ikarus/scheme/ikarus.io.ss

;;; Ikarus Scheme -- A compiler for R6RS Scheme.
;;; Copyright (C) 2006,2007,2008  Abdulaziz Ghuloum
;;; 
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License version 3 as
;;; published by the Free Software Foundation.
;;; 
;;; This program 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
;;; General Public License for more details.
;;; 
;;; You should have received a copy of the GNU General Public License
;;; along with this program.  If not, see <http://www.gnu.org/licenses/>.


(library (io-spec) 
  
  (export 
    port? input-port? output-port? textual-port? binary-port?
    open-file-input-port open-input-file 
    call-with-input-file with-input-from-file
    standard-input-port current-input-port
    open-bytevector-input-port
    open-string-input-port with-input-from-string
    make-custom-binary-input-port 
    make-custom-binary-output-port 
    make-custom-textual-input-port 
    make-custom-textual-output-port 
    transcoded-port port-transcoder
    close-port port-closed? close-input-port close-output-port
    port-eof?
    get-char lookahead-char read-char peek-char
    get-string-n get-string-n! get-string-all get-line
    get-u8 lookahead-u8 
    get-bytevector-n get-bytevector-n!
    get-bytevector-some get-bytevector-all 
    ;port-has-port-position? port-position
    ;port-has-set-port-position!? set-port-position!
    call-with-port
    flush-output-port
    put-u8 put-bytevector
    put-char write-char
    put-string
    open-bytevector-output-port
    call-with-bytevector-output-port
    open-string-output-port with-output-to-string
    with-output-to-port
    call-with-string-output-port 
    open-output-string get-output-string
    standard-output-port standard-error-port
    current-output-port current-error-port
    open-file-output-port open-output-file 
    call-with-output-file with-output-to-file
    console-output-port
    console-error-port
    console-input-port
    newline
    input-port-name
    output-port-name
    port-mode set-port-mode!
    reset-input-port!
    reset-output-port!
    port-id
    input-port-byte-position
    process process-nonblocking
    
    tcp-connect tcp-connect-nonblocking
    udp-connect udp-connect-nonblocking
    tcp-server-socket tcp-server-socket-nonblocking
    accept-connection accept-connection-nonblocking
    close-tcp-server-socket 
    register-callback
    input-socket-buffer-size output-socket-buffer-size
    )

  
  (import 
    (ikarus system $io)

    (except (ikarus)
      port? input-port? output-port? textual-port? binary-port? 
      open-file-input-port open-input-file 
      call-with-input-file with-input-from-file
      standard-input-port current-input-port
      open-bytevector-input-port
      open-string-input-port with-input-from-string
      make-custom-binary-input-port
      make-custom-binary-output-port 
      make-custom-textual-input-port 
      make-custom-textual-output-port 
      transcoded-port port-transcoder
      close-port port-closed? close-input-port close-output-port
      port-eof?
      get-char lookahead-char read-char peek-char
      get-string-n get-string-n! get-string-all get-line
      get-u8 lookahead-u8 
      get-bytevector-n get-bytevector-n!
      get-bytevector-some get-bytevector-all 
      ;port-has-port-position? port-position
      ;port-has-set-port-position!? set-port-position!
      call-with-port
      flush-output-port
      put-u8 put-bytevector
      put-char write-char
      put-string
      open-bytevector-output-port
      call-with-bytevector-output-port
      open-string-output-port with-output-to-string
      call-with-string-output-port
      open-output-string get-output-string
      standard-output-port standard-error-port
      current-output-port current-error-port
      open-file-output-port open-output-file 
      call-with-output-file with-output-to-file
      with-output-to-port
      console-output-port
      console-input-port
      console-error-port
      newline
      input-port-name
      output-port-name
      port-mode set-port-mode!
      reset-input-port!
      reset-output-port!
      port-id
      input-port-byte-position
      process process-nonblocking
      tcp-connect tcp-connect-nonblocking
      udp-connect udp-connect-nonblocking
      tcp-server-socket tcp-server-socket-nonblocking
      accept-connection accept-connection-nonblocking
      close-tcp-server-socket 
      register-callback
      input-socket-buffer-size output-socket-buffer-size
      ))

  (module UNSAFE  
    (fx< fx<= fx> fx>= fx= fx+ fx-
     fxior fxand fxsra fxsll
     integer->char char->integer
     string-ref string-set! string-length
     bytevector-u8-ref bytevector-u8-set!)
    (import 
      (rename (ikarus system $strings)
        ($string-length string-length)
        ($string-ref    string-ref)
        ($string-set!   string-set!))
      (rename (ikarus system $chars)
        ($char->fixnum char->integer)
        ($fixnum->char integer->char))
      (rename (ikarus system $bytevectors)
        ($bytevector-set!   bytevector-u8-set!)
        ($bytevector-u8-ref bytevector-u8-ref))
      (rename (ikarus system $fx) 
        ($fxsra    fxsra)
        ($fxsll    fxsll)
        ($fxlogor  fxior)
        ($fxlogand fxand)
        ($fx+      fx+)
        ($fx-      fx-)
        ($fx<      fx<)
        ($fx>      fx>)
        ($fx>=     fx>=)
        ($fx<=     fx<=)
        ($fx=      fx=))))

  (define (port? x)
    (import (only (ikarus) port?))
    (port? x))

  (define-syntax define-rrr
    (syntax-rules ()
      [(_ name)
       (define (name . args) 
         (apply die 'name "not implemented" args))]))
 
  (define-syntax u8?
    (let ()
      (import (ikarus system $fx))
      (syntax-rules ()
        [(_ x) 
         ($fxzero? ($fxlogand x -256))])))

  ;(define (u8? x) (and (fixnum? x) (fx>= x 0) (fx< x 256)))
  
  (define (textual-port? x) 
    (fx= (fxand ($port-tag x) textual-port-tag) textual-port-tag))

  (define (binary-port? x) 
    (fx= (fxand ($port-tag x) binary-port-tag) binary-port-tag))

  (define (output-port? x) 
    (fx= (fxand ($port-tag x) output-port-tag) output-port-tag))

  (define (input-port? x)
    (fx= (fxand ($port-tag x) input-port-tag) input-port-tag))

  ;;; everything above this line will turn into primitive
  ;;; ----------------------------------------------------------
  
  (define input-port-tag           #b00000000000001)
  (define output-port-tag          #b00000000000010)
  (define textual-port-tag         #b00000000000100)
  (define binary-port-tag          #b00000000001000)
  (define fast-char-text-tag       #b00000000010000)
  (define fast-u7-text-tag         #b00000000100000)
  (define fast-u8-text-tag         #b00000001100000)
  (define r6rs-mode-tag            #b01000000000000)
  (define closed-port-tag          #b10000000000000)

  (define port-type-mask           #b00000000001111)
  (define binary-input-port-bits   #b00000000001001)
  (define binary-output-port-bits  #b00000000001010)
  (define textual-input-port-bits  #b00000000000101)
  (define textual-output-port-bits #b00000000000110)

  (define fast-get-byte-tag        #b00000000001001)
  (define fast-get-char-tag        #b00000000010101)
  (define fast-get-utf8-tag        #b00000000100101)
  (define fast-get-latin-tag       #b00000001100101)

  (define fast-put-byte-tag        #b00000000001010)
  (define fast-put-char-tag        #b00000000010110)
  (define fast-put-utf8-tag        #b00000000100110)
  (define fast-put-latin-tag       #b00000001100110)

  (define fast-attrs-mask          #xFFF)
  (define-syntax $port-fast-attrs
    (identifier-syntax
      (lambda (x) 
        (import (ikarus system $fx))
        ($fxlogand ($port-tag x) fast-attrs-mask))))

  (define (input-port-name p)
    (if (input-port? p) 
        ($port-id p)
        (die 'input-port-name "not an input port" p)))

  (define (output-port-name p)
    (if (output-port? p) 
        ($port-id p)
        (die 'output-port-name "not an output port" p)))

  (define (port-id p)
    (if (port? p) 
        ($port-id p)
        (die 'port-id "not a port" p)))

  (define (input-port-byte-position p)
    (if (input-port? p) 
        (let ([pos ($port-position p)])
          (and pos (fx+ pos (fx+ ($port-index p) 1))))
        (error 'input-port-byte-position "not an input port" p)))

  (define guarded-port
    (let ([G (make-guardian)])
      (define (clean-up)
        (cond
          [(G) =>
           (lambda (p)
             (close-port p)
             (clean-up))]))
      (lambda (p)
        (clean-up)
        (when (fixnum? ($port-cookie p))
          (G p))
        p)))

  (define ($make-custom-binary-port attrs init-size id 
            read! write! get-position set-position! close buffer-size)
    (let ([bv (make-bytevector buffer-size)])
      ($make-port attrs 0 init-size bv #f id read! write! 
                  #f #f close #f)))

  (define ($make-custom-textual-port attrs init-size id 
            read! write! get-position set-position! close buffer-size)
    (let ([bv (make-string buffer-size)])
      ($make-port attrs 0 init-size bv #t id read! write! 
                  #f #f close #f)))

  (define (make-custom-binary-input-port id 
            read! get-position set-position! close)
    ;;; FIXME: get-position and set-position! are ignored for now
    (define who 'make-custom-binary-input-port)
    (unless (string? id)
      (die who "id is not a string" id))
    (unless (procedure? read!)
      (die who "read! is not a procedure" read!))
    (unless (or (procedure? close) (not close))
      (die who "close should be either a procedure or #f" close))
    ($make-custom-binary-port 
      binary-input-port-bits
      0
      id read! #f get-position
      set-position! close 256))

  (define (make-custom-binary-output-port id 
            write! get-position set-position! close)
    ;;; FIXME: get-position and set-position! are ignored for now
    (define who 'make-custom-binary-output-port)
    (unless (string? id)
      (die who "id is not a string" id))
    (unless (procedure? write!)
      (die who "write! is not a procedure" write!))
    (unless (or (procedure? close) (not close))
      (die who "close should be either a procedure or #f" close))
    ($make-custom-binary-port 
      binary-output-port-bits
      256
      id #f write! get-position
      set-position! close 256))

