[Eraser strings] Remove/replace some supervised user strings

[chromium-blink-merge.git] / components / url_formatter / url_formatter.cc

// Copyright 2015 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 "components/url_formatter/url_formatter.h"

#include <algorithm>
#include <map>
#include <utility>

#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/singleton.h"
#include "base/stl_util.h"
#include "base/strings/string_tokenizer.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_offset_string_conversions.h"
#include "base/strings/utf_string_conversions.h"
#include "base/synchronization/lock.h"
#include "third_party/icu/source/common/unicode/uidna.h"
#include "third_party/icu/source/common/unicode/uniset.h"
#include "third_party/icu/source/common/unicode/uscript.h"
#include "third_party/icu/source/i18n/unicode/regex.h"
#include "third_party/icu/source/i18n/unicode/ulocdata.h"
#include "url/gurl.h"
#include "url/third_party/mozilla/url_parse.h"

namespace url_formatter {

namespace {

base::string16 IDNToUnicodeWithAdjustments(
    const std::string& host,
    const std::string& languages,
    base::OffsetAdjuster::Adjustments* adjustments);
bool IDNToUnicodeOneComponent(const base::char16* comp,
                              size_t comp_len,
                              const std::string& languages,
                              base::string16* out);

class AppendComponentTransform {
 public:
  AppendComponentTransform() {}
  virtual ~AppendComponentTransform() {}

  virtual base::string16 Execute(
      const std::string& component_text,
      base::OffsetAdjuster::Adjustments* adjustments) const = 0;

  // NOTE: No DISALLOW_COPY_AND_ASSIGN here, since gcc < 4.3.0 requires an
  // accessible copy constructor in order to call AppendFormattedComponent()
  // with an inline temporary (see http://gcc.gnu.org/bugs/#cxx%5Frvalbind ).
};

class HostComponentTransform : public AppendComponentTransform {
 public:
  explicit HostComponentTransform(const std::string& languages)
      : languages_(languages) {}

 private:
  base::string16 Execute(
      const std::string& component_text,
      base::OffsetAdjuster::Adjustments* adjustments) const override {
    return IDNToUnicodeWithAdjustments(component_text, languages_, adjustments);
  }

  const std::string& languages_;
};

class NonHostComponentTransform : public AppendComponentTransform {
 public:
  explicit NonHostComponentTransform(net::UnescapeRule::Type unescape_rules)
      : unescape_rules_(unescape_rules) {}

 private:
  base::string16 Execute(
      const std::string& component_text,
      base::OffsetAdjuster::Adjustments* adjustments) const override {
    return (unescape_rules_ == net::UnescapeRule::NONE)
               ? base::UTF8ToUTF16WithAdjustments(component_text, adjustments)
               : net::UnescapeAndDecodeUTF8URLComponentWithAdjustments(
                     component_text, unescape_rules_, adjustments);
  }

  const net::UnescapeRule::Type unescape_rules_;
};

// Transforms the portion of |spec| covered by |original_component| according to
// |transform|.  Appends the result to |output|.  If |output_component| is
// non-NULL, its start and length are set to the transformed component's new
// start and length.  If |adjustments| is non-NULL, appends adjustments (if
// any) that reflect the transformation the original component underwent to
// become the transformed value appended to |output|.
void AppendFormattedComponent(const std::string& spec,
                              const url::Component& original_component,
                              const AppendComponentTransform& transform,
                              base::string16* output,
                              url::Component* output_component,
                              base::OffsetAdjuster::Adjustments* adjustments) {
  DCHECK(output);
  if (original_component.is_nonempty()) {
    size_t original_component_begin =
        static_cast<size_t>(original_component.begin);
    size_t output_component_begin = output->length();
    std::string component_str(spec, original_component_begin,
                              static_cast<size_t>(original_component.len));

    // Transform |component_str| and modify |adjustments| appropriately.
    base::OffsetAdjuster::Adjustments component_transform_adjustments;
    output->append(
        transform.Execute(component_str, &component_transform_adjustments));

