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124 lines
4.4 KiB
Plaintext
124 lines
4.4 KiB
Plaintext
Updated: July 3, 2012 (http://curl.haxx.se/docs/http-cookies.html)
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HTTP Cookies
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1. HTTP Cookies
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1.1 Cookie overview
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1.2 Cookies saved to disk
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1.3 Cookies with curl the command line tool
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1.4 Cookies with libcurl
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1.5 Cookies with javascript
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==============================================================================
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1. HTTP Cookies
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1.1 Cookie overview
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HTTP cookies are pieces of 'name=contents' snippets that a server tells the
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client to hold and then the client sends back those the server on subsequent
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requests to the same domains/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: http://curl.haxx.se/rfc/cookie_spec.html
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In 2011, RFC6265 (https://www.ietf.org/rfc/rfc6265.txt) was finally published
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and details how cookies work within HTTP.
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1.2 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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1.3 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
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it isn't a file it will pass on the given string. -b name=var works and so
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does -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
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load 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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1.4 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
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details set, or pass in a line from a netscape cookie file. This option
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can also be 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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1.5 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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