;;;; (web uri) --- URI manipulation tools
;;;;
;;;; Copyright (C) 1997,2001,2002,2010 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;; 
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;;; Lesser General Public License for more details.
;;;; 
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;;

;;; Commentary:

;; A data type for Universal Resource Identifiers, as defined in RFC
;; 3986. 

;;; Code:

(define-module (web uri)
  #:use-module (srfi srfi-9)
  #:use-module (ice-9 regex)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 control)
  #:use-module (rnrs bytevectors)
  #:use-module (rnrs io ports)
  #:export (uri?
            uri-scheme uri-userinfo uri-host uri-port
            uri-path uri-query uri-fragment

            build-uri
            declare-default-port!
            string->uri uri->string
            uri-decode uri-encode
            split-and-decode-uri-path
            encode-and-join-uri-path))

(define-record-type <uri>
  (make-uri scheme userinfo host port path query fragment)
  uri?
  (scheme uri-scheme)
  (userinfo uri-userinfo)
  (host uri-host)
  (port uri-port)
  (path uri-path)
  (query uri-query)
  (fragment uri-fragment))

(define (uri-error message . args)
  (throw 'uri-error message args))

(define (positive-exact-integer? port)
  (and (number? port) (exact? port) (integer? port) (positive? port)))

(define (validate-uri scheme userinfo host port path query fragment)
  (cond
   ((not (symbol? scheme))
    (uri-error "Expected a symbol for the URI scheme: ~s" scheme))
   ((and (or userinfo port) (not host))
    (uri-error "Expected a host, given userinfo or port"))
   ((and port (not (positive-exact-integer? port)))
    (uri-error "Expected port to be an integer: ~s" port))
   ((and host (or (not (string? host)) (not (valid-host? host))))
    (uri-error "Expected valid host: ~s" host))
   ((and userinfo (not (string? userinfo)))
    (uri-error "Expected string for userinfo: ~s" userinfo))
   ((not (string? path))
    (uri-error "Expected string for path: ~s" path))
   ((and host (not (string-null? path))
         (not (eqv? (string-ref path 0) #\/)))
    (uri-error "Expected path of absolute URI to start with a /: ~a" path))))

(define* (build-uri scheme #:key userinfo host port (path "") query fragment
                    (validate? #t))
  "Construct a URI object. If @var{validate?} is true, also run some
consistency checks to make sure that the constructed URI is valid."
  (if validate?
      (validate-uri scheme userinfo host port path query fragment))
  (make-uri scheme userinfo host port path query fragment))

;; See RFC 3986 #3.2.2 for comments on percent-encodings, IDNA (RFC
;; 3490), and non-ASCII host names.
;;
(define ipv4-regexp
  (make-regexp "^([0-9.]+)"))
(define ipv6-regexp
  (make-regexp "^\\[([0-9a-fA-F:]+)\\]+"))
(define domain-label-regexp
  (make-regexp "^[a-zA-Z0-9]([a-zA-Z0-9-]*[a-zA-Z0-9])?$"))
(define top-label-regexp
  (make-regexp "^[a-zA-Z]([a-zA-Z0-9-]*[a-zA-Z0-9])?$"))

(define (valid-host? host)
  (cond
   ((regexp-exec ipv4-regexp host)
    => (lambda (m)
         (false-if-exception (inet-pton AF_INET (match:substring m 1)))))
   ((regexp-exec ipv6-regexp host)
    => (lambda (m)
         (false-if-exception (inet-pton AF_INET6 (match:substring m 1)))))
   (else
    (let ((labels (reverse (string-split host #\.))))
      (and (pair? labels)
           (regexp-exec top-label-regexp (car labels))
           (and-map (lambda (label)
                      (regexp-exec domain-label-regexp label))
                    (cdr labels)))))))

(define userinfo-pat
  "[a-zA-Z0-9_.!~*'();:&=+$,-]+")
(define host-pat
  "[a-zA-Z0-9.-]+")
(define port-pat
  "[0-9]*")
(define authority-regexp
  (make-regexp
   (format #f "^//((~a)@)?(~a)(:(~a))?$"
           userinfo-pat host-pat port-pat)))

