1 /*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 //#define LOG_NDEBUG 0
18 #define LOG_TAG "CharacterEncodingDector"
19 #include <utils/Log.h>
20
21 #include <CharacterEncodingDetector.h>
22 #include "CharacterEncodingDetectorTables.h"
23
24 #include "utils/Vector.h"
25 #include "StringArray.h"
26
27 #include "unicode/ucnv.h"
28 #include "unicode/ucsdet.h"
29 #include "unicode/ustring.h"
30
31 namespace android {
32
CharacterEncodingDetector()33 CharacterEncodingDetector::CharacterEncodingDetector() {
34
35 UErrorCode status = U_ZERO_ERROR;
36 mUtf8Conv = ucnv_open("UTF-8", &status);
37 if (U_FAILURE(status)) {
38 ALOGE("could not create UConverter for UTF-8");
39 mUtf8Conv = NULL;
40 }
41 }
42
~CharacterEncodingDetector()43 CharacterEncodingDetector::~CharacterEncodingDetector() {
44 ucnv_close(mUtf8Conv);
45 }
46
addTag(const char * name,const char * value)47 void CharacterEncodingDetector::addTag(const char *name, const char *value) {
48 mNames.push_back(name);
49 mValues.push_back(value);
50 }
51
size()52 size_t CharacterEncodingDetector::size() {
53 return mNames.size();
54 }
55
getTag(int index,const char ** name,const char ** value)56 status_t CharacterEncodingDetector::getTag(int index, const char **name, const char**value) {
57 if (index >= mNames.size()) {
58 return BAD_VALUE;
59 }
60
61 *name = mNames.getEntry(index);
62 *value = mValues.getEntry(index);
63 return OK;
64 }
65
isPrintableAscii(const char * value,size_t len)66 static bool isPrintableAscii(const char *value, size_t len) {
67 for (size_t i = 0; i < len; i++) {
68 if ((value[i] & 0x80) || value[i] < 0x20 || value[i] == 0x7f) {
69 return false;
70 }
71 }
72 return true;
73 }
74
detectAndConvert()75 void CharacterEncodingDetector::detectAndConvert() {
76
77 int size = mNames.size();
78 ALOGV("%d tags before conversion", size);
79 for (int i = 0; i < size; i++) {
80 ALOGV("%s: %s", mNames.getEntry(i), mValues.getEntry(i));
81 }
82
83 if (size && mUtf8Conv) {
84
85 UErrorCode status = U_ZERO_ERROR;
86 UCharsetDetector *csd = ucsdet_open(&status);
87 const UCharsetMatch *ucm;
88
89 // try combined detection of artist/album/title etc.
90 char buf[1024];
91 buf[0] = 0;
92 int idx;
93 bool allprintable = true;
94 for (int i = 0; i < size; i++) {
95 const char *name = mNames.getEntry(i);
96 const char *value = mValues.getEntry(i);
97 if (!isPrintableAscii(value, strlen(value)) && (
98 !strcmp(name, "artist") ||
99 !strcmp(name, "albumartist") ||
100 !strcmp(name, "composer") ||
101 !strcmp(name, "genre") ||
102 !strcmp(name, "album") ||
103 !strcmp(name, "title"))) {
104 strlcat(buf, value, sizeof(buf));
105 // separate tags by space so ICU's ngram detector can do its job
106 strlcat(buf, " ", sizeof(buf));
107 allprintable = false;
108 }
109 }
110
111 const char *combinedenc = "UTF-8";
112 if (allprintable) {
113 // since 'buf' is empty, ICU would return a UTF-8 matcher with low confidence, so
114 // no need to even call it
115 ALOGV("all tags are printable, assuming ascii (%zu)", strlen(buf));
116 } else {
117 ucsdet_setText(csd, buf, strlen(buf), &status);
118 int32_t matches;
119 const UCharsetMatch** ucma = ucsdet_detectAll(csd, &matches, &status);
120 bool goodmatch = true;
121 int highest = 0;
122 const UCharsetMatch* bestCombinedMatch = getPreferred(buf, strlen(buf),
123 ucma, matches, &goodmatch, &highest);
124
125 ALOGV("goodmatch: %s, highest: %d", goodmatch ? "true" : "false", highest);
126 if (!goodmatch && (highest < 15 || strlen(buf) < 20)) {
127 ALOGV("not a good match, trying with more data");
128 // This string might be too short for ICU to do anything useful with.
