Commit of UpdateCheck 1.0b ( https://forums.alliedmods.net/showthread.php?p=2358118 ).

Pawn/UpdateCheck.sp

@@ -0,0 +1,129 @@
+#pragma semicolon 1
+#include <sourcemod>
+#include <SteamWorks>
+
+new g_iPatchVersion = 0;
+new g_iAppID = 0;
+
+new Handle:g_hForward = INVALID_HANDLE;
+
+public Plugin:myinfo =
+{
+    name 			=		"SteamWorks Update Check",				/* https://www.youtube.com/watch?v=Tq_0ht8HCcM */
+    author			=		"Kyle Sanderson",
+    description		=		"Queries SteamWeb for Updates.",
+    version			=		"1.0b",
+    url				=		"https://AlliedMods.net"
+};
+
+static stock bool:ReadSteamINF(const String:sPath[], &iAppID, &iPatchVersion)
+{
+	new Handle:hFile = OpenFile(sPath, "r");
+	if (hFile == INVALID_HANDLE)
+	{
+		return false;
+	}
+
+	decl String:sBuffer[256];
+
+	do
+	{
+		if (!ReadFileLine(hFile, sBuffer, sizeof(sBuffer)))
+		{
+			continue;
+		}
+
+		TrimString(sBuffer);
+		ReplaceString(sBuffer, sizeof(sBuffer), ".", ""); /* CS:GO uses decimals in steam.inf, WebAPI is Steam| style. */
+
+		new iPos = FindCharInString(sBuffer, '=');
+		if (iPos == -1)
+		{
+			continue;
+		}
+
+		sBuffer[iPos++] = '\0';
+		switch (CharToLower(sBuffer[0]))
+		{
+			case 'a':
+			{
+				if (!StrEqual(sBuffer, "appID", false))
+				{
+					continue;
+				}
+
+				iAppID = StringToInt(sBuffer[iPos]);
+			}
+
+			case 'p':
+			{
+				if (!StrEqual(sBuffer, "PatchVersion", false))
+				{
+					continue;
+				}
+
+				iPatchVersion = StringToInt(sBuffer[iPos]);
+			}
+		}
+	} while (!IsEndOfFile(hFile));
+
+	CloseHandle(hFile);
+	return true;
+}
+
+public OnPluginStart()
+{
+	if (!ReadSteamINF("steam.inf", g_iAppID, g_iPatchVersion) && !ReadSteamINF("../steam.inf", g_iAppID, g_iPatchVersion))
+	{
+		SetFailState("Unable to read steam.inf");
+	}
+
+	g_hForward = CreateGlobalForward("SteamWorks_RestartRequested", ET_Ignore);
+}
+
+public OnMapStart()
+{
+	CreateTimer(120.0, OnCheckForUpdate, _, TIMER_FLAG_NO_MAPCHANGE|TIMER_REPEAT);
+}
+
+public Action:OnCheckForUpdate(Handle:hTimer)
+{
+	static String:sRequest[256];
+	if (sRequest[0] == '\0')
+	{
+		FormatEx(sRequest, sizeof(sRequest), "http://api.steampowered.com/ISteamApps/UpToDateCheck/v0001/?appid=%u&version=%u&format=xml", g_iAppID, g_iPatchVersion);
+	}
+
+	new Handle:hRequest = SteamWorks_CreateHTTPRequest(k_EHTTPMethodGET, sRequest);
+	if (!hRequest || !SteamWorks_SetHTTPCallbacks(hRequest, OnTransferComplete) || !SteamWorks_SendHTTPRequest(hRequest))
+	{
+		CloseHandle(hRequest);
+	}
+
+	return Plugin_Continue;
+}
+
+public OnTransferComplete(Handle:hRequest, bool:bFailure, bool:bRequestSuccessful, EHTTPStatusCode:eStatusCode)
+{
+	if (!bFailure && bRequestSuccessful && eStatusCode == k_EHTTPStatusCode200OK)
+	{
+		SteamWorks_GetHTTPResponseBodyCallback(hRequest, APIWebResponse);
+	}
+
+	CloseHandle(hRequest);
+}
+
+public APIWebResponse(const String:sData[])
+{
+	new iPos = StrContains(sData, "<required_version>");
+	if (iPos == -1)
+	{
+		return;
+	}
+
+	if (g_iPatchVersion != StringToInt(sData[iPos+18]))
+	{
+		Call_StartForward(g_hForward);
+		Call_Finish();
+	}
+}