1/*
2 * Copyright (C) 2008, 2009 Google Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met:
7 *
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above
11 * copyright notice, this list of conditions and the following disclaimer
12 * in the documentation and/or other materials provided with the
13 * distribution.
14 * * Neither the name of Google Inc. nor the names of its
15 * contributors may be used to endorse or promote products derived from
16 * this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31#include "config.h"
32#include "TextEncodingDetector.h"
33
34#include "TextEncoding.h"
35#include <unicode/ucnv.h>
36#include <unicode/ucsdet.h>
37
38namespace WebCore {
39
40bool detectTextEncoding(const char* data, size_t len,
41 const char* hintEncodingName,
42 TextEncoding* detectedEncoding)
43{
44 *detectedEncoding = TextEncoding();
45 int matchesCount = 0;
46 UErrorCode status = U_ZERO_ERROR;
47 UCharsetDetector* detector = ucsdet_open(&status);
48 if (U_FAILURE(status))
49 return false;
50 ucsdet_enableInputFilter(detector, true);
51 ucsdet_setText(detector, data, static_cast<int32_t>(len), &status);
52 if (U_FAILURE(status))
53 return false;
54
55 // FIXME: A few things we can do other than improving
56 // the ICU detector itself.
57 // 1. Use ucsdet_detectAll and pick the most likely one given
58 // "the context" (parent-encoding, referrer encoding, etc).
59 // 2. 'Emulate' Firefox/IE's non-Universal detectors (e.g.
60 // Chinese, Japanese, Russian, Korean and Hebrew) by picking the
61 // encoding with a highest confidence among the detector-specific
62 // limited set of candidate encodings.
63 // Below is a partial implementation of the first part of what's outlined
64 // above.
65 const UCharsetMatch** matches = ucsdet_detectAll(detector, &matchesCount, &status);
66 if (U_FAILURE(status)) {
67 ucsdet_close(detector);
68 return false;
69 }
70
71 const char* encoding = 0;
72 if (hintEncodingName) {
73 TextEncoding hintEncoding(hintEncodingName);
74 // 10 is the minimum confidence value consistent with the codepoint
75 // allocation in a given encoding. The size of a chunk passed to
76 // us varies even for the same html file (apparently depending on
77 // the network load). When we're given a rather short chunk, we
78 // don't have a sufficiently reliable signal other than the fact that
79 // the chunk is consistent with a set of encodings. So, instead of
80 // setting an arbitrary threshold, we have to scan all the encodings
81 // consistent with the data.
82 const int32_t kThreshold = 10;
83 for (int i = 0; i < matchesCount; ++i) {
84 int32_t confidence = ucsdet_getConfidence(matches[i], &status);
85 if (U_FAILURE(status)) {
86 status = U_ZERO_ERROR;
87 continue;
88 }
89 if (confidence < kThreshold)
90 break;
91 const char* matchEncoding = ucsdet_getName(matches[i], &status);
92 if (U_FAILURE(status)) {
93 status = U_ZERO_ERROR;
94 continue;
95 }
96 if (TextEncoding(matchEncoding) == hintEncoding) {
97 encoding = hintEncodingName;
98 break;
99 }
100 }
101 }
102 // If no match is found so far, just pick the top match.
103 // This can happen, say, when a parent frame in EUC-JP refers to
104 // a child frame in Shift_JIS and both frames do NOT specify the encoding
105 // making us resort to auto-detection (when it IS turned on).
106 if (!encoding && matchesCount > 0)
107 encoding = ucsdet_getName(matches[0], &status);
108 if (U_SUCCESS(status)) {
109 *detectedEncoding = TextEncoding(encoding);
110 ucsdet_close(detector);
111 return true;
112 }
113 ucsdet_close(detector);
114 return false;
115}
116
117}
118