escape.cc

// Copyright (c) 2012 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 "net/base/escape.h"

#include <algorithm>

#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/strings/string_piece.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_offset_string_conversions.h"
#include "base/strings/utf_string_conversions.h"

namespace net {

namespace {

const char kHexString[] = "0123456789ABCDEF";
inline char IntToHex(int i) {
  DCHECK_GE(i, 0) << i << " not a hex value";
  DCHECK_LE(i, 15) << i << " not a hex value";
  return kHexString[i];
}

// A fast bit-vector map for ascii characters.
//
// Internally stores 256 bits in an array of 8 ints.
// Does quick bit-flicking to lookup needed characters.
struct Charmap {
  bool Contains(unsigned char c) const {
    return ((map[c >> 5] & (1 << (c & 31))) != 0);
  }

  uint32 map[8];
};

// Given text to escape and a Charmap defining which values to escape,
// return an escaped string.  If use_plus is true, spaces are converted
// to +, otherwise, if spaces are in the charmap, they are converted to
// %20.
std::string Escape(const std::string& text, const Charmap& charmap,
                   bool use_plus) {
  std::string escaped;
  escaped.reserve(text.length() * 3);
  for (unsigned int i = 0; i < text.length(); ++i) {
    unsigned char c = static_cast<unsigned char>(text[i]);
    if (use_plus && ' ' == c) {
      escaped.push_back('+');
    } else if (charmap.Contains(c)) {
      escaped.push_back('%');
      escaped.push_back(IntToHex(c >> 4));
      escaped.push_back(IntToHex(c & 0xf));
    } else {
      escaped.push_back(c);
    }
  }
  return escaped;
}

// Contains nonzero when the corresponding character is unescapable for normal
// URLs. These characters are the ones that may change the parsing of a URL, so
// we don't want to unescape them sometimes. In many case we won't want to
// unescape spaces, but that is controlled by parameters to Unescape*.
//
// The basic rule is that we can't unescape anything that would changing parsing
// like # or ?. We also can't unescape &, =, or + since that could be part of a
// query and that could change the server's parsing of the query. Nor can we
// unescape \ since src/url/ will convert it to a /.
//
// Lastly, we can't unescape anything that doesn't have a canonical
// representation in a URL. This means that unescaping will change the URL, and
// you could get different behavior if you copy and paste the URL, or press
// enter in the URL bar. The list of characters that fall into this category
// are the ones labeled PASS (allow either escaped or unescaped) in the big
// lookup table at the top of url/url_canon_path.cc.  Also, characters
// that have CHAR_QUERY set in url/url_canon_internal.cc but are not
// allowed in query strings according to http://www.ietf.org/rfc/rfc3261.txt are
// not unescaped, to avoid turning a valid url according to spec into an
// invalid one.
const char kUrlUnescape[128] = {
//   NULL, control chars...
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
//  ' ' !  "  #  $  %  &  '  (  )  *  +  ,  -  .  /
     0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0,
//   0  1  2  3  4  5  6  7  8  9  :  ;  <  =  >  ?
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 0,
//   @  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O
     0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
//   P  Q  R  S  T  U  V  W  X  Y  Z  [  \  ]  ^  _
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,
//   `  a  b  c  d  e  f  g  h  i  j  k  l  m  n  o
     0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
//   p  q  r  s  t  u  v  w  x  y  z  {  |  }  ~  <NBSP>
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 0
};

template<typename STR>
STR UnescapeURLWithOffsetsImpl(const STR& escaped_text,
                               UnescapeRule::Type rules,
                               std::vector<size_t>* offsets_for_adjustment) {
  if (offsets_for_adjustment) {
    std::for_each(offsets_for_adjustment->begin(),
                  offsets_for_adjustment->end(),
                  base::LimitOffset<STR>(escaped_text.length()));
  }
  // Do not unescape anything, return the |escaped_text| text.
  if (rules == UnescapeRule::NONE)
    return escaped_text;

  // The output of the unescaping is always smaller than the input, so we can
  // reserve the input size to make sure we have enough buffer and don't have
  // to allocate in the loop below.
  STR result;
  result.reserve(escaped_text.length());