    // Shift all the adjustments made for this component so the offsets are
    // valid for the original string and add them to |adjustments|.
    for (base::OffsetAdjuster::Adjustments::iterator comp_iter =
             component_transform_adjustments.begin();
         comp_iter != component_transform_adjustments.end(); ++comp_iter)
      comp_iter->original_offset += original_component_begin;
    if (adjustments) {
      adjustments->insert(adjustments->end(),
                          component_transform_adjustments.begin(),
                          component_transform_adjustments.end());
    }

    // Set positions of the parsed component.
    if (output_component) {
      output_component->begin = static_cast<int>(output_component_begin);
      output_component->len =
          static_cast<int>(output->length() - output_component_begin);
    }
  } else if (output_component) {
    output_component->reset();
  }
}

// If |component| is valid, its begin is incremented by |delta|.
void AdjustComponent(int delta, url::Component* component) {
  if (!component->is_valid())
    return;

  DCHECK(delta >= 0 || component->begin >= -delta);
  component->begin += delta;
}

// Adjusts all the components of |parsed| by |delta|, except for the scheme.
void AdjustAllComponentsButScheme(int delta, url::Parsed* parsed) {
  AdjustComponent(delta, &(parsed->username));
  AdjustComponent(delta, &(parsed->password));
  AdjustComponent(delta, &(parsed->host));
  AdjustComponent(delta, &(parsed->port));
  AdjustComponent(delta, &(parsed->path));
  AdjustComponent(delta, &(parsed->query));
  AdjustComponent(delta, &(parsed->ref));
}

// Helper for FormatUrlWithOffsets().
base::string16 FormatViewSourceUrl(
    const GURL& url,
    const std::string& languages,
    FormatUrlTypes format_types,
    net::UnescapeRule::Type unescape_rules,
    url::Parsed* new_parsed,
    size_t* prefix_end,
    base::OffsetAdjuster::Adjustments* adjustments) {
  DCHECK(new_parsed);
  const char kViewSource[] = "view-source:";
  const size_t kViewSourceLength = arraysize(kViewSource) - 1;

  // Format the underlying URL and record adjustments.
  const std::string& url_str(url.possibly_invalid_spec());
  adjustments->clear();
  base::string16 result(
      base::ASCIIToUTF16(kViewSource) +
      FormatUrlWithAdjustments(GURL(url_str.substr(kViewSourceLength)),
                               languages, format_types, unescape_rules,
                               new_parsed, prefix_end, adjustments));
  // Revise |adjustments| by shifting to the offsets to prefix that the above
  // call to FormatUrl didn't get to see.
  for (base::OffsetAdjuster::Adjustments::iterator it = adjustments->begin();
       it != adjustments->end(); ++it)
    it->original_offset += kViewSourceLength;

  // Adjust positions of the parsed components.
  if (new_parsed->scheme.is_nonempty()) {
    // Assume "view-source:real-scheme" as a scheme.
    new_parsed->scheme.len += kViewSourceLength;
  } else {
    new_parsed->scheme.begin = 0;
    new_parsed->scheme.len = kViewSourceLength - 1;
  }
  AdjustAllComponentsButScheme(kViewSourceLength, new_parsed);

  if (prefix_end)
    *prefix_end += kViewSourceLength;

  return result;
}

// TODO(brettw) bug 734373: check the scripts for each host component and
// don't un-IDN-ize if there is more than one. Alternatively, only IDN for
// scripts that the user has installed. For now, just put the entire
// path through IDN. Maybe this feature can be implemented in ICU itself?
//
// We may want to skip this step in the case of file URLs to allow unicode
// UNC hostnames regardless of encodings.
base::string16 IDNToUnicodeWithAdjustments(
    const std::string& host,
    const std::string& languages,
    base::OffsetAdjuster::Adjustments* adjustments) {
  if (adjustments)
    adjustments->clear();
  // Convert the ASCII input to a base::string16 for ICU.
  base::string16 input16;
  input16.reserve(host.length());
  input16.insert(input16.end(), host.begin(), host.end());

