Move language detection to a component

chrome/common/translate/language_detection_util.cc

-// Copyright 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "chrome/common/translate/language_detection_util.h"
-
-#include "base/logging.h"
-#include "base/metrics/field_trial.h"
-#include "base/strings/string_split.h"
-#include "base/strings/string_util.h"
-#include "base/strings/utf_string_conversions.h"
-#include "base/time/time.h"
-#include "chrome/common/chrome_constants.h"
-#include "chrome/common/translate/translate_common_metrics.h"
-#include "chrome/common/translate/translate_util.h"
-
-#if !defined(CLD_VERSION) || CLD_VERSION==1
-#include "third_party/cld/encodings/compact_lang_det/compact_lang_det.h"
-#include "third_party/cld/encodings/compact_lang_det/win/cld_unicodetext.h"
-#endif
-
-#if !defined(CLD_VERSION) || CLD_VERSION==2
-#include "third_party/cld_2/src/public/compact_lang_det.h"
-#endif
-
-namespace {
-
-// Similar language code list. Some languages are very similar and difficult
-// for CLD to distinguish.
-struct SimilarLanguageCode {
-  const char* const code;
-  int group;
-};
-
-const SimilarLanguageCode kSimilarLanguageCodes[] = {
-  {"bs", 1},
-  {"hr", 1},
-  {"hi", 2},
-  {"ne", 2},
-};
-
-// Checks |kSimilarLanguageCodes| and returns group code.
-int GetSimilarLanguageGroupCode(const std::string& language) {
-  for (size_t i = 0; i < arraysize(kSimilarLanguageCodes); ++i) {
-    if (language.find(kSimilarLanguageCodes[i].code) != 0)
-      continue;
-    return kSimilarLanguageCodes[i].group;
-  }
-  return 0;
-}
-
-// Well-known languages which often have wrong server configuration of
-// Content-Language: en.
-// TODO(toyoshim): Remove these static tables and caller functions to
-// chrome/common/translate, and implement them as std::set<>.
-const char* kWellKnownCodesOnWrongConfiguration[] = {
-  "es", "pt", "ja", "ru", "de", "zh-CN", "zh-TW", "ar", "id", "fr", "it", "th"
-};
-
-// Applies a series of language code modification in proper order.
-void ApplyLanguageCodeCorrection(std::string* code) {
-  // Correct well-known format errors.
-  LanguageDetectionUtil::CorrectLanguageCodeTypo(code);
-
-  if (!LanguageDetectionUtil::IsValidLanguageCode(*code)) {
-    *code = std::string();
-    return;
-  }
-
-  TranslateUtil::ToTranslateLanguageSynonym(code);
-}
-
-int GetCLDMajorVersion() {
-#if !defined(CLD_VERSION)
-  std::string group_name = base::FieldTrialList::FindFullName("CLD1VsCLD2");
-  if (group_name == "CLD2")
-    return 2;
-  else
-    return 1;
-#else
-  return CLD_VERSION;
-#endif
-}
-
-// Returns the ISO 639 language code of the specified |text|, or 'unknown' if it
-// failed.
-// |is_cld_reliable| will be set as true if CLD says the detection is reliable.
