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// -*- 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
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// 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_