• June 25, 2024

Cookies Http

Using HTTP cookies - MDN Web Docs

Using HTTP cookies – MDN Web Docs

An HTTP cookie (web cookie, browser cookie) is a small piece of data that a server sends to a user’s web browser. The browser may store the cookie and send it back to the same server with later requests.
Typically, an HTTP cookie is used to tell if two requests come from the same browser—keeping a user logged in, for example. It remembers stateful information for the stateless HTTP protocol.
Cookies are mainly used for three purposes:
Session management
Logins, shopping carts, game scores, or anything else the server should remember
User preferences, themes, and other settings
Recording and analyzing user behavior
Cookies were once used for general client-side storage. While this made sense when they were the only way to store data on the client, modern storage APIs are now recommended. Cookies are sent with every request, so they can worsen performance (especially for mobile data connections). Modern APIs for client storage are the Web Storage API (localStorage and sessionStorage) and IndexedDB.
Note: To see stored cookies (and other storage that a web page can use), you can enable the Storage Inspector in Developer Tools and select Cookies from the storage eating cookiesAfter receiving an HTTP request, a server can send one or more Set-Cookie headers with the response. The browser usually stores the cookie and sends it with requests made to the same server inside a Cookie HTTP header. You can specify an expiration date or time period after which the cookie shouldn’t be sent. You can also set additional restrictions to a specific domain and path to limit where the cookie is sent. For details about the header attributes mentioned below, refer to the Set-Cookie reference Set-Cookie and Cookie headersThe Set-Cookie HTTP response header sends cookies from the server to the user agent. A simple cookie is set like this:
Set-Cookie: =
This instructs the server sending headers to tell the client to store a pair of cookies:
HTTP/2. 0 200 OK
Content-Type: text/html
Set-Cookie: yummy_cookie=choco
Set-Cookie: tasty_cookie=strawberry
[page content]
Then, with every subsequent request to the server, the browser sends all previously stored cookies back to the server using the Cookie header.
GET / HTTP/2. 0
Host: Cookie: yummy_cookie=choco; tasty_cookie=strawberry
Define the lifetime of a cookieThe lifetime of a cookie can be defined in two ways:
Session cookies are deleted when the current session ends. The browser defines when the “current session” ends, and some browsers use session restoring when restarting. This can cause session cookies to last indefinitely.
Permanent cookies are deleted at a date specified by the Expires attribute, or after a period of time specified by the Max-Age attribute.
For example:
Set-Cookie: id=a3fWa; Expires=Thu, 31 Oct 2021 07:28:00 GMT;
Note: When you set an Expires date and time, they’re relative to the client the cookie is being set on, not the server.
If your site authenticates users, it should regenerate and resend session cookies, even ones that already exist, whenever a user authenticates. This approach helps prevent session fixation attacks, where a third party can reuse a user’s strict access to cookiesYou can ensure that cookies are sent securely and aren’t accessed by unintended parties or scripts in one of two ways: with the Secure attribute and the HttpOnly attribute.
A cookie with the Secure attribute is only sent to the server with an encrypted request over the HTTPS protocol. It’s never sent with unsecured HTTP (except on localhost), which means attackers man-in-the-middle can’t access it easily. Insecure sites (with: in the URL) can’t set cookies with the Secure attribute. However, don’t assume that Secure prevents all access to sensitive information in cookies. For example, someone with access to the client’s hard disk (or JavaScript if the HttpOnly attribute isn’t set) can read and modify the information.
A cookie with the HttpOnly attribute is inaccessible to the JavaScript API; it’s only sent to the server. For example, cookies that persist in server-side sessions don’t need to be available to JavaScript and should have the HttpOnly attribute. This precaution helps mitigate cross-site scripting (XSS) attacks.
Here’s an example:
Set-Cookie: id=a3fWa; Expires=Thu, 21 Oct 2021 07:28:00 GMT; Secure; HttpOnly
Define where cookies are sentThe Domain and Path attributes define the scope of a cookie: what URLs the cookies should be sent to.
Domain attribute
The Domain attribute specifies which hosts can receive a cookie. If unspecified, the attribute defaults to the same host that set the cookie, excluding subdomains. If Domain is specified, then subdomains are always included. Therefore, specifying Domain is less restrictive than omitting it. However, it can be helpful when subdomains need to share information about a user.
For example, if you set, cookies are available on subdomains like
Path attribute
The Path attribute indicates a URL path that must exist in the requested URL in order to send the Cookie header. The%x2F (“/”) character is considered a directory separator, and subdirectories match as well.
For example, if you set Path=/docs, these request paths match:
But these request paths don’t:
SameSite attribute
The SameSite attribute lets servers specify whether/when cookies are sent with cross-site requests (where Site is defined by the registrable domain). This provides some protection against cross-site request forgery attacks (CSRF). It takes three possible values: Strict, Lax, and None.
With Strict, the cookie is only sent to the site where it originated. Lax is similar, except that cookies are sent when the user navigates to the cookie’s origin site. For example, by following a link from an external site. None specifies that cookies are sent on both originating and cross-site requests, but only in secure contexts (i. e., if SameSite=None then the Secure attribute must also be set). If no SameSite attribute is set, the cookie is treated as Lax.
Set-Cookie: mykey=myvalue; SameSite=Strict
Note: The standard related to SameSite recently changed (MDN documents the new behavior above). See the cookies Browser compatibility table for information about how the attribute is handled in specific browser versions:
SameSite=Lax is the new default if SameSite isn’t specified. Previously, cookies were sent for all requests by default.
Cookies with SameSite=None must now also specify the Secure attribute (they require a secure context).
Cookie prefixes
Because of the design of the cookie mechanism, a server can’t confirm that a cookie was set from a secure origin or even tell where a cookie was originally set.
A vulnerable application on a subdomain can set a cookie with the Domain attribute, which gives access to that cookie on all other subdomains. This mechanism can be abused in a session fixation attack. See session fixation for primary mitigation methods.
As a defense-in-depth measure, however, you can use cookie prefixes to assert specific facts about the cookie. Two prefixes are available:
If a cookie name has this prefix, it’s accepted in a Set-Cookie header only if it’s also marked with the Secure attribute, was sent from a secure origin, does not include a Domain attribute, and has the Path attribute set to /. This way, these cookies can be seen as “domain-locked”.
If a cookie name has this prefix, it’s accepted in a Set-Cookie header only if it’s marked with the Secure attribute and was sent from a secure origin. This is weaker than the __Host- prefix.
The browser will reject cookies with these prefixes that don’t comply with their restrictions. Note that this ensures that subdomain-created cookies with prefixes are either confined to the subdomain or ignored completely. As the application server only checks for a specific cookie name when determining if the user is authenticated or a CSRF token is correct, this effectively acts as a defense measure against session fixation.
Note: On the application server, the web application must check for the full cookie name including the prefix. User agents do not strip the prefix from the cookie before sending it in a request’s Cookie header.
For more information about cookie prefixes and the current state of browser support, see the Prefixes section of the Set-Cookie reference article.
JavaScript access using
You can create new cookies via JavaScript using the property. You can access existing cookies from JavaScript as well if the HttpOnly flag isn’t set.
= “yummy_cookie=choco”;
= “tasty_cookie=strawberry”;
// logs “yummy_cookie=choco; tasty_cookie=strawberry”
Cookies created via JavaScript can’t include the HttpOnly flag.
Please note the security issues in the Security section below. Cookies available to JavaScript can be stolen through curityNote: When you store information in cookies, keep in mind that all cookie values are visible to, and can be changed by, the end user. Depending on the application, you may want to use an opaque identifier that the server looks up, or investigate alternative authentication/confidentiality mechanisms such as JSON Web Tokens.
Ways to mitigate attacks involving cookies:
Use the HttpOnly attribute to prevent access to cookie values via JavaScript.
Cookies that are used for sensitive information (such as indicating authentication) should have a short lifetime, with the SameSite attribute set to Strict or Lax. (See SameSite attribute, above. ) In browsers that support SameSite, this ensures that the authentication cookie isn’t sent with cross-site requests. This would make the request effectively unauthenticated to the application server.
Tracking and privacyThird-party cookiesA cookie is associated with a domain. If this domain is the same as the domain of the page you’re on, the cookie is called a first-party cookie. If the domain is different, it’s a third-party cookie. While the server hosting a web page sets first-party cookies, the page may contain images or other components stored on servers in other domains (for example, ad banners) that may set third-party cookies. These are mainly used for advertising and tracking across the web. For example, the types of cookies used by Google.
A third-party server can create a profile of a user’s browsing history and habits based on cookies sent to it by the same browser when accessing multiple sites. Firefox, by default, blocks third-party cookies that are known to contain trackers. Third-party cookies (or just tracking cookies) may also be blocked by other browser settings or extensions. Cookie blocking can cause some third-party components (such as social media widgets) not to function as intended.
Note: Servers can (and should) set the cookie SameSite attribute to specify whether or not cookies may be sent to third party sites. Legislation or regulations that cover the use of cookies include:
The General Data Privacy Regulation (GDPR) in the European Union
The ePrivacy Directive in the EU
The California Consumer Privacy Act
These regulations have global reach. They apply to any site on the World Wide Web that users from these jurisdictions access (the EU and California, with the caveat that California’s law applies only to entities with gross revenue over 25 million USD, among
These regulations include requirements such as:
Notifying users that your site uses cookies.
Allowing users to opt out of receiving some or all cookies.
Allowing users to use the bulk of your service without receiving cookies.
There may be other regulations that govern the use of cookies in your locality. The burden is on you to know and comply with these regulations. There are companies that offer “cookie banner” code that helps you comply with these ways to store information in the browserAnother approach to storing data in the browser is the Web Storage API. The ssionStorage and window. localStorage properties correspond to session and permanent cookies in duration, but have larger storage limits than cookies, and are never sent to a server. More structured and larger amounts of data can be stored using the IndexedDB API, or a library built on it.
There are some techniques designed to recreate cookies after they’re deleted. These are known as “zombie” cookies. These techniques violate the principles of user privacy and user control, may violate data privacy regulations, and could expose a website using them to legal also
SameSite cookies
Inspecting cookies using the Storage Inspector
Cookie specification: RFC 6265
HTTP cookie on Wikipedia
Cookies, the GDPR, and the ePrivacy Directive
What is a Cookie? How it works and ways to stay safe