  // Do each component of the host separately, since we enforce script matching
  // on a per-component basis.
  base::string16 out16;
  for (size_t component_start = 0, component_end;
       component_start < input16.length();
       component_start = component_end + 1) {
    // Find the end of the component.
    component_end = input16.find('.', component_start);
    if (component_end == base::string16::npos)
      component_end = input16.length();  // For getting the last component.
    size_t component_length = component_end - component_start;
    size_t new_component_start = out16.length();
    bool converted_idn = false;
    if (component_end > component_start) {
      // Add the substring that we just found.
      converted_idn =
          IDNToUnicodeOneComponent(input16.data() + component_start,
                                   component_length, languages, &out16);
    }
    size_t new_component_length = out16.length() - new_component_start;

    if (converted_idn && adjustments) {
      adjustments->push_back(base::OffsetAdjuster::Adjustment(
          component_start, component_length, new_component_length));
    }

    // Need to add the dot we just found (if we found one).
    if (component_end < input16.length())
      out16.push_back('.');
  }
  return out16;
}

// Does some simple normalization of scripts so we can allow certain scripts
// to exist together.
// TODO(brettw) bug 880223: we should allow some other languages to be
// oombined such as Chinese and Latin. We will probably need a more
// complicated system of language pairs to have more fine-grained control.
UScriptCode NormalizeScript(UScriptCode code) {
  switch (code) {
    case USCRIPT_KATAKANA:
    case USCRIPT_HIRAGANA:
    case USCRIPT_KATAKANA_OR_HIRAGANA:
    case USCRIPT_HANGUL:  // This one is arguable.
      return USCRIPT_HAN;
    default:
      return code;
  }
}

bool IsIDNComponentInSingleScript(const base::char16* str, int str_len) {
  UScriptCode first_script = USCRIPT_INVALID_CODE;
  bool is_first = true;

  int i = 0;
  while (i < str_len) {
    unsigned code_point;
    U16_NEXT(str, i, str_len, code_point);

    UErrorCode err = U_ZERO_ERROR;
    UScriptCode cur_script = uscript_getScript(code_point, &err);
    if (err != U_ZERO_ERROR)
      return false;  // Report mixed on error.
    cur_script = NormalizeScript(cur_script);

    // TODO(brettw) We may have to check for USCRIPT_INHERENT as well.
    if (is_first && cur_script != USCRIPT_COMMON) {
      first_script = cur_script;
      is_first = false;
    } else {
      if (cur_script != USCRIPT_COMMON && cur_script != first_script)
        return false;
    }
  }
  return true;
}

// Check if the script of a language can be 'safely' mixed with
// Latin letters in the ASCII range.
bool IsCompatibleWithASCIILetters(const std::string& lang) {
  // For now, just list Chinese, Japanese and Korean (positive list).
  // An alternative is negative-listing (languages using Greek and
  // Cyrillic letters), but it can be more dangerous.
  return !lang.substr(0, 2).compare("zh") || !lang.substr(0, 2).compare("ja") ||
         !lang.substr(0, 2).compare("ko");
}

typedef std::map<std::string, icu::UnicodeSet*> LangToExemplarSetMap;

class LangToExemplarSet {
 public:
  static LangToExemplarSet* GetInstance() {
    return Singleton<LangToExemplarSet>::get();
  }

 private:
  LangToExemplarSetMap map;
  LangToExemplarSet() {}
  ~LangToExemplarSet() {
    STLDeleteContainerPairSecondPointers(map.begin(), map.end());
  }

  friend class Singleton<LangToExemplarSet>;
  friend struct DefaultSingletonTraits<LangToExemplarSet>;
  friend bool GetExemplarSetForLang(const std::string&, icu::UnicodeSet**);
  friend void SetExemplarSetForLang(const std::string&, icu::UnicodeSet*);

  DISALLOW_COPY_AND_ASSIGN(LangToExemplarSet);
};

bool GetExemplarSetForLang(const std::string& lang,
                           icu::UnicodeSet** lang_set) {
  const LangToExemplarSetMap& map = LangToExemplarSet::GetInstance()->map;
  LangToExemplarSetMap::const_iterator pos = map.find(lang);
  if (pos != map.end()) {
    *lang_set = pos->second;
    return true;
  }
  return false;
}

void SetExemplarSetForLang(const std::string& lang, icu::UnicodeSet* lang_set) {
  LangToExemplarSetMap& map = LangToExemplarSet::GetInstance()->map;
  map.insert(std::make_pair(lang, lang_set));
}

static base::LazyInstance<base::Lock>::Leaky g_lang_set_lock =
    LAZY_INSTANCE_INITIALIZER;