  (define (make-custom-textual-input-port id 
            read! get-position set-position! close)
    ;;; FIXME: get-position and set-position! are ignored for now
    (define who 'make-custom-textual-input-port)
    (unless (string? id)
      (die who "id is not a string" id))
    (unless (procedure? read!)
      (die who "read! is not a procedure" read!))
    (unless (or (procedure? close) (not close))
      (die who "close should be either a procedure or #f" close))
    ($make-custom-textual-port 
      (fxior textual-input-port-bits fast-char-text-tag)
      0
      id read! #f get-position
      set-position! close 256))

  (define (make-custom-textual-output-port id 
            write! get-position set-position! close)
    ;;; FIXME: get-position and set-position! are ignored for now
    (define who 'make-custom-textual-output-port)
    (unless (string? id)
      (die who "id is not a string" id))
    (unless (procedure? write!)
      (die who "write! is not a procedure" write!))
    (unless (or (procedure? close) (not close))
      (die who "close should be either a procedure or #f" close))
    ($make-custom-textual-port 
      (fxior textual-output-port-bits fast-char-text-tag)
      256
      id #f write! get-position
      set-position! close 256))



  (define (input-transcoder-attrs x who)
    (cond
      [(not x) ;;; binary input port
       binary-input-port-bits]
      [(not (eq? 'none (transcoder-eol-style x)))
       (die who "unsupported transcoder eol-style" 
            (transcoder-eol-style x))]
      [(eq? 'latin-1-codec (transcoder-codec x))
       (fxior textual-input-port-bits fast-u8-text-tag)]
      ;;; attrs for utf-8-codec are set as part of the 
      ;;; bom-reading dance when the first char is read.
      [else textual-input-port-bits]))

  (define (output-transcoder-attrs x who)
    (cond
      [(not x) ;;; binary input port
       binary-output-port-bits]
      [(not (eq? 'none (transcoder-eol-style x)))
       (die who "unsupported transcoder eol-style" 
            (transcoder-eol-style x))]
      [(eq? 'latin-1-codec (transcoder-codec x))
       (fxior textual-output-port-bits fast-u8-text-tag)]
      [(eq? 'utf-8-codec (transcoder-codec x))
       (fxior textual-output-port-bits fast-u7-text-tag)]
      [else textual-output-port-bits]))

  (define open-bytevector-input-port
    (case-lambda
      [(bv) (open-bytevector-input-port bv #f)]
      [(bv maybe-transcoder) 
       (unless (bytevector? bv) 
         (die 'open-bytevector-input-port 
                "not a bytevector" bv))
       (when (and maybe-transcoder
                  (not (transcoder? maybe-transcoder)))
         (die 'open-bytevector-input-port 
                "not a transcoder" maybe-transcoder))
       ($make-port 
          (input-transcoder-attrs maybe-transcoder
            'open-bytevector-output-port)
          0 (bytevector-length bv) bv 
          maybe-transcoder 
          "*bytevector-input-port*" 
          (lambda (bv i c) 0) ;;; read!
          #f ;;; write!
          #f ;;; FIXME: get-position
          #f ;;; FIXME: set-position!
          #f ;;; close
          #f)]))

  (define open-bytevector-output-port
    (case-lambda
      [() (open-bytevector-output-port #f)]
      [(transcoder) 
       (define who 'open-bytevector-output-port)
       (unless (or (not transcoder) (transcoder? transcoder))
         (die who "invalid transcoder value" transcoder))
       (let ([buf* '()] [buffer-size 256])
         (let ([p 
                ($make-port 
                   (output-transcoder-attrs transcoder
                     'open-bytevector-output-port)
                   0 buffer-size (make-bytevector buffer-size)
                   transcoder
                   "*bytevector-output-port*"
                   #f
                   (lambda (bv i c) 
                     (unless (= c 0) 
                       (let ([x (make-bytevector c)])
                         (bytevector-copy! bv i x 0 c)
                         (set! buf* (cons x buf*))))
                     c)
                   #f  ;;; FIXME: get-position
                   #f  ;;; FIXME: set-position!
                   #f
                   #f)])
           (values
             p
             (lambda () 
               (define (append-bv-buf* ls) 
                 (let f ([ls ls] [i 0])
                   (cond
                     [(null? ls) 
                      (values (make-bytevector i) 0)]
                     [else 
                      (let* ([a (car ls)]
                             [n (bytevector-length a)])
                        (let-values ([(bv i) (f (cdr ls) (fx+ i n))])
                          (bytevector-copy! a 0 bv i n)
                          (values bv (fx+ i n))))])))
               (unless ($port-closed? p)
                 (flush-output-port p))
               (let-values ([(bv len) (append-bv-buf* buf*)])
                 (set! buf* '())
                 bv)))))]))

  (define call-with-bytevector-output-port
    (case-lambda
      [(proc) (call-with-bytevector-output-port proc #f)]
      [(proc transcoder) 
       (define who 'call-with-bytevector-output-port)
       (unless (procedure? proc) 
         (die who "not a procedure" proc))
       (unless (or (not transcoder) (transcoder? transcoder))
         (die who "invalid transcoder argument" transcoder))
       (let-values ([(p extract) 
                     (open-bytevector-output-port transcoder)])
         (proc p)
         (extract))]))

  (define (call-with-string-output-port proc)
    (define who 'call-with-string-output-port)
    (unless (procedure? proc) 
      (die who "not a procedure" proc))
    (let-values ([(p extract) (open-string-output-port)])
      (proc p)
      (extract)))

  (define (with-output-to-string proc) 
    (define who 'with-output-to-string)
    (unless (procedure? proc) 
      (die who "not a procedure" proc))
    (let-values ([(p extract) (open-string-output-port)])
      (parameterize ([*the-output-port* p])
        (proc))
      (extract)))

  (define (with-output-to-port p proc)
    (define who 'with-output-to-port)
    (unless (procedure? proc)
      (die who "not a procedure" proc))
    (unless (output-port? p) 
      (die who "not an output port" p))
    (unless (textual-port? p)
      (die who "not a textual port" p))
    (parameterize ([*the-output-port* p])
      (proc)))

  (define-struct output-string-cookie (strings))


  (define (open-output-string)
    (define who 'open-output-string)
    (let ([cookie (make-output-string-cookie '())]
          [buffer-size 256])
      ($make-port
         (fxior textual-output-port-bits fast-char-text-tag)
         0 buffer-size (make-string buffer-size)
         #t ;;; transcoder
         "*string-output-port*"
         #f
         (lambda (str i c) 
           (unless (= c 0) 
             (let ([x (make-string c)])
               (string-copy! str i x 0 c)
               (set-output-string-cookie-strings! cookie
                 (cons x (output-string-cookie-strings cookie)))))
           c)
         #f  ;;; FIXME: get-position
         #f  ;;; FIXME: set-position!
         #f
         cookie)))

  (define (open-string-output-port)
    (let ([p (open-output-string)])
      (values
        p
        (lambda ()
          (let ([str (get-output-string p)])
            (set-output-string-cookie-strings!  ($port-cookie p) '())
            str)))))

  (define (get-output-string-cookie-data cookie)
    (define (append-str-buf* ls) 
      (let f ([ls ls] [i 0])
        (cond
          [(null? ls) 
           (values (make-string i) 0)]
          [else 
           (let* ([a (car ls)]
                  [n (string-length a)])
             (let-values ([(bv i) (f (cdr ls) (fx+ i n))])
               (string-copy! a 0 bv i n)
               (values bv (fx+ i n))))])))
      (let ([buf* (output-string-cookie-strings cookie)])
        (let-values ([(bv len) (append-str-buf* buf*)])
          bv)))

  (define (get-output-string p)
    (if (port? p) 
        (let ([cookie ($port-cookie p)])
          (cond
            [(output-string-cookie? cookie)
             (unless ($port-closed? p)
               (flush-output-port p))
             (get-output-string-cookie-data cookie)]
            [else
             (die 'get-output-string "not an output-string port" p)]))
        (die 'get-output-string "not a port" p)))

  (define (open-string-input-port str)
    (unless (string? str) 
      (die 'open-string-input-port "not a string" str))
    ($make-port 
       (fxior textual-input-port-bits fast-char-text-tag)
       0 (string-length str) str
       #t ;;; transcoder
       "*string-input-port*" 
       (lambda (str i c) 0) ;;; read!
       #f ;;; write!
       #f ;;; FIXME: get-position
       #f ;;; FIXME: set-position!
       #f ;;; close
       #f))
    

  (define (transcoded-port p transcoder)
    (define who 'transcoded-port)
    (unless (transcoder? transcoder)
      (die who "not a transcoder" transcoder))
    (unless (port? p) (die who "not a port" p))
    (when ($port-transcoder p) (die who "not a binary port" p))
    (when ($port-closed? p) (die who "cannot transcode closed port" p))
    (let ([read! ($port-read! p)]
          [write! ($port-write! p)])
      ($mark-port-closed! p)
      (guarded-port
        ($make-port 
          (cond
            [read! (input-transcoder-attrs transcoder
                     'transcoded-port)]
            [write! (output-transcoder-attrs transcoder
                      'transcoded-port)]
            [else
             (die 'transcoded-port 
               "port is neither input nor output!")])
          ($port-index p)
          ($port-size p)
          ($port-buffer p)
          transcoder
          ($port-id p)
          read!
          write!
          ($port-get-position p)
          ($port-set-position! p)
          ($port-close p)
          ($port-cookie p)))))

  (define (reset-input-port! p)
    (if (input-port? p) 
        (begin
          ($set-port-index! p ($port-size p))
          (unregister-callback p))
        (die 'reset-input-port! "not an input port" p)))

  (define (reset-output-port! p)
    (if (output-port? p) 
        (begin
          ($set-port-index! p 0)
          (unregister-callback p))
        (die 'reset-output-port! "not an output port" p)))


  (define (port-transcoder p)
    (if (port? p)
        (let ([tr ($port-transcoder p)])
          (and (transcoder? tr) tr))
        (die 'port-transcoder "not a port" p)))
              
  (define ($port-closed? p) 
    (import UNSAFE)
    (not (fx= (fxand ($port-attrs p) closed-port-tag) 0)))

