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105 lines
3.6 KiB
Plaintext
105 lines
3.6 KiB
Plaintext
HTTP Cookies
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Overview
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========
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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 the
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cookies aren't session cookies they have expiration dates after which the
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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 (http://www.ietf.org/rfc/rfc6265.txt) was finally published
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and details how cookies work within HTTP.
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cookies saved to disk
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=====================
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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 sharing
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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 cookie file format stores one cookie per physical line in the file with a
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bunch of associated meta data, each field separated with TAB. That file is
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called the cookiejar in curl terminology.
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cookies with curl the command line tool
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=======================================
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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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cookies with libcurl
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====================
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libcurl options:
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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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cookies with javascript
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=======================
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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 can
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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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