Cookies: HTTP State Management

7.3

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Cookies: HTTP State Management

This library provides utilities for handling cookies as specified in RFC 6265 [RFC6265].

Provides all names exported from net/cookies/common, net/cookies/server, and net/cookies/user-agent.

The net/cookies/server and net/cookies/user-agent modules are designed to stand on their own, however, so for any program that is exclusively client- or server-side, it will suffice to import one of those two modules.

1 Cookies: Common Functionality

(require net/cookies/common)

package: net-cookies-lib

The net/cookies/common library contains cookie-related code common to servers and user agents.

procedure
(cookie-name? v) → boolean?
v : any/c

Returns #t if v is a valid cookie name (represented as a string or a byte string), #f otherwise.

Cookie names must consist of ASCII characters. They may not contain control characters (ASCII codes 0-31 or 127) or the following “separators”:

double quotes
whitespace characters
#\@ or #\?
parentheses, brackets, or curly braces
commas, colons, or semicolons
equals, greater-than, or less-than signs
slashes or backslashes

procedure
(cookie-value? v) → boolean?
v : any/c

Returns #t if v is a valid cookie value (represented as a string or byte string), #f otherwise.

Cookie values must consist of ASCII characters. They may not contain:

control characters
whitespace characters
double-quotes, except at the beginning and end if the entire value is double-quoted
commas
semicolons
backslashes

procedure
(path/extension-value? v) → boolean?
v : any/c

Returns #t iff v is a string that can be used as the value of a “Path=” attribute, or as an additional attribute (or attribute/value pair) whose meaning is not specified by RFC6265.

procedure
(domain-value? v) → boolean?
v : any/c

Returns #t iff v is a string that contains a (sub)domain name, as defined by RFCs 1034 (Section 3.5) [RFC1034] and 1123 (Section 2.1) [RFC1123].

2 Cookies and HTTP Servers

(require net/cookies/server)

package: net-cookies-lib

The net/cookies/server library is for handling cookies on the server side; it includes:

a serializable cookie structure definition
functions to convert a cookie structure to a string, or a value for the HTTP “Set-Cookie” response header
functions that allow reading an HTTP “Cookie” header generated by a user agent

struct
(struct cookie ( name
value
expires
max-age
domain
path
secure?
http-only?
extension))
  name : (and/c string? cookie-name?)
  value : (and/c string? cookie-value?)
  expires : (or/c date? #f)
  max-age : (or/c (and/c integer? positive?) #f)
  domain : (or/c domain-value? #f)
  path : (or/c path/extension-value? #f)
  secure? : boolean?
  http-only? : boolean?
  extension : (or/c path/extension-value? #f)

A structure type for cookies the server will send to the user agent. For client-side cookies, see net/cookies/user-agent. Programs using this library should construct their cookie structs via make-cookie, below.

procedure
(make-cookie name
value
[ #:expires exp-date
#:max-age max-age
#:domain domain
#:path path
#:secure? secure?
#:http-only? http-only?
#:extension extension]) → cookie?
  name : cookie-name?
  value : cookie-value?
  exp-date : (or/c date? #f) = #f
  max-age : (or/c (and/c integer? positive?) #f) = #f
  domain : (or/c domain-value? #f) = #f
  path : (or/c path/extension-value? #f) = #f
  secure? : boolean? = #f
  http-only? : boolean? = #f
  extension : (or/c path/extension-value? #f) = #f

Constructs a cookie for sending to a user agent. If name or value is a byte string, this procedure will convert it to a string using bytes->string/utf-8; programs requiring a different encoding should convert their byte strings before calling make-cookie.

Both exp-date and max-age are for specifying a time at which the user agent should remove the cookie from its cookie store. exp-date is for specifying this expiration time as a date; max-age is for specifying it as a number of seconds in the future. If both exp-date and max-age are given, an RFC6265-compliant user agent will disregard the exp-date and use the max-age.

domain indicates that the recipient should send the cookie back to the server only if the hostname in the request URI is either domain itself, or a host within domain.

path indicates that the recipient should send the cookie back to the server only if path is a prefix of the request URI’s path.

secure, when #t, sets a flag telling the recipient that the cookie may only be sent if the request URI’s scheme specifies a “secure” protocol (presumably HTTPS).