  (define (port-closed? p) 
    (if (port? p) 
        ($port-closed? p) 
        (error 'port-closed? "not a port" p)))

  (define ($mark-port-closed! p) 
    ($set-port-attrs! p 
      (fxior closed-port-tag 
             (fxand ($port-attrs p) port-type-mask))))


  (define (port-mode p)
    (if (port? p) 
        (if (fxzero? (fxand ($port-attrs p) r6rs-mode-tag))
            'ikarus-mode
            'r6rs-mode)
        (die 'port-mode "not a port" p)))

  (define (set-port-mode! p mode)
    (if (port? p) 
        (case mode
          [(r6rs-mode) 
           ($set-port-attrs! p
             (fxior ($port-attrs p) r6rs-mode-tag))]
          [(ikarus-mode)
           ($set-port-attrs! p
             (fxand ($port-attrs p) (fxnot r6rs-mode-tag)))]
          [else (die 'set-port-mode! "invalid mode" mode)])
        (die 'set-port-mode! "not a port" p)))


  (define flush-output-port
    (case-lambda
      [() (flush-output-port (*the-output-port*))] 
      [(p)
       (import UNSAFE)
       (unless (output-port? p) 
         (die 'flush-output-port "not an output port" p))
       (when ($port-closed? p) 
         (die 'flush-output-port "port is closed" p))
       (let ([idx ($port-index p)]
             [buf ($port-buffer p)])
         (unless (fx= idx 0)
           (let ([bytes (($port-write! p) buf 0 idx)])
             (unless (and (fixnum? bytes) (fx>= bytes 0) (fx<= bytes idx))
               (die 'flush-output-port 
                      "write! returned an invalid value" 
                      bytes))
             (cond
               [(fx= bytes idx) 
                ($set-port-index! p 0)]
               [(fx= bytes 0) 
                ($mark-port-closed! p)
                (die 'flush-output-port "could not write bytes to sink")]
               [else
                (bytevector-copy! buf bytes buf 0 (fx- idx bytes))
                ($set-port-index! p (fx- idx bytes))
                (flush-output-port p)]))))]))

  (define ($close-port p)
    (cond
      [($port-closed? p) (void)]
      [else
       (when ($port-write! p)
         (flush-output-port p))
       ($mark-port-closed! p)
       (let ([close ($port-close p)])
         (when (procedure? close)
           (close)))]))

  (define (close-port p)
    (unless (port? p)
       (die 'close-port "not a port" p))
    ($close-port p))

  (define (close-input-port p)
    (unless (input-port? p)
       (die 'close-input-port "not an input port" p))
    ($close-port p))

  (define (close-output-port p)
    (unless (output-port? p)
       (die 'close-output-port "not an output port" p))
    ($close-port p))

  ;(define-rrr port-has-port-position?)
  ;(define-rrr port-position)
  ;(define-rrr port-has-set-port-position!?)
  ;(define-rrr set-port-position!)

  (define (refill-bv-buffer p who)
    (when ($port-closed? p) (die who "port is closed" p))
    (let ([bv ($port-buffer p)] [i ($port-index p)] [j ($port-size p)])
      (let ([c0 (fx- j i)])
        (unless (fx= c0 0) (bytevector-copy! bv i bv 0 c0))
        (let ([pos ($port-position p)])
          (when pos
            ($set-port-position! p (fx+ pos i))))
        (let* ([max (fx- (bytevector-length bv) c0)]
               [c1 (($port-read! p) bv c0 max)])
          (unless (fixnum? c1)
            (die who "invalid return value from read! procedure" c1))
          (cond
            [(fx>= j 0)
             (unless (fx<= j max)
               (die who "read! returned a value out of range" j))
             ($set-port-index! p c0)
             ($set-port-size! p (fx+ c1 c0))
             c1]
            [else 
             (die who "read! returned a value out of range" c1)])))))

  ;;; ----------------------------------------------------------
  (module (read-char get-char lookahead-char)
    (import UNSAFE)
    (define (get-char-latin-mode p who inc)
      (let ([n (refill-bv-buffer p who)])
        (cond
          [(fx= n 0) (eof-object)]
          [else 
           (let ([idx ($port-index p)])
             ($set-port-index! p (fx+ idx inc))
             (integer->char (bytevector-u8-ref ($port-buffer p) idx)))])))
    (define (get-char-utf8-mode p who)
      (define (do-error p who)
        (case (transcoder-error-handling-mode ($port-transcoder p))
          [(ignore)  (get-char p)]
          [(replace) #\xFFFD]
          [(raise)
           (raise (make-i/o-decoding-error p))]
          [else (die who "cannot happen")]))
      (let ([i ($port-index p)] 
            [j ($port-size p)]
            [buf ($port-buffer p)])
        (cond
          [(fx= i j) ;;; exhausted
           (let ([bytes (refill-bv-buffer p who)])
             (cond
               [(fx= bytes 0) (eof-object)]
               [else (get-char p)]))]
          [else
           (let ([b0 (bytevector-u8-ref buf i)])
             (cond
               [(fx= (fxsra b0 5) #b110) ;;; two-byte-encoding
                (let ([i (fx+ i 1)])
                  (cond
                    [(fx< i j) 
                     (let ([b1 (bytevector-u8-ref buf i)])
                       (cond
                         [(fx= (fxsra b1 6) #b10)
                          ($set-port-index! p (fx+ i 1))
                          (integer->char
                            (fxior (fxand b1 #b111111)
                                   (fxsll (fxand b0 #b11111) 6)))]
                         [else
                          ($set-port-index! p i)
                          (do-error p who)]))]
                    [else
                     (let ([bytes (refill-bv-buffer p who)])
                       (cond
                         [(fx= bytes 0) 
                          ($set-port-index! p (fx+ ($port-index p) 1))
                          (do-error p who)]
                         [else (get-char-utf8-mode p who)]))]))]
               [(fx= (fxsra b0 4) #b1110) ;;; three-byte-encoding
                (cond
                  [(fx< (fx+ i 2) j) 
                   (let ([b1 (bytevector-u8-ref buf (fx+ i 1))]
                         [b2 (bytevector-u8-ref buf (fx+ i 2))])
                     (cond
                       [(fx= (fxsra (fxlogor b1 b2) 6) #b10) 
                        (let ([n (fxlogor 
                                   (fxsll (fxand b0 #b1111) 12)
                                   (fxsll (fxand b1 #b111111) 6)
                                   (fxand b2 #b111111))])
                          (cond
                            [(and (fx<= #xD800 n) (fx<= n #xDFFF))
                             ($set-port-index! p (fx+ i 1))
                             (do-error p who)]
                            [else
                             ($set-port-index! p (fx+ i 3))
                             (integer->char n)]))]
                       [else
                        ($set-port-index! p (fx+ i 1))
                        (do-error p who)]))]
                  [else
                   (let ([bytes (refill-bv-buffer p who)])
                     (cond
                       [(fx= bytes 0)
                        ($set-port-index! p (fx+ ($port-index p) 1))
                        (do-error p who)]
                       [else (get-char-utf8-mode p who)]))])]
               [(fx= (fxsra b0 3) #b11110) ;;; four-byte-encoding
                (cond
                  [(fx< (fx+ i 3) j) 
                   (let ([b1 (bytevector-u8-ref buf (fx+ i 1))]
                         [b2 (bytevector-u8-ref buf (fx+ i 2))]
                         [b3 (bytevector-u8-ref buf (fx+ i 3))])
                     (cond
                       [(fx= (fxsra (fxlogor b1 b2 b3) 6) #b10)
                        (let ([n (fxlogor 
                                   (fxsll (fxand b0 #b111) 18)
                                   (fxsll (fxand b1 #b111111) 12)
                                   (fxsll (fxand b2 #b111111) 6)
                                   (fxand b3 #b111111))])
                          (cond
                            [(and (fx<= #x10000 n) (fx<= n #x10FFFF))
                             ($set-port-index! p (fx+ i 4))
                             (integer->char n)]
                            [else
                             ($set-port-index! p (fx+ i 1))
                             (do-error p who)]))]
                       [else
                        ($set-port-index! p (fx+ i 1))
                        (do-error p who)]))]
                  [else
                   (let ([bytes (refill-bv-buffer p who)])
                     (cond
                       [(fx= bytes 0)
                        ($set-port-index! p (fx+ ($port-index p) 1))
                        (do-error p who)]
                       [else (get-char-utf8-mode p who)]))])]
               [else 
                ($set-port-index! p (fx+ i 1))
                (do-error p who)]))])))
    