// Returns true if all the characters in component_characters are used by
// the language |lang|.
bool IsComponentCoveredByLang(const icu::UnicodeSet& component_characters,
                              const std::string& lang) {
  CR_DEFINE_STATIC_LOCAL(const icu::UnicodeSet, kASCIILetters, ('a', 'z'));
  icu::UnicodeSet* lang_set = nullptr;
  // We're called from both the UI thread and the history thread.
  {
    base::AutoLock lock(g_lang_set_lock.Get());
    if (!GetExemplarSetForLang(lang, &lang_set)) {
      UErrorCode status = U_ZERO_ERROR;
      ULocaleData* uld = ulocdata_open(lang.c_str(), &status);
      // TODO(jungshik) Turn this check on when the ICU data file is
      // rebuilt with the minimal subset of locale data for languages
      // to which Chrome is not localized but which we offer in the list
      // of languages selectable for Accept-Languages. With the rebuilt ICU
      // data, ulocdata_open never should fall back to the default locale.
      // (issue 2078)
      // DCHECK(U_SUCCESS(status) && status != U_USING_DEFAULT_WARNING);
      if (U_SUCCESS(status) && status != U_USING_DEFAULT_WARNING) {
        lang_set = reinterpret_cast<icu::UnicodeSet*>(ulocdata_getExemplarSet(
            uld, nullptr, 0, ULOCDATA_ES_STANDARD, &status));
        // On success, if |lang| is compatible with ASCII Latin letters, add
        // them.
        if (lang_set && IsCompatibleWithASCIILetters(lang))
          lang_set->addAll(kASCIILetters);
      }

      if (!lang_set)
        lang_set = new icu::UnicodeSet(1, 0);

      lang_set->freeze();
      SetExemplarSetForLang(lang, lang_set);
      ulocdata_close(uld);
    }
  }
  return !lang_set->isEmpty() && lang_set->containsAll(component_characters);
}

// Returns true if the given Unicode host component is safe to display to the
// user.
bool IsIDNComponentSafe(const base::char16* str,
                        int str_len,
                        const std::string& languages) {
  // Most common cases (non-IDN) do not reach here so that we don't
  // need a fast return path.
  // TODO(jungshik) : Check if there's any character inappropriate
  // (although allowed) for domain names.
  // See http://www.unicode.org/reports/tr39/#IDN_Security_Profiles and
  // http://www.unicode.org/reports/tr39/data/xidmodifications.txt
  // For now, we borrow the list from Mozilla and tweaked it slightly.
  // (e.g. Characters like U+00A0, U+3000, U+3002 are omitted because
  //  they're gonna be canonicalized to U+0020 and full stop before
  //  reaching here.)
  // The original list is available at
  // http://kb.mozillazine.org/Network.IDN.blacklist_chars and
  // at
  // http://mxr.mozilla.org/seamonkey/source/modules/libpref/src/init/all.js#703

