#lang scheme/base
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; NET.plt
;; abstraction of common network behaviors and services
;; Bonzai Lab, LLC.  All rights reserved.
;; Licensed under LGPL.
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; function for parsing folded line as defined by RFC822.
;; yc 8/18/2009 - first version
(require mzlib/trace

;; read-folded-line
;; read folded line according to RFC822.
(define (read-folded-line in) 
  (define (folding? c)
    (or (equal? c #\space)
        (equal? c #\tab)))
  (define (return lines) 
    (apply string-append "" (reverse lines)))
  (define (convert-folding lines)
    (let ((c (peek-char in)))
      (cond ((folding? c) 
             (read-char in)
             (convert-folding lines))
             (helper (cons " " lines))))))
  (define (helper lines)
    (let ((l (read-line in 'return-linefeed)))
      (if (eof-object? l) 
          (return lines)
          (let ((c (peek-char in)))
            (if (folding? c) ;; we should keep going but first let's convert all folding whitespaces...
                (convert-folding (cons l lines))
                ;; otherwise we are done...
                (return (cons l lines)))))))
  (helper '()))

 (read-folded-line (-> input-port? string?))