1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
|
; Copyright (c) 1993-2008 by Richard Kelsey and Jonathan Rees. See file COPYING.
; Copyright (c) 2005-2006 by Basis Technology Corporation. See file COPYING.
; Utilities for setting and constructing text codecs
; This follows Richard Gillam: Unicode Demystified, Chapter 6
; The BOM is U+FEFF---we look for at the beginning of the stream.
; Note if this fails, you better re-open the port from the start
; Note that the UTF-32 detection suggested in Gillam's book is not
; practical, as it may confuse valid UTF-16 with UTF-32.
(define (guess-port-text-codec-according-to-bom port)
(let ((first (peek-byte port)))
(case first
((#xfe)
(read-byte port)
(if (eqv? #xff (read-byte port))
utf-16be-codec
#f))
((#xff)
(read-byte port)
(if (eqv? #xfe (read-byte port))
utf-16le-codec
#f))
((#xef)
(read-byte port)
(if (and (eqv? #xbb (read-byte port))
(eqv? #xbf (read-byte port)))
utf-8-codec
#f))
(else
#f))))
; The caller really should check the return code
(define (set-port-text-codec-according-to-bom! port)
(cond
((guess-port-text-codec-according-to-bom port)
=> (lambda (text-codec)
(set-port-text-codec! port text-codec)
#t))
(else
#f)))
|
