TCP client/server API for C++ (with SSL/TLS support)

About

This is a simple TCP server/client for C++. Under Windows, it wraps WinSock and under Linux it wraps the related socket API (BSD compatible). It wraps also OpenSSL to create secure client/server sockets.

It is meant to be a portable and easy-to-use API to create a TCP server or client with or without SSL/TLS support.

Upcoming features : using the sockets in an async way and proxy support.

Compilation has been tested with:

• GCC 5.4.0 (GNU/Linux Ubuntu 16.04 LTS)
• Microsoft Visual Studio 2015 (Windows 10)

Windows Users : vcpkg (Microsoft C++ Library Manager) can be used to easily install OpenSSL and generate the Visual Studio solution with CMake. With vcpkg, no need to manually copy the DLL in the output directory, vcpkg handles all that ! Look at "Building under Windows via Visual Studio" section, for instructions.

Usage

Create a server or client object and provide to its constructor a callable object (for log printing) having this signature :

void(const std::string&)

For now, you can disable log printing by choosing the flag ASocket::SettingsFlag::NO_FLAGS when creating a socket or by providing a callable object that does nothing with the string message.

#include "TCPClient.h"
#include "TCPServer.h"
#include "TCPSSLServer.h"
#include "TCPSSLClient.h"

auto LogPrinter = [](const std::string& strLogMsg) { std::cout << strLogMsg << std::endl;  }

CTCPClient TCPClient(LogPrinter); // creates a TCP client
CTCPServer TCPServer(LogPrinter, "12345"); // creates a TCP server to listen on port 12345

CTCPSSLClient SecureTCPClient(LogPrinter); // creates an SSL/TLS TCP client
CTCPSSLServer SecureTCPSSLServer(LogPrinter, "4242"); // creates an SSL/TLS TCP server to listen on port 4242

Please note that the constructor of CTCPServer or the SSL/TLS version throws only an exception in the Windows version when the address resolution fails, so you should use the try catch block in this particular context.

To listen for an incoming TCP connection :

ASocket::Socket ConnectedClient; // socket of the connected client, we can have a vector of them for example.
/* blocking call, should return true if the accept is OK, ConnectedClient should also be a valid socket
number */
m_pTCPServer->Listen(ConnectedClient);

A wait period (in milliseconds) can be set, to avoid waiting indefinitely for a client :

m_pTCPServer->Listen(ConnectedClient, 1000); // waits for 1 second. Will return true, if a client connected to the server

To connect to a particular server (e.g 127.0.0.1:669)

m_pTCPClient->Connect("127.0.0.1", "669"); // should return true if the connection succeeds

To send/receive data to/from a client :

const std::string strSendData = "Hello World !";
m_pTCPServer->Send(ConnectedClient, strSendData);
/* or */
m_pTCPServer->Send(ConnectedClient, strSendData.c_str(), 13);
/* or even an std::vector<char> as a second parameter */

char szRcvBuffer[14] = {};
m_pTCPServer->Receive(ConnectedClient, szRcvBuffer, 13);

To send/receive data to/from a server :

const std::string strSendData = "Hello World !";
m_pTCPClient->Send(strSendData);
/* or */
m_pTCPClient->Send(strSendData.c_str(), 13);
/* or even an std::vector<char> */

char szRcvBuffer[14] = {};
m_pTCPClient->Receive(szRcvBuffer, 13);

To disconnect from server or client side :

m_pTCPClient->Disconnect();

m_pTCPServer->Disconnect(ConnectedClient);

A client socket can be polled to ensure that a receive operation won't block indefinitely if a timeout has not been defined :

// client
int ret = ASocket::SelectSocket(tcpClient->GetSocketDescriptor(), 300); // poll for 300 ms
if (ret > 0)
{
    int readCount = m_pTCPClient->Receive(RcvBuffer.data() + readBytes, chunkSize);
    
    //...
}

// client socket managed by a server
int ret = ASocket::SelectSocket(ConnectedClient, 50);

Or you can define a recevive (or send) timeout value :

ASSERT_TRUE(m_pTCPClient->SetRcvTimeout(250));

m_pTCPServer->SetRcvTimeout(ConnectedClient, 250);

// Set timeout value to zero to disable timeout

Before using SSL/TLS secured classes, compile both library and the test program with the preprocessor macro OPENSSL. If you don't want to compile secure classes, you can indicate that to CMake when generating a makefile or Visual Studio solutions, by setting SOCKET_CPP_BUILD_WITHOUT_SECURE_CLASSES=TRUE (under Windows, in CMake-GUI, add the entry, select "BOOL" and check "Value") :

cmake -DCMAKE_BUILD_TYPE=Release -DSOCKET_CPP_BUILD_WITHOUT_SECURE_CLASSES etc...

