single header C api for http request

buffer.h

typedef struct
{
	size_t size, cap;
	char *data;
} Buffer;

static size_t next_power_of_two(size_t v)
{
	v--;
	v |= v >> 1;
	v |= v >> 2;
	v |= v >> 4;
	v |= v >> 8;
	v |= v >> 16;
	v++;
	return v;
}
static void buffer_init(Buffer *b, size_t initial)
{
	b->size = 0;
	b->cap = initial;
	b->data = malloc(sizeof(char) * initial);
}

static void buffer_grow(Buffer *b, size_t size)
{
	size_t n = b->size + size;
	if (n >= b->cap)
	{
		b->cap = next_power_of_two(n);
		b->data = realloc(b->data, b->cap);
	}
}

static void buffer_write(Buffer *b, char *data, size_t size)
{
	buffer_grow(b, size);
	memcpy(&b->data[b->size], data, size);
	b->size += size;
}

static void buffer_reset(Buffer *b)
{
	b->size = 0;
}

static void buffer_free(Buffer *b)
{
	free(b->data);
}

http.h

#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winhttp.h>


static int http(wchar_t *method, wchar_t *host, short port, wchar_t *path,
				wchar_t *headers, unsigned char *data, size_t size,
				Buffer *response)
{
	int code = 0;
	HINTERNET hConnect = NULL, hRequest = NULL;

	HINTERNET hSession = WinHttpOpen(NULL,
									 WINHTTP_ACCESS_TYPE_DEFAULT_PROXY,
									 WINHTTP_NO_PROXY_NAME,
									 WINHTTP_NO_PROXY_BYPASS, 0);
	if (!hSession)
	{
		code = 1;
		goto end;
	}
	hConnect = WinHttpConnect(hSession, host, port, 0);
	if (!hConnect)
	{
		code = 2;
		goto end;
	}
	hRequest = WinHttpOpenRequest(hConnect, method, path,
								  NULL, WINHTTP_NO_REFERER,
								  WINHTTP_DEFAULT_ACCEPT_TYPES,
								  WINHTTP_FLAG_SECURE);
	if (!hRequest)
	{
		code = 3;
		goto end;
	}
	DWORD dwFlags =
		SECURITY_FLAG_IGNORE_UNKNOWN_CA |
		SECURITY_FLAG_IGNORE_CERT_WRONG_USAGE |
		SECURITY_FLAG_IGNORE_CERT_CN_INVALID |
		SECURITY_FLAG_IGNORE_CERT_DATE_INVALID;
	if (!WinHttpSetOption(
			hRequest,
			WINHTTP_OPTION_SECURITY_FLAGS,
			&dwFlags,
			sizeof(dwFlags)))
	{
		code = 4;
		goto end;
	}
	if (!WinHttpSendRequest(hRequest, headers, headers != NULL ? -1L : 0,
							WINHTTP_NO_REQUEST_DATA, 0,
							size, 0))
	{
		code = 5;
		goto end;
	}
	if (size > 0)
	{
		DWORD dwBytesWritten;
		if (!WinHttpWriteData(hRequest, data, size, &dwBytesWritten))
		{
			code = 6;
			goto end;
		}
	}
	if (!WinHttpReceiveResponse(hRequest, NULL))
	{
		code = 7;
		goto end;
	}
	if (response != NULL)
	{
		DWORD dwDownloaded, dwSize;
		do
		{
			if (!WinHttpQueryDataAvailable(hRequest, &dwSize) && dwSize)
				break;
			buffer_growby(response, dwSize);
			WinHttpReadData(hRequest, (LPVOID)&response->data[response->size], dwSize, &dwDownloaded);
			response->size += dwSize;
			if (!dwDownloaded)
				break;
		} while (dwSize > 0);
	}
end:
	if (hRequest)
		WinHttpCloseHandle(hRequest);
	if (hConnect)
		WinHttpCloseHandle(hConnect);
	if (hSession)
		WinHttpCloseHandle(hSession);
	return code;
}

#else
#error "not supported"
#endif