(define (parse-authority authority fail)
  (let ((m (regexp-exec authority-regexp authority)))
    (if (and m (valid-host? (match:substring m 3)))
        (values (match:substring m 2)
                (match:substring m 3)
                (let ((port (match:substring m 5)))
                  (and port (not (string-null? port))
                       (string->number port))))
        (fail))))


;;; RFC 3986, #3.
;;;
;;;   URI         = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
;;;
;;;   hier-part   = "//" authority path-abempty
;;;               / path-absolute
;;;               / path-rootless
;;;               / path-empty

(define scheme-pat
  "[a-zA-Z][a-zA-Z0-9+.-]*")
(define authority-pat
  "[^/?#]*")
(define path-pat
  "[^?#]*")
(define query-pat
  "[^#]*")
(define fragment-pat
  ".*")
(define uri-pat
  (format #f "^(~a):(//~a)?(~a)(\\?(~a))?(#(~a))?$"
          scheme-pat authority-pat path-pat query-pat fragment-pat))
(define uri-regexp
  (make-regexp uri-pat))

(define (string->uri string)
  "Parse @var{string} into a URI object. Returns @code{#f} if the string
could not be parsed."
  (% (let ((m (regexp-exec uri-regexp string)))
       (if (not m) (abort))
       (let ((scheme (string->symbol
                      (string-downcase (match:substring m 1))))
             (authority (match:substring m 2))
             (path (match:substring m 3))
             (query (match:substring m 5))
             (fragment (match:substring m 7)))
         (call-with-values
             (lambda ()
               (if authority
                   (parse-authority authority abort)
                   (values #f #f #f)))
           (lambda (userinfo host port)
             (make-uri scheme userinfo host port path query fragment)))))
     (lambda (k)
       #f)))

(define *default-ports* (make-hash-table))

(define (declare-default-port! scheme port)
  "Declare a default port for the given URI scheme.

Default ports are for printing URI objects: a default port is not
printed."
  (hashq-set! *default-ports* scheme port))

(define (default-port? scheme port)
  (or (not port)
      (eqv? port (hashq-ref *default-ports* scheme))))

(declare-default-port! 'http 80)
(declare-default-port! 'https 443)

(define (uri->string uri)
  "Serialize @var{uri} to a string."
  (let* ((scheme-str (string-append
                      (symbol->string (uri-scheme uri)) ":"))
         (userinfo (uri-userinfo uri))
         (host (uri-host uri))
         (port (uri-port uri))
         (path (uri-path uri))
         (query (uri-query uri))
         (fragment (uri-fragment uri)))
    (string-append
     scheme-str
     (if host
         (string-append "//"
                        (if userinfo (string-append userinfo "@")
                            "")
                        host
                        (if (default-port? (uri-scheme uri) port)
                            ""
                            (string-append ":" (number->string port))))
         "")
     path
     (if query
         (string-append "?" query)
         "")
     (if fragment
         (string-append "#" fragment)
         ""))))


(define (call-with-encoded-output-string encoding proc)
  (if (string-ci=? encoding "utf-8")
      (string->utf8 (call-with-output-string proc))
      (call-with-values
          (lambda ()
            (open-bytevector-output-port))
        (lambda (port get-bytevector)
          (set-port-encoding! port encoding)
          (proc port)
          (get-bytevector)))))

(define (encode-string str encoding)
  (if (string-ci=? encoding "utf-8")
      (string->utf8 str)
      (call-with-encoded-output-string encoding
                                       (lambda (port)
                                         (display str port)))))

(define (decode-string bv encoding)
  (if (string-ci=? encoding "utf-8")
      (utf8->string bv)
      (let ((p (open-bytevector-input-port bv)))
        (set-port-encoding! p encoding)
        (read-delimited "" p))))


;; A note on characters and bytes: URIs are defined to be sequences of
;; characters in a subset of ASCII. Those characters may encode a
;; sequence of bytes (octets), which in turn may encode sequences of
;; characters in other character sets.
;;

;; Return a new string made from uri-decoding @var{str}.  Specifically,
;; turn @code{+} into space, and hex-encoded @code{%XX} strings into
;; their eight-bit characters.
;;
(define hex-chars
  (string->char-set "0123456789abcdefABCDEF"))

(define* (uri-decode str #:key (encoding "utf-8"))
  "Percent-decode the given @var{str}, according to @var{encoding}.

