This event is triggered when a request is about to be made, and before headers are available. This is a good place to listen if you want to cancel or redirect the request.
To cancel or redirect the request, first include
"blocking"
在
extraInfoSpec
array argument to
addListener()
. Then, in the listener function, return a
BlockingResponse
object, setting the appropriate property:
cancel
采用值
true
.
redirectUrl
with the value set to the URL to which you want to redirect.
If an extension wants to redirect a public (e.g. HTTPS) URL to an extension page , the extension's manifest.json file must contain a web_accessible_resources key that lists the URL for the extension page.
When multiple blocking handlers modify a request, only one set of modifications take effect. Redirects and cancellations have the same precedence. So if you canceled a request, you might see another request with the same
requestId
again if another blocking handler redirected the request.
From Firefox 52 onwards, instead of returning
BlockingResponse
, the listener can return a
Promise
which is resolved with a
BlockingResponse
. This enables the listener to process the request asynchronously.
若使用
"blocking"
, you must have the
"webRequestBlocking" API permission
in your manifest.json.
browser.webRequest.onBeforeRequest.addListener(
listener
,
// function
filter
,
// object
extraInfoSpec
// optional array of strings
)
浏览器
.
webRequest
.
onBeforeRequest
.
removeListener
(
listener
)
浏览器
.
webRequest
.
onBeforeRequest
.
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)
校验是否
listener
is registered for this event. Returns
true
if it is listening,
false
否则。
callback
Function that will be called when this event occurs. The function will be passed the following arguments:
返回：
webRequest.BlockingResponse
。若
"blocking"
is specified in the
extraInfoSpec
parameter, the event listener should return a
BlockingResponse
object, and can set either its
cancel
or its
redirectUrl
properties. From Firefox 52 onwards, instead of returning
BlockingResponse
, the listener can return a
Promise
which is resolved with a
BlockingResponse
. This enables the listener to process the request asynchronously.
filter
webRequest.RequestFilter
. A filter that restricts the events that will be sent to this listener.
extraInfoSpec
可选
array
of
string
. Extra options for the event. You can pass any of the following values:
"blocking"
: make the request synchronous, so you can cancel or redirect the request
"requestBody"
: include
requestBody
在
details
object passed to the listener
cookieStoreId
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
. Contains 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 actually for the top-level document, then this array is empty.
url
string
. The URL that the document was loaded from.
frameId
integer
。
frameId
of the document.
details.frameAncestors[0].frameId
如同
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.
incognito
boolean
. Whether the request is from a private browsing window.
方法
string
. Standard HTTP method: for example, "GET" or "POST".
originUrl
string
. URL of the resource which 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".
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 will be the iframe's parent document, but the
originUrl
will be the URL of the document in the iframe that contained the link.
parentFrameId
integer
. ID of the frame that contains the frame which sent the request. Set to -1 if no parent frame exists.
proxyInfo
对象
. 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.
requestBody
可选
对象
. Contains the HTTP request body data. Only provided if
extraInfoSpec
包含
"requestBody"
.
error
可选
string
. This is set if any errors were encountered when obtaining request body data.
formData
可选
对象
. This object is present if the request method is POST and the body is a sequence of key-value pairs encoded in UTF-8 as either "multipart/form-data" or "application/x-www-form-urlencoded".
It is a dictionary in which each key contains the list of all values for that key. For example:
{'key': ['value1', 'value2']}
. If the data is of another media type, or if it is malformed, the object is not present.
raw
可选
array
of
. If the request method is PUT or POST, and the body is not already parsed in
webRequest.UploadData
formData
, then this array contains the unparsed request body elements.
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.
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
编号
. 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
对象
. 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.
The classification flags include:
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
，和
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.
