obs-streamer-tools-plugin/core/src/http_winhttp.cpp

/*
streamer-tools OBS Camera Plugin - WinHTTP backend (Windows)
Copyright (C) 2026 CyberCoveLLC <jknapp85@gmail.com>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0
*/

// WinHTTP rather than libcurl on Windows: it ships with the OS, does TLS
// through SChannel (so no OpenSSL to build or ship), and needs no package
// manager on the self-hosted `winvm-builder` runner -- which, per the
// scaffold README, is a bare VM without even cmake preinstalled.

#include "stplugin/http.h"

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

#include <atomic>
#include <chrono>
#include <condition_variable>
#include <cstddef>
#include <mutex>
#include <string>
#include <thread>
#include <vector>

namespace stplugin {

namespace {

constexpr std::size_t kMaxResponseBytes = 4u * 1024u * 1024u;

std::wstring widen(const std::string &s)
{
    if (s.empty())
        return std::wstring();
    const int needed = MultiByteToWideChar(CP_UTF8, 0, s.c_str(), static_cast<int>(s.size()), nullptr, 0);
    if (needed <= 0)
        return std::wstring();
    std::wstring out(static_cast<std::size_t>(needed), L'\0');
    MultiByteToWideChar(CP_UTF8, 0, s.c_str(), static_cast<int>(s.size()), &out[0], needed);
    return out;
}

std::string lastErrorMessage(const char *what)
{
    return std::string(what) + " failed (GetLastError=" + std::to_string(GetLastError()) + ")";
}

/// RAII for the three WinHTTP handle kinds, which all close the same way.
class Handle {
public:
    Handle() = default;
    explicit Handle(HINTERNET h) : h_(h) {}
    ~Handle()
    {
        if (h_)
            WinHttpCloseHandle(h_);
    }
    Handle(const Handle &) = delete;
    Handle &operator=(const Handle &) = delete;

    void reset(HINTERNET h)
    {
        if (h_)
            WinHttpCloseHandle(h_);
        h_ = h;
    }
    HINTERNET get() const { return h_; }
    explicit operator bool() const { return h_ != nullptr; }

private:
    HINTERNET h_ = nullptr;
};

/// Hard deadline for one WinHTTP exchange, enforced by cancelling it.
///
/// Neither receive timeout is a guaranteed deadline: Microsoft documents both
/// as "checked only when data is received from the socket", so an expired
/// timeout is not surfaced until the peer finally sends something. Measured on
/// the Windows CI runner against a server that accepts and then stalls 5s: a
/// 700ms budget returned after 1490, 1529, 2485, 3493 and 4506ms across five
/// attempts -- always cancelled, never on time.
///
/// That overshoot matters because `fetchSlots` is called synchronously on the
/// OBS UI thread behind the properties dialog's "Refresh camera list" button
/// (obs-adapter/src/plugin-main.cpp), with a 5s budget. At the ratio above
/// that is a frozen dialog for half a minute.
///
/// The documented way to force cancellation is to close the handle from
/// another thread; the pending call then fails with
/// ERROR_WINHTTP_OPERATION_CANCELLED. This owns the request handle so that
/// exactly one of the two threads ever closes it: `handle_.exchange(nullptr)`
/// hands the close to whichever gets there first.
///
/// Known, accepted race: the caller may load the handle and have the watchdog
/// close it before the WinHttp* call reads it, in which case the call fails
/// with ERROR_INVALID_HANDLE instead. Both outcomes are "the deadline
/// expired", which is what the caller is told either way.
class RequestDeadline {
public:
    RequestDeadline(HINTERNET request, DWORD after_ms) : handle_(request)
    {
        watchdog_ = std::thread([this, after_ms] {
            std::unique_lock<std::mutex> lock(mutex_);
            if (cv_.wait_for(lock, std::chrono::milliseconds(after_ms), [this] { return finished_; }))
                return; // exchange finished inside the deadline
            if (closeOnce())
                expired_.store(true);
        });
    }

    ~RequestDeadline()
    {
        {
            std::lock_guard<std::mutex> lock(mutex_);
            finished_ = true;
        }
        cv_.notify_all();
        if (watchdog_.joinable())
            watchdog_.join();
        closeOnce(); // no-op if the watchdog got there first
    }

