proxy.onRequest

Fired when a web request is about to be made, to give the extension an opportunity to proxy it.

This event is closely modeled on the events defined in the webRequest API. Like those events, its addListener() function takes three arguments:

• the listener that is called when the event is fired.
• a RequestFilter object controlling which requests cause the event to fire.
• an array of strings to control other aspects of the event's behavior.

The event is fired before any of the webRequest events for the same request.

When the event is fired, the listener is called with an object containing information about the request. The listener returns a {{WebExtAPIRef("proxy.ProxyInfo")}} object representing a proxy to use (or an array of {{WebExtAPIRef("proxy.ProxyInfo")}} objects, enabling the browser to fail over if a proxy is unreachable). By default, the request fails over to any browser-defined proxy unless a null object or an array ending in a null object is returned.

To use proxy.onRequest, an extension must have the "proxy" API permission and the host permission for the URLs of the requests that it intercepts, which means that the match patterns in the filter argument must be a subset of the extension's host permissions.

Syntax

browser.proxy.onRequest.addListener(
  listener,             //  function
  filter,               //  object
  extraInfoSpec         //  optional array of strings
)
browser.proxy.onRequest.removeListener(listener)
browser.proxy.onRequest.hasListener(listener)

Events have three functions:

• addListener(listener, filter, extraInfoSpec)
  • : Adds a listener to this event.
• removeListener(listener)
  • : Stops listening to this event. The listener argument is the listener to remove.
• hasListener(listener)
  • : Checks whether listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax

Parameters

• listener

  • : The function called when this event occurs. The function is passed one argument, which is a {{WebExtAPIRef("proxy.RequestDetails")}} object containing details of the request.

    The listener can return any of:

    • a {{WebExtAPIRef("proxy.ProxyInfo")}} object.
    • an array of {{WebExtAPIRef("proxy.ProxyInfo")}} objects.
    • a Promise that resolves to a ProxyInfo object.
    • a Promise that resolves to an array of ProxyInfo objects.

    When the listener returns an array or a Promise that resolves to an array, the ProxyInfo objects after the first one represent failovers. If the proxy at position N in the array is not reachable when its ProxyInfo.failoverTimeout expires, the browser tries the proxy at position N+1.

    By default, the request fails over to any browser-defined proxy unless a null object or an array ending in a null object ([{ ... proxy info ...} , null]) is returned.

    If there is an error specifying the {{WebExtAPIRef("proxy.ProxyInfo")}} objects, then {{WebExtAPIRef("proxy.onError")}} is called.

• filter

  • : {{WebExtAPIRef('webRequest.RequestFilter')}}. A set of filters that restricts the events sent to the listener.

• extraInfoSpec {{optional_inline}}

  • : array of string. Extra options for the event. Pass "requestHeaders" to include the request headers in the details object passed to the listener.

Examples

This code intercepts requests to <all_urls>, and proxies them if they are not for a top-level frame.

function shouldProxyRequest(requestInfo) {
  return requestInfo.parentFrameId !== -1;
}

function handleProxyRequest(requestInfo) {
  if (shouldProxyRequest(requestInfo)) {
    console.log(`Proxying: ${requestInfo.url}`);
    return { type: "http", host: "127.0.0.1", port: 65535 };
  }
  return { type: "direct" };
}

browser.proxy.onRequest.addListener(handleProxyRequest, {
  urls: ["<all_urls>"],
});

{{WebExtExamples}}

Browser compatibility

{{Compat}}