### Installing libtorrent with VCPKG

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Instructions for cloning the vcpkg repository, bootstrapping it, integrating it with the system, and then installing libtorrent.

```bash
git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
./bootstrap-vcpkg.sh
./vcpkg integrate install
./vcpkg install libtorrent
```

--------------------------------

### Install libtorrent with b2

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Use the 'b2 install' command to install libtorrent. The --prefix argument specifies the installation directory.

```bash
b2 install --prefix=/usr/local
```

--------------------------------

### Simple libtorrent Client Example

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

A basic example demonstrating the usage of the libtorrent Python module. This snippet is intended to be a starting point for understanding the API.

```python
from __future__ import print_function

import libtorrent as lt
import time
import sys

print('starting torrent client')

# create a session object
s = lt.session()

# set the download rate limit to 200 KB/s
s.set_download_rate_limit(200 * 1024)

# create a torrent status alert object
alert = lt.torrent_alert

# set up the alert handler
def handle_alert(alert):
    if alert.what() == lt.alert.alert_type.torrent_alert:
        print(alert.message)

s.set_alert_handler(handle_alert)

# add a torrent to the session
info = lt.torrent_info("test.torrent")
handle = s.add_torrent(info)

print('torrent added')

# wait for the torrent to finish downloading
while not handle.is_seed():
    s.post_torrent_updates()
    time.sleep(1)

print('torrent finished')

```

--------------------------------

### Install libtorrent Python module with setup.py

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Use this command to install the libtorrent Python module into your current Python environment after building.

```bash
python setup.py install
```

--------------------------------

### Build and install with custom b2 arguments

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

When customizing the build with b2 arguments, run steps like 'install' inline with 'build_ext' to ensure the custom arguments are applied.

```bash
python setup.py build_ext --b2-args="optimization=space" install
```

--------------------------------

### Define Single File Examples

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/examples/CMakeLists.txt

Defines a list of example applications that are built from a single source file.

```cmake
set(single_file_examples
    simple_client
    custom_storage
    stats_counters
    dump_torrent
    dump_bdecode
    make_torrent
    connection_tester
    upnp_test)

```

--------------------------------

### Install Header Files

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/CMakeLists.txt

Installs the public header files for libtorrent from the 'include/libtorrent' directory.

```cmake
install(DIRECTORY include/libtorrent DESTINATION ${CMAKE_INSTALL_INCLUDEDIR} FILES_MATCHING PATTERN "*.h*")
```

--------------------------------

### Install Python Module to User Site

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Builds and installs the Python module to the user's site-packages directory. This is the default installation scope.

```bash
b2 release python=3.7 install_module
```

--------------------------------

### Simple libtorrent Client Example

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/examples.rst

A basic libtorrent client demonstrating core functionalities. Ensure necessary imports for libtorrent are included.

```cpp
#include <libtorrent/session.hpp>
#include <libtorrent/torrent_handle.hpp>
#include <libtorrent/add_torrent_params.hpp>
#include <libtorrent/alert_types.hpp>
#include <libtorrent/read_resume_data.hpp>
#include <libtorrent/write_resume_data.hpp>

#include <iostream>
#include <fstream>
#include <vector>

int main(int argc, char* argv[])
{
	using namespace libtorrent;

	// Initialize libtorrent session
	session ses;

	// Add a torrent to the session
	// For simplicity, this example assumes a torrent file is available
	// In a real client, you would typically get this from a user or network
	// For demonstration, let's assume a dummy torrent file path
	// std::string torrent_file_path = "/path/to/your/torrent.torrent";
	// torrent_handle th = ses.add_torrent(torrent_file_path);

	// This is a placeholder for actual torrent addition logic
	std::cout << "Simple client started. Add torrents to begin." << std::endl;

	// Example of handling alerts (e.g., download progress, errors)
	// alert_ptr alert;
	// while ((alert = ses.wait_for_alert(milliseconds(100)))) {
	// 	if (auto bt_alert = alert_cast<torrent_update_alert>(alert.get())) {
	// 		// Handle torrent update
	// 	}
	// }

	return 0;
}
```

--------------------------------

### Build a binary wheel package with setup.py

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

First, install the wheel package, then use this command to build a binary wheel package for the libtorrent Python module.

```bash
python -m pip install wheel
python setup.py bdist_wheel
```

