On this page:
4.1 Requests
binding: form
binding: file
request-bindings/ raw
4.2 Bindings
extract-binding/ single
4.3 Responses
response/ full
4.4 Placing Cookies
4.5 Extracting Cookies
4.6 Redirect
4.7 Basic Authentication
4.8 Digest Authentication
username*realm->password/ c
username*realm->digest-HA1/ c
4.9 X-expression Support
response/ xexpr

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 header (field value)
  #:extra-constructor-name make-header)
  field : bytes?
  value : bytes?
Represents a header of field to value.

(headers-assq id heads)  (or/c false/c header?)
  id : bytes?
  heads : (listof header?)
Returns the header with a field equal to id from heads or #f.

(headers-assq* id heads)  (or/c false/c header?)
  id : bytes?
  heads : (listof header?)
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 binding (id)
  #:extra-constructor-name make-binding)
  id : bytes?
Represents a binding of id.

(struct binding:form binding (value)
  #:extra-constructor-name make-binding:form)
  value : bytes?
Represents a form binding of id to value.

(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.)

(bindings-assq id binds)  (or/c false/c binding?)
  id : bytes?
  binds : (listof binding?)
Returns the binding with an id equal to id from binds or #f.

(struct request (method
  #: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.

Here is an example typical of what you will find in many applications:
(define (get-number req)
      (request-bindings/raw req))
    [(? binding:form? b)
       (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.

(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.

(request-headers req)  (listof (cons/c symbol? string?))
  req : request?
Translates the request-headers/raw of req by interpreting bytes? as string?s. Ids are then translated into lowercase symbols.

(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.

(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.

(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)
    (request-bindings req))))

4.3 Responses

(struct response (code message seconds mime headers output))
  code : number?
  message : bytes?
  seconds : number?
  mime : 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.)

 301 #"Moved Permanently"
 (current-seconds) TEXT/HTML-MIME-TYPE
 (list (make-header #"Location"
 (λ (op) (write-bytes #"Moved" op)))

(response/full code    
  body)  response?
  code : number?
  message : bytes?
  seconds : number?
  mime : bytes?
  headers : (listof header?)
  body : (listof bytes?)
A constructor for responses where body is the response body.

 301 #"Moved Permanently"
 (current-seconds) TEXT/HTML-MIME-TYPE
 (list (make-header #"Location"
 (list #"<html><body><p>"
       #"Please go to <a href=\""
       #"\">here</a> instead."

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.

(make-cookie name    
  [#: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.

(cookie->header c)  header?
  c : cookie?
Constructs a header that sets the cookie.

(define time-cookie
  (make-cookie "time" (number->string (current-seconds))))
(define id-cookie
  (make-cookie "id" "joseph" #:secure? #t))
 (map cookie->header
      (list time-cookie id-cookie)))
 (lambda (k-url)
    #:cookies (list time-cookie id-cookie)
    `(html (head (title "Cookie Example"))
           (body (h1 "You're cookie'd!"))))))

Warning: When using cookies, make sure you follow the advice of the MIT Cookie Eaters, or you will be susceptible to dangerous attacks.

4.5 Extracting Cookies

(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.

(request-cookies req)  (listof client-cookie?)
  req : request?
Extracts the cookies from req’s headers.

(define (start req)
  (define cookies (request-cookies req))
  (define id-cookie
    (findf (lambda (c)
             (string=? "id" (client-cookie-name c)))
  (if id-cookie
      (hello (client-cookie-value id-cookie))
       (url->string (request-uri req))
        (cookie->header (make-cookie "id" "joseph"))))))
 (define (hello who)
    `(html (head (title "Hello!"))
            (h1 "Hello "

4.6 Redirect

(redirect-to uri    
  #: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.

Example: (redirect-to "http://www.add-three-numbers.com" permanently)

(redirection-status? v)  boolean?
  v : any/c
Determines if v is one of the following values.

A redirection-status? for permanent redirections.

A redirection-status? for temporary redirections.

A redirection-status? for "see-other" redirections.

4.7 Basic Authentication

An implementation of HTTP Basic Authentication.

(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.

#lang web-server/insta
(define (start req)
  (match (request->basic-credentials req)
    [(cons user pass)
      `(html (head (title "Basic Auth Test"))
             (body (h1 "User: " ,(bytes->string/utf-8 user))
                   (h1 "Pass: " ,(bytes->string/utf-8 pass)))))]
      401 #"Unauthorized" (current-seconds) TEXT/HTML-MIME-TYPE
        (format "Basic Auth Test: ~a" (gensym))))

4.8 Digest Authentication

An implementation of HTTP Digest Authentication.

(make-digest-auth-header realm    
  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.

Equivalent to (-> string? string? string?).

Used to compute the user’s secret hash.

Equivalent to (-> string? string? bytes?).

(password->digest-HA1 lookup-password)
  lookup-password : username*realm->password/c
Uses lookup-password to find the password, then computes the secret hash of it.

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.

#lang web-server/insta
(require racket/pretty)
(define private-key "private-key")
(define opaque "opaque")
(define (start req)
  (match (request->digest-credentials req)
      401 #"Unauthorized" (current-seconds) TEXT/HTML-MIME-TYPE
      (list (make-digest-auth-header
             (format "Digest Auth Test: ~a" (gensym))
             private-key opaque))
     (define check
        (password->digest-HA1 (lambda (username realm) "pass"))))
     (define pass?
       (check "GET" alist))
      `(html (head (title "Digest Auth Test"))
              (h1 ,(if pass? "Pass!" "No Pass!"))
              (pre ,(pretty-format alist)))))]))

4.9 X-expression Support

(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 : bytes? = TEXT/HTML-MIME-TYPE
  headers : (listof header?) = empty
  cookies : (listof cookie?) = empty
  preamble : bytes? = #""
Equivalent to
 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!.