    (define (lookahead-char-utf8-mode p who)
      (define (do-error p who)
        (case (transcoder-error-handling-mode ($port-transcoder p))
          [(ignore)  (get-char p)]
          [(replace) #\xFFFD]
          [(raise)
           (raise (make-i/o-decoding-error p))]
          [else (die who "cannot happen")]))
      (let ([i ($port-index p)] 
            [j ($port-size p)]
            [buf ($port-buffer p)])
        (cond
          [(fx= i j) ;;; exhausted
           (let ([bytes (refill-bv-buffer p who)])
             (cond
               [(fx= bytes 0) (eof-object)]
               [else (lookahead-char p)]))]
          [else
           (let ([b0 (bytevector-u8-ref buf i)])
             (cond
               [(fx= (fxsra b0 5) #b110) ;;; two-byte-encoding
                (let ([i (fx+ i 1)])
                  (cond
                    [(fx< i j) 
                     (let ([b1 (bytevector-u8-ref buf i)])
                       (cond
                         [(fx= (fxsra b1 6) #b10)
                          (integer->char
                            (fxior (fxand b1 #b111111)
                                   (fxsll (fxand b0 #b11111) 6)))]
                         [else
                          (do-error p who)]))]
                    [else
                     (let ([bytes (refill-bv-buffer p who)])
                       (cond
                         [(fx= bytes 0) (do-error p who)]
                         [else (lookahead-char-utf8-mode p who)]))]))]
               [(fx= (fxsra b0 4) #b1110) ;;; three-byte-encoding
                (cond
                  [(fx< (fx+ i 2) j) 
                   (let ([b1 (bytevector-u8-ref buf (fx+ i 1))]
                         [b2 (bytevector-u8-ref buf (fx+ i 2))])
                     (cond
                       [(fx= (fxsra (fxlogor b1 b2) 6) #b10) 
                        (let ([n (fxlogor 
                                   (fxsll (fxand b0 #b1111) 12)
                                   (fxsll (fxand b1 #b111111) 6)
                                   (fxand b2 #b111111))])
                          (cond
                            [(and (fx<= #xD800 n) (fx<= n #xDFFF))
                             (do-error p who)]
                            [else (integer->char n)]))]
                       [else (do-error p who)]))]
                  [else
                   (let ([bytes (refill-bv-buffer p who)])
                     (cond
                       [(fx= bytes 0) (do-error p who)]
                       [else (lookahead-char-utf8-mode p who)]))])]
               [(fx= (fxsra b0 3) #b11110) ;;; four-byte-encoding
                (cond
                  [(fx< (fx+ i 3) j) 
                   (let ([b1 (bytevector-u8-ref buf (fx+ i 1))]
                         [b2 (bytevector-u8-ref buf (fx+ i 2))]
                         [b3 (bytevector-u8-ref buf (fx+ i 3))])
                     (cond
                       [(fx= (fxsra (fxlogor b1 b2 b3) 6) #b10)
                        (let ([n (fxlogor 
                                   (fxsll (fxand b0 #b111) 18)
                                   (fxsll (fxand b1 #b111111) 12)
                                   (fxsll (fxand b2 #b111111) 6)
                                   (fxand b3 #b111111))])
                          (cond
                            [(and (fx<= #x10000 n) (fx<= n #x10FFFF))
                             (integer->char n)]
                            [else
                             (do-error p who)]))]
                       [else
                        (do-error p who)]))]
                  [else
                   (let ([bytes (refill-bv-buffer p who)])
                     (cond
                       [(fx= bytes 0)
                        (do-error p who)]
                       [else (lookahead-char-utf8-mode p who)]))])]
               [else (do-error p who)]))])))
    ;;;
    (define (advance-bom p who bom-seq)
      ;;; return eof if port is eof, 
      ;;; #t if a bom is present, updating the port index to 
      ;;;    point just past the bom.
      ;;; #f otherwise. 
      (cond
        [(fx< ($port-index p) ($port-size p))
         (let f ([i 0] [ls bom-seq])
           (cond
             [(null? ls)
              ($set-port-index! p (fx+ ($port-index p) i))
              #t]
             [else
              (let ([idx (fx+ i ($port-index p))])
                (cond
                  [(fx< idx ($port-size p))
                   (if (fx=? (car ls)
                         (bytevector-u8-ref ($port-buffer p) idx))
                       (f (fx+ i 1) (cdr ls))
                       #f)]
                  [else
                   (let ([bytes (refill-bv-buffer p who)])
                     (if (fx= bytes 0)
                         #f
                         (f i ls)))]))]))]
        [else 
         (let ([bytes (refill-bv-buffer p who)])
           (if (fx= bytes 0)
               (eof-object)
               (advance-bom p who bom-seq)))]))
    ;;;
    (define (speedup-input-port p who)
      ;;; returns #t if port is eof, #f otherwise
      (unless (input-port? p) 
        (die who "not an input port" p))
      (let ([tr ($port-transcoder p)])
        (unless tr 
          (die who "not a textual port" p))
        (case (transcoder-codec tr)
          [(utf-8-codec)
           ;;;
           ($set-port-attrs! p 
             (fxior textual-input-port-bits fast-u7-text-tag))
           (eof-object? (advance-bom p who '(#xEF #xBB #xBF)))]
          [else 
           (die 'slow-get-char
              "BUG: codec not handled"
              (transcoder-codec tr))])))
    ;;;
    (define (lookahead-char-char-mode p who)
      (let ([str ($port-buffer p)]
            [read! ($port-read! p)])
        (let ([n (read! str 0 (string-length str))])
          (unless (fixnum? n) 
            (die who "invalid return value from read!" n))
          (unless (<= 0 n (string-length str))
            (die who "return value from read! is out of range" n))
          ($set-port-index! p 0) 
          ($set-port-size! p n)
          (cond
            [(fx= n 0)
             (eof-object)]
            [else
             (string-ref str 0)]))))
    ;;;
    (define (lookahead-char p)
      (define who 'lookahead-char)
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-get-utf8-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                (let ([b (bytevector-u8-ref ($port-buffer p) i)])
                  (cond
                    [(fx< b 128) (integer->char b)]
                    [else (lookahead-char-utf8-mode p who)]))]
               [else
                (lookahead-char-utf8-mode p who)]))]
          [(eq? m fast-get-char-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                (string-ref ($port-buffer p) i)]
               [else
                (lookahead-char-char-mode p who)]))]
          [(eq? m fast-get-latin-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                (integer->char 
                  (bytevector-u8-ref ($port-buffer p) i))]
               [else
                (get-char-latin-mode p who 0)]))]
          [else 
           (if (speedup-input-port p who)
               (eof-object)
               (lookahead-char p))])))
    ;;;
    (define (get-char-char-mode p who)
      (let ([str ($port-buffer p)]
            [read! ($port-read! p)])
        (let ([n (read! str 0 (string-length str))])
          (unless (fixnum? n) 
            (die who "invalid return value from read!" n))
          (unless (<= 0 n (string-length str))
            (die who "return value from read! is out of range" n))
          ($set-port-size! p n)
          (cond
            [(fx= n 0)
             ($set-port-index! p 0)
             (eof-object)]
            [else
             ($set-port-index! p 1) 
             (string-ref str 0)]))))
    (define read-char
      (case-lambda
        [(p) 
         (define who 'read-char)
         (let ([m ($port-fast-attrs p)])
           (cond
             [(eq? m fast-get-utf8-tag)
              (let ([i ($port-index p)])
                (cond
                  [(fx< i ($port-size p))
                   (let ([b (bytevector-u8-ref ($port-buffer p) i)])
                     (cond
                       [(fx< b 128) 
                        ($set-port-index! p (fx+ i 1))
                        (integer->char b)]
                       [else (get-char-utf8-mode p who)]))]
                  [else
                   (get-char-utf8-mode p who)]))]
             [(eq? m fast-get-char-tag)
              (let ([i ($port-index p)])
                (cond
                  [(fx< i ($port-size p))
                   ($set-port-index! p (fx+ i 1))
                   (string-ref ($port-buffer p) i)]
                  [else (get-char-char-mode p who)]))]
             [(eq? m fast-get-latin-tag)
              (let ([i ($port-index p)])
                (cond
                  [(fx< i ($port-size p))
                   ($set-port-index! p (fx+ i 1))
                   (integer->char 
                     (bytevector-u8-ref ($port-buffer p) i))]
                  [else
                   (get-char-latin-mode p who 1)]))]
             [else 
              (if (speedup-input-port p who)
                  (eof-object)
                  (get-char p))]))]
        [() (read-char (current-input-port))]))
    (define (get-char p)
      (define who 'get-char)
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-get-utf8-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                (let ([b (bytevector-u8-ref ($port-buffer p) i)])
                  (cond
                    [(fx< b 128) 
                     ($set-port-index! p (fx+ i 1))
                     (integer->char b)]
                    [else (get-char-utf8-mode p who)]))]
               [else
                (get-char-utf8-mode p who)]))]
          [(eq? m fast-get-char-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                ($set-port-index! p (fx+ i 1))
                (string-ref ($port-buffer p) i)]
               [else (get-char-char-mode p who)]))]
          [(eq? m fast-get-latin-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                ($set-port-index! p (fx+ i 1))
                (integer->char 
                  (bytevector-u8-ref ($port-buffer p) i))]
               [else
                (get-char-latin-mode p who 1)]))]
          [else 
           (if (speedup-input-port p who)
               (eof-object)
               (get-char p))]))))

  ;;; ----------------------------------------------------------
  (define (assert-binary-input-port p who)
    (unless (port? p) (die who "not a port" p))
    (when ($port-closed? p) (die who "port is closed" p))
    (when ($port-transcoder p) (die who "port is not binary" p))
    (unless ($port-read! p)
      (die who "port is not an input port" p)))

  (module (get-u8 lookahead-u8)
    (import UNSAFE)
    (define (get-u8-byte-mode p who start) 
      (when ($port-closed? p) (die who "port is closed" p))
      (let* ([bv ($port-buffer p)]
             [n (bytevector-length bv)])
        (let ([j (($port-read! p) bv 0 n)])
          (unless (fixnum? j)
            (die who "invalid return value from read! procedure" j))
          (cond
            [(fx> j 0) 
             (unless (fx<= j n)
               (die who "read! returned a value out of range" j))
             ($set-port-index! p start) 
             ($set-port-size! p j)
             (bytevector-u8-ref bv 0)]
            [(fx= j 0) (eof-object)]
            [else 
             (die who "read! returned a value out of range" j)]))))
    (define (slow-get-u8 p who start) 
      (assert-binary-input-port p who)
      ($set-port-attrs! p fast-get-byte-tag)
      (get-u8-byte-mode p who start))
    ;;;
    (define (get-u8 p)
      (define who 'get-u8)
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-get-byte-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                ($set-port-index! p (fx+ i 1))
                (bytevector-u8-ref ($port-buffer p) i)]
               [else (get-u8-byte-mode p who 1)]))]
          [else (slow-get-u8 p who 1)])))
    (define (lookahead-u8 p)
      (define who 'lookahead-u8)
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-get-byte-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                (bytevector-u8-ref ($port-buffer p) i)]
               [else (get-u8-byte-mode p who 0)]))]
          [else (slow-get-u8 p who 0)]))))

  (define (port-eof? p)
    (import UNSAFE)
    (define who 'port-eof?)
    (let ([m ($port-fast-attrs p)])
      (cond
        [(not (eq? m 0))
         (if (fx< ($port-index p) ($port-size p))
             #f
             (if ($port-transcoder p) 
                 (eof-object? (lookahead-char p))
                 (eof-object? (lookahead-u8 p))))]
        [(input-port? p)
         (when ($port-closed? p) 
           (die 'port-eof? "port is closed" p))
         (if (textual-port? p) 
             (eof-object? (lookahead-char p))
             (eof-object? (lookahead-u8 p)))]
        [else (die 'port-eof? "not an input port" p)])))

