Implement BinaryWriter class to allow writing binary data

src/CMakeLists.txt

@@ -79,6 +79,7 @@ set(SOURCES
     anbox/common/loop_device.cpp
     anbox/common/loop_device_allocator.cpp
     anbox/common/mount_entry.cpp
+    anbox/common/binary_writer.cpp
 
     anbox/testing/gtest_utils.h
 

src/anbox/common/binary_writer.cpp

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2016 Thomas Voss <thomas.voss.bochum@gmail.com>
+ *                    Simon Fels <morphis@gravedo.de>
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 3, as published
+ * by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranties of
+ * MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR
+ * PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "anbox/common/binary_writer.h"
+
+#include <cstring>
+#include <stdexcept>
+
+#include <boost/endian/buffers.hpp>
+
+namespace {
+bool is_little_endian() {
+  std::uint32_t v = 1;
+  return (*reinterpret_cast<std::uint8_t*>(&v) ==  1);
+}
+}
+
+namespace anbox {
+namespace common {
+
+BinaryWriter::BinaryWriter(std::vector<std::uint8_t>::iterator begin,
+                           std::vector<std::uint8_t>::iterator end) :
+  begin_{begin}, current_{begin}, end_{end},
+  byte_order_{is_little_endian() ? Order::Little : Order::Big} {}
+
+void BinaryWriter::set_byte_order(Order order) {
+  byte_order_ = order;
+}
+
+void BinaryWriter::write_unsigned_short(std::uint16_t value) {
+  if (current_ + sizeof(value) > end_)
+    throw std::out_of_range{"Write buffer exhausted"};
+
+  std::uint16_t v = value;
+  switch (byte_order_) {
+  case Order::Big:
+    v = boost::endian::native_to_big(value);
+    break;
+  case Order::Little:
+    v = boost::endian::native_to_little(value);
+    break;
+  default:
+    break;
+  }
+
+  *reinterpret_cast<std::uint16_t*>(&(*current_)) = v;
+  current_ += sizeof(v);
+}
+
+void BinaryWriter::write_unsigned_long(std::uint32_t value) {
+  if (current_ + sizeof(value) > end_)
+    throw std::out_of_range{"Write buffer exhausted"};
+
+  std::uint32_t v = value;
+  switch (byte_order_) {
+  case Order::Big:
+    v = boost::endian::native_to_big(value);
+    break;
+  case Order::Little:
+    v = boost::endian::native_to_little(value);
+    break;
+  default:
+    break;
+  }
+
+  *reinterpret_cast<std::uint32_t*>(&(*current_)) = v;
+  current_ += sizeof(v);
+}
+
+void BinaryWriter::write_string(const char *s, std::size_t size) {
+  if (current_ + size > end_)
+    throw std::out_of_range{"Write buffer exhausted"};
+
+  memcpy(&(*current_), s, size);
+  current_ += size;
+}
+
+void BinaryWriter::write_string_with_size(const std::string &str) {
+  write_string_with_size(str.c_str(), str.length());
+}
+
+void BinaryWriter::write_string_with_size(const char *s, std::size_t size) {
+  write_unsigned_short(size);
+  write_string(s, size);
+}
+
+std::size_t BinaryWriter::bytes_written() const {
+  return current_ - begin_;
+}
+} // namespace common
+} // namespace anbox

src/anbox/common/binary_writer.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2016 Thomas Voss <thomas.voss.bochum@gmail.com>
+ *                    Simon Fels <morphis@gravedo.de>
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 3, as published
+ * by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranties of
+ * MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR
+ * PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef ANBOX_COMMON_BINARY_WRITER_H_
+#define ANBOX_COMMON_BINARY_WRITER_H_
+
+#include <cstdint>
+#include <vector>
+#include <string>
+
+namespace anbox {
+namespace common {
+class BinaryWriter {
+ public:
+  enum class Order {
+    Big,
+    Little,
+  };
+
+  explicit BinaryWriter(std::vector<std::uint8_t>::iterator begin_,
+                        std::vector<std::uint8_t>::iterator end_);
+
+  void set_byte_order(Order order);
+
+  void write_unsigned_short(std::uint16_t value);
+  void write_unsigned_long(std::uint32_t value);
+  void write_string(const char *s, std::size_t size);
+  void write_string_with_size(const std::string &str);
+  void write_string_with_size(const char *s, std::size_t size);
+
+  std::size_t bytes_written() const;
+
+ private:
+  std::vector<std::uint8_t>::iterator begin_;
+  std::vector<std::uint8_t>::iterator current_;
+  std::vector<std::uint8_t>::iterator end_;
+  Order byte_order_;
+};
+} // namespace common
+} // namespace anbox
+
+#endif