Almost all the operations look similar to the operations above for unencrypted communications, the differences are :

The client socket to provide to the Listen method of an CTCPSSLServer is of type ASecureSocket::SSLSocket.

ASecureSocket::SSLSocket ConnectedClient;

Before listenning for incoming SSL/TLS connections, you have to set the server's certificate and private key paths via the proper methods :

m_pSSLTCPServer->SetSSLCertFile(SSL_CERT_FILE);
m_pSSLTCPServer->SetSSLKeyFile(SSL_KEY_FILE);

You can also set CA file if you want. Otherwise, for now, passphrase must be included in the private key file.

To create SSL test files, you can use this command :

openssl req -newkey rsa:2048 -new -nodes -x509 -days 3650 -keyout key.pem -out cert.pem

IMPORTANT: In the SSL/TLS server, ASecureSocket::SSLSocket objects must be disconnected with SSL/TLS server's disconnect method to free used OpenSSL context and connection structures. Otherwise, you will have memory leaks.

Thread Safety

Do not share ASocket or ASecureSocket objects across threads.

Installation

You will need CMake to generate a makefile for the static library or to build the tests/code coverage program.

Also make sure you have Google Test installed and OpenSSL updated to the lastest version.

This tutorial will help you installing properly Google Test on Ubuntu: https://www.eriksmistad.no/getting-started-with-google-test-on-ubuntu/

If you work under Centos7 or another Linux distribution that has an old version of OpenSSL, this tutorial may help you to install the latest version of OpenSSL : https://blacksaildivision.com/how-to-install-openssl-on-centos in /usr/local/openssl. With the GUI version of CMake, click on "Advanced" and change these OpenSSL entries (or you can use the command line if you're comfortable with :

OPENSSL_CRYPTO_LIBRARY : /usr/local/openssl/lib/libcrypto.so (.a will cause a link problem...) OPENSSL_INCLUDE_DIR : /usr/local/openssl/include OPENSSL_SSL_LIBRARY : /usr/local/openssl/lib/libssl.so (or .a if you want)

The CMake script located in the tree will produce Makefiles for the creation of the static library and for the unit tests program.

To create a debug static library and a test binary, change directory to the one containing the first CMakeLists.txt and :

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE:STRING=Debug
make

To create a release static library, just change "Debug" by "Release".

The library will be found under "build/[Debug|Release]/lib/libsocket.a" whereas the test program will be located in "build/[Debug|Release]/bin/test_socket"

To directly run the unit test binary, you must indicate the path of the INI conf file (see the section below)

./[Debug|Release]/bin/test_socket /path_to_your_ini_file/conf.ini

Building under Windows via Visual Studio

1. New Procedure (with vcpkg) :

Install vcpkg then install OpenSSL (use 'x86-windows' for the 32-bit version) :

.\vcpkg install openssl:x64-windows

If you have a french Visual Studio version, don't forget to install the english language pack (vcpkg will tell you this anyway).

Download and install the latest version of CMake : https://cmake.org/download/ (e.g. Windows win64-x64 Installer)

Open CMake (cmake-gui)

In "Where is the source code", put the socket-cpp path (e.g. C:/Users/Amine/Documents/Work/PROJECTS/GitHub/socket-cpp), where the main CMakeLists.txt file exist.

In "Where to build binaries", paste the directory where you want to build the project (e.g. C:/Users/Amine/Documents/Work/PROJECTS/GitHub/socket_build)

Click on "Configure".

Select your Visual Studio version (if it isn't already set). In "Optional platform for generator", you can leave it empty (x64 by default) or choose another value.

Click on the radio button "Specify toolchain file for cross-compiling, then hit the "Next" button.

In "Specify the toolchain file", browse to vcpkg toolchain file (vcpkg/scripts/buildsystems/vcpkg.cmake) and select it.

Press "Finish", wait until CMake configures the project then hit "Generate" to create the Visual Studio solution (library and unit test binary).

2. Old Procedure (without vcpkg) :

First of all, you can download and install OpenSSL : https://slproweb.com/products/Win32OpenSSL.html (32 and 64 bits).

Concerning Google Test, the library will be downloaded and built automatically from its github repository.

Download and install the latest version of CMake : https://cmake.org/download/ (e.g. Windows win64-x64 Installer).

