Implement `singleplayer` in the dedicated server.

When set to `1`, both `deathmatch` and `coop` are forced to `0`.
`maxclients` is forced to `1`. This makes it possible to play single
player campaigns over the dedicated server.

Closes #614.

doc/040_cvarlist.md

@@ -95,6 +95,16 @@ it's `+set busywait 0` (setting the `busywait` cvar) and `-portable`
   during gameplay and released otherwise (in menu, videos, console or if
   game is paused).
 
+* **singleplayer**: Only available in the dedicated server. Vanilla
+  Quake II enforced that either `coop` or `deathmatch` is set to `1`
+  when running the dedicated server. That made it impossible to play
+  single player campaigns over the dedicated server. When set to `1`,
+  both `coop` and `deathmatch` are forced to `0` and `maxclients` is
+  forced to `1`. This can be used to run a dedicated server with an old
+  single player mod, where the source code isn't available, inside a
+  Windows 98 or XP VM and connect over network from an non Windows
+  system.
+
 * **coop_pickup_weapons**: In coop a weapon can be picked up only once.
   For example, if the player already has the shotgun they cannot pickup
   a second shotgun found at a later time, thus not getting the ammo that

src/server/sv_init.c

@@ -333,6 +333,12 @@ SV_InitGame(void)
 
 	svs.initialized = true;
 
+	if (Cvar_VariableValue("singleplayer"))
+	{
+		Cvar_FullSet("coop", "0", CVAR_SERVERINFO | CVAR_LATCH);
+		Cvar_FullSet("deathmatch", "0", CVAR_SERVERINFO | CVAR_LATCH);
+	}
+
 	if (Cvar_VariableValue("coop") && Cvar_VariableValue("deathmatch"))
 	{
 		Com_Printf("Deathmatch and Coop both set, disabling Coop\n");
@@ -343,9 +349,12 @@ SV_InitGame(void)
 	   so unless they explicity set coop, force it to deathmatch */
 	if (dedicated->value)
 	{
-		if (!Cvar_VariableValue("coop"))
+		if (!Cvar_VariableValue("singleplayer"))
 		{
-			Cvar_FullSet("deathmatch", "1", CVAR_SERVERINFO | CVAR_LATCH);
+			if (!Cvar_VariableValue("coop"))
+			{
+				Cvar_FullSet("deathmatch", "1", CVAR_SERVERINFO | CVAR_LATCH);
+			}
 		}
 	}
 
@@ -358,9 +367,10 @@ SV_InitGame(void)
 		}
 		else if (maxclients->value > MAX_CLIENTS)
 		{
-			Cvar_FullSet("maxclients", va("%i",
-						MAX_CLIENTS), CVAR_SERVERINFO | CVAR_LATCH);
+			Cvar_FullSet("maxclients", va("%i", MAX_CLIENTS), CVAR_SERVERINFO | CVAR_LATCH);
 		}
+
+		Cvar_FullSet("singleplayer", "0", 0);
 	}
 	else if (Cvar_VariableValue("coop"))
 	{
@@ -368,20 +378,36 @@ SV_InitGame(void)
 		{
 			Cvar_FullSet("maxclients", "4", CVAR_SERVERINFO | CVAR_LATCH);
 		}
+
+		Cvar_FullSet("singleplayer", "0", 0);
 	}
 	else /* non-deathmatch, non-coop is one player */
 	{
 		Cvar_FullSet("maxclients", "1", CVAR_SERVERINFO | CVAR_LATCH);
+		Cvar_FullSet("singleplayer", "1", 0);
 	}
 
 	svs.spawncount = randk();
 	svs.clients = Z_Malloc(sizeof(client_t) * maxclients->value);
 	svs.num_client_entities = maxclients->value * UPDATE_BACKUP * 64;
-	svs.client_entities =
-		Z_Malloc( sizeof(entity_state_t) * svs.num_client_entities);
+	svs.client_entities = Z_Malloc( sizeof(entity_state_t) * svs.num_client_entities);
 
 	/* init network stuff */
-	NET_Config((maxclients->value > 1));
+	if (dedicated->value)
+	{
+		if (Cvar_VariableValue("singleplayer"))
+		{
+			NET_Config(true);
+		}
+		else
+		{
+			NET_Config((maxclients->value > 1));
+		}
+	}
+	else
+	{
+		NET_Config((maxclients->value > 1));
+	}
 
 	/* heartbeats will always be sent to the id master */
 	svs.last_heartbeat = -99999; /* send immediately */

src/server/sv_main.c

@@ -584,6 +584,7 @@ SV_Init(void)
 
 	rcon_password = Cvar_Get("rcon_password", "", 0);
 	Cvar_Get("skill", "1", 0);
+	Cvar_Get("singleplayer", "0", 0);
 	Cvar_Get("deathmatch", "0", CVAR_LATCH);
 	Cvar_Get("coop", "0", CVAR_LATCH);
 	Cvar_Get("dmflags", va("%i", DF_INSTANT_ITEMS), CVAR_SERVERINFO);