http-only?, when #t, sets a flag telling the recipient that the cookie may be communicated only to a server and only via HTTP or HTTPS. This flag is important for security reasons: Browsers provide JavaScript access to cookies (for example, via document.cookie), and consequently, when cookies contain sensitive data such as user session info, malicious JavaScript can compromise that data. The HttpOnly cookie flag, set by this keyword argument, instructs the browser not to make this cookie available to JavaScript code. If a cookie is intended to be confidential, both http-only? and secure? should be #t, and all connections should use HTTPS. (Some older browsers do not support this flag; see the OWASP page on HttpOnly for more info.)

procedure
(cookie->set-cookie-header c) → bytes?
c : cookie?

Produces a byte string containing the value portion of a “Set-Cookie:” HTTP response header suitable for sending c to a user agent.

Example:

> (cookie->set-cookie-header
(make-cookie "rememberUser" "bob" #:path "/main"))
#"rememberUser=bob; Path=/main"

This procedure uses string->bytes/utf-8 to convert the cookie to bytes; for an application that needs a different encoding function, use cookie->string and perform the bytes conversion with that function.

procedure
(clear-cookie-header name
[ #:domain domain
#:path path]) → bytes?
  name : cookie-name?
  domain : (or/c domain-value? #f) = #f
  path : (or/c path/extension-value? #f) = #f

Produces a byte string containing a “Set-Cookie:” header suitable for telling a user agent to clear the cookie with the given name. (This is done, as per RFC6265, by sending a cookie with an expiration date in the past.)

Example:

> (clear-cookie-header "rememberUser" #:path "/main")
#"rememberUser=; Expires=Thu, 01 Jan 2015 00:00:00 GMT; Path=/main"

procedure
(cookie-header->alist header) → (listof (cons/c bytes? bytes?))
  header : bytes?
(cookie-header->alist header decode) → (listof (cons/c X X))
  header : bytes?
  decode : (-> bytes? X)

Given the value part of a “Cookie:” header, produces an alist of all cookie name/value mappings in the header. If a decode function is given, applies decode to each key and each value before inserting the new key-value pair into the alist. Invalid cookies will not be present in the alist.

If a key in the header has no value, then #"", or (decode #"") if decode is present, is used as the value.

Examples:

> (cookie-header->alist #"SID=31d4d96e407aad42; lang=en-US")
'((#"SID" . #"31d4d96e407aad42") (#"lang" . #"en-US"))
> (cookie-header->alist #"SID=31d4d96e407aad42; lang=en-US"
                        bytes->string/utf-8)
'(("SID" . "31d4d96e407aad42") ("lang" . "en-US"))
> (cookie-header->alist #"seenIntro=; logins=3"
                        (compose (lambda (s) (or (string->number s) s))
                                 bytes->string/utf-8))
'(("seenIntro" . "") ("logins" . 3))

procedure
(cookie->string c) → string?
c : cookie?

Produces a string containing the given cookie as text.

Examples:

> (cookie->string
   (make-cookie "usesRacket" "true"))
"usesRacket=true"
> (cookie->string
   (make-cookie "favColor" "teal"
                #:max-age 86400
                #:domain "example.com"
                #:secure? #t))
"favColor=teal; Max-Age=86400; Domain=example.com; Secure"

3 Cookies and HTTP User Agents

(require net/cookies/user-agent)
	package: net-cookies-lib

The net/cookies/user-agent library provides facilities specific to user agents’ handling of cookies.

Many user agents will need only two of this library’s procedures:

extract-and-save-cookies!, for storing cookies
cookie-header, for retrieving them and generating a “Cookie:” header

struct
(struct ua-cookie ( name
value
domain
path
expiration-time
creation-time
access-time
persistent?
host-only?
secure-only?
http-only?))
  name : cookie-name?
  value : cookie-value?
  domain : domain-value?
  path : path/extension-value?
  expiration-time : (and/c integer? positive?)
  creation-time : (and/c integer? positive?)
  access-time : (and/c integer? positive?)
  persistent? : boolean?
  host-only? : boolean?
  secure-only? : boolean?
  http-only? : boolean?

A structure representing a cookie from a user agent’s point of view.

All times are represented as the number of seconds since midnight UTC, January 1, 1970, like the values produced by current-seconds.

