The Tor Browser: security/sandbox/chromium/base/strings/string16.h@141e0f1194b1 (annotated)

security/sandbox/chromium/base/strings/string16.h@141e0f1194b1 (annotated)

security/sandbox/chromium/base/strings/string16.h

Wed, 31 Dec 2014 07:16:47 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 07:16:47 +0100
branch: TOR_BUG_9701
changeset 3: 141e0f1194b1
permissions: -rw-r--r--

Revert simplistic fix pending revisit of Mozilla integration attempt.

 // 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.
 #ifndef BASE_STRINGS_STRING16_H_
 #define BASE_STRINGS_STRING16_H_
 // WHAT:
 // A version of std::basic_string that provides 2-byte characters even when
 // wchar_t is not implemented as a 2-byte type. You can access this class as
 // string16. We also define char16, which string16 is based upon.
 //
 // WHY:
 // On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2
 // data. Plenty of existing code operates on strings encoded as UTF-16.
 //
 // On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make
 // it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails
 // at run time, because it calls some functions (like wcslen) that come from
 // the system's native C library -- which was built with a 4-byte wchar_t!
 // It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's
 // entirely improper on those systems where the encoding of wchar_t is defined
 // as UTF-32.
 //
 // Here, we define string16, which is similar to std::wstring but replaces all
 // libc functions with custom, 2-byte-char compatible routines. It is capable
 // of carrying UTF-16-encoded data.
 #include <stdio.h>
 #include <string>
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #if defined(WCHAR_T_IS_UTF16)
 namespace base {
 typedef wchar_t char16;
 typedef std::wstring string16;
 typedef std::char_traits<wchar_t> string16_char_traits;
 }  // namespace base
 #elif defined(WCHAR_T_IS_UTF32)
 namespace base {
 typedef uint16 char16;
 // char16 versions of the functions required by string16_char_traits; these
 // are based on the wide character functions of similar names ("w" or "wcs"
 // instead of "c16").
 BASE_EXPORT int c16memcmp(const char16* s1, const char16* s2, size_t n);
 BASE_EXPORT size_t c16len(const char16* s);
 BASE_EXPORT const char16* c16memchr(const char16* s, char16 c, size_t n);
 BASE_EXPORT char16* c16memmove(char16* s1, const char16* s2, size_t n);
 BASE_EXPORT char16* c16memcpy(char16* s1, const char16* s2, size_t n);
 BASE_EXPORT char16* c16memset(char16* s, char16 c, size_t n);
 struct string16_char_traits {
   typedef char16 char_type;
   typedef int int_type;
   // int_type needs to be able to hold each possible value of char_type, and in
   // addition, the distinct value of eof().
   COMPILE_ASSERT(sizeof(int_type) > sizeof(char_type), unexpected_type_width);
   typedef std::streamoff off_type;
   typedef mbstate_t state_type;
   typedef std::fpos<state_type> pos_type;
   static void assign(char_type& c1, const char_type& c2) {
     c1 = c2;
   }
   static bool eq(const char_type& c1, const char_type& c2) {
     return c1 == c2;
   }
   static bool lt(const char_type& c1, const char_type& c2) {
     return c1 < c2;
   }
   static int compare(const char_type* s1, const char_type* s2, size_t n) {
     return c16memcmp(s1, s2, n);
   }
   static size_t length(const char_type* s) {
     return c16len(s);
   }
   static const char_type* find(const char_type* s, size_t n,
                                const char_type& a) {
     return c16memchr(s, a, n);
   }
   static char_type* move(char_type* s1, const char_type* s2, int_type n) {
     return c16memmove(s1, s2, n);
   }
   static char_type* copy(char_type* s1, const char_type* s2, size_t n) {
     return c16memcpy(s1, s2, n);
   }
   static char_type* assign(char_type* s, size_t n, char_type a) {
     return c16memset(s, a, n);
   }
   static int_type not_eof(const int_type& c) {
     return eq_int_type(c, eof()) ? 0 : c;
   }
   static char_type to_char_type(const int_type& c) {
     return char_type(c);
   }
   static int_type to_int_type(const char_type& c) {
     return int_type(c);
   }
   static bool eq_int_type(const int_type& c1, const int_type& c2) {
     return c1 == c2;
   }
   static int_type eof() {
     return static_cast<int_type>(EOF);
   }
 };
 typedef std::basic_string<char16, base::string16_char_traits> string16;
 BASE_EXPORT extern std::ostream& operator<<(std::ostream& out,
                                             const string16& str);
 // This is required by googletest to print a readable output on test failures.
 BASE_EXPORT extern void PrintTo(const string16& str, std::ostream* out);
 }  // namespace base
 // The string class will be explicitly instantiated only once, in string16.cc.
 //
 // std::basic_string<> in GNU libstdc++ contains a static data member,
 // _S_empty_rep_storage, to represent empty strings.  When an operation such
 // as assignment or destruction is performed on a string, causing its existing
 // data member to be invalidated, it must not be freed if this static data
 // member is being used.  Otherwise, it counts as an attempt to free static
 // (and not allocated) data, which is a memory error.
 //
 // Generally, due to C++ template magic, _S_empty_rep_storage will be marked
 // as a coalesced symbol, meaning that the linker will combine multiple
 // instances into a single one when generating output.
 //
 // If a string class is used by multiple shared libraries, a problem occurs.
 // Each library will get its own copy of _S_empty_rep_storage.  When strings
 // are passed across a library boundary for alteration or destruction, memory
 // errors will result.  GNU libstdc++ contains a configuration option,
 // --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which
 // disables the static data member optimization, but it's a good optimization
 // and non-STL code is generally at the mercy of the system's STL
 // configuration.  Fully-dynamic strings are not the default for GNU libstdc++
 // libstdc++ itself or for the libstdc++ installations on the systems we care
 // about, such as Mac OS X and relevant flavors of Linux.
 //
 // See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 .
 //
 // To avoid problems, string classes need to be explicitly instantiated only
 // once, in exactly one library.  All other string users see it via an "extern"
 // declaration.  This is precisely how GNU libstdc++ handles
 // std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring).
 //
 // This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2),
 // in which the linker does not fully coalesce symbols when dead code
 // stripping is enabled.  This bug causes the memory errors described above
 // to occur even when a std::basic_string<> does not cross shared library
 // boundaries, such as in statically-linked executables.
 //
 // TODO(mark): File this bug with Apple and update this note with a bug number.
 extern template
 class BASE_EXPORT std::basic_string<base::char16, base::string16_char_traits>;
 #endif  // WCHAR_T_IS_UTF32
 // TODO(brettw) update users of string16 to use the namespace and remove
 // this "using".
 using base::char16;
 using base::string16;
 #endif  // BASE_STRINGS_STRING16_H_

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security/sandbox/chromium/base/strings/string16.h@141e0f1194b1 (annotated)

security/sandbox/chromium/base/strings/string16.h