What is a Cookie? How it works and ways to stay safe

HTTP cookies are essential to the modern Internet but a vulnerability to your privacy. As a necessary part of web browsing, HTTP cookies help web developers give you more personal, convenient website visits. Cookies let websites remember you, your website logins, shopping carts and more. But they can also be a treasure trove of private info for criminals to spy arding your privacy online can be overwhelming. Fortunately, even a basic understanding of cookies can help you keep unwanted eyes off your internet most cookies are perfectly safe, some can be used to track you without your consent. Worse, legitimate cookies can sometimes be spied upon if a criminal gets this article, we will guide you through how cookies work and how you can stay safe online. We’ll answer key questions like:What are cookies? What are cookies on a computer? What are cookies on a website? Can cookies contain viruses? How can I remove cookies? What Are Cookies? Cookies are text files with small pieces of data — like a username and password — that are used to identify your computer as you use a computer network. Specific cookies known as HTTP cookies are used to identify specific users and improve your web browsing stored in a cookie is created by the server upon your connection. This data is labeled with an ID unique to you and your the cookie is exchanged between your computer and the network server, the server reads the ID and knows what information to specifically serve to you. Different types of cookies – Magic Cookies and HTTP CookiesMagic CookiesHTTP CookiesCookies generally function the same but have been applied to different use cases:”Magic cookies” are an old computing term that refers to packets of information that are sent and received without changes. Commonly, this would be used for a login to computer database systems, such as a business internal network. This concept predates the modern “cookie” we use cookies are a repurposed version of the “magic cookie” built for internet browsing. Web browser programmer Lou Montulli used the “magic cookie” as inspiration in 1994. He recreated this concept for browsers when he helped an online shopping store fix their overloaded HTTP cookie is what we currently use to manage our online experiences. It is also what some malicious people can use to spy on your online activity and steal your personal explain, you’ll want to understand exactly what are internet cookies and why do they matter? What are HTTP Cookies? HTTP cookies, or internet cookies, are built specifically for Internet web browsers to track, personalize, and save information about each user’s session. A “session” just refers to the time you spend on a okies are created to identify you when you visit a new website. The web server — which stores the website’s data — sends a short stream of identifying info to your web owser cookies are identified and read by “name-value” pairs. These tell cookies where to be sent and what data to server only sends the cookie when it wants the web browser to save it. If you’re wondering “where are cookies stored, ” it’s simple: your web browser will store it locally to remember the “name-value pair” that identifies a user returns to that site in the future, the web browser returns that data to the web server in the form of a cookie. This is when your browser will send it back to the server to recall data from your previous put it simply, cookies are a bit like getting a ticket for a coat check:You hand over your “coat” to the cloak desk. In this case, a pocket of data is linked to you on the website server when you connect. This data can be your personal account, your shopping cart, or even just what pages you’ve get a “ticket” to identify you as the “coat” owner. The cookie for the website is given to you and stored in your web browser. It has a unique ID especially for you leave and return, you can get the “coat” with your “ticket”. Your browser gives the website your cookie. It reads the unique ID in the cookie to assemble your activity data and recall your visit just as you left Are Cookies Used For? Websites use HTTP cookies to streamline your web experiences. Without cookies, you’d have to login again after you leave a site or rebuild your shopping cart if you accidentally close the page. Making cookies an important a part of the internet on this, you’ll want to understand why they’re worth keeping — and when they’re ’s how cookie are intended to be used:Session management. For example, cookies let websites recognize users and recall their individual login information and preferences, such as sports news versus rsonalization. Customized advertising is the main way cookies are used to personalize your sessions. You may view certain items or parts of a site, and cookies use this data to help build targeted ads that you might acking. Shopping sites use cookies to track items users previously viewed, allowing the sites to suggest other goods they might like and keep items in shopping carts while they continue