  (define EAGAIN-error-code -22) ;;; from ikarus-io.c
  (define io-errors-vec
    '#(#|  0 |# "unknown error"
       #|  1 |# "bad file name"
       #|  2 |# "operation interrupted"
       #|  3 |# "not a directory"
       #|  4 |# "file name too long"
       #|  5 |# "missing entities"
       #|  6 |# "insufficient access privileges"
       #|  7 |# "circular path"
       #|  8 |# "file is a directory"
       #|  9 |# "file system is read-only"
       #| 10 |# "maximum open files reached"
       #| 11 |# "maximum open files reached"
       #| 12 |# "ENXIO"
       #| 13 |# "operation not supported"
       #| 14 |# "not enough space on device"
       #| 15 |# "quota exceeded"
       #| 16 |# "io error"
       #| 17 |# "device is busy"
       #| 18 |# "access fault"
       #| 19 |# "file already exists"
       #| 20 |# "invalid file name"
       #| 21 |# "non-blocking operation would block"
       #| 22 |# "broken pipe (e.g., writing to a closed process or socket)"
       #| 23 |# "connection refused"
       #| 24 |# "not a socket"
       #| 25 |# "not enough memory to perform operation"
       ))

  (define (io-error who id err . other-conditions)
    (let ([err (fxnot err)])
      (let ([msg 
             (cond
               [(fx< err (vector-length io-errors-vec))
                (vector-ref io-errors-vec err)]
               [else "unknown error"])])
        (raise 
          (apply condition
            (make-who-condition who)
            (make-i/o-error)
            (case err
              [(6 9 18) (make-i/o-file-protection-error)]
              [(19)     (make-i/o-file-already-exists-error id)]
              [else     (condition)])
            (make-message-condition msg)
            (make-i/o-filename-error id)
            other-conditions)))))

  ;(define block-size 4096)
  ;(define block-size (* 4 4096))
  (define input-block-size (* 4 4096))
  (define output-block-size (* 4 4096))

  (define input-file-buffer-size (+ input-block-size 128))
  (define output-file-buffer-size output-block-size)

  (define input-socket-buffer-size 
    (make-parameter (+ input-block-size 128)
      (lambda (x) 
        (import (ikarus system $fx))
        (if (and (fixnum? x) ($fx>= x 128))
            x
            (error 'input-socket-buffer-size 
              "buffer size should be a fixnum >= 128"
              x)))))

  (define output-socket-buffer-size 
    (make-parameter output-block-size
      (lambda (x) 
        (import (ikarus system $fx))
        (if (and (fixnum? x) ($fx> x 0))
            x
            (error 'output-socket-buffer-size 
              "buffer size should be a positive fixnum"
              x)))))

  (define (fh->input-port fd id size transcoder close who)
    (letrec ([port
              ($make-port 
                (input-transcoder-attrs transcoder who)
                0 0 (make-bytevector size)
                transcoder
                id
                (letrec ([refill
                          (lambda (bv idx cnt) 
                            (import UNSAFE)
                            (let ([bytes
                                   (foreign-call "ikrt_read_fd" fd bv idx 
                                      (if (fx< input-block-size cnt)
                                          input-block-size
                                          cnt))])
                              (cond
                                [(fx>= bytes 0) bytes]
                                [(fx= bytes EAGAIN-error-code)
                                 ;(raise-continuable 
                                 ;  (make-i/o-would-block-condition port))
                                 (call/cc 
                                   (lambda (k) 
                                     (add-io-event fd k 'r)
                                     (process-events)))
                                 (refill bv idx cnt)]
                                [else 
                                 (io-error 'read id bytes
                                   (make-i/o-write-error))])))])
                  refill)
                #f ;;; write!
                #f ;;; get-position
                #f ;;; set-position!
                (cond
                  [(procedure? close) close]
                  [(eqv? close #t) (file-close-proc id fd)]
                  [else #f])
                fd)])
    (guarded-port port)))

  (define (fh->output-port fd id size transcoder close who)
    (letrec ([port
              ($make-port 
                (output-transcoder-attrs transcoder who)
                0 size (make-bytevector size)
                transcoder
                id
                #f
                (letrec ([refill
                          (lambda (bv idx cnt) 
                            (import UNSAFE)
                            (let ([bytes
                                   (foreign-call "ikrt_write_fd" fd bv idx
                                     (if (fx< output-block-size cnt)
                                         output-block-size
                                         cnt))])

                              (cond
                                [(fx>= bytes 0) bytes]
                                [(fx= bytes EAGAIN-error-code)
                                 ;(raise-continuable 
                                 ;  (make-i/o-would-block-condition port))
                                 (call/cc 
                                   (lambda (k)
                                     (add-io-event fd k 'w)
                                     (process-events)))
                                 (refill bv idx cnt)]
                                [else 
                                 (io-error 'write id bytes
                                    (make-i/o-write-error))])))])
                  refill)
                #f ;;; get-position
                #f ;;; set-position!
                (cond
                  [(procedure? close) close]
                  [(eqv? close #t) (file-close-proc id fd)]
                  [else #f])
                fd)])
      (guarded-port port)))

  (define (file-close-proc id fd)
    (lambda () 
      (cond
        [(foreign-call "ikrt_close_fd" fd) =>
         (lambda (err) 
           (io-error 'close id err))])))

  (define (open-input-file-handle filename who)
    (let ([fh (foreign-call "ikrt_open_input_fd"
                 (string->utf8 filename))])
      (cond
        [(fx< fh 0) (io-error who filename fh)]
        [else fh])))
  
  (define (open-output-file-handle filename file-options who)
    (let ([opt (case file-options
                 [(fo:default)                       0]
                 [(fo:no-create)                     1]
                 [(fo:no-fail)                       2]
                 [(fo:no-fail/no-create)             3]
                 [(fo:no-truncate)                   4]
                 [(fo:no-truncate/no-create)         5]
                 [(fo:no-truncate/no-fail)           6]
                 [(fo:no-truncate/no-fail/no-create) 7]
                 [else (die who "invalid file option" file-options)])])
      (let ([fh (foreign-call "ikrt_open_output_fd"
                   (string->utf8 filename)
                   opt)])
        (cond
          [(fx< fh 0) (io-error who filename fh)]
          [else fh]))))

  (define open-file-input-port
    (case-lambda
      [(filename) 
       (open-file-input-port filename (file-options) 'block #f)]
      [(filename file-options) 
       (open-file-input-port filename file-options 'block #f)]
      [(filename file-options buffer-mode) 
       (open-file-input-port filename file-options buffer-mode #f)]
      [(filename file-options buffer-mode transcoder)
       (unless (string? filename)
         (die 'open-file-input-port "invalid filename" filename))
       (unless (or (not transcoder) (transcoder? transcoder)) 
         (die 'open-file-input-port "invalid transcoder" transcoder))
       ; FIXME: file-options ignored
       ; FIXME: buffer-mode ignored
       (fh->input-port 
         (open-input-file-handle filename 'open-file-input-port)
         filename
         input-file-buffer-size
         transcoder
         #t
         'open-file-input-port)]))


  (define open-file-output-port
    (case-lambda
      [(filename) 
       (open-file-output-port filename (file-options) 'block #f)]
      [(filename file-options) 
       (open-file-output-port filename file-options 'block #f)]
      [(filename file-options buffer-mode) 
       (open-file-output-port filename file-options buffer-mode #f)]
      [(filename file-options buffer-mode transcoder)
       (unless (string? filename)
         (die 'open-file-output-port "invalid filename" filename))
       ; FIXME: file-options ignored
       ; FIXME: buffer-mode ignored
       (unless (or (not transcoder) (transcoder? transcoder)) 
         (die 'open-file-output-port "invalid transcoder" transcoder))
       (fh->output-port
         (open-output-file-handle filename file-options 
            'open-file-output-port)
         filename
         output-file-buffer-size
         transcoder
         #t
         'open-file-output-port)]))

  (define (open-output-file filename)
    (unless (string? filename)
      (die 'open-output-file "invalid filename" filename))
    (fh->output-port 
       (open-output-file-handle filename (file-options) 
          'open-output-file)
       filename
       output-file-buffer-size
       (native-transcoder)
       #t
       'open-output-file))

  (define (open-input-file filename)
    (unless (string? filename)
      (die 'open-input-file "invalid filename" filename))
    (fh->input-port 
       (open-input-file-handle filename 'open-input-file) 
       filename
       input-file-buffer-size
       (native-transcoder)
       #t
       'open-input-file))


  (define (with-output-to-file filename proc)
    (unless (string? filename)
      (die 'with-output-to-file "invalid filename" filename))
    (unless (procedure? proc)
      (die 'with-output-to-file "not a procedure" proc))
    (call-with-port
      (fh->output-port
        (open-output-file-handle filename (file-options) 
          'with-output-to-file)
        filename
        output-file-buffer-size
        (native-transcoder)
        #t
        'with-output-to-file)
      (lambda (p)
        (parameterize ([*the-output-port* p])
          (proc)))))

  (define (call-with-output-file filename proc)
    (unless (string? filename)
      (die 'call-with-output-file "invalid filename" filename))
    (unless (procedure? proc)
      (die 'call-with-output-file "not a procedure" proc))
    (call-with-port
      (fh->output-port
        (open-output-file-handle filename (file-options) 
          'call-with-output-file)
        filename
        output-file-buffer-size
        (native-transcoder)
        #t
        'call-with-output-file)
      proc))

  (define (call-with-input-file filename proc)
    (unless (string? filename)
      (die 'call-with-input-file "invalid filename" filename))
    (unless (procedure? proc)
      (die 'call-with-input-file "not a procedure" proc))
    (call-with-port
      (fh->input-port 
        (open-input-file-handle filename 'call-with-input-file) 
        filename
        input-file-buffer-size
        (native-transcoder)
        #t
        'call-with-input-file)
      proc))

