LCOV - code coverage report
Current view: directory - toolkit/crashreporter/google-breakpad/src/common - byte_cursor.h (source / functions) Found Hit Coverage
Test: app.info Lines: 31 0 0.0 %
Date: 2012-06-02 Functions: 11 0 0.0 %

       1                 : // -*- mode: c++ -*-
       2                 : 
       3                 : // Copyright (c) 2010, Google Inc.
       4                 : // All rights reserved.
       5                 : //
       6                 : // Redistribution and use in source and binary forms, with or without
       7                 : // modification, are permitted provided that the following conditions are
       8                 : // met:
       9                 : //
      10                 : //     * Redistributions of source code must retain the above copyright
      11                 : // notice, this list of conditions and the following disclaimer.
      12                 : //     * Redistributions in binary form must reproduce the above
      13                 : // copyright notice, this list of conditions and the following disclaimer
      14                 : // in the documentation and/or other materials provided with the
      15                 : // distribution.
      16                 : //     * Neither the name of Google Inc. nor the names of its
      17                 : // contributors may be used to endorse or promote products derived from
      18                 : // this software without specific prior written permission.
      19                 : //
      20                 : // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
      21                 : // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
      22                 : // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
      23                 : // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
      24                 : // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
      25                 : // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
      26                 : // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
      27                 : // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
      28                 : // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
      29                 : // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
      30                 : // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
      31                 : 
      32                 : // Original author: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com>
      33                 : 
      34                 : // byte_cursor.h: Classes for parsing values from a buffer of bytes.
      35                 : // The ByteCursor class provides a convenient interface for reading
      36                 : // fixed-size integers of arbitrary endianness, being thorough about
      37                 : // checking for buffer overruns.
      38                 : 
      39                 : #ifndef COMMON_BYTE_CURSOR_H_
      40                 : #define COMMON_BYTE_CURSOR_H_
      41                 : 
      42                 : #include <assert.h>
      43                 : #include <stdint.h>
      44                 : #include <stdlib.h>
      45                 : #include <string.h>
      46                 : #include <string>
      47                 : 
      48                 : namespace google_breakpad {
      49                 : 
      50                 : // A buffer holding a series of bytes.
      51                 : struct ByteBuffer {
      52                 :   ByteBuffer() : start(0), end(0) { }
      53               0 :   ByteBuffer(const uint8_t *set_start, size_t set_size)
      54               0 :       : start(set_start), end(set_start + set_size) { }
      55               0 :   ~ByteBuffer() { };
      56                 : 
      57                 :   // Equality operators. Useful in unit tests, and when we're using
      58                 :   // ByteBuffers to refer to regions of a larger buffer.
      59                 :   bool operator==(const ByteBuffer &that) const {
      60                 :     return start == that.start && end == that.end;
      61                 :   }
      62                 :   bool operator!=(const ByteBuffer &that) const {
      63                 :     return start != that.start || end != that.end;
      64                 :   }
      65                 : 
      66                 :   // Not C++ style guide compliant, but this definitely belongs here.
      67               0 :   size_t Size() const {
      68               0 :     assert(start <= end);
      69               0 :     return end - start;
      70                 :   }
      71                 : 
      72                 :   const uint8_t *start, *end;
      73                 : };
      74                 : 
      75                 : // A cursor pointing into a ByteBuffer that can parse numbers of various
      76                 : // widths and representations, strings, and data blocks, advancing through
      77                 : // the buffer as it goes. All ByteCursor operations check that accesses
      78                 : // haven't gone beyond the end of the enclosing ByteBuffer.
      79                 : class ByteCursor {
      80                 :  public:
      81                 :   // Create a cursor reading bytes from the start of BUFFER. By default, the
      82                 :   // cursor reads multi-byte values in little-endian form.
      83               0 :   ByteCursor(const ByteBuffer *buffer, bool big_endian = false)
      84                 :       : buffer_(buffer), here_(buffer->start), 
      85               0 :         big_endian_(big_endian), complete_(true) { }
      86                 : 
      87                 :   // Accessor and setter for this cursor's endianness flag.