  // Locations of adjusted text.
  net::internal::AdjustEncodingOffset::Adjustments adjustments;
  for (size_t i = 0, max = escaped_text.size(); i < max; ++i) {
    if (static_cast<unsigned char>(escaped_text[i]) >= 128) {
      // Non ASCII character, append as is.
      result.push_back(escaped_text[i]);
      continue;
    }

    char current_char = static_cast<char>(escaped_text[i]);
    if (current_char == '%' && i + 2 < max) {
      const typename STR::value_type most_sig_digit(
          static_cast<typename STR::value_type>(escaped_text[i + 1]));
      const typename STR::value_type least_sig_digit(
          static_cast<typename STR::value_type>(escaped_text[i + 2]));
      if (IsHexDigit(most_sig_digit) && IsHexDigit(least_sig_digit)) {
        unsigned char value = HexDigitToInt(most_sig_digit) * 16 +
            HexDigitToInt(least_sig_digit);
        if (value >= 0x80 ||  // Unescape all high-bit characters.
            // For 7-bit characters, the lookup table tells us all valid chars.
            (kUrlUnescape[value] ||
             // ...and we allow some additional unescaping when flags are set.
             (value == ' ' && (rules & UnescapeRule::SPACES)) ||
             // Allow any of the prohibited but non-control characters when
             // we're doing "special" chars.
             (value > ' ' && (rules & UnescapeRule::URL_SPECIAL_CHARS)) ||
             // Additionally allow control characters if requested.
             (value < ' ' && (rules & UnescapeRule::CONTROL_CHARS)))) {
          // Use the unescaped version of the character.
          adjustments.push_back(i);
          result.push_back(value);
          i += 2;
        } else {
          // Keep escaped. Append a percent and we'll get the following two
          // digits on the next loops through.
          result.push_back('%');
        }
      } else {
        // Invalid escape sequence, just pass the percent through and continue
        // right after it.
        result.push_back('%');
      }
    } else if ((rules & UnescapeRule::REPLACE_PLUS_WITH_SPACE) &&
               escaped_text[i] == '+') {
      result.push_back(' ');
    } else {
      // Normal case for unescaped characters.
      result.push_back(escaped_text[i]);
    }
  }

  // Make offset adjustment.
  if (offsets_for_adjustment && !adjustments.empty()) {
    std::for_each(offsets_for_adjustment->begin(),
                   offsets_for_adjustment->end(),
                   net::internal::AdjustEncodingOffset(adjustments));
  }

  return result;
}

template <class str>
void AppendEscapedCharForHTMLImpl(typename str::value_type c, str* output) {
  static const struct {
    char key;
    const char* replacement;
  } kCharsToEscape[] = {
    { '<', "&lt;" },
    { '>', "&gt;" },
    { '&', "&amp;" },
    { '"', "&quot;" },
    { '\'', "&#39;" },
  };
  size_t k;
  for (k = 0; k < ARRAYSIZE_UNSAFE(kCharsToEscape); ++k) {
    if (c == kCharsToEscape[k].key) {
      const char* p = kCharsToEscape[k].replacement;
      while (*p)
        output->push_back(*p++);
      break;
    }
  }
  if (k == ARRAYSIZE_UNSAFE(kCharsToEscape))
    output->push_back(c);
}

template <class str>
str EscapeForHTMLImpl(const str& input) {
  str result;
  result.reserve(input.size());  // Optimize for no escaping.

  for (typename str::const_iterator i = input.begin(); i != input.end(); ++i)
    AppendEscapedCharForHTMLImpl(*i, &result);

  return result;
}

// Everything except alphanumerics and !'()*-._~
// See RFC 2396 for the list of reserved characters.
static const Charmap kQueryCharmap = {{
  0xffffffffL, 0xfc00987dL, 0x78000001L, 0xb8000001L,
  0xffffffffL, 0xffffffffL, 0xffffffffL, 0xffffffffL
}};

// non-printable, non-7bit, and (including space)  "#%:<>?[\]^`{|}
static const Charmap kPathCharmap = {{
  0xffffffffL, 0xd400002dL, 0x78000000L, 0xb8000001L,
  0xffffffffL, 0xffffffffL, 0xffffffffL, 0xffffffffL
}};

// non-printable, non-7bit, and (including space) ?>=<;+'&%$#"![\]^`{|}
static const Charmap kUrlEscape = {{
  0xffffffffL, 0xf80008fdL, 0x78000001L, 0xb8000001L,
  0xffffffffL, 0xffffffffL, 0xffffffffL, 0xffffffffL
}};

// non-7bit
static const Charmap kNonASCIICharmap = {{
  0x00000000L, 0x00000000L, 0x00000000L, 0x00000000L,
  0xffffffffL, 0xffffffffL, 0xffffffffL, 0xffffffffL
}};

// Everything except alphanumerics, the reserved characters(;/?:@&=+$,) and
// !'()*-._~%
static const Charmap kExternalHandlerCharmap = {{
  0xffffffffL, 0x5000080dL, 0x68000000L, 0xb8000001L,
  0xffffffffL, 0xffffffffL, 0xffffffffL, 0xffffffffL
}};