  UErrorCode status = U_ZERO_ERROR;
#ifdef U_WCHAR_IS_UTF16
  icu::UnicodeSet dangerous_characters(
      icu::UnicodeString(
          L"[[\\ \u00ad\u00bc\u00bd\u01c3\u0337\u0338"
          L"\u05c3\u05f4\u06d4\u0702\u115f\u1160][\u2000-\u200b]"
          L"[\u2024\u2027\u2028\u2029\u2039\u203a\u2044\u205f]"
          L"[\u2154-\u2156][\u2159-\u215b][\u215f\u2215\u23ae"
          L"\u29f6\u29f8\u2afb\u2afd][\u2ff0-\u2ffb][\u3014"
          L"\u3015\u3033\u3164\u321d\u321e\u33ae\u33af\u33c6\u33df\ufe14"
          L"\ufe15\ufe3f\ufe5d\ufe5e\ufeff\uff0e\uff06\uff61\uffa0\ufff9]"
          L"[\ufffa-\ufffd]\U0001f50f\U0001f510\U0001f512\U0001f513]"),
      status);
  DCHECK(U_SUCCESS(status));
  icu::RegexMatcher dangerous_patterns(
      icu::UnicodeString(
          // Lone katakana no, so, or n
          L"[^\\p{Katakana}][\u30ce\u30f3\u30bd][^\\p{Katakana}]"
          // Repeating Japanese accent characters
          L"|[\u3099\u309a\u309b\u309c][\u3099\u309a\u309b\u309c]"),
      0, status);
#else
  icu::UnicodeSet dangerous_characters(
      icu::UnicodeString(
          "[[\\u0020\\u00ad\\u00bc\\u00bd\\u01c3\\u0337\\u0338"
          "\\u05c3\\u05f4\\u06d4\\u0702\\u115f\\u1160][\\u2000-\\u200b]"
          "[\\u2024\\u2027\\u2028\\u2029\\u2039\\u203a\\u2044\\u205f]"
          "[\\u2154-\\u2156][\\u2159-\\u215b][\\u215f\\u2215\\u23ae"
          "\\u29f6\\u29f8\\u2afb\\u2afd][\\u2ff0-\\u2ffb][\\u3014"
          "\\u3015\\u3033\\u3164\\u321d\\u321e\\u33ae\\u33af\\u33c6\\u33df\\ufe"
          "14"
          "\\ufe15\\ufe3f\\ufe5d\\ufe5e\\ufeff\\uff0e\\uff06\\uff61\\uffa0\\uff"
          "f9]"
          "[\\ufffa-\\ufffd]\\U0001f50f\\U0001f510\\U0001f512\\U0001f513]",
          -1, US_INV),
      status);
  DCHECK(U_SUCCESS(status));
  icu::RegexMatcher dangerous_patterns(
      icu::UnicodeString(
          // Lone katakana no, so, or n
          "[^\\p{Katakana}][\\u30ce\\u30f3\\u30bd][^\\p{Katakana}]"
          // Repeating Japanese accent characters
          "|[\\u3099\\u309a\\u309b\\u309c][\\u3099\\u309a\\u309b\\u309c]"),
      0, status);
#endif
  DCHECK(U_SUCCESS(status));
  icu::UnicodeSet component_characters;
  icu::UnicodeString component_string(str, str_len);
  component_characters.addAll(component_string);
  if (dangerous_characters.containsSome(component_characters))
    return false;

  DCHECK(U_SUCCESS(status));
  dangerous_patterns.reset(component_string);
  if (dangerous_patterns.find())
    return false;

  // If the language list is empty, the result is completely determined
  // by whether a component is a single script or not. This will block
  // even "safe" script mixing cases like <Chinese, Latin-ASCII> that are
  // allowed with |languages| (while it blocks Chinese + Latin letters with
  // an accent as should be the case), but we want to err on the safe side
  // when |languages| is empty.
  if (languages.empty())
    return IsIDNComponentInSingleScript(str, str_len);

  // |common_characters| is made up of  ASCII numbers, hyphen, plus and
  // underscore that are used across scripts and allowed in domain names.
  // (sync'd with characters allowed in url_canon_host with square
  // brackets excluded.) See kHostCharLookup[] array in url_canon_host.cc.
  icu::UnicodeSet common_characters(UNICODE_STRING_SIMPLE("[[0-9]\\-_+\\ ]"),
                                    status);
  DCHECK(U_SUCCESS(status));
  // Subtract common characters because they're always allowed so that
  // we just have to check if a language-specific set contains
  // the remainder.
  component_characters.removeAll(common_characters);

  base::StringTokenizer t(languages, ",");
  while (t.GetNext()) {
    if (IsComponentCoveredByLang(component_characters, t.token()))
      return true;
  }
  return false;
}

// A wrapper to use LazyInstance<>::Leaky with ICU's UIDNA, a C pointer to
// a UTS46/IDNA 2008 handling object opened with uidna_openUTS46().
//
// We use UTS46 with BiDiCheck to migrate from IDNA 2003 to IDNA 2008 with
// the backward compatibility in mind. What it does:
//
// 1. Use the up-to-date Unicode data.
// 2. Define a case folding/mapping with the up-to-date Unicode data as
//    in IDNA 2003.
// 3. Use transitional mechanism for 4 deviation characters (sharp-s,
//    final sigma, ZWJ and ZWNJ) for now.
// 4. Continue to allow symbols and punctuations.
// 5. Apply new BiDi check rules more permissive than the IDNA 2003 BiDI rules.
// 6. Do not apply STD3 rules
// 7. Do not allow unassigned code points.
//
// It also closely matches what IE 10 does except for the BiDi check (
// http://goo.gl/3XBhqw ).
// See http://http://unicode.org/reports/tr46/ and references therein
// for more details.
struct UIDNAWrapper {
  UIDNAWrapper() {
    UErrorCode err = U_ZERO_ERROR;
    // TODO(jungshik): Change options as different parties (browsers,
    // registrars, search engines) converge toward a consensus.
    value = uidna_openUTS46(UIDNA_CHECK_BIDI, &err);
    if (U_FAILURE(err))
      value = NULL;
  }