--------------------------------

### Example: Non-blocking Operations and Resume Data

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/tutorial.rst

This example demonstrates using non-blocking calls like async_add_torrent(), handling torrent status updates, and managing resume data by saving and loading it.

```c++
#include <libtorrent/session.hpp>
#include <libtorrent/torrent_handle.hpp>
#include <libtorrent/add_torrent_params.hpp>
#include <libtorrent/alert.hpp>
#include <libtorrent/state_update_alert.hpp>
#include <libtorrent/save_resume_data_alert.hpp>
#include <libtorrent/read_resume_data.hpp>
#include <libtorrent/write_resume_data.hpp>

#include <iostream>
#include <vector>
#include <fstream>

#ifdef _WIN32
#include <winsock2.inc>
#endif

using namespace libtorrent;

// Helper function to write resume data to a file
void write_resume_data(const add_torrent_params& p, const char* filename)
{
	std::vector<char> buf;
	write_resume_data_buf(buf, p);

	std::ofstream file(filename, std::ios::binary);
	file.write(buf.data(), buf.size());
}

// Helper function to read resume data from a file
std::unique_ptr<add_torrent_params> read_resume_data(const char* filename)
{
	std::ifstream file(filename, std::ios::binary);
	if (!file.is_open()) return nullptr;

	file.seekg(0, std::ios::end);
	size_t size = file.tellg();
	file.seekg(0, std::ios::beg);

	std::vector<char> buf(size);
	if (!file.read(buf.data(), size))
		return nullptr;

	return read_resume_data_from_buf(buf);
}

int main(int argc, char* argv[])
{
#ifdef _WIN32
	WSADATA wsa;
	WSAStartup(MAKEWORD(2, 2), &wsa);
#endif

	session ses;

	// Load session state if available
	if (auto p = read_resume_data("session.resume"))
	{
		ses.apply_settings(*p);
	}

	// Load torrents from resume data
	std::vector<add_torrent_params> torrents_to_add;
	for (int i = 1; i < argc; ++i)
	{
		if (auto p = read_resume_data(argv[i]))
		{
			torrents_to_add.push_back(*p);
		}
	}

	// If no torrents were loaded, add a new one from a .torrent file or URL
	if (torrents_to_add.empty() && argc > 1)
	{
		add_torrent_params p;
		p.url = argv[1];
		orrents_to_add.push_back(p);
	}

	// Add torrents to the session
	std::vector<torrent_handle> handles;
	for (const auto& p : torrents_to_add)
	{
		handles.push_back(ses.add_torrent(p));
	}

	// Main loop to process alerts
	while (true)
	{
		sstd::vector<alert*> alerts;
		ses.pop_alerts(alerts);

		bool shutdown = false;
		for (const auto* a : alerts)
		{
			std::cout << *a << std::endl;

			// Handle state update alerts
			if (auto* st = alert_cast<state_update_alert>(a))
			{
				for (const auto& status : st->status)
				{
					std::cout << "Torrent: " << status.name << std::endl;
					std::cout << "  Progress: " << status.progress_ppm / 10000.0 << std::endl;
					std::cout << "  State: " << torrent_state_to_string(status.state) << std::endl;
				}
			}

			// Handle save resume data alerts
			if (auto* sd = alert_cast<save_resume_data_alert>(a))
			{
				write_resume_data(sd->params, "session.resume");
				ses.remove_torrent(sd->handle);
			}

			// Handle save resume data failed alerts
			if (auto* sf = alert_cast<save_resume_data_failed_alert>(a))
			{
				std::cerr << "Failed to save resume data for torrent: " << sf->handle.name() << std::endl;
				ses.remove_torrent(sf->handle);
			}

			// Check for shutdown condition (e.t., user input or specific alert)
			// For simplicity, we'll break after a few seconds or if all torrents are done
			if (a->category() & alert::status_notification)
			{
				bool all_done = true;
				for (const auto& h : handles)
				{
					if (h.is_valid() && h.status().state != torrent_metainfo::seeding && h.status().state != torrent_metainfo::finished)
					{
						all_done = false;
						break;
					}
				}
				if (all_done)
				{
					shutdown = true;
					break;
				}
			}
		}

		if (shutdown)
		{
			// Save resume data for all torrents before shutting down
			for (auto& h : handles)
			{
				if (h.is_valid())
					h.save_resume_data();
			}
			// Wait for save_resume_data_alerts to be processed
			// In a real application, you'd have a more robust shutdown mechanism
			break;
		}

		// Post torrent updates to get status changes
		ses.post_torrent_updates();

		// Sleep for a short duration to avoid busy-waiting
		std::this_thread::sleep_for(std::chrono::milliseconds(100));
	}

	// Save session state before exiting
	auto session_params = ses.session_state();
	write_resume_data(session_params, "session.resume");

#ifdef _WIN32
	WSACleanup();
#endif

	return 0;
}
```