}  // namespace

std::string EscapeQueryParamValue(const std::string& text, bool use_plus) {
  return Escape(text, kQueryCharmap, use_plus);
}

std::string EscapePath(const std::string& path) {
  return Escape(path, kPathCharmap, false);
}

std::string EscapeUrlEncodedData(const std::string& path, bool use_plus) {
  return Escape(path, kUrlEscape, use_plus);
}

std::string EscapeNonASCII(const std::string& input) {
  return Escape(input, kNonASCIICharmap, false);
}

std::string EscapeExternalHandlerValue(const std::string& text) {
  return Escape(text, kExternalHandlerCharmap, false);
}

void AppendEscapedCharForHTML(char c, std::string* output) {
  AppendEscapedCharForHTMLImpl(c, output);
}

std::string EscapeForHTML(const std::string& input) {
  return EscapeForHTMLImpl(input);
}

base::string16 EscapeForHTML(const base::string16& input) {
  return EscapeForHTMLImpl(input);
}

std::string UnescapeURLComponent(const std::string& escaped_text,
                                 UnescapeRule::Type rules) {
  return UnescapeURLWithOffsetsImpl(escaped_text, rules, NULL);
}

base::string16 UnescapeURLComponent(const base::string16& escaped_text,
                                    UnescapeRule::Type rules) {
  return UnescapeURLWithOffsetsImpl(escaped_text, rules, NULL);
}

base::string16 UnescapeAndDecodeUTF8URLComponent(
    const std::string& text,
    UnescapeRule::Type rules,
    size_t* offset_for_adjustment) {
  std::vector<size_t> offsets;
  if (offset_for_adjustment)
    offsets.push_back(*offset_for_adjustment);
  base::string16 result =
      UnescapeAndDecodeUTF8URLComponentWithOffsets(text, rules, &offsets);
  if (offset_for_adjustment)
    *offset_for_adjustment = offsets[0];
  return result;
}

base::string16 UnescapeAndDecodeUTF8URLComponentWithOffsets(
    const std::string& text,
    UnescapeRule::Type rules,
    std::vector<size_t>* offsets_for_adjustment) {
  base::string16 result;
  std::vector<size_t> original_offsets;
  if (offsets_for_adjustment)
    original_offsets = *offsets_for_adjustment;
  std::string unescaped_url(
      UnescapeURLWithOffsetsImpl(text, rules, offsets_for_adjustment));
  if (base::UTF8ToUTF16AndAdjustOffsets(unescaped_url.data(),
                                        unescaped_url.length(),
                                        &result, offsets_for_adjustment))
    return result;  // Character set looks like it's valid.

  // Not valid.  Return the escaped version.  Undo our changes to
  // |offset_for_adjustment| since we haven't changed the string after all.
  if (offsets_for_adjustment)
    *offsets_for_adjustment = original_offsets;
  return base::UTF8ToUTF16AndAdjustOffsets(text, offsets_for_adjustment);
}

base::string16 UnescapeForHTML(const base::string16& input) {
  static const struct {
    const char* ampersand_code;
    const char replacement;
  } kEscapeToChars[] = {
    { "&lt;", '<' },
    { "&gt;", '>' },
    { "&amp;", '&' },
    { "&quot;", '"' },
    { "&#39;", '\''},
  };

  if (input.find(ASCIIToUTF16("&")) == std::string::npos)
    return input;

  base::string16 ampersand_chars[ARRAYSIZE_UNSAFE(kEscapeToChars)];
  base::string16 text(input);
  for (base::string16::iterator iter = text.begin();
       iter != text.end(); ++iter) {
    if (*iter == '&') {
      // Potential ampersand encode char.
      size_t index = iter - text.begin();
      for (size_t i = 0; i < ARRAYSIZE_UNSAFE(kEscapeToChars); i++) {
        if (ampersand_chars[i].empty())
          ampersand_chars[i] = ASCIIToUTF16(kEscapeToChars[i].ampersand_code);
        if (text.find(ampersand_chars[i], index) == index) {
          text.replace(iter, iter + ampersand_chars[i].length(),
                       1, kEscapeToChars[i].replacement);
          break;
        }
      }
    }
  }
  return text;
}

namespace internal {

AdjustEncodingOffset::AdjustEncodingOffset(const Adjustments& adjustments)
  : adjustments(adjustments) {}

void AdjustEncodingOffset::operator()(size_t& offset) {
  // For each encoded character occurring before an offset subtract 2.
  if (offset == base::string16::npos)
    return;
  size_t adjusted_offset = offset;
  for (Adjustments::const_iterator i = adjustments.begin();
       i != adjustments.end(); ++i) {
    size_t location = *i;
    if (offset <= location) {
      offset = adjusted_offset;
      return;
    }
    if (offset <= (location + 2)) {
      offset = base::string16::npos;
      return;
    }
    adjusted_offset -= 2;
  }
  offset = adjusted_offset;
}

}  // namespace internal

}  // namespace net