      88                 :   bool big_endian() const { return big_endian_; }
      89                 :   void set_big_endian(bool big_endian) { big_endian_ = big_endian; }
      90                 : 
      91                 :   // Accessor and setter for this cursor's current position. The setter
      92                 :   // returns a reference to this cursor.
      93                 :   const uint8_t *here() const { return here_; }
      94                 :   ByteCursor &set_here(const uint8_t *here) {
      95                 :     assert(buffer_->start <= here && here <= buffer_->end);
      96                 :     here_ = here;
      97                 :     return *this;
      98                 :   }
      99                 : 
     100                 :   // Return the number of bytes available to read at the cursor.
     101               0 :   size_t Available() const { return size_t(buffer_->end - here_); }
     102                 : 
     103                 :   // Return true if this cursor is at the end of its buffer.
     104                 :   bool AtEnd() const { return Available() == 0; }
     105                 : 
     106                 :   // When used as a boolean value this cursor converts to true if all
     107                 :   // prior reads have been completed, or false if we ran off the end
     108                 :   // of the buffer.
     109               0 :   operator bool() const { return complete_; }
     110                 : 
     111                 :   // Read a SIZE-byte integer at this cursor, signed if IS_SIGNED is true,
     112                 :   // unsigned otherwise, using the cursor's established endianness, and set
     113                 :   // *RESULT to the number. If we read off the end of our buffer, clear
     114                 :   // this cursor's complete_ flag, and store a dummy value in *RESULT.
     115                 :   // Return a reference to this cursor.
     116                 :   template<typename T>
     117               0 :   ByteCursor &Read(size_t size, bool is_signed, T *result) {
     118               0 :     if (CheckAvailable(size)) {
     119               0 :       T v = 0;
     120               0 :       if (big_endian_) {
     121               0 :         for (size_t i = 0; i < size; i++)
     122               0 :           v = (v << 8) + here_[i];
     123                 :       } else {
     124                 :         // This loop condition looks weird, but size_t is unsigned, so
     125                 :         // decrementing i after it is zero yields the largest size_t value.
     126               0 :         for (size_t i = size - 1; i < size; i--)
     127               0 :           v = (v << 8) + here_[i];
     128                 :       }
     129               0 :       if (is_signed && size < sizeof(T)) {
     130               0 :         size_t sign_bit = (T)1 << (size * 8 - 1);
     131               0 :         v = (v ^ sign_bit) - sign_bit;
     132                 :       }
     133               0 :       here_ += size;
     134               0 :       *result = v;
     135                 :     } else {
     136               0 :       *result = (T) 0xdeadbeef;
     137                 :     }
     138               0 :     return *this;
     139                 :   }
     140                 : 
     141                 :   // Read an integer, using the cursor's established endianness and
     142                 :   // *RESULT's size and signedness, and set *RESULT to the number. If we
     143                 :   // read off the end of our buffer, clear this cursor's complete_ flag.
     144                 :   // Return a reference to this cursor.
     145                 :   template<typename T>
     146                 :   ByteCursor &operator>>(T &result) {
     147                 :     bool T_is_signed = (T)-1 < 0;
     148                 :     return Read(sizeof(T), T_is_signed, &result); 
     149                 :   }
     150                 : 
     151                 :   // Copy the SIZE bytes at the cursor to BUFFER, and advance this
     152                 :   // cursor to the end of them. If we read off the end of our buffer,
     153                 :   // clear this cursor's complete_ flag, and set *POINTER to NULL.
     154                 :   // Return a reference to this cursor.
     155                 :   ByteCursor &Read(uint8_t *buffer, size_t size) {
     156                 :     if (CheckAvailable(size)) {
     157                 :       memcpy(buffer, here_, size);
     158                 :       here_ += size;
     159                 :     }
     160                 :     return *this;
     161                 :   }
     162                 : 
     163                 :   // Set STR to a copy of the '\0'-terminated string at the cursor. If the
     164                 :   // byte buffer does not contain a terminating zero, clear this cursor's
     165                 :   // complete_ flag, and set STR to the empty string. Return a reference to
     166                 :   // this cursor.