--------------------------------

### Install Find Module

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/CMakeLists.txt

Installs the FindLibtorrentRasterbar.cmake module, which helps other projects find the installed libtorrent library.

```cmake
install(
	FILES
		${CMAKE_CURRENT_SOURCE_DIR}/examples/cmake/FindLibtorrentRasterbar.cmake
	DESTINATION
		${CMAKE_INSTALL_DATADIR}/cmake/Modules
)
```

--------------------------------

### Generate and Install Pkg-Config File

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/CMakeLists.txt

Generates and installs the pkg-config file for the library, excluding MSVC builds. This is primarily for Linux-like environments.

```cmake
if (NOT MSVC)
	generate_and_install_pkg_config_file(torrent-rasterbar libtorrent-rasterbar)
endif()
```

--------------------------------

### Configure Python for b2 build

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Update the user-config.jam file to help b2 locate your Python installation. This example shows a basic configuration for Python 3.7.

```jam
using python : 3.7 ;
```

--------------------------------

### Install Python Extension Module

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/bindings/python/CMakeLists.txt

Installs the compiled 'python-libtorrent' target to the determined Python 3 site-packages directory.

```cmake
install(TARGETS python-libtorrent DESTINATION "${_PYTHON3_SITE_ARCH}")
```

--------------------------------

### Install Library Targets

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/CMakeLists.txt

Installs the main library target 'torrent-rasterbar' with its associated files to the specified destinations based on CMake variables.

```cmake
install(TARGETS torrent-rasterbar EXPORT LibtorrentRasterbarTargets
	LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
	ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
	RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)
```

--------------------------------

### Dump Torrent Information using libtorrent

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/examples.rst

This example shows how to read a torrent file and print its metadata to standard output. It requires a valid torrent file path as a command-line argument.

```cpp
#include <libtorrent/torrent_info.hpp>
#include <libtorrent/read_torrent_limits.hpp>

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

int main(int argc, char* argv[])
{
	if (argc != 2) {
		std::cerr << "Usage: " << argv[0] << " <torrent_file>\n";
		return 1;
	}

	std::string torrent_file_path = argv[1];

	try {
		// Load torrent information from file
		libtorrent::torrent_info ti(torrent_file_path);

		// Print basic torrent information
		std::cout << "Torrent Name: " << ti.name() << std::endl;
		std::cout << "Total Size: " << ti.total_size() << " bytes" << std::endl;
		std::cout << "Number of Pieces: " << ti.num_pieces() << std::endl;
		std::cout << "Piece Size: " << ti.piece_size() << " bytes" << std::endl;

		// You can access more details like file list, trackers, etc.
		// For example, to list files:
		// std::cout << "Files:" << std::endl;
		// for (const auto& file_entry : ti.files()) {
		// 	std::cout << "  - " << file_entry.path.string() << " (" << file_entry.size << " bytes)" << std::endl;
		// }

	} catch (const std::exception& e) {
		std::cerr << "Error loading torrent file: " << e.what() << std::endl;
		return 1;
	}

	return 0;
}
```

--------------------------------

### Build with Boost Build on Linux

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Install necessary Boost development packages and build libtorrent using boost-build with OpenSSL and C++14 standard.

```bash
sudo apt install libboost-tools-dev libboost-dev libboost-system-dev
echo "using gcc ;" >>~/user-config.jam
b2 crypto=openssl cxxstd=14 release
```

--------------------------------

### Build with Boost Build on macOS

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Install Boost Build and Boost libraries using Homebrew, configure the user-config.jam, and build libtorrent with OpenSSL and C++14.

```bash
brew install boost-build boost openssl@3
echo "using darwin ;" >>~/user-config.jam
b2 crypto=openssl cxxstd=14 release
```

--------------------------------

### Install Python Module to System Site

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Installs the Python module to the system's site-packages directory. Requires specifying the 'python-install-scope=system' feature.

```bash
b2 release python=3.7 install_module python-install-scope=system
```