129 // (real world example: "Björk" in ISO-8859-1 might be detected as GB18030, because
130 // the ISO detector reports a confidence of 0, while the GB18030 detector reports
131 // a confidence of 10 with no invalid characters)
132 // Append artist, album and title if they were previously omitted because they
133 // were printable ascii.
134 bool added = false;
135 for (int i = 0; i < size; i++) {
136 const char *name = mNames.getEntry(i);
137 const char *value = mValues.getEntry(i);
138 if (isPrintableAscii(value, strlen(value)) && (
139 !strcmp(name, "artist") ||
140 !strcmp(name, "album") ||
141 !strcmp(name, "title"))) {
142 strlcat(buf, value, sizeof(buf));
143 strlcat(buf, " ", sizeof(buf));
144 added = true;
145 }
146 }
147 if (added) {
148 ucsdet_setText(csd, buf, strlen(buf), &status);
149 ucma = ucsdet_detectAll(csd, &matches, &status);
150 bestCombinedMatch = getPreferred(buf, strlen(buf),
151 ucma, matches, &goodmatch, &highest);
152 if (!goodmatch && highest <= 15) {
153 ALOGV("still not a good match after adding printable tags");
154 bestCombinedMatch = NULL;
155 }
156 } else {
157 ALOGV("no printable tags to add");
158 }
159 }
160
161 if (bestCombinedMatch != NULL) {
162 combinedenc = ucsdet_getName(bestCombinedMatch, &status);
163 } else {
164 combinedenc = "ISO-8859-1";
165 }
166 }
167
168 for (int i = 0; i < size; i++) {
169 const char *name = mNames.getEntry(i);
170 uint8_t* src = (uint8_t *)mValues.getEntry(i);
171 int len = strlen((char *)src);
172 uint8_t* dest = src;
173
174 ALOGV("@@@ checking %s", name);
175 const char *s = mValues.getEntry(i);
176 int32_t inputLength = strlen(s);
177 const char *enc;
178
179 if (!allprintable && (!strcmp(name, "artist") ||
180 !strcmp(name, "albumartist") ||
181 !strcmp(name, "composer") ||
182 !strcmp(name, "genre") ||
183 !strcmp(name, "album") ||
184 !strcmp(name, "title"))) {
185 // use encoding determined from the combination of artist/album/title etc.
186 enc = combinedenc;
187 } else {
188 if (isPrintableAscii(s, inputLength)) {
189 enc = "UTF-8";
190 ALOGV("@@@@ %s is ascii", mNames.getEntry(i));
191 } else {
192 ucsdet_setText(csd, s, inputLength, &status);
193 ucm = ucsdet_detect(csd, &status);
194 if (!ucm) {
195 mValues.setEntry(i, "???");
196 continue;
197 }
198 enc = ucsdet_getName(ucm, &status);
199 ALOGV("@@@@ recognized charset: %s for %s confidence %d",
200 enc, mNames.getEntry(i), ucsdet_getConfidence(ucm, &status));
201 }
202 }
203
204 if (strcmp(enc,"UTF-8") != 0) {
205 // only convert if the source encoding isn't already UTF-8
206 ALOGV("@@@ using converter %s for %s", enc, mNames.getEntry(i));
207 status = U_ZERO_ERROR;
208 UConverter *conv = ucnv_open(enc, &status);
209 if (U_FAILURE(status)) {
210 ALOGW("could not create UConverter for %s (%d), falling back to ISO-8859-1",
211 enc, status);
212 status = U_ZERO_ERROR;
213 conv = ucnv_open("ISO-8859-1", &status);
214 if (U_FAILURE(status)) {
215 ALOGW("could not create UConverter for ISO-8859-1 either");
216 continue;
217 }
218 }
219
220 // convert from native encoding to UTF-8
221 const char* source = mValues.getEntry(i);
222 int targetLength = len * 3 + 1;
223 char* buffer = new char[targetLength];
224 // don't normally check for NULL, but in this case targetLength may be large
225 if (!buffer)
226 break;
227 char* target = buffer;
228
229 ucnv_convertEx(mUtf8Conv, conv, &target, target + targetLength,
230 &source, source + strlen(source),
231 NULL, NULL, NULL, NULL, TRUE, TRUE, &status);
232
233 if (U_FAILURE(status)) {
234 ALOGE("ucnv_convertEx failed: %d", status);
235 mValues.setEntry(i, "???");
236 } else {
237 // zero terminate
238 *target = 0;
239 // strip trailing spaces
240 while (--target > buffer && *target == ' ') {
241 *target = 0;
242 }
243 // skip leading spaces
244 char *start = buffer;
245 while (*start == ' ') {
246 start++;
247 }
248 mValues.setEntry(i, start);
249 }
250
251 delete[] buffer;
252
253 ucnv_close(conv);
254 }
255 }
256
257 for (int i = size - 1; i >= 0; --i) {
258 if (strlen(mValues.getEntry(i)) == 0) {
259 ALOGV("erasing %s because entry is empty", mNames.getEntry(i));
260 mNames.erase(i);
261 mValues.erase(i);
262 }
263 }
264
265 ucsdet_close(csd);
266 }
267 }
268
269 /*
270 * When ICU detects multiple encoding matches, apply additional heuristics to determine
271 * which one is the best match, since ICU can't always be trusted to make the right choice.
