Exit Zen
72
../../protocols/http.rst:383
English
As illustrated above, a client can send several HTTP requests over the same persistent TCP connection. However, it is important to note that all of these HTTP requests are considered to be independent by the server. Each HTTP request must be self-contained. This implies that each request must include all the header lines that are required by the server to understand the request. The independence of these requests is one of the key design choices of HTTP. As a consequence of this design choice, when a server processes a HTTP request, it does not use any other information than what is contained in the request itself. This explains why the client adds its `User-Agent:` header in all of the HTTP requests that it sends over the persistent TCP connection.
0/7590 · 759
73
../../protocols/http.rst:385
English
However, in practice, some servers want to provide content tuned for each user. For example, some servers can provide information in several languages. Other servers want to provide advertisements that are targeted to different types of users. To do this, servers need to maintain some information about the preferences of each user and use this information to produce content matching the user's preferences. HTTP contains several mechanisms to solve this problem. We discuss three of them below.
0/4970 · 497
74
../../protocols/http.rst:387
English
A first solution is to force the users to be authenticated. This was the solution used by `FTP` to control the files that each user could access. Initially, user names and passwords could be included inside URIs :rfc:`1738`. However, placing passwords in the clear in a potentially publicly visible URI is completely insecure and this usage has now been deprecated :rfc:`3986`. HTTP supports several extension headers :rfc:`2617` that can be used by a server to request the authentication of the client by providing his/her credentials. However, user names and passwords have not been popular on web servers as they force human users to remember one user name and one password per server. Remembering a password is acceptable when a user needs to access protected content, but users will not accept to remember a unique user name and password for each web sites that they visit.
0/8780 · 878
75
../../protocols/http.rst:389
English
A second solution to allow servers to tune that content to the needs and capabilities of the user is to rely on the different types of `Accept-*` HTTP headers. For example, the `Accept-Language:` header can be used by the client to indicate its preferred languages. Unfortunately, in practice this header is usually set based on the default language of the browser and it is difficult for a user to indicate the language it prefers by selecting options for each visited web server.
0/4810 · 481
76
../../protocols/http.rst:391
English
The third and widely adopted solution are HTTP cookies. HTTP cookies were initially developed as a private extension by Netscape_. They are now part of the standard :rfc:`6265`. In a nutshell, a cookie is a short string that is chosen by a server to represent a given client. Two HTTP headers are used : `Cookie:` and `Set-Cookie:`. When a server receives an HTTP request from a new client (i.e. an HTTP request that does not contain the `Cookie:` header), it generates a cookie for the client and includes it in the `Set-Cookie:` header of the returned HTTP response. The `Set-Cookie:` header contains several additional parameters including the domain names for which the cookie is valid. The client stores all received cookies on disk and every time it sends an HTTP request, it verifies whether it already knows a cookie for this domain. If so, it attaches the `Cookie:` header to the HTTP request. This is illustrated in the figure below with HTTP 1.1, but cookies also work with HTTP 1.0.
0/9940 · 994
77
../../protocols/http.rst:438
English
Privacy issues with HTTP cookies
0/320 · 32
78
../../protocols/http.rst:440
English
The HTTP cookies introduced by Netscape_ are key for large e-commerce websites. However, they have also raised many discussions concerning their `potential misuses <http://www.nytimes.com/2001/09/04/technology/04COOK.html>`_. Consider `ad.com`, a company that delivers lots of advertisements on web sites. A web site that wishes to include `ad.com`'s advertisements next to its content will add links to `ad.com` inside its HTML pages. If `ad.com` is used by many web sites, `ad.com` could be able to track the interests of all the users that visit its client websites and use this information to provide targeted advertisements. Privacy advocates have even `sued <http://epic.org/privacy/internet/cookies/>`_ online advertisement companies to force them to comply with the privacy regulations. More recent related technologies also raise `privacy concerns <http://www.eff.org/deeplinks/2009/09/new-cookie-technologies-harder-see-and-remove-wide>`_.
0/9490 · 949
79
../../protocols/http.rst:443
English
Footnotes
0/100 · 9
80
../../protocols/http.rst:444
English
An example of a non-retrievable URI is `urn:isbn:0-380-81593-1` which is an unique identifier for a book, through the urn scheme (see :rfc:`3187`). Of course, any URI can be made retrievable via a dedicated server or a new protocol but this one has no explicit protocol. Same thing for the scheme tag (see :rfc:`4151`), often used in Web syndication (see :rfc:`4287` about the Atom syndication format). Even when the scheme is retrievable (for instance with `http`), it is often used only as an identifier, not as a way to get a resource. See http://norman.walsh.name/2006/07/25/namesAndAddresses for a good explanation.
0/6200 · 620
81
../../protocols/http.rst:447
English
The list of standard URI schemes is maintained by IANA_ at http://www.iana.org/assignments/uri-schemes.html
0/1070 · 107
82
../../protocols/http.rst:449
English
Favorite icons are small icons that are used to represent web servers in the toolbar of Internet browsers. Microsoft added this feature in their browsers without taking into account the W3C standards. See http://www.w3.org/2005/10/howto-favicon for a discussion on how to cleanly support such favorite icons.
0/3080 · 308
The translation has come to an end.