--------------------------------

### Building OpenSSL for Windows with Visual Studio 7.1

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Execute these commands in a command shell to build OpenSSL for Windows using Visual Studio 7.1 (2003). This process installs headers and library files into the Visual Studio directories for libtorrent to use.

```bash
perl Configure VC-WIN32 --prefix="c:/openssl"
call ms\do_nasm
call "C:\Program Files\Microsoft Visual Studio .NET 2003\vc7\bin\vcvars32.bat"
nmake -f ms\nt.mak
copy inc32\openssl "C:\Program Files\Microsoft Visual Studio .NET 2003\vc7\include\"
copy out32\libeay32.lib "C:\Program Files\Microsoft Visual Studio .NET 2003\vc7\lib"
copy out32\ssleay32.lib "C:\Program Files\Microsoft Visual Studio .NET 2003\vc7\lib"
```

--------------------------------

### Build Single File Executables

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/examples/CMakeLists.txt

Iterates through the list of single-file examples and creates an executable for each, linking against the 'torrent-rasterbar' library.

```cmake
foreach(example ${single_file_examples})
    add_executable(${example} "${example}.cpp")
    target_link_libraries(${example} PRIVATE torrent-rasterbar)
endforeach(example)

```

--------------------------------

### Configure Boost Build with Clang (Linux Example)

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/fuzzers/README.rst

This configuration is used for Boost Build (b2) to specify the use of the system's Clang compiler.

```bash
using clang ;
```

--------------------------------

### Process Alerts and Monitor Torrent Completion

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/tutorial.rst

Extends the previous example to continuously poll the session for alerts, print them, and specifically listen for the torrent_finished_alert to know when a download is complete.

```c++
/*
 * This is an example of how to use libtorrent to download a torrent.
 * It demonstrates how to set up a session, add a torrent, and
 * process alerts to monitor download progress and completion.
 */

#include <libtorrent/session.hpp>
#include <libtorrent/torrent_handle.hpp>
#include <libtorrent/alert.hpp>
#include <libtorrent/alert_types.hpp>
#include <libtorrent/magnet_uri.hpp>
#include <libtorrent/add_torrent_params.hpp>

#include <iostream>
#include <vector>
#include <chrono>
#include <thread>

int main(int argc, char const* argv[])
{
	if (argc != 2) {
		std::cerr << "usage: " << argv[0] << " <magnet-url>\n";
		return 1;
	}

	// Initialize libtorrent session
	lt::session ses;

	// Parse magnet URI and set save path
	lt::add_torrent_params atp = lt::parse_magnet_uri(argv[1]);
	atp.save_path = "."; // Save in the current directory

	// Add the torrent to the session
	lt::torrent_handle h = ses.add_torrent(atp);

	std::cout << "Torrent added. Starting download...\n";

	// Main loop to process alerts
	bool torrent_finished = false;
	while (!torrent_finished) {
		std::vector<lt::alert*> alerts;
		ses.pop_alerts(alerts);

		for (lt::alert const* a : alerts) {
			// Print all alerts for debugging purposes
			// std::cout << a->message() << std::endl;

			// Check for torrent finished alert
			if (auto* tf = lt::alert_cast<lt::torrent_finished_alert>(a)) {
				if (tf->handle == h) {
					torrent_finished = true;
					std::cout << "Torrent finished downloading!\n";
				}
			}

			// You can also check for other alert types, e.g., errors
			if (auto* err = lt::alert_cast<lt::torrent_error_alert>(a)) {
				if (err->handle == h) {
					std::cerr << "Torrent error: " << err->message() << std::endl;
				}
			}

			// Example: Print progress
			if (auto* st = lt::alert_cast<lt::torrent_status_alert>(a)) {
				if (st->handle == h) {
					lt::torrent_status status = st->handle.status();
					std::cout << "Progress: " << status.progress_ppm / 10000.0 * 100.0 << "%\r";
				}
			}
		}

		// Avoid busy-waiting, sleep for a short duration
		if (!torrent_finished) {
			std::this_thread::sleep_for(std::chrono::milliseconds(100));
		}
	}

	return 0;
}

```

--------------------------------

### Listen for SSL Torrent Connections

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/manual.rst

Example of adding a listen interface for SSL torrent connections. SSL torrent connections are enabled by appending 's' to the port number.

```text
0.0.0.0:6881,0.0.0.0:6882s
```