Note that this function should not generally be applied to a full URI
string. For paths, use split-and-decode-uri-path instead. For query
strings, split the query on @code{&} and @code{=} boundaries, and decode
the components separately.

Note that percent-encoded strings encode @emph{bytes}, not characters.
There is no guarantee that a given byte sequence is a valid string
encoding. Therefore this routine may signal an error if the decoded
bytes are not valid for the given encoding. Pass @code{#f} for
@var{encoding} if you want decoded bytes as a bytevector directly."
  (let ((len (string-length str)))
    (call-with-values open-bytevector-output-port
      (lambda (port get-bytevector)
        (let lp ((i 0))
          (if (= i len)
              (if encoding
                  (decode-string (get-bytevector) encoding)
                  (get-bytevector)) ; raw bytevector
              (let ((ch (string-ref str i)))
                (cond
                 ((eqv? ch #\+)
                  (put-u8 port (char->integer #\space))
                  (lp (1+ i)))
                 ((and (< (+ i 2) len) (eqv? ch #\%)
                       (let ((a (string-ref str (+ i 1)))
                             (b (string-ref str (+ i 2))))
                         (and (char-set-contains? hex-chars a)
                              (char-set-contains? hex-chars b)
                              (string->number (string a b) 16))))
                  => (lambda (u8)
                       (put-u8 port u8)
                       (lp (+ i 3))))
                 ((< (char->integer ch) 128)
                  (put-u8 port (char->integer ch))
                  (lp (1+ i)))
                 (else
                  (uri-error "Invalid character in encoded URI ~a: ~s"
                             str ch))))))))))
  
(define ascii-alnum-chars
  (string->char-set
   "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"))

;; RFC 3986, #2.2.
(define gen-delims
  (string->char-set ":/?#[]@"))
(define sub-delims
  (string->char-set "!$&'()*+,l="))
(define reserved-chars
  (char-set-union gen-delims sub-delims))

;; RFC 3986, #2.3
(define unreserved-chars
  (char-set-union ascii-alnum-chars
                  (string->char-set "-._~")))

;; Return a new string made from uri-encoding @var{str}, unconditionally
;; transforming any characters not in @var{unescaped-chars}.
;;
(define* (uri-encode str #:key (encoding "utf-8")
                     (unescaped-chars unreserved-chars))
  "Percent-encode any character not in the character set, @var{unescaped-chars}.

Percent-encoding first writes out the given character to a bytevector
within the given @var{encoding}, then encodes each byte as
@code{%@var{HH}}, where @var{HH} is the hexadecimal representation of
the byte."
  (if (string-index str unescaped-chars)
      (call-with-output-string
       (lambda (port)
         (string-for-each
          (lambda (ch)
            (if (char-set-contains? unescaped-chars ch)
                (display ch port)
                (let* ((bv (encode-string (string ch) encoding))
                       (len (bytevector-length bv)))
                  (let lp ((i 0))
                    (if (< i len)
                        (let ((byte (bytevector-u8-ref bv i)))
                          (display #\% port)
                          (display (number->string byte 16) port)
                          (lp (1+ i))))))))
          str)))
      str))

(define (split-and-decode-uri-path path)
  "Split @var{path} into its components, and decode each
component, removing empty components.

For example, @code{\"/foo/bar/\"} decodes to the two-element list,
@code{(\"foo\" \"bar\")}."
  (filter (lambda (x) (not (string-null? x)))
          (map uri-decode (string-split path #\/))))

(define (encode-and-join-uri-path parts)
  "URI-encode each element of @var{parts}, which should be a list of
strings, and join the parts together with @code{/} as a delimiter."
  (string-join (map uri-encode parts) "/"))