this is mostly for your benefit, web developers get a lot out of this set-up as okies are stored on your device locally to free up storage space on a website’s servers. In turn, websites can personalize while saving money on server maintenance and storage are the different types of HTTP Cookies? With a few variations, cookies in the cyber world come in two types: session and ssion cookies are used only while navigating a website. They are stored in random access memory and are never written to the hard the session ends, session cookies are automatically deleted. They also help the “back” button or third-party anonymizer plugins work. These plugins are designed for specific browsers to work and help maintain user rsistent cookies remain on a computer indefinitely, although many include an expiration date and are automatically removed when that date is rsistent cookies are used for two primary purposes:Authentication. These cookies track whether a user is logged in and under what name. They also streamline login information, so users don’t have to remember site acking. These cookies track multiple visits to the same site over time. Some online merchants, for example, use cookies to track visits from particular users, including the pages and products viewed. The information they gain allows them to suggest other items that might interest visitors. Gradually, a profile is built based on a user’s browsing history on that Cookies Can Be DangerousSince the data in cookies doesn’t change, cookies themselves aren’t can’t infect computers with viruses or other malware. However, some cyberattacks can hijack cookies and enable access to your browsing danger lies in their ability to track individuals’ browsing histories. To explain, let’s discuss what cookies to watch out vs. Third-Party CookiesSome cookies may pack more of a threat than others depending on where they come cookies are directly created by the website you are using. These are generally safer, as long as you are browsing reputable websites or ones that have not been cookies are more troubling. They are generated by websites that are different from the web pages users are currently surfing, usually because they’re linked to ads on that siting a site with 10 ads may generate 10 cookies, even if users never click on those cookies let advertisers or analytics companies track an individual’s browsing history across the web on any sites that contain their nsequently, the advertiser could determine that a user first searched for running apparel at a specific outdoor store before checking a particular sporting goods site and then a certain online sportswear cookies are from a third-party and permanently installed on users’ computers, even when they opt not to install cookies. They also reappear after they’ve been deleted. When zombie cookies first appeared, they were created from data stored in the Adobe Flash storage bin. They are sometimes called “flash cookies” and are extremely difficult to other third-party cookies, zombie cookies can be used by web analytics companies to track unique individuals’ browsing histories. Websites may also use zombies to ban specific lowing or Removing CookiesCookies can be an optional part of your internet experience. If you so choose, you can limit what cookies end up on your computer or mobile you allow cookies, it will streamline your surfing. For some users, no cookies security risk is more important than a convenient internet ’s how to allow cookies:Find the cookie section — typically under Settings > the boxes to allow cookies. Sometimes the option says, “Allow local data. ”If you don’t want cookies, you can simply uncheck these moving cookies can help you mitigate your risks of privacy breaches. It can also reset your browser tracking and personalization. To help, Kaspersky offers step-by-step instructions for removing cookies from the most popular web moving normal cookies is easy, but it could make certain web sites harder to navigate. Without cookies internet, users may have to re-enter their data for each visit. Different browsers store cookies in different places, but usually, you can:Find the Settings, Privacy section — sometimes listed under Tools, Internet Options, or the prompts on the available options to manage or remove remove tracking cookie infestations and more malicious types, you’ll want to enlist the help of some internet security removing cookies, evaluate the ease of use expected from a website that uses cookies. In most cases, cookies improve the web experience, but they should be handled the future, you can anonymize your web use by using a virtual private network (VPN). These services tunnel your web connection to a remote server that poses as you. Cookies will be labeled for that remote server in another country, instead of your local gardless of how you handle cookies, it’s best to remain on guard and clean up your cookies lated articles:What is Adware? What is a Trojan? Computer Viruses and Malware Facts and FAQSpam and Phishing
Learn how HTTP Cookies work - Flavio Copes