--------------------------------

### Build with Boost Build on Windows

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Set Boost root and build path environment variables, bootstrap Boost Build, configure user-config.jam for MSVC, and build libtorrent.

```bash
set BOOST_ROOT=c:\boost_1_69_0
set BOOST_BUILD_PATH=%BOOST_ROOT%\tools\build
(cd %BOOST_ROOT% && .\bootstrap.bat)
echo using msvc ; >>%HOMEDRIVE%%HOMEPATH%\user-config.jam
%BOOST_ROOT%\b2.exe --hash cxxstd=14 release
```

--------------------------------

### Build libtorrent Python module with setup.py

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Use this command to build the libtorrent Python module using the setup.py script. This command invokes b2 internally.

```bash
python setup.py build
```

--------------------------------

### Build libtorrent with All Defines

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Use this command to build libtorrent and display all compiler defines, which is useful for verifying compile-time configurations.

```bash
b2 -n -a toolset=msvc-14.2 link=static runtime-link=static boost-link=static variant=release
```

--------------------------------

### Extended Handshake Dictionary Example

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/extension_protocol.rst

An example of the dictionary structure for an extended handshake message, showing supported extensions and client information.

```text
+------------------------------------------------------+
| Dictionary                                           |
+===================+==================================+
| ``m``             |  +--------------------------+    |
|                   |  | Dictionary               |    |
|                   |  +======================+===+    |
|                   |  | ``LT_metadata``      | 1 |    |
|                   |  +----------------------+---+    |
|                   |  | ``ut_pex``           | 2 |    |
|                   |  +----------------------+---+    |
|                   |                                  |
+-------------------+----------------------------------+
| ``p``             | 6881                             |
+-------------------+----------------------------------+
| ``v``             | "uTorrent 1.2"                   |
+-------------------+----------------------------------+
```

--------------------------------

### Building with Ninja

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

After configuring the build with CMake, use the ninja build system to compile libtorrent.

```bash
ninja
```

--------------------------------

### DHT Get Request Format

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_store.rst

Format for a 'get' request to retrieve data from the DHT. Requires the node ID and a target hash.

```json
{
		"a":
		{
			"id": *<20 byte id of sending node (string)>*,
			"target:" *<20 byte SHA-1 hash of public key and salt (string)>*
		},
		"t": *<transaction-id (string)>*,
		"y": "q",
		"q": "get"
	}
```

--------------------------------

### Install Python Module to Custom Path

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Installs the Python module to a custom directory. Specify the desired path using the 'python-install-path' feature.

```bash
b2 release python=3.7 install_module python-install-path=/home/foobar/python-site/
```

--------------------------------

### Create Torrent from Directory using libtorrent

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/examples.rst

Demonstrates how to create a torrent file from a given directory using libtorrent. This is useful for seeding files.

```cpp
#include <libtorrent/create_torrent.hpp>
#include <libtorrent/set_piece_hashes.hpp>
#include <libtorrent/torrent_info.hpp>
#include <libtorrent/write_torrent_limits.hpp>

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <filesystem>

namespace fs = std::filesystem;

int main(int argc, char* argv[])
{
	if (argc != 3) {
		std::cerr << "Usage: " << argv[0] << " <directory> <output_torrent_file>\n";
		return 1;
	}

	fs::path directory_path = argv[1];
	fs::path output_path = argv[2];

	if (!fs::exists(directory_path) || !fs::is_directory(directory_path)) {
		std::cerr << "Error: Directory '" << directory_path << "' not found or is not a directory.\n";
		return 1;
	}

	try {
		// Create a torrent object
		libtorrent::create_torrent ct(libtorrent::torrent_info::binit(directory_path.string()));

		// Set piece hashes for the torrent
		libtorrent::set_piece_hashes(ct, directory_path.string());

		// Write the torrent file to disk
		std::ofstream of(output_path, std::ios::binary);
		if (!of) {
			std::cerr << "Error: Could not open output file '" << output_path << "' for writing.\n";
			return 1;
		}
		std::vector<char> buf;
		ct.write_torrent(of);

		std::cout << "Successfully created torrent file: " << output_path << std::endl;

	} catch (const std::exception& e) {
		std::cerr << "Error creating torrent: " << e.what() << std::endl;
		return 1;
	}

	return 0;
}
```

