| // -*- mode: c++ -*- |
| |
| // Copyright (c) 2010, Google Inc. |
| // All rights reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| // Original author: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com> |
| |
| // byte_cursor.h: Classes for parsing values from a buffer of bytes. |
| // The ByteCursor class provides a convenient interface for reading |
| // fixed-size integers of arbitrary endianness, being thorough about |
| // checking for buffer overruns. |
| |
| #ifndef COMMON_BYTE_CURSOR_H_ |
| #define COMMON_BYTE_CURSOR_H_ |
| |
| #include <assert.h> |
| #include <stdint.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <string> |
| |
| #include "common/using_std_string.h" |
| |
| namespace google_breakpad { |
| |
| // A buffer holding a series of bytes. |
| struct ByteBuffer { |
| ByteBuffer() : start(0), end(0) { } |
| ByteBuffer(const uint8_t* set_start, size_t set_size) |
| : start(set_start), end(set_start + set_size) { } |
| ~ByteBuffer() { }; |
| |
| // Equality operators. Useful in unit tests, and when we're using |
| // ByteBuffers to refer to regions of a larger buffer. |
| bool operator==(const ByteBuffer& that) const { |
| return start == that.start && end == that.end; |
| } |
| bool operator!=(const ByteBuffer& that) const { |
| return start != that.start || end != that.end; |
| } |
| |
| // Not C++ style guide compliant, but this definitely belongs here. |
| size_t Size() const { |
| assert(start <= end); |
| return end - start; |
| } |
| |
| const uint8_t* start; |
| const uint8_t* end; |
| }; |
| |
| // A cursor pointing into a ByteBuffer that can parse numbers of various |
| // widths and representations, strings, and data blocks, advancing through |
| // the buffer as it goes. All ByteCursor operations check that accesses |
| // haven't gone beyond the end of the enclosing ByteBuffer. |
| class ByteCursor { |
| public: |
| // Create a cursor reading bytes from the start of BUFFER. By default, the |
| // cursor reads multi-byte values in little-endian form. |
| ByteCursor(const ByteBuffer* buffer, bool big_endian = false) |
| : buffer_(buffer), here_(buffer->start), |
| big_endian_(big_endian), complete_(true) { } |
| |
| // Accessor and setter for this cursor's endianness flag. |
| bool big_endian() const { return big_endian_; } |
| void set_big_endian(bool big_endian) { big_endian_ = big_endian; } |
| |
| // Accessor and setter for this cursor's current position. The setter |
| // returns a reference to this cursor. |
| const uint8_t* here() const { return here_; } |
| ByteCursor& set_here(const uint8_t* here) { |
| assert(buffer_->start <= here && here <= buffer_->end); |
| here_ = here; |
| return *this; |
| } |
| |
| // Return the number of bytes available to read at the cursor. |
| size_t Available() const { return size_t(buffer_->end - here_); } |
| |
| // Return true if this cursor is at the end of its buffer. |
| bool AtEnd() const { return Available() == 0; } |
| |
| // When used as a boolean value this cursor converts to true if all |
| // prior reads have been completed, or false if we ran off the end |
| // of the buffer. |
| operator bool() const { return complete_; } |
| |
| // Read a SIZE-byte integer at this cursor, signed if IS_SIGNED is true, |
| // unsigned otherwise, using the cursor's established endianness, and set |
| // *RESULT to the number. If we read off the end of our buffer, clear |
| // this cursor's complete_ flag, and store a dummy value in *RESULT. |
| // Return a reference to this cursor. |
| template<typename T> |
| ByteCursor& Read(size_t size, bool is_signed, T* result) { |
| if (CheckAvailable(size)) { |
| T v = 0; |
| if (big_endian_) { |
| for (size_t i = 0; i < size; i++) |
| v = (v << 8) + here_[i]; |
| } else { |
| // This loop condition looks weird, but size_t is unsigned, so |
| // decrementing i after it is zero yields the largest size_t value. |
| for (size_t i = size - 1; i < size; i--) |
| v = (v << 8) + here_[i]; |
| } |
| if (is_signed && size < sizeof(T)) { |
| size_t sign_bit = (T)1 << (size * 8 - 1); |
| v = (v ^ sign_bit) - sign_bit; |
| } |
| here_ += size; |
| *result = v; |
| } else { |
| *result = (T) 0xdeadbeef; |
| } |