  (define (with-input-from-file filename proc)
    (unless (string? filename)
      (die 'with-input-from-file "invalid filename" filename))
    (unless (procedure? proc)
      (die 'with-input-from-file "not a procedure" proc))
    (call-with-port
      (fh->input-port 
        (open-input-file-handle filename 'with-input-from-file)
        filename
        input-file-buffer-size
        (native-transcoder)
        #t
        'with-input-from-file)
      (lambda (p)
        (parameterize ([*the-input-port* p])
          (proc)))))

  (define (with-input-from-string string proc)
    (unless (string? string)
      (die 'with-input-from-string "not a string" string))
    (unless (procedure? proc)
      (die 'with-input-from-string "not a procedure" proc))
    (parameterize ([*the-input-port*
                    (open-string-input-port string)])
      (proc)))

  (define (standard-input-port)
    (fh->input-port 0 '*stdin* 256 #f #f 'standard-input-port))

  (define (standard-output-port)
    (fh->output-port 1 '*stdout* 256 #f #f 'standard-output-port))
  
  (define (standard-error-port)
    (fh->output-port 2 '*stderr* 256 #f #f 'standard-error-port))

  (define *the-input-port* 
    (make-parameter
      (transcoded-port 
        (fh->input-port 0 '*stdin* input-file-buffer-size #f #f #f)
        (native-transcoder))))

  (define *the-output-port* 
    (make-parameter
      (transcoded-port
        (fh->output-port 1 '*stdout* output-file-buffer-size #f #f #f)
        (native-transcoder))))
  
  (define *the-error-port* 
    (make-parameter
      (transcoded-port 
        (fh->output-port 2 '*stderr* output-file-buffer-size #f #f #f)
        (native-transcoder))))

  (define console-output-port
    (let ([p (*the-output-port*)])
      (lambda () p)))

  (define console-error-port
    (let ([p (*the-error-port*)])
      (lambda () p)))

  (define console-input-port
    (let ([p (*the-input-port*)])
      (lambda () p)))

  (define (current-input-port) (*the-input-port*))
  (define (current-output-port) (*the-output-port*))
  (define (current-error-port) (*the-error-port*))

  (define (call-with-port p proc)
    (if (port? p) 
        (if (procedure? proc) 
            (dynamic-wind
              void
              (lambda () (proc p))
              (lambda () (close-port p)))
            (die 'call-with-port "not a procedure" proc))
        (die 'call-with-port "not a port" p)))

  ;;;
  (define peek-char
    (case-lambda
      [() (lookahead-char (*the-input-port*))]
      [(p)
       (if (input-port? p)
           (if (textual-port? p)
               (lookahead-char p)
               (die 'peek-char "not a textual port" p))
           (die 'peek-char "not an input-port" p))]))

  (define (get-bytevector-n p n) 
    (import (ikarus system $fx) (ikarus system $bytevectors))
    (define (subbytevector s n)
      (let ([p ($make-bytevector n)])
        (let f ([s s] [n n] [p p])
          (let ([n ($fx- n 1)])
            ($bytevector-set! p n ($bytevector-u8-ref s n))
            (if ($fx= n 0) 
                p
                (f s n p))))))
    (unless (input-port? p) 
      (die 'get-bytevector-n "not an input port" p))
    (unless (binary-port? p)
      (die 'get-bytevector-n "not a binary port" p))
    (unless (fixnum? n) 
      (die 'get-bytevector-n "count is not a fixnum" n))
    (cond
      [($fx> n 0) 
       (let ([s ($make-bytevector n)])
         (let f ([p p] [n n] [s s] [i 0])
           (let ([x (get-u8 p)])
             (cond
               [(eof-object? x) 
                (if ($fx= i 0) 
                    (eof-object)
                    (subbytevector s i))]
               [else
                ($bytevector-set! s i x)
                (let ([i ($fxadd1 i)])
                  (if ($fx= i n) 
                      s
                      (f p n s i)))]))))]
      [($fx= n 0) '#vu8()]
      [else (die 'get-bytevector-n "count is negative" n)]))

  (define (get-bytevector-n! p s i c) 
    (import (ikarus system $fx) (ikarus system $bytevectors))
    (unless (input-port? p) 
      (die 'get-bytevector-n! "not an input port" p))
    (unless (binary-port? p)
      (die 'get-bytevector-n! "not a binary port" p))
    (unless (bytevector? s) 
      (die 'get-bytevector-n! "not a bytevector" s))
    (let ([len ($bytevector-length s)])
      (unless (fixnum? i) 
        (die 'get-bytevector-n! "starting index is not a fixnum" i))
      (when (or ($fx< i 0) ($fx> i len))
        (die 'get-bytevector-n! 
          (format "starting index is out of range 0..~a" len)
          i))
      (unless (fixnum? c)
        (die 'get-bytevector-n! "count is not a fixnum" c))
      (cond
        [($fx> c 0)
         (let ([j (+ i c)])
           (when (> j len)
             (die 'get-bytevector-n! 
               (format "count is out of range 0..~a" (- len i))
               c))
           (let ([x (get-u8 p)])
             (cond
               [(eof-object? x) x]
               [else
                ($bytevector-set! s i x)
                (let f ([p p] [s s] [start i] [i 1] [c c])
                  (let ([x (get-u8 p)])
                    (cond
                      [(eof-object? x) i]
                      [else
                       ($bytevector-set! s ($fx+ start i) x)
                       (let ([i ($fxadd1 i)])
                         (if ($fx= i c)
                             i
                             (f p s start i c)))])))])))]
        [($fx= c 0) 0]
        [else (die 'get-bytevector-n! "count is negative" c)])))

  (define (get-bytevector-some p)
    (define who 'get-bytevector-some)
;    (import UNSAFE)
    (let ([m ($port-fast-attrs p)])
      (cond
        [(eq? m fast-get-byte-tag)
         (let ([i ($port-index p)] [j ($port-size p)])
           (let ([cnt (fx- j i)])
             (cond
               [(fx> cnt 0)
                (let f ([bv (make-bytevector cnt)]
                        [buf ($port-buffer p)]
                        [i i] [j j] [idx 0])
                  (cond
                    [(fx= i j)
                     ($set-port-index! p j)
                     bv]
                    [else
                     (bytevector-u8-set! bv idx (bytevector-u8-ref buf i))
                     (f bv buf (fx+ i 1) j (fx+ idx 1))]))]
               [else 
                (refill-bv-buffer p who)
                (if (fx= ($port-index p) ($port-size p))
                    (eof-object)
                    (get-bytevector-some p))])))]
        [else (die who "invalid port argument" p)])))

  (define (get-bytevector-all p)
    (define (get-it p)
      (let f ([p p] [n 0] [ac '()])
        (let ([x (get-u8 p)])
          (cond
            [(eof-object? x)
             (if (null? ac) 
                 (eof-object)
                 (make-it n ac))]
            [else (f p (+ n 1) (cons x ac))]))))
    (define (make-it n revls)
      (let f ([s (make-bytevector n)] [i (- n 1)] [ls revls])
        (cond
          [(pair? ls)
           (bytevector-u8-set! s i (car ls))
           (f s (- i 1) (cdr ls))]
          [else s])))
    (if (input-port? p)
        (if (binary-port? p)
            (get-it p)
            (die 'get-bytevector-all "not a binary port" p))
        (die 'get-bytevector-all "not an input port" p)))

  (define (get-string-n p n) 
    (import (ikarus system $fx) (ikarus system $strings))
    (unless (input-port? p) 
      (die 'get-string-n "not an input port" p))
    (unless (textual-port? p) 
      (die 'get-string-n "not a textual port" p))
    (unless (fixnum? n) 
      (die 'get-string-n "count is not a fixnum" n))
    (cond
      [($fx> n 0) 
       (let ([s ($make-string n)])
         (let f ([p p] [n n] [s s] [i 0])
           (let ([x (get-char p)])
             (cond
               [(eof-object? x) 
                (if ($fx= i 0) 
                    (eof-object)
                    (substring s 0 i))]
               [else
                ($string-set! s i x) 
                (let ([i ($fxadd1 i)])
                  (if ($fx= i n) 
                      s
                      (f p n s i)))]))))]
      [($fx= n 0) ""]
      [else (die 'get-string-n "count is negative" n)]))

  (define (get-string-n! p s i c) 
    (import (ikarus system $fx) (ikarus system $strings))
    (unless (input-port? p) 
      (die 'get-string-n! "not an input port" p))
    (unless (textual-port? p) 
      (die 'get-string-n! "not a textual port" p))
    (unless (string? s) 
      (die 'get-string-n! "not a string" s))
    (let ([len ($string-length s)])
      (unless (fixnum? i) 
        (die 'get-string-n! "starting index is not a fixnum" i))
      (when (or ($fx< i 0) ($fx> i len))
        (die 'get-string-n! 
          (format "starting index is out of range 0..~a" len)
          i))
      (unless (fixnum? c) 
        (die 'get-string-n! "count is not a fixnum" c))
      (cond
        [($fx> c 0)
         (let ([j (+ i c)])
           (when (> j len)
             (die 'get-string-n! 
               (format "count is out of range 0..~a" (- len i))
               c))
           (let ([x (get-char p)])
             (cond
               [(eof-object? x) x]
               [else
                ($string-set! s i x)
                (let f ([p p] [s s] [start i] [i 1] [c c])
                  (let ([x (get-char p)])
                    (cond
                      [(eof-object? x) i]
                      [else
                       ($string-set! s ($fx+ start i) x)
                       (let ([i ($fxadd1 i)])
                         (if ($fx= i c)
                             i
                             (f p s start i c)))])))])))]
        [($fx= c 0) 0]
        [else (die 'get-string-n! "count is negative" c)])))

  (define (get-line p)
    (import UNSAFE)
    (define (get-it p)
      (let f ([p p] [n 0] [ac '()])
        (let ([x (get-char p)])
          (cond
            [(eqv? x #\newline) 
             (make-it n ac)]
            [(eof-object? x) 
             (if (null? ac) x (make-it n ac))]
            [else (f p (fx+ n 1) (cons x ac))]))))
    (define (make-it n revls)
      (let f ([s (make-string n)] [i (fx- n 1)] [ls revls])
        (cond
          [(pair? ls)
           (string-set! s i (car ls))
           (f s (fx- i 1) (cdr ls))]
          [else s])))
    (if (input-port? p)
        (if (textual-port? p)
            (get-it p)
            (die 'get-line "not a textual port" p))
        (die 'get-line "not an input port" p)))