272 *
273 * What this method does is:
274 * - decode the input using each of the matches found
275 * - recalculate the starting confidence level for multibyte encodings using a different
276 * algorithm and larger frequent character lists than ICU
277 * - devalue encoding where the conversion contains unlikely characters (symbols, reserved, etc)
278 * - pick the highest match
279 * - signal to the caller whether this match is considered good: confidence > 15, and confidence
280 * delta with the next runner up > 15
281 */
getPreferred(const char * input,size_t len,const UCharsetMatch ** ucma,size_t nummatches,bool * goodmatch,int * highestmatch)282 const UCharsetMatch *CharacterEncodingDetector::getPreferred(
283 const char *input, size_t len,
284 const UCharsetMatch** ucma, size_t nummatches,
285 bool *goodmatch, int *highestmatch) {
286
287 *goodmatch = false;
288 Vector<const UCharsetMatch*> matches;
289 UErrorCode status = U_ZERO_ERROR;
290
291 ALOGV("%zu matches", nummatches);
292 for (size_t i = 0; i < nummatches; i++) {
293 const char *encname = ucsdet_getName(ucma[i], &status);
294 int confidence = ucsdet_getConfidence(ucma[i], &status);
295 ALOGV("%zu: %s %d", i, encname, confidence);
296 matches.push_back(ucma[i]);
297 }
298
299 size_t num = matches.size();
300 if (num == 0) {
301 return NULL;
302 }
303 if (num == 1) {
304 int confidence = ucsdet_getConfidence(matches[0], &status);
305 if (confidence > 15) {
306 *goodmatch = true;
307 }
308 return matches[0];
309 }
310
311 ALOGV("considering %zu matches", num);
312
313 // keep track of how many "special" characters result when converting the input using each
314 // encoding
315 Vector<int> newconfidence;
316 for (size_t i = 0; i < num; i++) {
317 const uint16_t *freqdata = NULL;
318 float freqcoverage = 0;
319 status = U_ZERO_ERROR;
320 const char *encname = ucsdet_getName(matches[i], &status);
321 int confidence = ucsdet_getConfidence(matches[i], &status);
322 if (!strcmp("GB18030", encname)) {
323 freqdata = frequent_zhCN;
324 freqcoverage = frequent_zhCN_coverage;
325 } else if (!strcmp("Big5", encname)) {
326 freqdata = frequent_zhTW;
327 freqcoverage = frequent_zhTW_coverage;
328 } else if (!strcmp("EUC-KR", encname)) {
329 freqdata = frequent_ko;
330 freqcoverage = frequent_ko_coverage;
331 } else if (!strcmp("EUC-JP", encname)) {
332 freqdata = frequent_ja;
333 freqcoverage = frequent_ja_coverage;
334 } else if (!strcmp("Shift_JIS", encname)) {
335 freqdata = frequent_ja;
336 freqcoverage = frequent_ja_coverage;
337 }
338
339 ALOGV("%zu: %s %d", i, encname, confidence);
340 status = U_ZERO_ERROR;
341 UConverter *conv = ucnv_open(encname, &status);
342 int demerit = 0;
343 if (U_FAILURE(status)) {
344 ALOGV("failed to open %s: %d", encname, status);
345 confidence = 0;
346 demerit += 1000;
347 }
348 const char *source = input;
349 const char *sourceLimit = input + len;
350 status = U_ZERO_ERROR;
351 int frequentchars = 0;
352 int totalchars = 0;
353 while (true) {
354 // demerit the current encoding for each "special" character found after conversion.