| return *this; |
| } |
| |
| // Read an integer, using the cursor's established endianness and |
| // *RESULT's size and signedness, and set *RESULT to the number. If we |
| // read off the end of our buffer, clear this cursor's complete_ flag. |
| // Return a reference to this cursor. |
| template<typename T> |
| ByteCursor& operator>>(T& result) { |
| bool T_is_signed = (T)-1 < 0; |
| return Read(sizeof(T), T_is_signed, &result); |
| } |
| |
| // Copy the SIZE bytes at the cursor to BUFFER, and advance this |
| // cursor to the end of them. If we read off the end of our buffer, |
| // clear this cursor's complete_ flag, and set *POINTER to NULL. |
| // Return a reference to this cursor. |
| ByteCursor& Read(uint8_t* buffer, size_t size) { |
| if (CheckAvailable(size)) { |
| memcpy(buffer, here_, size); |
| here_ += size; |
| } |
| return *this; |
| } |
| |
| // Set STR to a copy of the '\0'-terminated string at the cursor. If the |
| // byte buffer does not contain a terminating zero, clear this cursor's |
| // complete_ flag, and set STR to the empty string. Return a reference to |
| // this cursor. |
| ByteCursor& CString(string* str) { |
| const uint8_t* end |
| = static_cast<const uint8_t*>(memchr(here_, '\0', Available())); |
| if (end) { |
| str->assign(reinterpret_cast<const char*>(here_), end - here_); |
| here_ = end + 1; |
| } else { |
| str->clear(); |
| here_ = buffer_->end; |
| complete_ = false; |
| } |
| return *this; |
| } |
| |
| // Like CString(STR), but extract the string from a fixed-width buffer |
| // LIMIT bytes long, which may or may not contain a terminating '\0' |
| // byte. Specifically: |
| // |
| // - If there are not LIMIT bytes available at the cursor, clear the |
| // cursor's complete_ flag and set STR to the empty string. |
| // |
| // - Otherwise, if the LIMIT bytes at the cursor contain any '\0' |
| // characters, set *STR to a copy of the bytes before the first '\0', |
| // and advance the cursor by LIMIT bytes. |
| // |
| // - Otherwise, set *STR to a copy of those LIMIT bytes, and advance the |
| // cursor by LIMIT bytes. |
| ByteCursor& CString(string* str, size_t limit) { |
| if (CheckAvailable(limit)) { |
| const uint8_t* end |
| = static_cast<const uint8_t*>(memchr(here_, '\0', limit)); |
| if (end) |
| str->assign(reinterpret_cast<const char*>(here_), end - here_); |
| else |
| str->assign(reinterpret_cast<const char*>(here_), limit); |
| here_ += limit; |
| } else { |
| str->clear(); |
| } |
| return *this; |
| } |
| |
| // Set *POINTER to point to the SIZE bytes at the cursor, and advance |
| // this cursor to the end of them. If SIZE is omitted, don't move the |
| // cursor. If we read off the end of our buffer, clear this cursor's |
| // complete_ flag, and set *POINTER to NULL. Return a reference to this |
| // cursor. |
| ByteCursor& PointTo(const uint8_t** pointer, size_t size = 0) { |
| if (CheckAvailable(size)) { |
| *pointer = here_; |
| here_ += size; |
| } else { |
| *pointer = NULL; |
| } |
| return *this; |
| } |
| |
| // Skip SIZE bytes at the cursor. If doing so would advance us off |
| // the end of our buffer, clear this cursor's complete_ flag, and |
| // set *POINTER to NULL. Return a reference to this cursor. |
| ByteCursor& Skip(size_t size) { |
| if (CheckAvailable(size)) |
| here_ += size; |
| return *this; |
| } |
| |
| private: |
| // If there are at least SIZE bytes available to read from the buffer, |
| // return true. Otherwise, set here_ to the end of the buffer, set |
| // complete_ to false, and return false. |
| bool CheckAvailable(size_t size) { |
| if (Available() >= size) { |
| return true; |
| } else { |
| here_ = buffer_->end; |
| complete_ = false; |
| return false; |
| } |
| } |
| |
| // The buffer we're reading bytes from. |
| const ByteBuffer* buffer_; |
| |
| // The next byte within buffer_ that we'll read. |
| const uint8_t* here_; |
| |
| // True if we should read numbers in big-endian form; false if we |
| // should read in little-endian form. |
| bool big_endian_; |
| |
| // True if we've been able to read all we've been asked to. |
| bool complete_; |
| }; |
| |
| } // namespace google_breakpad |
| |
| #endif // COMMON_BYTE_CURSOR_H_ |