What is the difference between server side cookie and client side cookie?

Question

HTTP COOKIES

Cookies are key/value pairs used by websites to store state information on the browser. Say you have a website (example.com), when the browser requests a webpage the website can send cookies to store information on the browser.

Browser request example:

GET /index.html HTTP/1.1
Host: www.example.com

Example answer from the server:

HTTP/1.1 200 OK
Content-type: text/html
Set-Cookie: foo=10
Set-Cookie: bar=20; Expires=Fri, 30 Sep 2011 11:48:00 GMT
... rest  of the response

Here two cookies foo=10 and bar=20 are stored on the browser. The second one will expire on 30 September. In each subsequent request the browser will send the cookies back to the server.

GET /spec.html HTTP/1.1
Host: www.example.com
Cookie: foo=10; bar=20
Accept: */*

SESSIONS: Server side cookies

Server side cookies are known as "sessions". The website in this case stores a single cookie on the browser containing a unique Session Identifier. Status information (foo=10 and bar=20 above) are stored on the server and the Session Identifier is used to match the request with the data stored on the server.

Examples of usage

You can use both sessions and cookies to store: authentication data, user preferences, the content of a chart in an e-commerce website, etc...

Pros and Cons

Below pros and cons of the solutions. These are the first that comes to my mind, there are surely others.

Cookie Pros:

• scalability: all the data is stored in the browser so each request can go through a load balancer to different webservers and you have all the information needed to fullfill the request;
• they can be accessed via javascript on the browser;
• not being on the server they will survive server restarts;
• RESTful: requests don't depend on server state

Cookie Cons:

• storage is limited to 80 KB (20 cookies, 4 KB each)
• secure cookies are not easy to implement: take a look at the paper A secure cookie protocol

Session Pros:

• generally easier to use, in PHP there's probably not much difference.
• unlimited storage

Session Cons:

• more difficult to scale
• on web server restarts you can lose all sessions or not depending on the implementation
• not RESTful

You probably mean the difference between Http Only cookies and their counter part?

Http Only cookies cannot be accessed (read from or written to) in client side JavaScript, only server side. If the Http Only flag is not set, or the cookie is created in (client side) JavaScript, the cookie can be read from and written to in (client side) JavaScript as well as server side.

All cookies are client and server

There is no difference. A regular cookie can be set server side or client side. The 'classic' cookie will be sent back with each request. A cookie that is set by the server, will be sent to the client in a response. The server only sends the cookie when it is explicitly set or changed, while the client sends the cookie on each request.

But essentially it's the same cookie.

But, behavior can change

A cookie is basically a name=value pair, but after the value can be a bunch of semi-colon separated attributes that affect the behavior of the cookie if it is so implemented by the client (or server). Those attributes can be about lifetime, context and various security settings.

HTTP-only (is not server-only)

One of those attributes can be set by a server to indicate that it's an HTTP-only cookie. This means that the cookie is still sent back and forth, but it won't be available in JavaScript. Do note, though, that the cookie is still there! It's only a built in protection in the browser, but if somebody would use a ridiculously old browser like IE5, or some custom client, they can actually read the cookie!

So it seems like there are 'server cookies', but there are actually not. Those cookies are still sent to the client. On the client there is no way to prevent a cookie from being sent to the server.

Alternatives to achieve 'only-ness'

If you want to store a value only on the server, or only on the client, then you'd need some other kind of storage, like a file or database on the server, or Local Storage on the client.

What is the difference between creating cookies on the server and on the client?

What you are referring to are the 2 ways in which cookies can be directed to be set on the client, which are:

• By server
• By client ( browser in most cases )

By server: The Set-cookie response header from the server directs the client to set a cookie on that particular domain. The implementation to actually create and store the cookie lies in the browser. For subsequent requests to the same domain, the browser automatically sets the Cookie request header for each request, thereby letting the server have some state to an otherwise stateless HTTP protocol. The Domain and Path cookie attributes are used by the browser to determine which cookies are to be sent to a server. The server only receives name=value pairs, and nothing more.

By Client: One can create a cookie on the browser using document.cookie = cookiename=cookievalue. However, if the server does not intend to respond to any random cookie a user creates, then such a cookie serves no purpose.

Are these called server side cookies and client side cookies?

Cookies always belong to the client. There is no such thing as server side cookie.

Is there a way to create cookies that can only be read on the server or on the client?

Since reading cookie values are upto the server and client, it depends if either one needs to read the cookie at all. On the client side, by setting the HttpOnly attribute of the cookie, it is possible to prevent scripts ( mostly Javscript ) from reading your cookies , thereby acting as a defence mechanism against Cookie theft through XSS, but sends the cookie to the intended server only.

Therefore, in most of the cases since cookies are used to bring 'state' ( memory of past user events ), creating cookies on client side does not add much value, unless one is aware of the cookies the server uses / responds to.

Reference: Wikipedia

1. Yes you can create cookies that can only be read on the server-side. These are called "HTTP Only" -cookies, as explained in other answers already

2. No, there is no way (I know of) to create "cookies" that can be read only on the client-side. Cookies are meant to facilitate client-server communication.

3. BUT, if you want something LIKE "client-only-cookies" there is a simple answer: Use "Local Storage".

Local Storage is actually syntactically simpler to use than cookies. A good simple summary of cookies vs. local storage can be found at:

https://courses.cs.washington.edu/courses/cse154/12au/lectures/slides/lecture21-client-storage.shtml#slide8

A point: You might use cookies created in JavaScript to store GUI-related things you only need on the client-side. BUT the cookie is sent to the server for EVERY request made, it becomes part of the http-request headers thus making the request contain more data and thus slower to send.

If your page has 50 resources like images and css-files and scripts then the cookie is (typically) sent with each request. More on this in Does every web request send the browser cookies?

Local storage does not have those data-transfer related disadvantages, it sends no data. It is great.