LCOV - app.info - toolkit/crashreporter/google-breakpad/src/common/byte_cursor.h

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: | 2012-04-07 | 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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