HTTP with WinINet

This chapter covers a minimal HTTP GET using WinINet (wininet.dll), plus readable errors via FormatMessageW pulling messages from wininet.dll.

Link Wininet.lib and include Wininet.h.

Flow in main

Typical sequence:

1. InitSession — InternetOpenA with a user agent and INTERNET_OPEN_TYPE_PRECONFIG.
2. MakeRequest — InternetConnectA, then HttpOpenRequestA (and related) to obtain an HINTERNET request handle.
3. SendRequest — send headers/body; on failure, call your error helper.
4. ProcessResults — InternetReadFile (or similar) in a loop until done.
5. CloseSession — InternetCloseHandle for each open handle (request, connection, session).

Split these across .c files in your template (HttpApis.c, Errors.c, etc.) if your rubric asks for separation—the book describes the pattern; your repo holds the actual file names.

Formatting WinINet errors

#define BUFFER_SIZE 1024

void CheckLastInetError(LPCWSTR message, DWORD dwLastErr)
{
    WCHAR buf[BUFFER_SIZE];
    DWORD n = FormatMessageW(
        FORMAT_MESSAGE_FROM_HMODULE,
        GetModuleHandleW(L"wininet.dll"),
        dwLastErr,
        0UL,
        buf,
        BUFFER_SIZE,
        NULL
    );
    if (n)
        wprintf(L"%s: %s", message, buf);
}

Tip

Distinguish Win32 errors from InternetError / extended WinINet codes your debugger shows—always thread GetLastError (or the API’s documented error path) into FormatMessage with the right module when possible.

Note

Samples often target 127.0.0.1:8080. Run a local listener or change host / port to match your lab.

Implement

1. Add WinINet session/connect/request/send/read/close in your template.
2. Wire CheckLastInetError (or equivalent) for failed steps.
3. Build, test against a real or mock server, commit, and push.