4 HTTP: Hypertext Transfer Protocol
| (require web-server/http) |
The Web Server implements many HTTP libraries that are provided by this module.
4.1 Requests
struct
(struct header (field value) #:extra-constructor-name make-header) field : bytes? value : bytes?
Represents a header of field to value.
Returns the header with a field equal to id from heads or #f.
Returns the header with a field case-insensitively equal to id from heads or #f.
You almost always want to use this, rather than headers-assq because Web browsers may send headers with arbitrary casing.
struct
(struct binding (id) #:extra-constructor-name make-binding) id : bytes?
Represents a binding of id.
struct
(struct binding:form binding (value) #:extra-constructor-name make-binding:form) value : bytes?
Represents a form binding of id to value.
struct
(struct binding:file binding (filename headers content) #:extra-constructor-name make-binding:file) filename : bytes? headers : (listof header?) content : bytes?
Represents the uploading of the file filename with the id id
and the content content, where headers are the additional headers from
the MIME envelope the file was in. (For example, the #"Content-Type" header may
be included by some browsers.)
Returns the binding with an id equal to id from binds or #f.
Like bindings-assq, but returns a list of all bindings matching id.
struct
(struct request ( method uri headers/raw bindings/raw-promise post-data/raw host-ip host-port client-ip) #:extra-constructor-name make-request) method : bytes? uri : url? headers/raw : (listof header?) bindings/raw-promise : (promise/c (listof binding?)) post-data/raw : (or/c false/c bytes?) host-ip : string? host-port : number? client-ip : string?
An HTTP method request to uri from client-ip
to the server at host-ip:host-port with headers/raw
headers, bindings/raw GET and POST queries and post-data/raw
POST data.
You are unlikely to need to construct a request struct.
procedure
(request-bindings/raw r) → (listof binding?)
r : request?
Here is an example typical of what you will find in many applications:
(define (get-number req) (match (bindings-assq #"number" (request-bindings/raw req)) [(? binding:form? b) (string->number (bytes->string/utf-8 (binding:form-value b)))] [_ (get-number (request-number))]))
4.2 Bindings
These functions, while convenient, could introduce subtle bugs into your
application. Examples: that they are case-insensitive could introduce
a bug; if the data submitted is not in UTF-8 format, then the conversion
to a string will fail; if an attacker submits a form field as if it were
a file, when it is not, then the request-bindings will hold a
bytes? object and your program will error; and, for file uploads
you lose the filename. Therefore, we recommend against their use, but
they are provided for compatibility with old code.
procedure
(request-bindings req)
→
(listof (or/c (cons/c symbol? string?) (cons/c symbol? bytes?))) req : request?
Translates the request-bindings/raw of req by
interpreting bytes? as string?s, except in the case
of binding:file bindings, which are left as is. Ids are then
translated into lowercase symbols.
Translates the request-headers/raw of req by
interpreting bytes? as string?s. Ids are then
translated into lowercase symbols.
procedure
(extract-binding/single id binds) → string?
id : symbol? binds : (listof (cons/c symbol? string?))
Returns the single binding associated with id in the a-list binds
if there is exactly one binding. Otherwise raises exn:fail.
procedure
(extract-bindings id binds) → (listof string?)
id : symbol? binds : (listof (cons/c symbol? string?))
Returns a list of all the bindings of id in the a-list binds.
procedure
(exists-binding? id binds) → boolean?
id : symbol? binds : (listof (cons/c symbol? string))
Returns #t if binds contains a binding for id.
Otherwise, #f.
Here is an example typical of what you will find in many applications:
(define (get-number req) (string->number (extract-binding/single 'number (request-bindings req))))
4.3 Responses
struct
(struct response (code message seconds mime headers output))
code : number? message : bytes? seconds : number? mime : (or/c false/c bytes?) headers : (listof header?) output : (output-port? . -> . void)
An HTTP response where output produces the body. code is the response code,
message the message, seconds the generation time, mime
the MIME type of the file, and headers are the headers. If headers does not include Date, Last-Modified, Server, or Content-Type headers, then the server will automatically add them. The server will always replace your Connection header if it needs to ensure the connection will be closed. (Typically with an HTTP/1.0 client.)
Example:
(response 301 #"Moved Permanently" (current-seconds) TEXT/HTML-MIME-TYPE (list (make-header #"Location" #"http://racket-lang.org/download")) (λ (op) (write-bytes #"Moved" op)))
procedure
(response/full code message seconds mime headers body) → response? code : number? message : bytes? seconds : number? mime : (or/c false/c bytes?) headers : (listof header?) body : (listof bytes?)
