UI: Add intro startup page (windows)

Allows the ability to show a web page via CEF to the users on startup to
present and announce new features.

UI/win-update/win-update.cpp

@@ -27,11 +27,15 @@ using namespace std;
 #define WIN_MANIFEST_URL "https://obsproject.com/update_studio/manifest.json"
 #endif
 
+#ifndef WIN_WHATSNEW_URL
+#define WIN_WHATSNEW_URL "https://obsproject.com/update_studio/whatsnew.json"
+#endif
+
 #ifndef WIN_UPDATER_URL
 #define WIN_UPDATER_URL "https://obsproject.com/update_studio/updater.exe"
 #endif
 
-static HCRYPTPROV provider = 0;
+static __declspec(thread) HCRYPTPROV provider = 0;
 
 #pragma pack(push, r1, 1)
 
@@ -780,3 +784,114 @@ try {
 } catch (string text) {
 	blog(LOG_WARNING, "%s: %s", __FUNCTION__, text.c_str());
 }
+
+/* ------------------------------------------------------------------------ */
+
+void WhatsNewInfoThread::run()
+try {
+	long           responseCode;
+	vector<string> extraHeaders;
+	string         text;
+	string         error;
+	string         signature;
+	CryptProvider  localProvider;
+	BYTE           whatsnewHash[BLAKE2_HASH_LENGTH];
+	bool           success;
+
+	BPtr<char> whatsnewPath = GetConfigPathPtr(
+			"obs-studio\\updates\\whatsnew.json");
+
+	/* ----------------------------------- *
+	 * create signature provider           */
+
+	if (!CryptAcquireContext(&localProvider,
+	                         nullptr,
+	                         MS_ENH_RSA_AES_PROV,
+	                         PROV_RSA_AES,
+	                         CRYPT_VERIFYCONTEXT))
+		throw strprintf("CryptAcquireContext failed: %lu",
+				GetLastError());
+
+	provider = localProvider;
+
+	/* ----------------------------------- *
+	 * avoid downloading json again        */
+
+	if (CalculateFileHash(whatsnewPath, whatsnewHash)) {
+		char hashString[BLAKE2_HASH_STR_LENGTH];
+		HashToString(whatsnewHash, hashString);
+
+		string header = "If-None-Match: ";
+		header += hashString;
+		extraHeaders.push_back(move(header));
+	}
+
+	/* ----------------------------------- *
+	 * get current install GUID            */
+
+	const char *pguid = config_get_string(GetGlobalConfig(),
+			"General", "InstallGUID");
+	string guid;
+	if (pguid)
+		guid = pguid;
+
+	if (guid.empty()) {
+		GenerateGUID(guid);
+
+		if (!guid.empty())
+			config_set_string(GetGlobalConfig(),
+					"General", "InstallGUID",
+					guid.c_str());
+	}
+
+	if (!guid.empty()) {
+		string header = "X-OBS2-GUID: ";
+		header += guid;
+		extraHeaders.push_back(move(header));
+	}
+
+	/* ----------------------------------- *
+	 * get json from server                */
+
+	success = GetRemoteFile(WIN_WHATSNEW_URL, text, error, &responseCode,
+			nullptr, nullptr, extraHeaders, &signature);
+
+	if (!success || (responseCode != 200 && responseCode != 304)) {
+		if (responseCode == 404)
+			return;
+
+		throw strprintf("Failed to fetch whatsnew file: %s",
+				error.c_str());
+	}
+
+	/* ----------------------------------- *
+	 * verify file signature               */
+
+	if (responseCode == 200) {
+		success = CheckDataSignature(text, "whatsnew",
+				signature.data(), signature.size());
+		if (!success)
+			throw string("Invalid whatsnew signature");
+	}
+
+	/* ----------------------------------- *
+	 * write or load json                  */
+
+	if (responseCode == 200) {
+		if (!QuickWriteFile(whatsnewPath, text.data(), text.size()))
+			throw strprintf("Could not write file '%s'",
+					whatsnewPath.Get());
+	} else {
+		if (!QuickReadFile(whatsnewPath, text))
+			throw strprintf("Could not read file '%s'",
+					whatsnewPath.Get());
+	}
+
+	/* ----------------------------------- *
+	 * success                             */
+
+	emit Result(QString::fromUtf8(text.c_str()));
+
+} catch (string text) {
+	blog(LOG_WARNING, "%s: %s", __FUNCTION__, text.c_str());
+}