Under C:\OpenSSL-Win64\bin, you will find the DLLs : libcrypto-1_1-x64.dll and libssl-1_1-x64.dll that you will need, later, to place in the same directory as the binary file that used the socket-cpp library.

Open CMake (cmake-gui).

In "Where is the source code", put the socket-cpp path (e.g. C:/Users/Amine/Documents/Work/PROJECTS/GitHub/socket-cpp), where the main CMakeLists.txt file exist.

In "Where to build binaries", paste the directory where you want to build the project (e.g. C:/Users/Amine/Documents/Work/PROJECTS/GitHub/socket-cpp/build).

Click on "Configure".

If you want to indicate a configuration file to run unit tests with "CTest", before clicking on "Configure", click on "Add entry" and add this entry : TEST_INI_FILE : C:/Users/Amine/Documents/Work/PROJECTS/GitHub/socket-cpp/my_test_conf.ini (tour configuration file).

Then click on "Generate", you can choose a Visual Studio version if it is not done before (e.g. Visual Studio 15 2017 Win64)

Finally, click on "Open Project" to open the solution in Visual Studio.

In Visual Studio, you can change the build type (Debug -> Release). Build the solution (press F7). It must succeed without any errors. You can close Visual Studio.

The library will be found under C:\Users\Amine\Documents\Work\PROJECTS\GitHub\socket-cpp\build\lib\Release\socket.lib

After building a program using "socket.lib", do not forget to copy OpenSSL DLLs in the directory where the program binary is located.

For example, in the build directory (e.g. C:\Users\Amine\Documents\Work\PROJECTS\GitHub\socket_build), under "bin", directory, you may find "Debug", "Release" or both according to the build type used during the build in Visual Studio, and in it, the test program "test_socket.exe".

Before executing it, make sure to copy the OpenSSL DLLs in the same directory (e.g. copy C:\OpenSSL-Win64\bin\libcrypto-1_1-x64.dll and C:\OpenSSL-Win64\bin\libssl-1_1-x64.dll, do not change the name of the DLL !)

If you have provided a valid configuration file to CMake-gui (TEST_INI_FILE), you can run unit tests in the command prompt (cmd.exe - after building the project in VS) by changing directory to the one where CMake generated the build files and by running :

ctest -c "Release"

to test the "Debug" library, just change "Release" by "Debug" (but ensure that you have build it before). Do not forget to place the DLLs near "test_socket.exe" before launching "ctest", otherwise, tests will fail.

Run Unit Tests

simpleini is used to gather unit tests parameters from an INI configuration file. You need to fill that file with some parameters. You can also disable some tests (SSL/TLS for instance) and indicate parameters only for the enabled tests. A template of the INI file already exists under SocketTest/

e.g. to enable SSL/TLS tests :

[tests]
tcp-ssl=yes

[tcp-ssl]
server_port=4242
ca_file=CAfile.pem
ssl_cert_file=site.cert
ssl_key_file=privkey.pem

You can also generate an XML file of test results by adding --getst_output argument when calling the test program

./[Debug|Release]/bin/test_socket /path_to_your_ini_file/conf.ini --gtest_output="xml:./TestSocket.xml"

An alternative way to compile and run unit tests :

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Debug -DTEST_INI_FILE="full_or_relative_path_to_your_test_conf.ini"
make
make test

You may use a tool like https://github.com/adarmalik/gtest2html to convert your XML test result in an HTML file.

Memory Leak Check

Visual Leak Detector has been used to check memory leaks with the Windows build (Visual Sutdio 2015) You can download it here: https://vld.codeplex.com/

To perform a leak check with the Linux build, you can do so :

valgrind --leak-check=full ./Debug/bin/test_socket /path_to_ini_file/conf.ini

Code Coverage

The code coverage build doesn't use the static library but compiles and uses directly the socket API in the test program.

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Coverage -DCOVERAGE_INI_FILE:STRING="full_path_to_your_test_conf.ini"
make
make coverage_socket

If everything is OK, the results will be found under ./SocketTest/coverage/index.html

Make sure you feed CMake with a full path to your test conf INI file, otherwise, the coverage test will be useless.

Under Visual Studio, you can simply use OpenCppCoverage (https://opencppcoverage.codeplex.com/)

CppCheck Compliancy

The C++ code of the Socket C++ API classes is Cppcheck compliant.

Contribute

All contributions are highly appreciated. This includes updating documentation, cleaning and writing code and unit tests to increase code coverage and enhance tools.

Try to preserve the existing coding style (Hungarian notation, indentation etc...).