Learn how HTTP Cookies work – Flavio Copes

Restrictions of cookies
Set cookies
Set a cookie expiration date
Set a cookie path
Set a cookie domain
Cookie Security
Update a cookie value or parameter
Delete a cookie
Access the cookies values
Check if a cookie exists
Abstractions libraries
Use cookies server-side
Inspect cookies with the Browser DevTools
Alternatives to cookies
By using Cookies we can exchange information between the server and the browser to provide a way to customize a user session, and for servers to recognize the user between requests.
HTTP is stateless, which means all request origins to a server are exactly the same and a server cannot determine if a request comes from a client that already did a request before, or it’s a new one.
Cookies are sent by the browser to the server when an HTTP request starts, and they are sent back from the server, which can edit their content.
Cookies are essentially used to store a session id.
In the past cookies were used to store various types of data, since there was no alternative. But nowadays with the Web Storage API (Local Storage and Session Storage) and IndexedDB, we have much better alternatives.
Especially because cookies have a very low limit in the data they can hold, since they are sent back-and-forth for every HTTP request to our server – including requests for assets like images or CSS / JavaScript files.
Cookies have a long history, they had their first version in 1994, and over time they were standardized in multiple RFC revisions.
RFC stands for Request for Comments, the way standards are defined by the Internet Engineering Task Force (IETF), the entity responsible for setting standards for the Internet
The latest specification for Cookies is defined in the RFC 6265, which is dated 2011.
Cookies can only store 4KB of data
Cookies are private to the domain. A site can only read the cookies it set, not other domains cookies
You can have up to 20 limits of cookies per domain (but the exact number depends on the specific browser implementation)
Cookies are limited in their total number (but the exact number depends on the specific browser implementation). If this number is exceeded, new cookies replace the older ones.
Cookies can be set or read server side, or client side.
In the client side, cookies are exposed by the document object as
The simplest example to set a cookie is:
= ‘name=Flavio’
This will add a new cookie to the existing ones (it does not overwrite existing cookies)
The cookie value should be url encoded with encodeURIComponent(), to make sure it does not contain any whitespace, comma or semicolon which are not valid in cookie values.
If you don’t set anything else, the cookie will expire when the browser is closed. To prevent so, add an expiration date, expressed in the UTC format (Mon, 26 Mar 2018 17:04:05 UTC)
= ‘name=Flavio; expires=Mon, 26 Mar 2018 17:04:05 UTC’
A simple JavaScript snippet to set a cookie that expires in 24 hours is:
const date = new Date()
tHours(tHours() + 24)
= ‘name=Flavio; expires=’ + UTCString()
Alternatively you can use the max-age parameter to set an expiration expressed in number of seconds:
= ‘name=Flavio; max-age=3600’ //expires in 60 minutes
= ‘name=Flavio; max-age=31536000’ //expires in 1 year
The path parameter specifies a document location for the cookie, so it’s assigned to a specific path, and sent to the server only if the path matches the current document location, or a parent:
= ‘name=Flavio; path=/dashboard’
this cookie is sent on /dashboard, /dashboard/today and other sub-urls of /dashboard/, but not on /posts for example.
If you don’t set a path, it defaults to the current document location. This means that to apply a global cookie from an inner page, you need to specify path=/.
The domain can be used to specify a subdomain for your cookie.
= ‘name=Flavio;;’
If not set, it defaults to the host portion even if using a subdomain (if on, by default it’s set to). Domain cookies are included in subdomains.
Adding the Secure parameter makes sure the cookie can only be transmitted securely over HTTPS, and it will not be sent over unencrypted HTTP connections:
= ‘name=Flavio; Secure;’
Note that this does not make cookies secure in any way – always avoid adding sensitive information to cookies
