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    1: # HTTP Cookies
    2: 
    3: ## Cookie overview
    4: 
    5:   Cookies are `name=contents` pairs that a HTTP server tells the client to
    6:   hold and then the client sends back those to the server on subsequent
    7:   requests to the same domains and paths for which the cookies were set.
    8: 
    9:   Cookies are either "session cookies" which typically are forgotten when the
   10:   session is over which is often translated to equal when browser quits, or
   11:   the cookies aren't session cookies they have expiration dates after which
   12:   the client will throw them away.
   13: 
   14:   Cookies are set to the client with the Set-Cookie: header and are sent to
   15:   servers with the Cookie: header.
   16: 
   17:   For a very long time, the only spec explaining how to use cookies was the
   18:   original [Netscape spec from 1994](https://curl.haxx.se/rfc/cookie_spec.html).
   19: 
   20:   In 2011, [RFC6265](https://www.ietf.org/rfc/rfc6265.txt) was finally
   21:   published and details how cookies work within HTTP. In 2016, an update which
   22:   added support for prefixes was
   23:   [proposed](https://tools.ietf.org/html/draft-ietf-httpbis-cookie-prefixes-00),
   24:   and in 2017, another update was
   25:   [drafted](https://tools.ietf.org/html/draft-ietf-httpbis-cookie-alone-01)
   26:   to deprecate modification of 'secure' cookies from non-secure origins. Both
   27:   of these drafts have been incorporated into a proposal to
   28:   [replace](https://tools.ietf.org/html/draft-ietf-httpbis-rfc6265bis-02)
   29:   RFC6265. Cookie prefixes and secure cookie modification protection has been
   30:   implemented by curl.
   31: 
   32: ## Cookies saved to disk
   33: 
   34:   Netscape once created a file format for storing cookies on disk so that they
   35:   would survive browser restarts. curl adopted that file format to allow
   36:   sharing the cookies with browsers, only to see browsers move away from that
   37:   format. Modern browsers no longer use it, while curl still does.
   38: 
   39:   The netscape cookie file format stores one cookie per physical line in the
   40:   file with a bunch of associated meta data, each field separated with
   41:   TAB. That file is called the cookiejar in curl terminology.
   42: 
   43:   When libcurl saves a cookiejar, it creates a file header of its own in which
   44:   there is a URL mention that will link to the web version of this document.
   45: 
   46: ## Cookie file format
   47: 
   48:   The cookie file format is text based and stores one cookie per line. Lines
   49:   that start with `#` are treated as comments.
   50: 
   51:   Each line that each specifies a single cookie consists of seven text fields
   52:   separated with TAB characters. A valid line must end with a newline
   53:   character.
   54: 
   55: ### Fields in the file
   56: 
   57:   Field number, what type and example data and the meaning of it:
   58: 
   59:   0. string `example.com` - the domain name
   60:   1. boolean `FALSE` - include subdomains
   61:   2. string `/foobar/` - path
   62:   3. boolean `TRUE` - send/receive over HTTPS only
   63:   4. number `1462299217` - expires at - seconds since Jan 1st 1970, or 0
   64:   5. string `person` - name of the cookie
   65:   6. string `daniel` - value of the cookie
   66: 
   67: ## Cookies with curl the command line tool
   68: 
   69:   curl has a full cookie "engine" built in. If you just activate it, you can
   70:   have curl receive and send cookies exactly as mandated in the specs.
   71: 
   72:   Command line options:
   73: 
   74:   `-b, --cookie`
   75: 
   76:   tell curl a file to read cookies from and start the cookie engine, or if it
   77:   isn't a file it will pass on the given string. -b name=var works and so does
   78:   -b cookiefile.
   79: 
   80:   `-j, --junk-session-cookies`
   81: 
   82:   when used in combination with -b, it will skip all "session cookies" on load
   83:   so as to appear to start a new cookie session.
   84: 
   85:   `-c, --cookie-jar`
   86: 
   87:   tell curl to start the cookie engine and write cookies to the given file
   88:   after the request(s)
   89: 
   90: ## Cookies with libcurl
   91: 
   92:   libcurl offers several ways to enable and interface the cookie engine. These
   93:   options are the ones provided by the native API. libcurl bindings may offer
   94:   access to them using other means.
   95: 
   96:   `CURLOPT_COOKIE`
   97: 
   98:   Is used when you want to specify the exact contents of a cookie header to
   99:   send to the server.
  100: 
  101:   `CURLOPT_COOKIEFILE`
  102: 
  103:   Tell libcurl to activate the cookie engine, and to read the initial set of
  104:   cookies from the given file. Read-only.
  105: 
  106:   `CURLOPT_COOKIEJAR`
  107: 
  108:   Tell libcurl to activate the cookie engine, and when the easy handle is
  109:   closed save all known cookies to the given cookiejar file. Write-only.
  110: 
  111:   `CURLOPT_COOKIELIST`
  112: 
  113:   Provide detailed information about a single cookie to add to the internal
  114:   storage of cookies. Pass in the cookie as a HTTP header with all the details
  115:   set, or pass in a line from a netscape cookie file. This option can also be
  116:   used to flush the cookies etc.
  117: 
  118:   `CURLINFO_COOKIELIST`
  119: 
  120:   Extract cookie information from the internal cookie storage as a linked
  121:   list.
  122: 
  123: ## Cookies with javascript
  124: 
  125:   These days a lot of the web is built up by javascript. The webbrowser loads
  126:   complete programs that render the page you see. These javascript programs
  127:   can also set and access cookies.
  128: 
  129:   Since curl and libcurl are plain HTTP clients without any knowledge of or
  130:   capability to handle javascript, such cookies will not be detected or used.
  131: 
  132:   Often, if you want to mimic what a browser does on such web sites, you can
  133:   record web browser HTTP traffic when using such a site and then repeat the
  134:   cookie operations using curl or libcurl.