    RequestDeadline(const RequestDeadline &) = delete;
    RequestDeadline &operator=(const RequestDeadline &) = delete;

    HINTERNET get() const { return handle_.load(); }
    bool expired() const { return expired_.load(); }

private:
    bool closeOnce()
    {
        HINTERNET h = handle_.exchange(nullptr);
        if (!h)
            return false;
        WinHttpCloseHandle(h);
        return true;
    }

    std::atomic<HINTERNET> handle_;
    std::atomic<bool> expired_{false};
    std::mutex mutex_;
    std::condition_variable cv_;
    bool finished_ = false;
    std::thread watchdog_;
};

class WinHttpClient : public HttpClient {
public:
    HttpResponse send(const HttpRequest &request) override
    {
        HttpResponse response;

        const std::wstring url = widen(request.url);
        if (url.empty()) {
            response.network_error = "empty or non-UTF-8 URL";
            return response;
        }

        URL_COMPONENTS parts{};
        parts.dwStructSize = sizeof(parts);
        wchar_t host[256] = {0};
        wchar_t path[4096] = {0};
        wchar_t extra[4096] = {0};
        parts.lpszHostName = host;
        parts.dwHostNameLength = static_cast<DWORD>(sizeof(host) / sizeof(host[0]));
        parts.lpszUrlPath = path;
        parts.dwUrlPathLength = static_cast<DWORD>(sizeof(path) / sizeof(path[0]));
        parts.lpszExtraInfo = extra;
        parts.dwExtraInfoLength = static_cast<DWORD>(sizeof(extra) / sizeof(extra[0]));

        if (!WinHttpCrackUrl(url.c_str(), static_cast<DWORD>(url.size()), 0, &parts)) {
            response.network_error = lastErrorMessage("WinHttpCrackUrl");
            return response;
        }
        if (parts.nScheme != INTERNET_SCHEME_HTTP && parts.nScheme != INTERNET_SCHEME_HTTPS) {
            response.network_error = "unsupported URL scheme";
            return response;
        }

        Handle session(WinHttpOpen(L"streamer-tools-obs-plugin/1.0", WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY,
                                   WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0));
        if (!session) {
            response.network_error = lastErrorMessage("WinHttpOpen");
            return response;
        }

        const DWORD timeout = static_cast<DWORD>(request.timeout_ms);
        WinHttpSetTimeouts(session.get(), static_cast<int>(timeout), static_cast<int>(timeout),
                           static_cast<int>(timeout), static_cast<int>(timeout));

        // WinHttpSetTimeouts' receive parameter maps to
        // WINHTTP_OPTION_RECEIVE_TIMEOUT, which Microsoft documents as a
        // PER-PACKET Winsock-layer read timeout ("applies to fetching each
        // packet of data off the socket"), not a deadline on the response.
        // The wait for the response HEADERS is a *separate* option,
        // WINHTTP_OPTION_RECEIVE_RESPONSE_TIMEOUT ("to wait to receive all
        // response headers to a request"), which WinHttpSetTimeouts does not
        // touch and which defaults to 90 SECONDS. Without this call a server
        // that accepts, reads the request and then stalls can hold this
        // thread for a minute and a half regardless of request.timeout_ms --
        // exactly the "blocking an OBS thread indefinitely" failure
        // testPlatformBackendTimeout exists to prevent, and the likely
        // mechanism behind that test's intermittent Windows failures.
        //
        // Caveat, also documented: this timeout "is checked only when data is
        // received from the socket", so it bounds the wait but does not
        // guarantee a hard deadline. A guaranteed deadline needs a watchdog
        // thread calling WinHttpCloseHandle; not done here.
        //
        // Guarded because the constant postdates some Windows SDK headers; a
        // toolchain without it keeps the previous (90s default) behaviour
        // rather than failing to build.
#ifdef WINHTTP_OPTION_RECEIVE_RESPONSE_TIMEOUT
        DWORD response_timeout = timeout;
        // Return value deliberately unchecked: a rejected option leaves the
        // documented default in place, which is degraded but still correct
        // behaviour, and there is no logging sink in this layer to report it
        // to. The timeout probe in test_api_client.cpp is what would catch a
        // regression here.
        WinHttpSetOption(session.get(), WINHTTP_OPTION_RECEIVE_RESPONSE_TIMEOUT, &response_timeout,
                         sizeof(response_timeout));
#endif