  UIDNA* value;
};

static base::LazyInstance<UIDNAWrapper>::Leaky g_uidna =
    LAZY_INSTANCE_INITIALIZER;

// Converts one component of a host (between dots) to IDN if safe. The result
// will be APPENDED to the given output string and will be the same as the input
// if it is not IDN or the IDN is unsafe to display.  Returns whether any
// conversion was performed.
bool IDNToUnicodeOneComponent(const base::char16* comp,
                              size_t comp_len,
                              const std::string& languages,
                              base::string16* out) {
  DCHECK(out);
  if (comp_len == 0)
    return false;

  // Only transform if the input can be an IDN component.
  static const base::char16 kIdnPrefix[] = {'x', 'n', '-', '-'};
  if ((comp_len > arraysize(kIdnPrefix)) &&
      !memcmp(comp, kIdnPrefix, sizeof(kIdnPrefix))) {
    UIDNA* uidna = g_uidna.Get().value;
    DCHECK(uidna != NULL);
    size_t original_length = out->length();
    int output_length = 64;
    UIDNAInfo info = UIDNA_INFO_INITIALIZER;
    UErrorCode status;
    do {
      out->resize(original_length + output_length);
      status = U_ZERO_ERROR;
      // This returns the actual length required. If this is more than 64
      // code units, |status| will be U_BUFFER_OVERFLOW_ERROR and we'll try
      // the conversion again, but with a sufficiently large buffer.
      output_length = uidna_labelToUnicode(
          uidna, comp, static_cast<int32_t>(comp_len), &(*out)[original_length],
          output_length, &info, &status);
    } while ((status == U_BUFFER_OVERFLOW_ERROR && info.errors == 0));

    if (U_SUCCESS(status) && info.errors == 0) {
      // Converted successfully. Ensure that the converted component
      // can be safely displayed to the user.
      out->resize(original_length + output_length);
      if (IsIDNComponentSafe(out->data() + original_length, output_length,
                             languages))
        return true;
    }

    // Something went wrong. Revert to original string.
    out->resize(original_length);
  }

  // We get here with no IDN or on error, in which case we just append the
  // literal input.
  out->append(comp, comp_len);
  return false;
}

}  // namespace

const FormatUrlType kFormatUrlOmitNothing = 0;
const FormatUrlType kFormatUrlOmitUsernamePassword = 1 << 0;
const FormatUrlType kFormatUrlOmitHTTP = 1 << 1;
const FormatUrlType kFormatUrlOmitTrailingSlashOnBareHostname = 1 << 2;
const FormatUrlType kFormatUrlOmitAll =
    kFormatUrlOmitUsernamePassword | kFormatUrlOmitHTTP |
    kFormatUrlOmitTrailingSlashOnBareHostname;

base::string16 FormatUrl(const GURL& url,
                         const std::string& languages,
                         FormatUrlTypes format_types,
                         net::UnescapeRule::Type unescape_rules,
                         url::Parsed* new_parsed,
                         size_t* prefix_end,
                         size_t* offset_for_adjustment) {
  std::vector<size_t> offsets;
  if (offset_for_adjustment)
    offsets.push_back(*offset_for_adjustment);
  base::string16 result =
      FormatUrlWithOffsets(url, languages, format_types, unescape_rules,
                           new_parsed, prefix_end, &offsets);
  if (offset_for_adjustment)
    *offset_for_adjustment = offsets[0];
  return result;
}

