Fired when the HTTP response headers for a request are received. 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.
If you use "blocking"
, you must have the "webRequestBlocking" API permission in your manifest.json.
It is possible for extensions to make conflicting requests. If two extensions listen to onHeadersReceived
for the same request and return responseHeaders
to set the same header (for example, Set-Cookie
) not present in the original response, only one of the changes will succeed.
However, the Content-Security-Policy
header is treated differently; its values are combined to apply all the specified policies. But, if two extensions set a CSP value that conflicts, the CSP service makes the restriction more strict to resolve the conflict. For example, if one extension sets img-src: example.com
, and another extension sets img-src: example.org
, the result is img-src: 'none'
. Merged modifications always lean towards being more restrictive, though an extension may remove the original CSP header.
If you want to see the headers that are processed by the system, without the risk that another extension will alter them, use webRequest.onResponseStarted
, although you can't modify headers on this event.
browser.webRequest.onHeadersReceived.addListener( listener, // function filter, // object extraInfoSpec // optional array of strings ) browser.webRequest.onHeadersReceived.removeListener(listener) browser.webRequest.onHeadersReceived.hasListener(listener)
Events have three functions:
addListener(callback, filter, extraInfoSpec)
removeListener(listener)
listener
argument is the listener to remove.hasListener(listener)
listener
is registered for this event. Returns true
if it is listening, false
otherwise.callback
The function called when this event occurs. The function is 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 will return a BlockingResponse
object, and can set its responseHeaders
property. In Firefox, the return value can be a Promise
that resolves to a BlockingResponse
.
filter
webRequest.RequestFilter
. A set of filters that restricts the events that are sent to this listener.extraInfoSpec
Optional
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 and response headers"responseHeaders"
to include the response headers in the details
object passed to the listenercookieStoreId
string
. If the request is from a tab open in a contextual identity, the cookie store ID of the contextual identity.documentUrl
string
. URL of the document in which the resource will be loaded. For example, if the web page at "https://example.com" contains an image or an iframe, then the documentUrl
for the image or iframe will be "https://example.com". For a top-level document, documentUrl
is undefined.frameAncestors
array
. Information for each document in the frame hierarchy up to the top-level document. The first element in the array contains information about the immediate parent of the document being requested, and the last element contains information about the top-level document. If the load is for the top-level document, then this array is empty.url
string
. The URL that the document was loaded from.frameId
integer
. The frameId
of the document. details.frameAncestors[0].frameId
is the same as details.parentFrameId
.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.fromCache
boolean
. Whether the response is fetched from disk cache.incognito
boolean
. Whether the request is from a private browsing window.ip
string
. The IP address of the server the request was sent to. It may be a literal IPv6 address.method
string
. Standard HTTP method: for example, "GET" or "POST".originUrl
string
. URL of the resource that triggered the request. For example, if "https://example.com" contains a link, and the user clicks the link, then the originUrl
for the resulting request is "https://example.com".
The originUrl
is often but not always the same as the documentUrl
. For example, if a page contains an iframe, and the iframe contains a link that loads a new document into the iframe, then the documentUrl
for the resulting request is the iframe's parent document, but the originUrl
is the URL of the document in the iframe that contained the link.
parentFrameId
integer
. ID of the frame that contains the frame that sent the request. Set to -1 if no parent frame exists.proxyInfo
object
. This property is present only if the request is being proxied. It contains the following properties:
host
string
. The hostname of the proxy server.port
integer
. The port number of the proxy server.type
string
. The type of proxy server. One of:
username
string
. Username for the proxy service.proxyDNS
boolean
. True if the proxy will perform domain name resolution based on the hostname supplied, meaning that the client should not do its own DNS lookup.failoverTimeout
integer
. Failover timeout in seconds. If the proxy connection fails, the proxy will not be used again for this period.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.responseHeaders
Optional
webRequest.HttpHeaders
. The HTTP response headers that were received for this request.statusCode
integer
. Standard HTTP status code returned by the server.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).tabId
integer
. ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab.thirdParty
boolean
. Indicates whether the request and its content window hierarchy are third party.timeStamp
number
. The time when this event fired, in milliseconds since the epoch.type
webRequest.ResourceType
. The type of resource being requested: for example, "image", "script", "stylesheet".url
string
. Target of the request.urlClassification
object
. The type of tracking associated with the request, if with the request has been classified by Firefox Tracking Protection. This is an object with the following properties:firstParty
array
of strings
. Classification flags for the request's first party.thirdParty
array
of strings
. Classification flags for the request or its window hierarchy's third parties.fingerprinting
and fingerprinting_content
: indicates the request is involved in fingerprinting. fingerprinting_content
indicates the request is loaded from an origin that has been found to fingerprint but is not considered to participate in tracking, such as a payment provider.cryptomining
and cryptomining_content
: similar to the fingerprinting category but for cryptomining resources.tracking
, tracking_ad
, tracking_analytics
, tracking_social
, and tracking_content
: indicates the request is involved in tracking. tracking
is any generic tracking request, the ad
, analytics
, social
, and content
suffixes identify the type of tracker.any_basic_tracking
: a meta flag that combines any tracking and fingerprinting flags, excluding tracking_content
and fingerprinting_content
.any_strict_tracking
: a meta flag that combines any tracking and fingerprinting flags, including tracking_content
and fingerprinting_content
.any_social_tracking
: a meta flag that combines any social tracking flags.Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
onHeadersReceived |
Yes
Asynchronous event listeners are not supported.
|
14
Asynchronous event listeners are not supported.
|
45
["Modification of the 'Content-Type' header is supported from version 51.", "Asynchronous event listeners are supported from version 52."]
|
? |
Yes
Asynchronous event listeners are not supported.
|
14
extraInfoSpec options are not supported.
|
? |
? |
48
["Modification of the 'Content-Type' header is supported from version 51.", "Asynchronous event listeners are supported from version 52."]
|
? |
? |
? |
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". browser.webRequest.onHeadersReceived.addListener( setCookie, {urls: [targetPage]}, ["blocking", "responseHeaders"] );
This code does the same thing the previous example, except that the listener is asynchronous, returning a Promise
which is resolved with the new headers:
var targetPage = "https://developer.mozilla.org/en-US/Firefox/Developer_Edition"; // Return a Promise that sets a timer. // When the timer fires, resolve the promise with // modified set of response headers. function setCookieAsync(e) { var asyncSetCookie = new Promise((resolve, reject) => { window.setTimeout(() => { var setMyCookie = { name: "Set-Cookie", value: "my-cookie1=my-cookie-value1" }; e.responseHeaders.push(setMyCookie); resolve({responseHeaders: e.responseHeaders}); }, 2000); }); return asyncSetCookie; } // Listen for onHeaderReceived for the target page. // Set "blocking" and "responseHeaders". browser.webRequest.onHeadersReceived.addListener( setCookieAsync, {urls: [targetPage]}, ["blocking", "responseHeaders"] );
Note: This API is based on Chromium's chrome.webRequest
API. This documentation is derived from web_request.json
in the Chromium code.
Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.
© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest/onHeadersReceived