  (define (get-string-all p)
    (define (get-it p)
      (let f ([p p] [n 0] [ac '()])
        (let ([x (get-char p)])
          (cond
            [(eof-object? x)
             (if (null? ac) 
                 (eof-object)
                 (make-it n ac))]
            [else (f p (+ n 1) (cons x ac))]))))
    (define (make-it n revls)
      (let f ([s (make-string n)] [i (- n 1)] [ls revls])
        (cond
          [(pair? ls)
           (string-set! s i (car ls))
           (f s (- i 1) (cdr ls))]
          [else s])))
    (if (input-port? p)
        (if (textual-port? p)
            (get-it p)
            (die 'get-string-all "not a textual port" p))
        (die 'get-string-all "not an input port" p)))



  ;;; ----------------------------------------------------------
  
  (module (put-char write-char put-string)
    (import UNSAFE)
    (define (put-char-utf8-mode p b who) 
      (cond
        [(fx< b 128) 
         (flush-output-port p) 
         (let ([i ($port-index p)] [j ($port-size p)])
           (cond
             [(fx< i j) 
              (bytevector-u8-set! ($port-buffer p) i b) 
              ($set-port-index! p (fx+ i 1))]
             [else
              (die who "insufficient space on port" p)]))]
        [(fx<= b #x7FF) 
         (let ([i ($port-index p)] 
               [j ($port-size p)]
               [buf ($port-buffer p)])
           (cond
             [(fx< (fx+ i 1) j) 
              (bytevector-u8-set! buf i 
                (fxior #b11000000 (fxsra b 6)))
              (bytevector-u8-set! buf (fx+ i 1) 
                (fxior #b10000000 (fxand b #b111111)))
              ($set-port-index! p (fx+ i 2))]
             [else 
              (flush-output-port p) 
              (put-char-utf8-mode p b who)]))]
        [(fx<= b #xFFFF) 
         (let ([i ($port-index p)] 
               [j ($port-size p)]
               [buf ($port-buffer p)])
           (cond
             [(fx< (fx+ i 2) j) 
              (bytevector-u8-set! buf i 
                (fxior #b11100000 (fxsra b 12)))
              (bytevector-u8-set! buf (fx+ i 1) 
                (fxior #b10000000 (fxand (fxsra b 6) #b111111)))
              (bytevector-u8-set! buf (fx+ i 2) 
                (fxior #b10000000 (fxand b #b111111)))
              ($set-port-index! p (fx+ i 3))]
             [else 
              (flush-output-port p) 
              (put-char-utf8-mode p b who)]))]
        [else
         (let ([i ($port-index p)] 
               [j ($port-size p)]
               [buf ($port-buffer p)])
           (cond
             [(fx< (fx+ i 3) j) 
              (bytevector-u8-set! buf i 
                (fxior #b11110000 (fxsra b 18)))
              (bytevector-u8-set! buf (fx+ i 1)
                (fxior #b10000000 (fxand (fxsra b 12) #b111111)))
              (bytevector-u8-set! buf (fx+ i 2)
                (fxior #b10000000 (fxand (fxsra b 6) #b111111)))
              (bytevector-u8-set! buf (fx+ i 3) 
                (fxior #b10000000 (fxand b #b111111)))
              ($set-port-index! p (fx+ i 4))]
             [else 
              (flush-output-port p) 
              (put-char-utf8-mode p b who)]))]))
    (define (put-char-latin-mode p b who) 
      (cond
        [(fx< b 256) 
         (flush-output-port p)
         (let ([i ($port-index p)] [j ($port-size p)])
           (cond
             [(fx< i j) 
              (bytevector-u8-set! ($port-buffer p) i b)
              ($set-port-index! p (fx+ i 1))]
             [else 
              (die who "insufficient space in port" p)]))]
        [else
         (case (transcoder-error-handling-mode (port-transcoder p))
           [(ignore) (void)]
           [(replace) (put-char p #\?)]
           [(raise) 
            (raise (make-i/o-encoding-error p))]
           [else (die who "BUG: invalid die handling mode" p)])]))
    (define (put-char-char-mode p c who)
      (flush-output-port p)
      (let ([i ($port-index p)] [j ($port-size p)])
        (cond
          [(fx< i j) 
           (string-set! ($port-buffer p) i c)
           ($set-port-index! p (fx+ i 1))]
          [else 
           (die who "insufficient space in port" p)])))
    ;;;
    (define write-char
      (case-lambda
        [(c p) (do-put-char p c 'write-char)]
        [(c) (do-put-char (*the-output-port*) c 'write-char)]))
    (define (put-char p c) 
      (do-put-char p c 'put-char))
    (define (put-string p str)
      (unless (string? str) (die 'put-string "not a string" str))
      (unless (output-port? p)
        (die 'put-string "not an output port" p))
      (unless (textual-port? p)
        (die 'put-string "not a textual port" p))
      (let f ([i 0] [n (string-length str)])
        (unless (fx= i n)
          (do-put-char p (string-ref str i) 'put-string)
          (f (fx+ i 1) n))))
    (define (do-put-char p c who)
      (unless (char? c) (die who "not a char" c))
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-put-utf8-tag)
           (let ([i ($port-index p)])
             (let ([b (char->integer c)])
               (cond
                 [(and (fx< i ($port-size p)) (fx< b 128))
                  (bytevector-u8-set! ($port-buffer p) i b)
                  ($set-port-index! p (fx+ i 1))]
                 [else
                  (put-char-utf8-mode p b who)])))]
          [(eq? m fast-put-char-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                ($set-port-index! p (fx+ i 1))
                (string-set! ($port-buffer p) i c)]
               [else
                (put-char-char-mode p c who)]))]
          [(eq? m fast-put-latin-tag)
           (let ([i ($port-index p)])
             (let ([b (char->integer c)])
               (cond
                 [(and (fx< i ($port-size p)) (fx< b 256))
                  (bytevector-u8-set! ($port-buffer p) i b)
                  ($set-port-index! p (fx+ i 1))]
                 [else
                  (put-char-latin-mode p b who)])))]
          [else 
           (if (output-port? p)
               (if (textual-port? p) 
                   (if (port-closed? p)
                       (die who "port is closed" p)
                       (die who "unsupported port" p))
                   (die who "not a textual port" p))
               (die who "not an output port" p))]))))

  (define newline
    (case-lambda
      [() 
       (put-char (*the-output-port*) #\newline)
       (flush-output-port (*the-output-port*))]
      [(p)
       (unless (output-port? p) 
         (die 'newline "not an output port" p))
       (unless (textual-port? p) 
         (die 'newline "not a textual port" p))
       (when ($port-closed? p)
         (die 'newline "port is closed" p))
       (put-char p #\newline)
       (flush-output-port p)]))
       

       
  (module (put-u8 put-bytevector)
    (import UNSAFE)
    (define (put-u8-byte-mode p b who)
      (let ([write! ($port-write! p)])
        (let ([i ($port-index p)] 
              [buf ($port-buffer p)])
          (let ([bytes (write! buf 0 i)])
            (when (or (not (fixnum? bytes))
                      (fx< bytes 0)
                      (fx> bytes i))
              (die who "write! returned an invalid value" bytes))
            (cond
              [(fx= bytes i) 
               (bytevector-u8-set! buf 0 b)
               ($set-port-index! p 1)]
              [(fx= bytes 0) 
               (die who "could not write bytes to sink")]
              [else
               (let ([i (fx- i bytes)])
                 (bytevector-copy! buf bytes buf 0 i)
                 (bytevector-u8-set! buf i b)
                 ($set-port-index! p (fx+ i 1)))])))))
    ;;;
    (define (put-u8 p b)
      (define who 'put-u8)
      (unless (u8? b) (die who "not a u8" b))
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-put-byte-tag)
           (let ([i ($port-index p)])
             (cond
               [(fx< i ($port-size p))
                ($set-port-index! p (fx+ i 1))
                (bytevector-u8-set! ($port-buffer p) i b)]
               [else
                (put-u8-byte-mode p b who)]))]
          [else 
           (if (output-port? p)
               (die who "not a binary port" p)
               (die who "not an output port" p))])))
    ;;;
    (define ($put-bytevector p bv i c) 
      (define who 'put-bytevector)
      (define (copy! src dst si di c)
        (when (fx> c 0) 
          (bytevector-u8-set! dst di (bytevector-u8-ref src si))
          (copy! src dst (fx+ si 1) (fx+ di 1) (fx- c 1))))
      (let ([m ($port-fast-attrs p)])
        (cond
          [(eq? m fast-put-byte-tag)
           (let ([idx ($port-index p)])
             (let ([room (fx- ($port-size p) idx)])
               (cond
                 [(fx>= room c)
                  ;; hurray
                  ($set-port-index! p (fx+ idx c))
                  (copy! bv ($port-buffer p) i idx c)]
                 [else
                  ($set-port-index! p (fx+ idx room))
                  (copy! bv ($port-buffer p) i idx room)
                  (flush-output-port p)
                  ($put-bytevector p bv (fx+ i room) (fx- c room))])))]
          [else
           (if (output-port? p)
               (die who "not a binary port" p)
               (die who "not an output port" p))])))
    (define put-bytevector
      (case-lambda
        [(p bv) 
         (if (bytevector? bv) 
             ($put-bytevector p bv 0 (bytevector-length bv))
             (die 'put-bytevector "not a bytevector" bv))]
        [(p bv i) 
         (if (bytevector? bv) 
             (if (fixnum? i) 
                 (let ([n (bytevector-length bv)])
                   (if (and (fx< i n) (fx>= i 0))
                       ($put-bytevector p bv i (fx- n i))
                       (die 'put-bytevector "index out of range" i)))
                 (die 'put-bytevector "invalid index" i))
             (die 'put-bytevector "not a bytevector" bv))]
        [(p bv i c) 
         (if (bytevector? bv) 
             (if (fixnum? i) 
                 (let ([n (bytevector-length bv)])
                   (if (and (fx< i n) (fx>= i 0))
                       (if (fixnum? c) 
                           (if (and (fx>= c 0) (fx>= (fx- n c) i))
                               ($put-bytevector p bv i c)
                               (die 'put-bytevector "count out of range" c))
                           (die 'put-bytevector "invalid count" c))
                       (die 'put-bytevector "index out of range" i)))
                 (die 'put-bytevector "invalid index" i))
             (die 'put-bytevector "not a bytevector" bv))]))
    ;;; module 
    )