base::string16 FormatUrlWithOffsets(
    const GURL& url,
    const std::string& languages,
    FormatUrlTypes format_types,
    net::UnescapeRule::Type unescape_rules,
    url::Parsed* new_parsed,
    size_t* prefix_end,
    std::vector<size_t>* offsets_for_adjustment) {
  base::OffsetAdjuster::Adjustments adjustments;
  const base::string16& format_url_return_value =
      FormatUrlWithAdjustments(url, languages, format_types, unescape_rules,
                               new_parsed, prefix_end, &adjustments);
  base::OffsetAdjuster::AdjustOffsets(adjustments, offsets_for_adjustment);
  if (offsets_for_adjustment) {
    std::for_each(
        offsets_for_adjustment->begin(), offsets_for_adjustment->end(),
        base::LimitOffset<std::string>(format_url_return_value.length()));
  }
  return format_url_return_value;
}

base::string16 FormatUrlWithAdjustments(
    const GURL& url,
    const std::string& languages,
    FormatUrlTypes format_types,
    net::UnescapeRule::Type unescape_rules,
    url::Parsed* new_parsed,
    size_t* prefix_end,
    base::OffsetAdjuster::Adjustments* adjustments) {
  DCHECK(adjustments != NULL);
  adjustments->clear();
  url::Parsed parsed_temp;
  if (!new_parsed)
    new_parsed = &parsed_temp;
  else
    *new_parsed = url::Parsed();

  // Special handling for view-source:.  Don't use content::kViewSourceScheme
  // because this library shouldn't depend on chrome.
  const char kViewSource[] = "view-source";
  // Reject "view-source:view-source:..." to avoid deep recursion.
  const char kViewSourceTwice[] = "view-source:view-source:";
  if (url.SchemeIs(kViewSource) &&
      !base::StartsWith(url.possibly_invalid_spec(), kViewSourceTwice,
                        base::CompareCase::INSENSITIVE_ASCII)) {
    return FormatViewSourceUrl(url, languages, format_types, unescape_rules,
                               new_parsed, prefix_end, adjustments);
  }

  // We handle both valid and invalid URLs (this will give us the spec
  // regardless of validity).
  const std::string& spec = url.possibly_invalid_spec();
  const url::Parsed& parsed = url.parsed_for_possibly_invalid_spec();

  // Scheme & separators.  These are ASCII.
  base::string16 url_string;
  url_string.insert(
      url_string.end(), spec.begin(),
      spec.begin() + parsed.CountCharactersBefore(url::Parsed::USERNAME, true));
  const char kHTTP[] = "http://";
  const char kFTP[] = "ftp.";
  // url_formatter::FixupURL() treats "ftp.foo.com" as ftp://ftp.foo.com.  This
  // means that if we trim "http://" off a URL whose host starts with "ftp." and
  // the user inputs this into any field subject to fixup (which is basically
  // all input fields), the meaning would be changed.  (In fact, often the
  // formatted URL is directly pre-filled into an input field.)  For this reason
  // we avoid stripping "http://" in this case.
  bool omit_http =
      (format_types & kFormatUrlOmitHTTP) &&
      base::EqualsASCII(url_string, kHTTP) &&
      !base::StartsWith(url.host(), kFTP, base::CompareCase::SENSITIVE);
  new_parsed->scheme = parsed.scheme;

  // Username & password.
  if ((format_types & kFormatUrlOmitUsernamePassword) != 0) {
    // Remove the username and password fields. We don't want to display those
    // to the user since they can be used for attacks,
    // e.g. "http://google.com:search@evil.ru/"
    new_parsed->username.reset();
    new_parsed->password.reset();
    // Update the adjustments based on removed username and/or password.
    if (parsed.username.is_nonempty() || parsed.password.is_nonempty()) {
      if (parsed.username.is_nonempty() && parsed.password.is_nonempty()) {
        // The seeming off-by-two is to account for the ':' after the username
        // and '@' after the password.
        adjustments->push_back(base::OffsetAdjuster::Adjustment(
            static_cast<size_t>(parsed.username.begin),
            static_cast<size_t>(parsed.username.len + parsed.password.len + 2),
            0));
      } else {
        const url::Component* nonempty_component =
            parsed.username.is_nonempty() ? &parsed.username : &parsed.password;
        // The seeming off-by-one is to account for the '@' after the
        // username/password.
        adjustments->push_back(base::OffsetAdjuster::Adjustment(
            static_cast<size_t>(nonempty_component->begin),
            static_cast<size_t>(nonempty_component->len + 1), 0));
      }
    }
  } else {
    AppendFormattedComponent(spec, parsed.username,
                             NonHostComponentTransform(unescape_rules),
                             &url_string, &new_parsed->username, adjustments);
    if (parsed.password.is_valid())
      url_string.push_back(':');
    AppendFormattedComponent(spec, parsed.password,
                             NonHostComponentTransform(unescape_rules),
                             &url_string, &new_parsed->password, adjustments);
    if (parsed.username.is_valid() || parsed.password.is_valid())
      url_string.push_back('@');
  }
  if (prefix_end)
    *prefix_end = static_cast<size_t>(url_string.length());

