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