-std::string DetermineTextLanguage(const base::string16& text,
-                                  bool* is_cld_reliable) {
-  std::string language = chrome::kUnknownLanguageCode;
-  int text_bytes = 0;
-  bool is_reliable = false;
-
-  // Language or CLD2::Language
-  int cld_language = 0;
-  bool is_valid_language = false;
-
-  switch (GetCLDMajorVersion()) {
-#if !defined(CLD_VERSION) || CLD_VERSION==1
-    case 1: {
-      int num_languages = 0;
-      cld_language =
-          DetectLanguageOfUnicodeText(NULL, text.c_str(), true, &is_reliable,
-                                      &num_languages, NULL, &text_bytes);
-      is_valid_language = cld_language != NUM_LANGUAGES &&
-          cld_language != UNKNOWN_LANGUAGE &&
-          cld_language != TG_UNKNOWN_LANGUAGE;
-      break;
-    }
-#endif
-#if !defined(CLD_VERSION) || CLD_VERSION==2
-    case 2: {
-      std::string utf8_text(UTF16ToUTF8(text));
-      CLD2::Language language3[3];
-      int percent3[3];
-      cld_language =
-          CLD2::DetectLanguageSummary(utf8_text.c_str(), utf8_text.size(), true,
-                                      language3, percent3,
-                                      &text_bytes, &is_reliable);
-      is_valid_language = cld_language != CLD2::NUM_LANGUAGES &&
-          cld_language != CLD2::UNKNOWN_LANGUAGE &&
-          cld_language != CLD2::TG_UNKNOWN_LANGUAGE;
-      break;
-    }
-#endif
-    default:
-      NOTREACHED();
-  }
-
-  if (is_cld_reliable != NULL)
-    *is_cld_reliable = is_reliable;
-
-  // We don't trust the result if the CLD reports that the detection is not
-  // reliable, or if the actual text used to detect the language was less than
-  // 100 bytes (short texts can often lead to wrong results).
-  // TODO(toyoshim): CLD provides |is_reliable| flag. But, it just says that
-  // the determined language code is correct with 50% confidence. Chrome should
-  // handle the real confidence value to judge.
-  if (is_reliable && text_bytes >= 100 && is_valid_language) {
-    // We should not use LanguageCode_ISO_639_1 because it does not cover all
-    // the languages CLD can detect. As a result, it'll return the invalid
-    // language code for tradtional Chinese among others.
-    // |LanguageCodeWithDialect| will go through ISO 639-1, ISO-639-2 and
-    // 'other' tables to do the 'right' thing. In addition, it'll return zh-CN
-    // for Simplified Chinese.
-    switch (GetCLDMajorVersion()) {
-#if !defined(CLD_VERSION) || CLD_VERSION==1
-      case 1:
-        language =
-            LanguageCodeWithDialects(static_cast<Language>(cld_language));
-        break;
-#endif
-#if !defined(CLD_VERSION) || CLD_VERSION==2
-      case 2:
-        // (1) CLD2's LanguageCode returns general Chinese 'zh' for
-        // CLD2::CHINESE, but Translate server doesn't accept it. This is
-        // converted to 'zh-CN' in the same way as CLD1's
-        // LanguageCodeWithDialects.
-        //
-        // (2) CLD2's LanguageCode returns zh-Hant instead of zh-TW for
-        // CLD2::CHINESE_T. This is technically more precise for the language
-        // code of traditional Chinese, while Translate server hasn't accepted
-        // zh-Hant yet.
-        if (cld_language == CLD2::CHINESE) {
-          language = "zh-CN";
-        } else if (cld_language == CLD2::CHINESE_T) {
-          language = "zh-TW";
-        } else {
-          language =
-              CLD2::LanguageCode(static_cast<CLD2::Language>(cld_language));
-        }
-        break;
-#endif
-      default:
-        NOTREACHED();
-    }
-  }
-  VLOG(9) << "Detected lang_id: " << language << ", from Text:\n" << text
-          << "\n*************************************\n";
-  return language;
-}
-
-// Checks if CLD can complement a sub code when the page language doesn't know
-// the sub code.
-bool CanCLDComplementSubCode(
-    const std::string& page_language, const std::string& cld_language) {
-  // Translate server cannot treat general Chinese. If Content-Language and
-  // CLD agree that the language is Chinese and Content-Language doesn't know
-  // which dialect is used, CLD language has priority.
-  // TODO(hajimehoshi): How about the other dialects like zh-MO?