     167                 :   ByteCursor &CString(std::string *str) {
     168                 :     const uint8_t *end
     169                 :       = static_cast<const uint8_t *>(memchr(here_, '\0', Available()));
     170                 :     if (end) {
     171                 :       str->assign(reinterpret_cast<const char *>(here_), end - here_);
     172                 :       here_ = end + 1;
     173                 :     } else {
     174                 :       str->clear();
     175                 :       here_ = buffer_->end;
     176                 :       complete_ = false;
     177                 :     }
     178                 :     return *this;
     179                 :   }
     180                 : 
     181                 :   // Like CString(STR), but extract the string from a fixed-width buffer
     182                 :   // LIMIT bytes long, which may or may not contain a terminating '\0'
     183                 :   // byte. Specifically:
     184                 :   //
     185                 :   // - If there are not LIMIT bytes available at the cursor, clear the
     186                 :   //   cursor's complete_ flag and set STR to the empty string.
     187                 :   //
     188                 :   // - Otherwise, if the LIMIT bytes at the cursor contain any '\0'
     189                 :   //   characters, set *STR to a copy of the bytes before the first '\0',
     190                 :   //   and advance the cursor by LIMIT bytes.
     191                 :   //   
     192                 :   // - Otherwise, set *STR to a copy of those LIMIT bytes, and advance the
     193                 :   //   cursor by LIMIT bytes.
     194                 :   ByteCursor &CString(std::string *str, size_t limit) {
     195                 :     if (CheckAvailable(limit)) {
     196                 :       const uint8_t *end
     197                 :         = static_cast<const uint8_t *>(memchr(here_, '\0', limit));
     198                 :       if (end)
     199                 :         str->assign(reinterpret_cast<const char *>(here_), end - here_);
     200                 :       else
     201                 :         str->assign(reinterpret_cast<const char *>(here_), limit);
     202                 :       here_ += limit;
     203                 :     } else {
     204                 :       str->clear();
     205                 :     }
     206                 :     return *this;
     207                 :   }
     208                 : 
     209                 :   // Set *POINTER to point to the SIZE bytes at the cursor, and advance
     210                 :   // this cursor to the end of them. If SIZE is omitted, don't move the
     211                 :   // cursor. If we read off the end of our buffer, clear this cursor's
     212                 :   // complete_ flag, and set *POINTER to NULL. Return a reference to this
     213                 :   // cursor.
     214                 :   ByteCursor &PointTo(const uint8_t **pointer, size_t size = 0) {
     215                 :     if (CheckAvailable(size)) {
     216                 :       *pointer = here_;
     217                 :       here_ += size;
     218                 :     } else {
     219                 :       *pointer = NULL;
     220                 :     }
     221                 :     return *this;
     222                 :   }
     223                 : 
     224                 :   // Skip SIZE bytes at the cursor. If doing so would advance us off
     225                 :   // the end of our buffer, clear this cursor's complete_ flag, and
     226                 :   // set *POINTER to NULL. Return a reference to this cursor.
     227                 :   ByteCursor &Skip(size_t size) {
     228                 :     if (CheckAvailable(size))
     229                 :       here_ += size;
     230                 :     return *this;
     231                 :   }
     232                 : 
     233                 :  private:
     234                 :   // If there are at least SIZE bytes available to read from the buffer,
     235                 :   // return true. Otherwise, set here_ to the end of the buffer, set
     236                 :   // complete_ to false, and return false.
     237               0 :   bool CheckAvailable(size_t size) {
     238               0 :     if (Available() >= size) {
     239               0 :       return true;
     240                 :     } else {
     241               0 :       here_ = buffer_->end;
     242               0 :       complete_ = false;
     243               0 :       return false;
     244                 :     }
     245                 :   }
     246                 : 
     247                 :   // The buffer we're reading bytes from.
     248                 :   const ByteBuffer *buffer_;
     249                 : 
     250                 :   // The next byte within buffer_ that we'll read.
     251                 :   const uint8_t *here_;
     252                 : 
     253                 :   // True if we should read numbers in big-endian form; false if we
     254                 :   // should read in little-endian form.
     255                 :   bool big_endian_;
     256                 : 
     257                 :   // True if we've been able to read all we've been asked to.
     258                 :   bool complete_;
     259                 : };
     260                 : 
     261                 : }  // namespace google_breakpad
     262                 : 
     263                 : #endif  // COMMON_BYTE_CURSOR_H_

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