355 // The amount of demerit is somewhat arbitrarily chosen.
356 int inchar;
357 if (source != sourceLimit) {
358 inchar = (source[0] << 8) + source[1];
359 }
360 UChar32 c = ucnv_getNextUChar(conv, &source, sourceLimit, &status);
361 if (!U_SUCCESS(status)) {
362 break;
363 }
364 if (c < 0x20 || (c >= 0x7f && c <= 0x009f)) {
365 ALOGV("control character %x", c);
366 demerit += 100;
367 } else if ((c == 0xa0) // no-break space
368 || (c >= 0xa2 && c <= 0xbe) // symbols, superscripts
369 || (c == 0xd7) || (c == 0xf7) // multiplication and division signs
370 || (c >= 0x2000 && c <= 0x209f)) { // punctuation, superscripts
371 ALOGV("unlikely character %x", c);
372 demerit += 10;
373 } else if (c >= 0xe000 && c <= 0xf8ff) {
374 ALOGV("private use character %x", c);
375 demerit += 30;
376 } else if (c >= 0x2190 && c <= 0x2bff) {
377 // this range comprises various symbol ranges that are unlikely to appear in
378 // music file metadata.
379 ALOGV("symbol %x", c);
380 demerit += 10;
381 } else if (c == 0xfffd) {
382 ALOGV("replacement character");
383 demerit += 50;
384 } else if (c >= 0xfff0 && c <= 0xfffc) {
385 ALOGV("unicode special %x", c);
386 demerit += 50;
387 } else if (freqdata != NULL) {
388 totalchars++;
389 if (isFrequent(freqdata, c)) {
390 frequentchars++;
391 }
392 }
393 }
394 if (freqdata != NULL && totalchars != 0) {
395 int myconfidence = 10 + float((100 * frequentchars) / totalchars) / freqcoverage;
396 ALOGV("ICU confidence: %d, my confidence: %d (%d %d)", confidence, myconfidence,
397 totalchars, frequentchars);
398 if (myconfidence > 100) myconfidence = 100;
399 if (myconfidence < 0) myconfidence = 0;
400 confidence = myconfidence;
401 }
402 ALOGV("%d-%d=%d", confidence, demerit, confidence - demerit);
403 newconfidence.push_back(confidence - demerit);
404 ucnv_close(conv);
405 if (i == 0 && (confidence - demerit) == 100) {
406 // no need to check any further, we'll end up using this match anyway
407 break;
408 }
409 }
410
411 // find match with highest confidence after adjusting for unlikely characters
412 int highest = newconfidence[0];
413 size_t highestidx = 0;
414 int runnerup = -10000;
415 int runnerupidx = -10000;
416 num = newconfidence.size();
417 for (size_t i = 1; i < num; i++) {
418 if (newconfidence[i] > highest) {
419 runnerup = highest;
420 runnerupidx = highestidx;
421 highest = newconfidence[i];
422 highestidx = i;
423 } else if (newconfidence[i] > runnerup){
424 runnerup = newconfidence[i];
425 runnerupidx = i;
426 }
427 }
428 status = U_ZERO_ERROR;
429 ALOGV("selecting: '%s' w/ %d confidence",
430 ucsdet_getName(matches[highestidx], &status), highest);
431 if (runnerupidx < 0) {
432 ALOGV("no runner up");
433 if (highest > 15) {
434 *goodmatch = true;
435 }
436 } else {
437 ALOGV("runner up: '%s' w/ %d confidence",
438 ucsdet_getName(matches[runnerupidx], &status), runnerup);
439 if (runnerup < 0) {
440 runnerup = 0;
441 }
442 if ((highest - runnerup) > 15) {
443 *goodmatch = true;
444 }
445 }
446 *highestmatch = highest;
447 return matches[highestidx];
448 }
449
450
isFrequent(const uint16_t * values,uint32_t c)451 bool CharacterEncodingDetector::isFrequent(const uint16_t *values, uint32_t c) {
452
453 int start = 0;
454 int end = 511; // All the tables have 512 entries
455 int mid = (start+end)/2;
456
457 while(start <= end) {
458 if(c == values[mid]) {
459 return true;
460 } else if (c > values[mid]) {
461 start = mid + 1;
462 } else {
463 end = mid - 1;
464 }
465
466 mid = (start + end) / 2;
467 }
468
469 return false;
470 }
471
472
473 } // namespace android
474