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105 lines
3.8 KiB
Markdown
105 lines
3.8 KiB
Markdown
# HTTP Cookies
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## Cookie overview
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Cookies are `name=contents` pairs that a HTTP server tells the client to
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hold and then the client sends back those to the server on subsequent
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requests to the same domains and paths for which the cookies were set.
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Cookies are either "session cookies" which typically are forgotten when the
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session is over which is often translated to equal when browser quits, or
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the cookies aren't session cookies they have expiration dates after which
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the client will throw them away.
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Cookies are set to the client with the Set-Cookie: header and are sent to
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servers with the Cookie: header.
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For a very long time, the only spec explaining how to use cookies was the
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original [Netscape spec from 1994](https://curl.haxx.se/rfc/cookie_spec.html).
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In 2011, [RFC6265](https://www.ietf.org/rfc/rfc6265.txt) was finally
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published and details how cookies work within HTTP.
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## Cookies saved to disk
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Netscape once created a file format for storing cookies on disk so that they
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would survive browser restarts. curl adopted that file format to allow
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sharing the cookies with browsers, only to see browsers move away from that
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format. Modern browsers no longer use it, while curl still does.
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The netscape cookie file format stores one cookie per physical line in the
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file with a bunch of associated meta data, each field separated with
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TAB. That file is called the cookiejar in curl terminology.
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When libcurl saves a cookiejar, it creates a file header of its own in which
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there is a URL mention that will link to the web version of this document.
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## Cookies with curl the command line tool
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curl has a full cookie "engine" built in. If you just activate it, you can
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have curl receive and send cookies exactly as mandated in the specs.
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Command line options:
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`-b, --cookie`
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tell curl a file to read cookies from and start the cookie engine, or if it
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isn't a file it will pass on the given string. -b name=var works and so does
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-b cookiefile.
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`-j, --junk-session-cookies`
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when used in combination with -b, it will skip all "session cookies" on load
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so as to appear to start a new cookie session.
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`-c, --cookie-jar`
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tell curl to start the cookie engine and write cookies to the given file
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after the request(s)
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## Cookies with libcurl
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libcurl offers several ways to enable and interface the cookie engine. These
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options are the ones provided by the native API. libcurl bindings may offer
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access to them using other means.
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`CURLOPT_COOKIE`
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Is used when you want to specify the exact contents of a cookie header to
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send to the server.
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`CURLOPT_COOKIEFILE`
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Tell libcurl to activate the cookie engine, and to read the initial set of
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cookies from the given file. Read-only.
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`CURLOPT_COOKIEJAR`
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Tell libcurl to activate the cookie engine, and when the easy handle is
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closed save all known cookies to the given cookiejar file. Write-only.
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`CURLOPT_COOKIELIST`
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Provide detailed information about a single cookie to add to the internal
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storage of cookies. Pass in the cookie as a HTTP header with all the details
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set, or pass in a line from a netscape cookie file. This option can also be
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used to flush the cookies etc.
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`CURLINFO_COOKIELIST`
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Extract cookie information from the internal cookie storage as a linked
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list.
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## Cookies with javascript
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These days a lot of the web is built up by javascript. The webbrowser loads
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complete programs that render the page you see. These javascript programs
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can also set and access cookies.
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Since curl and libcurl are plain HTTP clients without any knowledge of or
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capability to handle javascript, such cookies will not be detected or used.
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Often, if you want to mimic what a browser does on such web sites, you can
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record web browser HTTP traffic when using such a site and then repeat the
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cookie operations using curl or libcurl.
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