-  return page_language == "zh" && StartsWithASCII(cld_language, "zh-", false);
-}
-
-}  // namespace
-
-namespace LanguageDetectionUtil {
-
-std::string DeterminePageLanguage(const std::string& code,
-                                  const std::string& html_lang,
-                                  const base::string16& contents,
-                                  std::string* cld_language_p,
-                                  bool* is_cld_reliable_p) {
-  base::TimeTicks begin_time = base::TimeTicks::Now();
-  bool is_cld_reliable;
-  std::string cld_language = DetermineTextLanguage(contents, &is_cld_reliable);
-  TranslateCommonMetrics::ReportLanguageDetectionTime(begin_time,
-                                                      base::TimeTicks::Now());
-
-  if (cld_language_p != NULL)
-    *cld_language_p = cld_language;
-  if (is_cld_reliable_p != NULL)
-    *is_cld_reliable_p = is_cld_reliable;
-  TranslateUtil::ToTranslateLanguageSynonym(&cld_language);
-
-  // Check if html lang attribute is valid.
-  std::string modified_html_lang;
-  if (!html_lang.empty()) {
-    modified_html_lang = html_lang;
-    ApplyLanguageCodeCorrection(&modified_html_lang);
-    TranslateCommonMetrics::ReportHtmlLang(html_lang, modified_html_lang);
-    VLOG(9) << "html lang based language code: " << modified_html_lang;
-  }
-
-  // Check if Content-Language is valid.
-  std::string modified_code;
-  if (!code.empty()) {
-    modified_code = code;
-    ApplyLanguageCodeCorrection(&modified_code);
-    TranslateCommonMetrics::ReportContentLanguage(code, modified_code);
-  }
-
-  // Adopt |modified_html_lang| if it is valid. Otherwise, adopt
-  // |modified_code|.
-  std::string language = modified_html_lang.empty() ? modified_code :
-                                                      modified_html_lang;
-
-  // If |language| is empty, just use CLD result even though it might be
-  // chrome::kUnknownLanguageCode.
-  if (language.empty()) {
-    TranslateCommonMetrics::ReportLanguageVerification(
-        TranslateCommonMetrics::LANGUAGE_VERIFICATION_CLD_ONLY);
-    return cld_language;
-  }
-
-  if (cld_language == chrome::kUnknownLanguageCode) {
-    TranslateCommonMetrics::ReportLanguageVerification(
-        TranslateCommonMetrics::LANGUAGE_VERIFICATION_UNKNOWN);
-    return language;
-  } else if (CanCLDComplementSubCode(language, cld_language)) {
-    TranslateCommonMetrics::ReportLanguageVerification(
-        TranslateCommonMetrics::LANGUAGE_VERIFICATION_CLD_COMPLEMENT_SUB_CODE);
-    return cld_language;
-  } else if (IsSameOrSimilarLanguages(language, cld_language)) {
-    TranslateCommonMetrics::ReportLanguageVerification(
-        TranslateCommonMetrics::LANGUAGE_VERIFICATION_CLD_AGREE);
-    return language;
-  } else if (MaybeServerWrongConfiguration(language, cld_language)) {
-    TranslateCommonMetrics::ReportLanguageVerification(
-        TranslateCommonMetrics::LANGUAGE_VERIFICATION_TRUST_CLD);
-    return cld_language;
-  } else {
-    TranslateCommonMetrics::ReportLanguageVerification(
-        TranslateCommonMetrics::LANGUAGE_VERIFICATION_CLD_DISAGREE);
-    // Content-Language value might be wrong because CLD says that this page
-    // is written in another language with confidence.
-    // In this case, Chrome doesn't rely on any of the language codes, and
-    // gives up suggesting a translation.
-    return std::string(chrome::kUnknownLanguageCode);
-  }
-
-  return language;
-}
-
-void CorrectLanguageCodeTypo(std::string* code) {
-  DCHECK(code);
-
-  size_t coma_index = code->find(',');
-  if (coma_index != std::string::npos) {
-    // There are more than 1 language specified, just keep the first one.
-    *code = code->substr(0, coma_index);
-  }
-  TrimWhitespaceASCII(*code, TRIM_ALL, code);
-
-  // An underscore instead of a dash is a frequent mistake.
-  size_t underscore_index = code->find('_');
-  if (underscore_index != std::string::npos)
-    (*code)[underscore_index] = '-';
-
-  // Change everything up to a dash to lower-case and everything after to upper.