--------------------------------

### DHT Get Message Request Format

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_store.rst

This is the request format for the 'get' message. It is used to retrieve data from the DHT using its SHA-1 hash as the target.

```json
{
	"a":
	{
		"id": *<20 byte id of sending node (string)>*,
		"target": *<SHA-1 hash of item (string)>*,
	},
	"t": *<transaction-id (string)>*,
	"y": "q",
	"q": "get"
}
```

--------------------------------

### DHT Get Response Format

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_store.rst

Format for a 'get' response from the DHT. Includes node information, public key, sequence number, signature, token, and value.

```json
{
		"r":
		{
			"id": *<20 byte id of sending node (string)>*,
			"k": *<ed25519 public key (32 bytes string)>*,
			"nodes": *<IPv4 nodes close to 'target'>*,
			"nodes6": *<IPv6 nodes close to 'target'>*,
			"seq": *<monotonically increasing sequence number (integer)>*,
			"sig": *<ed25519 signature (64 bytes string)>*,
			"token": *<write-token (string)>*,
			"v": *<any bencoded type, whose encoded size <= 1000>*
		},
		"t": *<transaction-id (string)>*,
		"y": "r",
	}
```

--------------------------------

### Build libtorrent with Specified Toolset

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Invoke the b2 command to build libtorrent, optionally specifying the toolset (compiler) to use.

```shell
b2 msvc-14.2
```

```shell
b2 gcc-7.0
```

```shell
b2 darwin-4.0
```

--------------------------------

### DHT Get Message Response Format

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_store.rst

This is the response format for the 'get' message. It includes the retrieved value 'v', a write token, and network node information.

```json
{
	"r":
	{
		"id": *<20 byte id of sending node (string)>*,
		"token": *<write token (string)>*,
		"v": *<any bencoded type whose SHA-1 hash matches 'target'>*,
		"nodes": *<IPv4 nodes close to 'target'>*,
		"nodes6": *<IPv6 nodes close to 'target'>*
	},
	"t": *<transaction-id>*
	"y": "r"
}
```

--------------------------------

### MSVC Specific Properties and PDB Installation

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/CMakeLists.txt

Sets PDB file properties for the 'torrent-rasterbar' target on MSVC builds and optionally installs the PDB file for debug configurations.

```cmake
if (MSVC)
	set_target_properties(torrent-rasterbar
	PROPERTIES
		PDB_NAME torrent-rasterbar
		PDB_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}
		COMPILE_PDB_NAME torrent-rasterbar
		COMPILE_PDB_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}
	)

	if (static_runtime)
		set(PDB_INSTALL_DIR lib)
	else()
		set(PDB_INSTALL_DIR bin)
	endif()

	install(
		FILES
			${CMAKE_BINARY_DIR}/torrent-rasterbar.pdb
		DESTINATION
			${PDB_INSTALL_DIR}
		CONFIGURATIONS
			Debug RelWithDebInfo
		OPTIONAL
	)
endif()
```

--------------------------------

### Customize libtorrent Python build with b2 arguments

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/python_binding.rst

Pass custom arguments to b2 through setup.py's build_ext step to customize the build process, such as specifying toolsets or link flags.

```bash
python setup.py build_ext --b2-args="toolset=msvc-14.2 linkflags=-L../../src/.libs"
```

--------------------------------

### DHT Put Request Signature Data with Salt Example

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_store.rst

When a salt is present in the 'put' request, it is included in the data to be signed. This example demonstrates the bencoded format of the salt prepended to the sequence number and 'v' key.

```text
4:salt6:foobar3:seqi4e1:v12:Hello world!
```

--------------------------------

### Build and stage all libtorrent fuzzers with clang

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/fuzzing.rst

Use the 'b2' build system with the 'clang' toolset and 'stage' target to build and stage all fuzzers. Binaries will be placed in the fuzzers/fuzzers directory.

```bash
b2 clang stage

