Windows API Documentation

Overview

Windows provides a rich set of networking APIs ranging from low‑level socket programming to high‑level HTTP client libraries. Key components include:

• Winsock (Windows Sockets) – the primary socket API.
• WinHTTP – high‑level HTTP client API.
• Network Isolation – IPsec policy management.
• Network Configuration – GetAdaptersInfo, GetIfTable.

Winsock (Socket Programming)

Winsock follows the Berkeley sockets model with Windows‑specific extensions.

int main() {
    WSADATA wsaData;
    WSAStartup(MAKEWORD(2,2), &wsaData);
    SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    struct sockaddr_in server = {0};
    server.sin_family = AF_INET;
    server.sin_port = htons(80);
    inet_pton(AF_INET, "93.184.216.34", &server.sin_addr);
    connect(s, (SOCKADDR*)&server, sizeof(server));
    const char *msg = "GET / HTTP/1.1\r\nHost: example.com\r\n\r\n";
    send(s, msg, (int)strlen(msg), 0);
    char buf[1024];
    int received = recv(s, buf, sizeof(buf)-1, 0);
    buf[received] = 0;
    printf("%s", buf);
    closesocket(s);
    WSACleanup();
    return 0;
}

WinHTTP – HTTP Client

WinHTTP simplifies HTTP calls with built‑in handling of redirects, proxy, and TLS.

#include <windows.h>
#include <winhttp.h>

int main() {
    HINTERNET hSession = WinHttpOpen(L"Example/1.0", WINHTTP_ACCESS_TYPE_DEFAULT_PROXY, WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0);
    HINTERNET hConnect = WinHttpConnect(hSession, L"example.com", INTERNET_DEFAULT_HTTP_PORT, 0);
    HINTERNET hRequest = WinHttpOpenRequest(hConnect, L"GET", L"/", NULL, WINHTTP_NO_REFERER, WINHTTP_DEFAULT_ACCEPT_TYPES, 0);
    WinHttpSendRequest(hRequest, WINHTTP_NO_ADDITIONAL_HEADERS, 0, WINHTTP_NO_REQUEST_DATA, 0, 0, 0);
    WinHttpReceiveResponse(hRequest, NULL);
    DWORD dwSize = 0;
    while (WinHttpQueryDataAvailable(hRequest, &dwSize) && dwSize) {
        BYTE *buffer = (BYTE*)malloc(dwSize);
        DWORD dwRead = 0;
        WinHttpReadData(hRequest, buffer, dwSize, &dwRead);
        fwrite(buffer, 1, dwRead, stdout);
        free(buffer);
    }
    WinHttpCloseHandle(hRequest);
    WinHttpCloseHandle(hConnect);
    WinHttpCloseHandle(hSession);
    return 0;
}

Best Practices

• Always initialize Winsock with WSAStartup and call WSACleanup when done.
• Validate all input parameters to prevent buffer overflows.
• Prefer asynchronous I/O (IOCP) for high‑throughput servers.
• Use TLS (Schannel) for secure communications.
• Leverage the Windows Filtering Platform (WFP) for firewall rules.