A constructor for responses where body is the response body.
Example:
(response/full 301 #"Moved Permanently" (current-seconds) TEXT/HTML-MIME-TYPE (list (make-header #"Location" #"http://racket-lang.org/download")) (list #"<html><body><p>" #"Please go to <a href=\"" #"http://racket-lang.org/download" #"\">here</a> instead." #"</p></body></html>"))
value
Equivalent to #"text/html; charset=utf-8".
Warning: If you include a Content-Length header in a response that is inaccurate, there will be an error in
transmission that the server will not catch.
4.4 Placing Cookies
This module provides functions to create cookies and responses that set them.
procedure
(make-cookie name value [ #:comment comment #:domain domain #:max-age max-age #:path path #:secure? secure?]) → cookie? name : cookie-name? value : cookie-value? comment : (or/c false/c string?) = #f domain : (or/c false/c valid-domain?) = #f max-age : (or/c false/c exact-nonnegative-integer?) = #f path : (or/c false/c string?) = #f secure? : (or/c false/c boolean?) = #f
Constructs a cookie with the appropriate fields.
procedure
(cookie->header c) → header?
c : cookie?
Constructs a header that sets the cookie.
Examples:
(define time-cookie (make-cookie "time" (number->string (current-seconds)))) (define id-cookie (make-cookie "id" "joseph" #:secure? #t)) (redirect-to "http://localhost/logged-in" see-other #:headers (map cookie->header (list time-cookie id-cookie))) (send/suspend (lambda (k-url) (response/xexpr #:cookies (list time-cookie id-cookie) `(html (head (title "Cookie Example")) (body (h1 "You're cookie'd!"))))))
4.5 Authenticated Cookies
Cookies are useful for storing information of user’s browsers and
particularly useful for storing identifying information for
authentication, sessions, etc. However, there are inherent
difficulties when using cookies as authenticators, because cookie data
is fully controlled by the user, and thus cannot be trusted.
This module provides functions for creating and verifying
authenticated cookies that are intrinsically timestamped. It is based
on the algorithm proposed by the
MIT Cookie Eaters: if you store
the data data at thime authored-seconds, then the
user will receive digest&authored-seconds&data, where
digest is an HMAC-SHA1 digest of authored-seconds
and data, using an arbitrary secret key. When you receive a
cookie, it will reverify this digest and check that the cookie’s
authored-seconds is not after a timeout period, and only
then return the cookie data to the program.
The interface represents the secret key as a byte string. The best way
to generate this is by using random bytes from something like OpenSSL
or
/dev/random. This
FAQ lists a few options. A convenient purely Racket-based option is
available (make-secret-salt/file), but it will not have as
good entropy, if you care about that sort of thing.
procedure
(make-id-cookie name secret-salt value) → cookie?
name : cookie-name? secret-salt : bytes? value : cookie-value?
Generates an authenticated cookie named name containing value, signed with secret-salt.
procedure
(request-id-cookie name secret-salt request #:timeout timeout) → (or/c false/c cookie-value?) name : cookie-name? secret-salt : bytes? request : request? timeout : +inf.0
Extracts the first authenticated cookie named name that was previously signed with secret-salt before timeout from request. If no valid cookie is available, returns #f.
procedure
(logout-id-cookie name) → cookie?
name : cookie-name?
Generates a cookie named name that is not validly authenticated.
This will cause non-malicious browsers to overwrite a previously set
cookie. If you use authenticated cookies for login information, you
could send this to cause a "logout". However, malicious browsers do
not need to respect such an overwrite. Therefore, this is not an
effective way to implement timeouts or protect users on
public (i.e. possibly compromised) computers. The only way to securely
logout on the compromised computer is to have server-side state
keeping track of which cookies (sessions, etc.) are invalid. Depending
on your application, it may be better to track live sessions or dead
sessions, or never set cookies to begin with and just use
continuations, which you can revoke with send/finish.
procedure
(make-secret-salt/file secret-salt-path) → bytes?
secret-salt-path : path-string?
Extracts the bytes from secret-salt-path. If
secret-salt-path does not exist, then it is created and
initialized with 128 random bytes.
4.6 Extracting Cookies
struct
(struct client-cookie (name value domain path) #:extra-constructor-name make-client-cookie) name : string? value : string? domain : (or/c false/c valid-domain?) path : (or/c false/c string?)
While server cookies are represented with cookie?s, cookies
that come from the client are represented with a
client-cookie structure.
procedure
(request-cookies req) → (listof client-cookie?)
req : request?