```

--------------------------------

### RSS Feed Item Structure Example

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_rss.rst

An example of an 'announce_item' message for an RSS feed, detailing the required keys like 'ih', 'size', and 'n'. Strings are shown in hex for printability, but actual encoding is binary.

```json
{
   "a":
   {
      "item":
      {
         "key": "6bc1de5443d1a7c536cdf69433ac4a7163d3c63e2f9c92d
            78f6011cf63dbcd5b638bbc2119cdad0c57e4c61bc69ba5e2c08
            b918c2db8d1848cf514bd9958d307",
         "info-hash": "7ea94c240691311dc0916a2a91eb7c3db2c6f3e4",
         "size": 24315329,
         "n": "my stuff",
         "next": "c68f29156404e8e0aas8761ef5236bcagf7f8f2e"
      }
      "sig": *<signature>*
      "id": "b46989156404e8e0acdb751ef553b210ef77822e",
      "target": "b4692ef0005639e86d7165bf378474107bf3a762"
      "token": "23ba"
   },
   "y": "q",
   "q": "announce_item",
"t": "a421"
}
```

--------------------------------

### DHT Put Request Signature Data Example

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/dht_store.rst

This example shows the format of the data that needs to be signed for a DHT 'put' request, including the sequence number and the 'v' key. The signature ensures the integrity and authenticity of the update.

```text
3:seqi4e1:v12:Hello world!
```

--------------------------------

### Clone libtorrent Repository

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Clone the libtorrent repository and its submodules to get the latest source code.

```bash
git clone --recurse-submodules https://github.com/arvidn/libtorrent.git
```

--------------------------------

### Load and Save Session Parameters

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/tutorial.rst

Demonstrates loading and saving session parameters to a file, and handling shutdown signals.

```cpp
#include <libtorrent/session.hpp>
#include <libtorrent/session_params.hpp>
#include <libtorrent.hpp>
#include <fstream>
#include <csignal>

#include <boost/asio/signal_set.hpp>

#include "../examples/bt-get3.cpp"

namespace lt = libtorrent;

std::shared_ptr<lt::session> sess;

void signal_handler(int signo)
{
    if (signo == SIGINT)
    {
        std::cerr << "SIGINT received, shutting down.\n";
        if (sess)
        {
            sess->pause();
            // save session state
            std::ofstream fs(".session", std::ios::binary);
            fs << lt::write_session_params_to_buffer(sess->params());
            sess.reset();
        }
        exit(0);
    }
}

int main(int argc, char* argv[])
{
    // setup signal handler
    signal(SIGINT, signal_handler);

    lt::session_params params;
    // load session state
    std::ifstream fs(".session", std::ios::binary);
    if (fs.is_open())
    {
        std::vector<char> buf(std::istreambuf_iterator<char>(fs), std::istreambuf_iterator<char>());
        params = lt::read_session_params_from_buffer(buf);
    }

    // override settings if needed
    // params.settings.user_agent = "my-awesome-client/1.0";

    sess = std::make_shared<lt::session>(params);

    // ... rest of the example code ...

    return 0;
}

```

--------------------------------

### Generate CMake Build System

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/building.rst

Create a build directory and run cmake to generate the build system files. Specify CMAKE_BUILD_TYPE and CMAKE_CXX_STANDARD. The -G flag selects the build tool, like Ninja.

```bash
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_STANDARD=14 -G Ninja ..
```

--------------------------------

### Disabling an Extension

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/extension_protocol.rst

Example of a subsequent handshake message used to disable the 'LT_metadata' extension at runtime by setting its value to 0.

```bencode
d11:LT_metadatai0ee
```

--------------------------------

### Configure clang for libtorrent fuzzing

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/docs/fuzzing.rst

Specify the clang compiler and version in user-config.jam to build fuzzers. Ensure clang is installed and accessible.

```jam
using clang : 7 : clang++-7 ;

```

--------------------------------

### Add DHT Sample Executable

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/tools/CMakeLists.txt

Defines the 'dht_sample' executable and links it to the 'torrent-rasterbar' library.

```cmake
add_executable(dht_sample dht_sample.cpp)
target_link_libraries(dht_sample PRIVATE torrent-rasterbar)
```

--------------------------------

### Feature Option Configuration

Source: https://github.com/arvidn/libtorrent/blob/RC_2_0/CMakeLists.txt

Defines boolean feature options for the build, such as enabling tests, examples, tools, or specific language bindings.

```cmake
feature_option(build_tests "build tests" OFF)
```

```cmake
feature_option(build_examples "build examples" OFF)
```

```cmake
feature_option(build_tools "build tools" OFF)
```

```cmake
feature_option(python-bindings "build python bindings" OFF)
```

```cmake
feature_option(python-egg-info "generate python egg info" OFF)
```

```cmake
feature_option(python-install-system-dir "Install python bindings to the system installation directory rather than the CMake installation prefix" OFF)
```