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    webRequest.onHeadersReceived

    Fired when the HTTP response headers associated with a request have been received. You can use this event to modify HTTP response headers.

    To have the response headers passed into the listener along with the rest of the request data, pass "responseHeaders" in the extraInfoSpec array.

    To modify the headers, pass "blocking" in extraInfoSpec. Then in your event listener, return an object with a property named responseHeaders, whose value is the set of response headers to use. The browser will behave as if the server had sent the modified headers.

    If you use "blocking", you must have the "webRequestBlocking" API permission in your manifest.json.

    Note that it is possible for add-ons to conflict here. If two add-ons listen to onHeadersReceived for the same request, then the second listener will see modifications made by the first listener, and will be able to undo any changes made by the first listener. For example, if the first listener adds a Set-Cookie header, and the second listener strips all Set-Cookie headers, then the first listener's modifications will be lost. If you want to see the headers that are actually processed by the system, without the risk that another add-on will subsequently alter them, use onResponseStarted, although you can't modify headers on this event.

    Syntax

    browser.webRequest.onHeadersReceived.addListener(function(
  details // object
) {...})
browser.webRequest.onHeadersReceived.removeListener(listener)
browser.webRequest.onHeadersReceived.hasListener(listener)

    Events have three functions:

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

    addListener syntax

    Parameters

    callback

    Function that will be called when this event occurs. The function will be passed the following arguments:

    details
    object. Details of the request. This will include response headers if you have included "responseHeaders" in extraInfoSpec.

    Returns: webRequest.BlockingResponse. If "blocking" is specified in the extraInfoSpec parameter, the event listener should return a BlockingResponse object, and can set its responseHeaders property.

    filter
    webRequest.RequestFilter. A set of filters that restricts the events that will be sent to this listener.
    extraInfoSpecOptional
    array of string. Extra options for the event. You can pass any of the following values:
    • "blocking" to make the request synchronous, so you can modify request headers
    • "responseHeaders" to include the response headers in the details object passed to the listener

    Additional objects

    details

    requestId
    string. The ID of the request. Request IDs are unique within a browser session, so you can use them to relate different events associated with the same request.
    url
    string. Target of the request.
    method
    string. Standard HTTP method: for example, "GET" or "POST".
    frameId
    integer. Zero if the request happens in the main frame; a positive value is the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (type is main_frame or sub_frame), frameId indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab.
    parentFrameId
    integer. ID of the frame that contains the frame which sent the request. Set to -1 if no parent frame exists.
    tabId
    integer. ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab.
    type
    webRequest.ResourceType. The type of resource being requested: for example, "image", "script", "stylesheet".
    timeStamp
    number. The time when this event fired, in milliseconds since the epoch.
    statusLine
    string. HTTP status line of the response or the 'HTTP/0.9 200 OK' string for HTTP/0.9 responses (that is, responses that lack a status line).
    responseHeadersOptional
    webRequest.HttpHeaders. The HTTP response headers that were received for this request.
    statusCode
    integer. Standard HTTP status code returned by the server.

    Browser compatibility

    EdgeFirefoxChromeOpera
    Basic support?45.0Yes33
    Firefox
    Basic support48.0

    Examples

    This code sets an extra cookie when requesting a resource from the target URL:

    var targetPage = "https://developer.mozilla.org/en-US/Firefox/Developer_Edition";

// Add the new header to the original array,
// and return it.
function setCookie(e) {
  var setMyCookie = {
    name: "Set-Cookie",
    value: "my-cookie1=my-cookie-value1"
  };
  e.responseHeaders.push(setMyCookie);
  return {responseHeaders: e.responseHeaders};
}

// Listen for onHeaderReceived for the target page.
// Set "blocking" and "responseHeaders".
chrome.webRequest.onHeadersReceived.addListener(
  setCookie,
  {urls: [targetPage]},
  ["blocking", "responseHeaders"]
);

    Acknowledgements

    This API is based on Chromium's chrome.webRequest API. This documentation is derived from web_request.json in the Chromium code.

    Document Tags and Contributors

    Tags: 
     Contributors to this page: wbamberg, johnadungan
     Last updated by: wbamberg,