BCD tables only load in the browser
Regarding DNS resolution when BlockingResponse is used with OnBeforeRequest: In HTTP Channel, onBeforeRequest with blocking response does happen prior to DNS resolution and also prior to speculative connect. For other channels, speculative connect may cause DNS requests to happen before onBeforeRequest. This ordering is not something an extension developer ought to rely on as it may vary across browsers, and from one browser version to another, let alone one request channel to another. Refer BugZilla issue clarification provided by Mozilla developers on DNS resolution ordering
This code logs the URL for every resource requested which matches the <all_urls> pattern:
function logURL(requestDetails) {
console.log("Loading: " + requestDetails.url);
}
browser.webRequest.onBeforeRequest.addListener(
logURL,
{urls: ["<all_urls>"]}
);
This code cancels requests for images that are made to URLs under "https://mdn.mozillademos.org/" (to see the effect, visit any page on MDN that contains images, such as webRequest ):
// match pattern for the URLs to redirect
var pattern = "https://mdn.mozillademos.org/*";
// cancel function returns an object
// which contains a property `cancel` set to `true`
function cancel(requestDetails) {
console.log("Canceling: " + requestDetails.url);
return {cancel: true};
}
// add the listener,
// passing the filter argument and "blocking"
browser.webRequest.onBeforeRequest.addListener(
cancel,
{urls: [pattern], types: ["image"]},
["blocking"]
);
This code replaces, by redirection, all network requests for images that are made to URLs under "https://mdn.mozillademos.org/" (to see the effect, visit any page on MDN that contains images, such as webRequest ):
// match pattern for the URLs to redirect
var pattern = "https://mdn.mozillademos.org/*";
// redirect function
// returns an object with a property `redirectURL`
// set to the new URL
function redirect(requestDetails) {
console.log("Redirecting: " + requestDetails.url);
return {
redirectUrl: "https://38.media.tumblr.com/tumblr_ldbj01lZiP1qe0eclo1_500.gif"
};
}
// add the listener,
// passing the filter argument and "blocking"
browser.webRequest.onBeforeRequest.addListener(
redirect,
{urls:[pattern], types:["image"]},
["blocking"]
);
This code is exactly like the previous example, except that the listener handles the request asynchronously. It returns a
Promise
that sets a timer, and resolves with the redirect URL when the timer expires:
// match pattern for the URLs to redirect
var pattern = "https://mdn.mozillademos.org/*";
// URL we will redirect to
var redirectUrl = "https://38.media.tumblr.com/tumblr_ldbj01lZiP1qe0eclo1_500.gif";
// redirect function returns a Promise
// which is resolved with the redirect URL when a timer expires
function redirectAsync(requestDetails) {
console.log("Redirecting async: " + requestDetails.url);
return new Promise((resolve, reject) => {
window.setTimeout(() => {
resolve({redirectUrl});
}, 2000);
});
}
// add the listener,
// passing the filter argument and "blocking"
browser.webRequest.onBeforeRequest.addListener(
redirectAsync,
{urls: [pattern], types: ["image"]},
["blocking"]
);
Another example, that redirects all images to a data url:
var pattern = "https://mdn.mozillademos.org/*";
var image = `
<svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%">
<rect style="stroke-width: 10; stroke: #666;" width="100%" height="100%" fill="#d4d0c8" />
<text transform="translate(0, 9)" x="50%" y="50%" width="100%" fill="#666" height="100%" style="text-anchor: middle; font: bold 10pt 'Segoe UI', Arial, Helvetica, Sans-serif;">Blocked</text>
</svg>
`;
function listener(details) {
let redirectUrl = "data:image/svg+xml," + encodeURIComponent(image);
return {redirectUrl};
}
browser.webRequest.onBeforeRequest.addListener(
listener,
{urls: [pattern], types: ["image"]},
["blocking"]
);
Here's another version:
function randomColor() {
return "#" + Math.floor(Math.random()*16777215).toString(16);
}
var pattern = "https://mdn.mozillademos.org/*";
var image = `
<svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%">
<rect width="100%" height="100%" fill="${randomColor()}"/>
</svg>
`;
function listener(details) {
let redirectUrl = "data:image/svg+xml," + encodeURIComponent(image);
return {redirectUrl};
}
browser.webRequest.onBeforeRequest.addListener(
listener,
{urls: [pattern], types: ["image"]},
["blocking"]
);
注意：
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.
最后修改： , 由 MDN 贡献者