Simple C++ TCP Client with SSL wrapper using OpenSSL

1. Demo

The demo program is to retrieve my public IP address, but this can be used for any TCP request over SSL

Go to demo

2. Installation

• Note: this has only been tested on Mac M2

make all
./client

3. Explanation

1) Project structure (made with https://marketplace.visualstudio.com/items?itemName=jmkrivocapich.drawfolderstructure)

└── 📁cpp-tcp-client
    └── 📁include
        ├── http_client.h
        ├── tcp_socket.h
        ├── tls_client.h
    └── 📁src
        ├── http_client.cpp
        ├── main.cpp
        ├── tcp_socket.cpp
        ├── tls_client.cpp
    ├── Makefile

2) How it works

1. Resolve host: get IP from hostname (gethostbyname)
2. Open TCP socket: socket() + connect() to server:443
3. Start TLS: wrap socket with OpenSSL (SSL_connect)
4. Send HTTP request: SSL_write("GET ...")
5. Receive response: SSL_read() until done
6. Parse body: extract the data
7. Cleanup: shutdown TLS, free SSL, close socket

4. References

• https://man7.org/linux/man-pages/man3/gethostbyname.3.html
• https://www.geeksforgeeks.org/cpp/socket-programming-in-cpp/
• https://wiki.openssl.org/index.php/SSL/TLS_Client
• https://www.ibm.com/docs/en/ztpf/1.1.2024?topic=apis-tls-client-method
• https://www.ibm.com/docs/en/ztpf/1.1.2024?topic=layer-ssl-examples