  (define (process cmd . args)
    (define who 'process)
    (unless (string? cmd)
      (die who "command is not a string" cmd))
    (unless (andmap string? args) 
      (die who "all arguments must be strings"))
    (let ([r (foreign-call "ikrt_process" 
                (make-vector 4)
                (string->utf8 cmd)
                (map string->utf8 (cons cmd args)))])
      (if (fixnum? r) 
          (io-error who cmd r)
          (values
            (vector-ref r 0) ; pid
            (fh->output-port (vector-ref r 1) 
                cmd output-file-buffer-size #f #t
                'process)
            (fh->input-port (vector-ref r 2) 
                cmd input-file-buffer-size #f #t
                'process)
            (fh->input-port (vector-ref r 3) 
                cmd input-file-buffer-size #f #t
                'process)))))


  (define (process-nonblocking cmd . args)
    (define who 'process-nonblocking)
    (unless (string? cmd)
      (die who "command is not a string" cmd))
    (unless (andmap string? args) 
      (die who "all arguments must be strings"))
    (let ([r (foreign-call "ikrt_process" 
                (make-vector 4)
                (string->utf8 cmd)
                (map string->utf8 (cons cmd args)))])
      (if (fixnum? r) 
          (io-error who cmd r)
          (begin 
            (set-fd-nonblocking (vector-ref r 1) who cmd)
            (set-fd-nonblocking (vector-ref r 2) who cmd)
            (set-fd-nonblocking (vector-ref r 3) who cmd)
            (values
              (vector-ref r 0) ; pid
              (fh->output-port (vector-ref r 1) 
                  cmd output-file-buffer-size #f #t
                  'process)
              (fh->input-port (vector-ref r 2) 
                  cmd input-file-buffer-size #f #t
                  'process)
              (fh->input-port (vector-ref r 3) 
                  cmd input-file-buffer-size #f #t
                  'process))))))


  (define (set-fd-nonblocking fd who id)
    (let ([rv (foreign-call "ikrt_make_fd_nonblocking" fd)])
      (unless (eq? rv 0) 
        (io-error who id rv))))

  (define (socket->ports socket who id block?)
    (if (< socket 0)
        (io-error who id socket)
        (let ([close
               (let ([closed-once? #f])
                 (lambda () 
                   (if closed-once?
                       ((file-close-proc id socket))
                       (set! closed-once? #t))))])
          (unless block?
            (set-fd-nonblocking socket who id))
          (values 
            (fh->output-port socket
               id (output-socket-buffer-size) #f close who)
            (fh->input-port socket
               id (input-socket-buffer-size) #f close who)))))

  (define-syntax define-connector 
    (syntax-rules ()
      [(_ who foreign-name block?)
       (define (who host srvc)
         (unless (and (string? host) (string? srvc))
           (die 'who "host and service must both be strings" host srvc))
         (socket->ports 
           (foreign-call foreign-name
             (string->utf8 host) (string->utf8 srvc))
           'who
           (string-append host ":" srvc)
           block?))]))

  (define-connector tcp-connect             "ikrt_tcp_connect" #t)
  (define-connector udp-connect             "ikrt_udp_connect" #t)
  (define-connector tcp-connect-nonblocking "ikrt_tcp_connect" #f)
  (define-connector udp-connect-nonblocking "ikrt_udp_connect" #f)

  (module (add-io-event rem-io-event process-events)
    (define-struct t (fd proc type))
    ;;; callbacks
    (define pending '())
    (define out-queue '())
    (define in-queue '())

    (define (process-events) 
      (if (null? out-queue) 
          (if (null? in-queue) 
              (if (null? pending) 
                  (error 'process-events "no more events")
                  (begin 
                    (do-select) 
                    (process-events)))
              (begin
                (set! out-queue (reverse in-queue))
                (set! in-queue '())
                (process-events)))
          (let ([t (car out-queue)])
            (set! out-queue (cdr out-queue))
            ((t-proc t))
            (process-events))))

    (define (add-io-event fd proc event-type) 
      (set! pending 
        (cons (make-t fd proc event-type) pending)))

    (define (rem-io-event fd) 
      (define (p x) (eq? (t-fd x) fd))
      (set! pending (remp p pending))
      (set! out-queue (remp p out-queue))
      (set! in-queue (remp p in-queue)))
    
    (define (get-max-fd)
      (assert (pair? pending))
      (let f ([m (t-fd (car pending))]
              [ls (cdr pending)])
        (cond
          [(null? ls) m]
          [else (f (max m (t-fd (car ls))) (cdr ls))])))

    (define (do-select)
      (let ([n (add1 (get-max-fd))])
        (let ([rbv (make-bytevector n 0)]
              [wbv (make-bytevector n 0)]
              [xbv (make-bytevector n 0)])
          ;;; add all fds to their bytevectors depending on type
          (for-each 
            (lambda (t) 
              (let ([fd (t-fd t)])
                (let ([i (div fd 8)] [j (mod fd 8)])
                  (let ([bv (case (t-type t)
                              [(r) rbv]
                              [(w) wbv]
                              [(x) xbv]
                              [else 
                               (error 'do-select "invalid type" t)])])
                    (bytevector-u8-set! bv i 
                      (fxlogor (fxsll 1 j) 
                        (bytevector-u8-ref bv i)))))))
            pending)
          ;;; do select
          (let ([rv (foreign-call "ikrt_select" n rbv wbv xbv)])
            (when (< rv 0) 
              (die 'select "error selecting from fds")))
          ;;; go through fds again and see if they're selected
          (for-each 
            (lambda (t) 
              (let ([fd (t-fd t)])
                (let ([i (div fd 8)] [j (mod fd 8)])
                  (let ([bv (case (t-type t)
                              [(r) rbv]
                              [(w) wbv]
                              [(x) xbv]
                              [else 
                               (error 'do-select "invalid type" t)])])
                    (cond
                      [(fxzero? 
                         (fxlogand (fxsll 1 j) 
                           (bytevector-u8-ref bv i)))
                       ;;; not selected
                       (set! pending (cons t pending))]
                      [else 
                       ;;; ready
                       (set! in-queue (cons t in-queue))])))))
            (let ([ls pending])
              (set! pending '())
              ls)))))
    )

  
  (define-struct tcp-server (portnum fd))
  
  (define (tcp-server-socket portnum) 
    (unless (fixnum? portnum)
      (error 'tcp-server-socket "not a fixnum" portnum))
    (let ([sock (foreign-call "ikrt_listen" portnum)])
      (cond
        [(fx>= sock 0) (make-tcp-server portnum sock)]
        [else (die 'tcp-server-socket "failed to start server")])))
  
  (define (tcp-server-socket-nonblocking portnum) 
    (let ([s (tcp-server-socket portnum)])
      (set-fd-nonblocking (tcp-server-fd s) 
        'tcp-server-socket-nonblocking
        '#f)
      s))


  (define (do-accept-connection s who blocking?)
    (define (make-socket-info x) 
      (unless (= (bytevector-length x) 16) 
        (error who "BUG: unexpected return value" x))
      (format "~s.~s.~s.~s:~s" 
        (bytevector-u8-ref x 4)
        (bytevector-u8-ref x 5)
        (bytevector-u8-ref x 6)
        (bytevector-u8-ref x 7)
        (+ (* 256 (bytevector-u8-ref x 2))
           (bytevector-u8-ref x 3))))
    (unless (tcp-server? s) 
      (die who "not a tcp server" s))
    (let ([fd (tcp-server-fd s)] [bv (make-bytevector 16)])
      (unless fd 
        (die who "server is closed" s))
      (let ([sock (foreign-call "ikrt_accept" fd bv)])
        (cond
          [(eq? sock EAGAIN-error-code)
           (call/cc 
             (lambda (k) 
               (add-io-event fd k 'r)
               (process-events)))
           (do-accept-connection s who blocking?)]
          [(< sock 0)
           (io-error who s sock)]
          [else
           (socket->ports sock who (make-socket-info bv) blocking?)]))))

  (define (accept-connection s)
    (do-accept-connection s 'accept-connection #t))

  (define (accept-connection-nonblocking s)
    (do-accept-connection s 'accept-connection-nonblocking #f))

  (define (close-tcp-server-socket s)
    (define who 'close-tcp-server-socket)
    (unless (tcp-server? s) 
      (die who "not a tcp server" s))
    (let ([fd (tcp-server-fd s)])
      (unless fd 
        (die who "server is closed" s))
      (let ([rv (foreign-call "ikrt_shutdown" fd)])
        (when (fx< rv 0)
          (die who "failed to shutdown")))))

  (define (unregister-callback what)
    (define who 'unregister-callback)
    (cond
      [(output-port? what)
       (let ([c ($port-cookie what)])
         (unless (fixnum? c) (die who "not a file-based port" what))
         (rem-io-event c))]
      [(input-port? what)
       (let ([c ($port-cookie what)])
         (unless (fixnum? c) (die who "not a file-based port" what))
         (rem-io-event c))]
      [(tcp-server? what)
       (rem-io-event (tcp-server-fd what))]
      [else (die who "invalid argument" what)]))

  (define (register-callback what proc)
    (define who 'register-callback) 
    (unless (procedure? proc) 
      (die who "not a procedure" proc))
    (cond
      [(output-port? what) 
       (let ([c ($port-cookie what)])
         (unless (fixnum? c) (die who "not a file-based port" what))
         (add-io-event c proc 'w))]
      [(input-port? what) 
       (let ([c ($port-cookie what)])
         (unless (fixnum? c) (die who "not a file-based port" what))
         (add-io-event c proc 'r))]
      [(tcp-server? what)
       (add-io-event (tcp-server-fd what) proc 'r)]
      [else (die who "invalid argument" what)]))


  ;(set-fd-nonblocking 0 'init '*stdin*)
  )