It’s unlikely a client will need to construct a ua-cookie instance directly (except perhaps for testing); extract-cookies produces struct instances for all the cookies received in a server’s response.

procedure
(cookie-expired? cookie [current-time]) → boolean?
cookie : ua-cookie?
current-time : integer? = (current-seconds)

True iff the given cookie’s expiration time precedes current-time.

3.1 Cookie jars: Client storage

procedure
(extract-and-save-cookies! headers
url
[ decode]) → void?
  headers : (or/c (listof (cons/c bytes? bytes?)) (listof bytes?))
  url : url?
  decode : (-> bytes? string?) = bytes->string/utf-8

Reads all cookies from any “Set-Cookie” headers present in headers received in an HTTP response from url, converts them to strings using decode, and stores them in the current-cookie-jar.

The given headers may be provided either as an alist mapping header names to header values, or as a raw list of bytes such as the second return value produced by http-conn-recv! in net/http-client. Here is an example of each:

Examples:

> (require net/url)
> (define site-url
    (string->url "http://test.example.com/apps/main"))
> (extract-and-save-cookies!
   '((#"X-Test-Header" . #"isThisACookie=no")
     (#"Set-Cookie" . #"a=b; Max-Age=2000; Path=/")
     (#"Set-Cookie" . #"user=bob; Max-Age=86400; Path=/apps"))
   site-url)
> (cookie-header site-url)
#"user=bob; a=b"
> (extract-and-save-cookies!
   '(#"X-Ignore-This: thisIsStillNotACookie=yes"
     #"Set-Cookie: p=q; Max-Age=2000; Path=/"
     #"Set-Cookie: usersMom=alice; Max-Age=86400; Path=/apps")
   site-url)
> (cookie-header site-url)
#"usersMom=alice; user=bob; p=q; a=b"

procedure
(save-cookie! c [via-http?]) → void?
c : ua-cookie?
via-http? : boolean? = #t

Attempts to save a single cookie c, received via an HTTP API iff via-http?, to the current-cookie-jar. Per Section 5.3 of RFC 6265, the cookie will be ignored if its http-only? flag (or that of the cookie it would replace) is set and it wasn’t received via an HTTP API.

procedure
(cookie-header url [encode #:filter-with ok?]) → (or/c bytes? #f)
  url : url?
  encode : (-> string? bytes?) = string->bytes/utf-8
  ok? : (-> ua-cookie? boolean?) = (lambda (x) #t)

Finds any unexpired cookies matching url in the current-cookie-jar, removes any for which ok? produces #f, and produces the value portion of a “Cookie:” HTTP request header. Produces #f if no cookies match.

Cookies with the “Secure” flag will be included in this header iff (url-scheme url) is "https", unless you remove them manually using the ok? parameter.

Example:

> (cookie-header
(string->url "http://test.example.com/home"))
#"p=q; a=b"

interface
cookie-jar<%> : interface?

An interface for storing cookies received from servers. Implemented by list-cookie-jar%. Provides for saving cookies (imperatively) and extracting all cookies that match a given URL.

Most clients will not need to deal with this interface, and none should need to call its methods directly. (Use cookie-header and extract-and-save-cookies!, instead.) It is provided for situations in which the default list-cookie-jar% class will not suffice. For example, if the user agent will be storing thousands of cookies, the linear insertion time of list-cookie-jar% could mean that writing a cookie-jar<%> implementation based on hash tables, trees, or a DBMS might be a better alternative.

Programs requiring such a class should install an instance of it using the current-cookie-jar parameter.