One useful parameter is HttpOnly, which makes cookies inaccessible via the API, so they are only editable by the server:
= ‘name=Flavio; Secure; HttpOnly’
SameSite, unfortunately still not supported by all browsers (but many do!, lets servers require that a cookie is not sent on cross-site requests, but only on resources that have the cookie domain as the origin, which should be a great help towards reducing the risk of CSRF (Cross Site Request Forgery) attacks.
To update the value of a cookie, just assign a new value to the cookie name:
= ‘name=Flavio2’
Similar to updating the value, to update the expiration date, reassign the value with a new expires or max-age property:
Just remember to also add any additional parameters you added in the first place, like path or domain.
To delete a cookie, unset its value and pass a date in the past:
= ‘name=; expires=Thu, 01 Jan 1970 00:00:00 UTC;’
(and again, with all the parameters you used to set it)
To access a cookie, lookup
const cookies =
This will return a string with all the cookies set for the page, semicolon separated:
‘name1=Flavio1; name2=Flavio2; name3=Flavio3’
if (
(‘;’)(item => {
return dexOf(‘name=’) >= 0})) {
//name exists}
return cludes(‘name=’)})) {
There are a number of different libraries that will provide a friendlier API to manage cookies. One of them is, which supports up to IE7, and has a lot of stars on GitHub (which is always good).
Some examples of its usage:
(‘name’, ‘value’)
(‘name’, ‘value’, {
expires: 7,
path: ”,
domain: ”,
secure: true})
(‘name’) // => ‘value’
(‘name’, { name: ‘Flavio’})
tJSON(‘name’) // => { name: ‘Flavio’}
Use that or the native Cookies API?
It all comes down to adding more kilobytes to download for each user, so it’s your choice.
Every environment used to build an HTTP server allows you to interact with cookies, because cookies are a pillar of the Modern Web, and not much could be built without them.
Go has cookies facilities in the net/ standard library
and so on.
Let’s do an example with
When using, you can create cookies using the API:
(‘name1’, ‘1Flavio’, {
domain: ‘. ‘,
path: ‘/admin’,
(‘name2’, ‘Flavio2’, {
expires: new Date(() + 900000),
Only: true})
(‘name3’, ‘Flavio3’, { maxAge: 900000, Only: true})
//takes care of serializing JSON
(‘name4’, { items: [1, 2, 3]}, { maxAge: 900000})
To parse cookies, a good choice is to use the middleware. Every Request object will have cookies information in the property:
me1 //Flavio1
If you create your cookies using signed: true:
(‘name5’, ‘Flavio5’, { signed: true})
they will be available in the gnedCookies object instead. Signed cookies are protected against modifications on the client. The signature used to sign a cookie value makes sure that you can know, server-side, if the client has modified it.
and are two different middleware options to build cookie-based authentication, which one to use depends on your needs.
All browsers in their DevTools provide an interface to inspect and edit cookies.
Are cookies the only way to build authentication and sessions on the Web?
No! There is a technology that recently got popular, called JSON Web Tokens (JWT), which is a Token-based Authentication.

Frequently Asked Questions about cookies http

What are HTTP cookies used for?

HTTP cookies, or internet cookies, are built specifically for Internet web browsers to track, personalize, and save information about each user’s session. A “session” just refers to the time you spend on a site. Cookies are created to identify you when you visit a new website.

How do cookies work with HTTP?

Cookies are sent by the browser to the server when an HTTP request starts, and they are sent back from the server, which can edit their content. Cookies are essentially used to store a session id. In the past cookies were used to store various types of data, since there was no alternative.Mar 30, 2018

What is cookie in HTTP header?

A cookie is an HTTP request header i.e. used in the requests sent by the user to the server. It contains the cookies previously sent by the server using set-cookies. It is an optional header. … <cookie-list> It is the list of name=value pair separated by ; and space i.e ‘;’.Oct 30, 2019

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