        Handle connect(WinHttpConnect(session.get(), host, parts.nPort, 0));
        if (!connect) {
            response.network_error = lastErrorMessage("WinHttpConnect");
            return response;
        }

        std::wstring target(path);
        target += extra;

        const DWORD flags = (parts.nScheme == INTERNET_SCHEME_HTTPS) ? WINHTTP_FLAG_SECURE : 0u;
        HINTERNET raw_req = WinHttpOpenRequest(connect.get(), widen(request.method).c_str(), target.c_str(),
                                               nullptr, WINHTTP_NO_REFERER, WINHTTP_DEFAULT_ACCEPT_TYPES,
                                               flags);
        if (!raw_req) {
            response.network_error = lastErrorMessage("WinHttpOpenRequest");
            return response;
        }

        // Ceiling at twice the caller's budget: each of the four
        // WinHttpSetTimeouts phases (resolve, connect, send, receive) is
        // allowed `timeout` on its own, so a slow-but-progressing exchange can
        // legitimately exceed one budget, and this must not cancel those. The
        // floor keeps a very small timeout_ms from producing a deadline the
        // exchange cannot meet on a cold connection.
        const DWORD deadline_ms = (timeout > 500u) ? (timeout * 2u) : 1000u;
        RequestDeadline req(raw_req, deadline_ms);

        // From here on, `req.get()` can be closed underneath us by the
        // watchdog; every WinHttp* failure below is therefore checked against
        // req.expired() before its GetLastError text is reported, so an
        // expired deadline reads as a timeout rather than as
        // "WinHttpReceiveResponse failed (GetLastError=12017)".
        const auto fail = [&](const char *what) -> HttpResponse {
            if (req.expired())
                response.network_error = "timed out after " + std::to_string(deadline_ms) + " ms";
            else
                response.network_error = lastErrorMessage(what);
            return response;
        };

        std::wstring headers;
        if (!request.content_type.empty())
            headers = L"Content-Type: " + widen(request.content_type) + L"\r\n";

        const LPCWSTR header_ptr = headers.empty() ? WINHTTP_NO_ADDITIONAL_HEADERS : headers.c_str();
        const DWORD header_len = headers.empty() ? 0u : static_cast<DWORD>(headers.size());

        void *body_ptr = request.body.empty() ? WINHTTP_NO_REQUEST_DATA
                                              : const_cast<char *>(request.body.data());
        const DWORD body_len = static_cast<DWORD>(request.body.size());

        if (!WinHttpSendRequest(req.get(), header_ptr, header_len, body_ptr, body_len, body_len, 0))
            return fail("WinHttpSendRequest");
        if (!WinHttpReceiveResponse(req.get(), nullptr))
            return fail("WinHttpReceiveResponse");

        DWORD status = 0;
        DWORD status_size = sizeof(status);
        if (!WinHttpQueryHeaders(req.get(), WINHTTP_QUERY_STATUS_CODE | WINHTTP_QUERY_FLAG_NUMBER,
                                 WINHTTP_HEADER_NAME_BY_INDEX, &status, &status_size, WINHTTP_NO_HEADER_INDEX))
            return fail("WinHttpQueryHeaders");
        response.status = static_cast<long>(status);

        std::string body;
        for (;;) {
            DWORD available = 0;
            if (!WinHttpQueryDataAvailable(req.get(), &available))
                return fail("WinHttpQueryDataAvailable");
            if (available == 0)
                break;
            if (body.size() + available > kMaxResponseBytes) {
                response.network_error = "response body exceeded 4 MiB";
                return response;
            }
            std::vector<char> chunk(available);
            DWORD read = 0;
            if (!WinHttpReadData(req.get(), chunk.data(), available, &read))
                return fail("WinHttpReadData");
            if (read == 0)
                break;
            body.append(chunk.data(), read);
        }

        response.body = std::move(body);
        return response;
    }
};

} // namespace

HttpClient *createPlatformHttpClient()
{
    return new WinHttpClient();
}

} // namespace stplugin