Extracts the cookies from req’s headers.
Examples:
(define (start req) (define cookies (request-cookies req)) (define id-cookie (findf (lambda (c) (string=? "id" (client-cookie-name c))) cookies)) (if id-cookie (hello (client-cookie-value id-cookie)) (redirect-to (url->string (request-uri req)) see-other #:headers (list (cookie->header (make-cookie "id" "joseph")))))) (define (hello who) (response/xexpr `(html (head (title "Hello!")) (body (h1 "Hello " ,who)))))
4.7 Redirect
procedure
(redirect-to uri [ perm/temp #:headers headers]) → response? uri : non-empty-string/c perm/temp : redirection-status? = temporarily headers : (listof header?) = (list)
Generates an HTTP response that redirects the browser to uri,
while including the headers in the response.
procedure
(redirection-status? v) → boolean?
v : any/c
Determines if v is one of the following values.
value
A redirection-status? for permanent redirections.
value
A redirection-status? for temporary redirections.
value
A redirection-status? for "see-other" redirections.
4.8 Basic Authentication
An implementation of HTTP Basic Authentication.
procedure
(make-basic-auth-header realm) → header?
realm : string?
Returns a header that instructs the Web browser to request a username and password from the client using
Basic authentication with realm as the realm.
Returns a pair of the username and password from the authentication
header in req if they are present, or #f.
Example:
#lang web-server/insta (define (start req) (match (request->basic-credentials req) [(cons user pass) (response/xexpr `(html (head (title "Basic Auth Test")) (body (h1 "User: " ,(bytes->string/utf-8 user)) (h1 "Pass: " ,(bytes->string/utf-8 pass)))))] [else (response 401 #"Unauthorized" (current-seconds) TEXT/HTML-MIME-TYPE (list (make-basic-auth-header (format "Basic Auth Test: ~a" (gensym)))) void)]))
4.9 Digest Authentication
An implementation of HTTP Digest Authentication.
procedure
(make-digest-auth-header realm private-key opaque) → header? realm : string? private-key : string? opaque : string?
Returns a header that instructs the Web browser to request a username and password from the client
using Digest authentication with realm as the realm, private-key as the server’s
contribution to the nonce, and opaque as the opaque data passed through the client.
Returns the Digest credentials from req (if they appear) as an association list.
Used to look up the password for a user is a realm.
Used to compute the user’s secret hash.
procedure
(password->digest-HA1 lookup-password)
→ username*realm->digest-HA1/c lookup-password : username*realm->password/c
Uses lookup-password to find the password, then computes the
secret hash of it.
procedure
(make-check-digest-credentials lookup-HA1)
→ (string? (listof (cons/c symbol? string?)) . -> . boolean?) lookup-HA1 : username*realm->digest-HA1/c
Constructs a function that checks whether particular Digest credentials
(the second argument of the returned function) are correct given the
HTTP method provided as the first argument and the secret hash computed
by lookup-HA1.
This is will result in an exception if the Digest credentials are
missing portions.
Example:
#lang web-server/insta (require racket/pretty) (define private-key "private-key") (define opaque "opaque") (define (start req) (match (request->digest-credentials req) [#f (response 401 #"Unauthorized" (current-seconds) TEXT/HTML-MIME-TYPE (list (make-digest-auth-header (format "Digest Auth Test: ~a" (gensym)) private-key opaque)) void)] [alist (define check (make-check-digest-credentials (password->digest-HA1 (lambda (username realm) "pass")))) (define pass? (check "GET" alist)) (response/xexpr `(html (head (title "Digest Auth Test")) (body (h1 ,(if pass? "Pass!" "No Pass!")) (pre ,(pretty-format alist)))))]))
4.10 X-expression Support
| (require web-server/http/xexpr) |
procedure
(response/xexpr xexpr [ #:code code #:message message #:seconds seconds #:mime-type mime-type #:headers headers #:cookies cookies #:preamble preamble]) → response? xexpr : xexpr/c code : number? = 200 message : bytes? = #"Okay" seconds : number? = (current-seconds) mime-type : (or/c false/c bytes?) = TEXT/HTML-MIME-TYPE headers : (listof header?) = empty cookies : (listof cookie?) = empty preamble : bytes? = #""
Equivalent to
(response/full code message seconds mime-type (append headers (map cookie->header cookies)) (list preamble (string->bytes/utf-8 (xexpr->string xexpr))))
This is a viable function to pass to set-any->response!.