  // Host.
  AppendFormattedComponent(spec, parsed.host, HostComponentTransform(languages),
                           &url_string, &new_parsed->host, adjustments);

  // Port.
  if (parsed.port.is_nonempty()) {
    url_string.push_back(':');
    new_parsed->port.begin = url_string.length();
    url_string.insert(url_string.end(), spec.begin() + parsed.port.begin,
                      spec.begin() + parsed.port.end());
    new_parsed->port.len = url_string.length() - new_parsed->port.begin;
  } else {
    new_parsed->port.reset();
  }

  // Path & query.  Both get the same general unescape & convert treatment.
  if (!(format_types & kFormatUrlOmitTrailingSlashOnBareHostname) ||
      !CanStripTrailingSlash(url)) {
    AppendFormattedComponent(spec, parsed.path,
                             NonHostComponentTransform(unescape_rules),
                             &url_string, &new_parsed->path, adjustments);
  } else {
    if (parsed.path.len > 0) {
      adjustments->push_back(base::OffsetAdjuster::Adjustment(
          parsed.path.begin, parsed.path.len, 0));
    }
  }
  if (parsed.query.is_valid())
    url_string.push_back('?');
  AppendFormattedComponent(spec, parsed.query,
                           NonHostComponentTransform(unescape_rules),
                           &url_string, &new_parsed->query, adjustments);

  // Ref.  This is valid, unescaped UTF-8, so we can just convert.
  if (parsed.ref.is_valid())
    url_string.push_back('#');
  AppendFormattedComponent(spec, parsed.ref,
                           NonHostComponentTransform(net::UnescapeRule::NONE),
                           &url_string, &new_parsed->ref, adjustments);

  // If we need to strip out http do it after the fact.
  if (omit_http && base::StartsWith(url_string, base::ASCIIToUTF16(kHTTP),
                                    base::CompareCase::SENSITIVE)) {
    const size_t kHTTPSize = arraysize(kHTTP) - 1;
    url_string = url_string.substr(kHTTPSize);
    // Because offsets in the |adjustments| are already calculated with respect
    // to the string with the http:// prefix in it, those offsets remain correct
    // after stripping the prefix.  The only thing necessary is to add an
    // adjustment to reflect the stripped prefix.
    adjustments->insert(adjustments->begin(),
                        base::OffsetAdjuster::Adjustment(0, kHTTPSize, 0));

    if (prefix_end)
      *prefix_end -= kHTTPSize;

    // Adjust new_parsed.
    DCHECK(new_parsed->scheme.is_valid());
    int delta = -(new_parsed->scheme.len + 3);  // +3 for ://.
    new_parsed->scheme.reset();
    AdjustAllComponentsButScheme(delta, new_parsed);
  }

  return url_string;
}

bool CanStripTrailingSlash(const GURL& url) {
  // Omit the path only for standard, non-file URLs with nothing but "/" after
  // the hostname.
  return url.IsStandard() && !url.SchemeIsFile() && !url.SchemeIsFileSystem() &&
         !url.has_query() && !url.has_ref() && url.path() == "/";
}

void AppendFormattedHost(const GURL& url,
                         const std::string& languages,
                         base::string16* output) {
  AppendFormattedComponent(
      url.possibly_invalid_spec(), url.parsed_for_possibly_invalid_spec().host,
      HostComponentTransform(languages), output, NULL, NULL);
}

base::string16 IDNToUnicode(const std::string& host,
                            const std::string& languages) {
  return IDNToUnicodeWithAdjustments(host, languages, NULL);
}

}  // url_formatter