browser.abortInterceptedRequest`	Fail with an error reason
`Fetch.continueWithAuth`	`Browser.handleAuthRequest`	Handle HTTP auth challenges
`Fetch.getResponseBody`	`Browser.getResponseBody`	Read intercepted response body
`Fetch.continueResponse`	`Browser.continueInterceptedRequest`	Continue with modified response headers

Error Reason Mapping

Fetch.failRequest accepts a CDP Network.ErrorReason which is mapped to Juggler error codes:

CDP ErrorReason	Juggler Code
`Failed`	`failed`
`Aborted`	`aborted`
`TimedOut`	`timedout`
`AccessDenied`	`accessdenied`
`ConnectionRefused`	`connectionrefused`
`NameNotResolved`	`namenotresolved`
`InternetDisconnected`	`internetdisconnected`
`BlockedByClient`	`blockedbyclient`
`BlockedByResponse`	`blockedbyresponse`

Event Flow

When a request is intercepted, Juggler emits Browser.requestIntercepted. Foxbridge translates this into two CDP events in order:

Network.requestWillBeSent — so Puppeteer has the request metadata
Fetch.requestPaused — so Puppeteer knows to call continue/abort/fulfill

The requestId is shared between both events. Foxbridge resolves the correct CDP session from the request’s frameId.

Response Body

Fetch.getResponseBody returns the body from Juggler’s base64-encoded format. If the content is valid UTF-8 text, it is decoded and returned as plain text (base64Encoded: false). Binary content is returned as-is with base64Encoded: true.

BiDi Backend

On the BiDi backend, request interception uses network.addIntercept with the beforeRequestSent phase. Intercept IDs are tracked for cleanup when interception is disabled.