-  size_t dash_index = code->find('-');
-  if (dash_index != std::string::npos) {
-    *code = StringToLowerASCII(code->substr(0, dash_index)) +
-        StringToUpperASCII(code->substr(dash_index));
-  } else {
-    *code = StringToLowerASCII(*code);
-  }
-}
-
-bool IsValidLanguageCode(const std::string& code) {
-  // Roughly check if the language code follows /[a-zA-Z]{2,3}(-[a-zA-Z]{2})?/.
-  // TODO(hajimehoshi): How about es-419, which is used as an Accept language?
-  std::vector<std::string> chunks;
-  base::SplitString(code, '-', &chunks);
-
-  if (chunks.size() < 1 || 2 < chunks.size())
-    return false;
-
-  const std::string& main_code = chunks[0];
-
-  if (main_code.size() < 1 || 3 < main_code.size())
-    return false;
-
-  for (std::string::const_iterator it = main_code.begin();
-       it != main_code.end(); ++it) {
-    if (!IsAsciiAlpha(*it))
-      return false;
-  }
-
-  if (chunks.size() == 1)
-    return true;
-
-  const std::string& sub_code = chunks[1];
-
-  if (sub_code.size() != 2)
-    return false;
-
-  for (std::string::const_iterator it = sub_code.begin();
-       it != sub_code.end(); ++it) {
-    if (!IsAsciiAlpha(*it))
-      return false;
-  }
-
-  return true;
-}
-
-bool IsSameOrSimilarLanguages(const std::string& page_language,
-                              const std::string& cld_language) {
-  std::vector<std::string> chunks;
-
-  base::SplitString(page_language, '-', &chunks);
-  if (chunks.size() == 0)
-    return false;
-  std::string page_language_main_part = chunks[0];
-
-  base::SplitString(cld_language, '-', &chunks);
-  if (chunks.size() == 0)
-    return false;
-  std::string cld_language_main_part = chunks[0];
-
-  // Language code part of |page_language| is matched to one of |cld_language|.
-  // Country code is ignored here.
-  if (page_language_main_part == cld_language_main_part) {
-    // Languages are matched strictly. Reports false to metrics, but returns
-    // true.
-    TranslateCommonMetrics::ReportSimilarLanguageMatch(false);
-    return true;
-  }
-
-  // Check if |page_language| and |cld_language| are in the similar language
-  // list and belong to the same language group.
-  int page_code = GetSimilarLanguageGroupCode(page_language);
-  bool match = page_code != 0 &&
-               page_code == GetSimilarLanguageGroupCode(cld_language);
-
-  TranslateCommonMetrics::ReportSimilarLanguageMatch(match);
-  return match;
-}
-
-bool MaybeServerWrongConfiguration(const std::string& page_language,
-                                   const std::string& cld_language) {
-  // If |page_language| is not "en-*", respect it and just return false here.
-  if (!StartsWithASCII(page_language, "en", false))
-    return false;
-
-  // A server provides a language meta information representing "en-*". But it
-  // might be just a default value due to missing user configuration.
-  // Let's trust |cld_language| if the determined language is not difficult to
-  // distinguish from English, and the language is one of well-known languages
-  // which often provide "en-*" meta information mistakenly.
-  for (size_t i = 0; i < arraysize(kWellKnownCodesOnWrongConfiguration); ++i) {
-    if (cld_language == kWellKnownCodesOnWrongConfiguration[i])
-      return true;
-  }
-  return false;
-}
-
-std::string GetCLDVersion() {
-  switch (GetCLDMajorVersion()) {
-#if !defined(CLD_VERSION) || CLD_VERSION==1
-    case 1:
-      return CompactLangDet::DetectLanguageVersion();
-#endif
-#if !defined(CLD_VERSION) || CLD_VERSION==2
-    case 2:
-      return CLD2::DetectLanguageVersion();
-#endif
-    default:
-      NOTREACHED();
-  }
-  return "";
-}
-
-}  // namespace LanguageDetectionUtil