method
(send a-cookie-jar save-cookie! c
[ via-http?]) → void?
  c : ua-cookie?
  via-http? : boolean? = #t
Saves c to the jar, and removes any expired cookies from the jar as well.
via-http? should be #t if the cookie was received via an HTTP API; it is for properly ignoring the cookie if the cookie’s http-only? flag is set, or if the cookie is attempting to replace an “HTTP only” cookie already present in the jar.
method
(send a-cookie-jar save-cookies! cs
[ via-http?]) → void?
  cs : (listof ua-cookie?)
  via-http? : boolean? = #t
Saves each cookie in cs to the jar, and removes any expired cookies from the jar. See the note immediately above, for explanation of the via-http? flag.
method
(send a-cookie-jar cookies-matching url
[ secure?])
→ (listof ua-cookie?)
  url : url?
  secure? : boolean? = (equal? (url-scheme url) "https")
Produces all cookies in the jar that should be sent in the “Cookie” header for a request made to url. secure? specifies whether the cookies will be sent via a secure protocol. (If not, cookies with the “Secure” flag set should not be returned by this method.)
This method should produce its cookies in the order expected according to RFC6265:
Cookies with longer paths are listed before cookies with shorter paths.
Among cookies that have equal-length path fields, cookies with earlier creation-times are listed before cookies with later creation-times.
If there are multiple cookies in the jar with the same name and different domains or paths, the RFC does not specify which to send. The default list-cookie-jar% class’s implementation of this method produces all cookies that match the domain and path of the given URL, in the order specified above.

class
list-cookie-jar% : class?

superclass: object%

extends:

cookie-jar<%>

Stores cookies in a list, internally maintaining a sorted order that mirrors the sort order specified by the RFC for the “Cookie” header.

parameter
(current-cookie-jar) → (is-a?/c cookie-jar<%>)
(current-cookie-jar jar) → void?
jar : (is-a?/c cookie-jar<%>)
= (new list-cookie-jar%)

A parameter that specifies the cookie jar to use for storing and retrieving cookies.

3.2 Reading the Set-Cookie header

procedure
(extract-cookies headers url [decode]) → (listof ua-cookie?)
   headers :
(or/c (listof (cons/c bytes? bytes?))
      (listof bytes?))
  url : url?
  decode : (-> bytes? string?) = bytes->string/utf-8

Given a list of all the headers received in the response to a request from the given url, produces a list of cookies corresponding to all the “Set-Cookie” headers present. The decode function is used to convert the cookie’s fields to strings.

The given headers may be provided either as an alist mapping header names to header values, or as a raw list of bytes such as the second return value produced by http-conn-recv! in net/http-client.

This function is suitable for use with the headers/raw field of a request structure (from web-server/http/request-structs), or with the output of (extract-all-fields h), where h is a byte string.

procedure
(parse-cookie set-cookie-bytes url [decode]) → (or/c ua-cookie? #f)
  set-cookie-bytes : bytes?
  url : url?
  decode : (-> bytes? string?) = bytes->string/utf-8

Given a single “Set-Cookie” header’s value set-cookie-bytes received in response to a request from the given url, produces a ua-cookie representing the cookie received, or #f if set-cookie-bytes can’t be parsed as a cookie.

The decode function is used to convert the cookie’s textual fields (name, value, domain, and path) to strings.

procedure
(default-path url) → string?
url : url?

Given a URL, produces the path that should be used for a cookie that has no “Path” attribute, as specified in Section 5.1.4 of the RFC.

value
max-cookie-seconds : (and/c integer? positive?)
value
min-cookie-seconds : (and/c integer? negative?)

The largest and smallest integers that this user agent library will use, or be guaranteed to accept, as time measurements in seconds since midnight UTC on January 1, 1970.

procedure
(parse-date s) → (or/c string? #f)
s : string?

Parses the given string for a date, producing #f if it is not possible to extract a date from the string using the algorithm specified in Section 5.1.1 of the RFC.

4 Acknowledgements

The server-side library is based on the original net/cookie library by Francisco Solsona <solsona@acm.org>. Many of the cookie-construction tests for this library are adapted from the net/cookie tests.

Roman Klochkov <kalimehtar@mail.ru> wrote the first client-side cookie library on which this user-agent library is based. In particular, this library relies on his code for parsing dates and other cookie components.

Bibliography

[RFC1034]		P. Mockapetris, “Domain Names - Concepts and Facilities,” RFC, 1987. http://tools.ietf.org/html/rfc1034.html
[RFC1123]		R. Braden (editor), “Requirements for Internet Hosts - Application and Support,” RFC, 1989. http://tools.ietf.org/html/rfc1123.html
[RFC6265]		A. Barth, “HTTP State Management Mechanism,” RFC, 2011. http://tools.ietf.org/html/rfc6265.html

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1	Cookies: Common Functionality
2	Cookies and HTTP Servers
3	Cookies and HTTP User Agents
4	Acknowledgements
	Bibliography