Server: add "Cheaters Lament", a proof of concept detection mechanism for suspicious player behaviour

src/server/defs.h

@@ -26,6 +26,7 @@
 
 #include "route.h"
 #include "way.h"
+#include "lament.h"
 
 /* helper macros */
 #define EVALUATE_FIELD(fieldname, changedflag) {\

src/server/entry.qc

@@ -255,6 +255,8 @@ SV_RunClientCommand(void)
 	if (self.classname != "player" && self.classname != "spectator")
 		return;
 
+	CheatersLament((NSClientPlayer)cl, input_angles, input_buttons, input_timelength);
+
 	if (!Plugin_RunClientCommand()) {
 		/* TODO */
 	}

src/server/include.src

@@ -9,6 +9,7 @@ NSGameRules.qc
 client.qc
 NSTraceAttack.qc
 vote.qc
+lament.qc
 weapons.qc
 modelevent.qc
 mapcycle.qc

src/server/lament.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2023 Vera Visions LLC.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+void CheatersLament(NSClientPlayer, vector, float, float);

src/server/lament.qc

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2023 Vera Visions LLC.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+/* cheaters lament
+
+a system designed to analyze movement deltas and warn about suspicious
+behaviour as it is happening.
+
+explanation:
+
+intense movement comes with decreased accuracy. if a player is
+showcasing signs of above average reaction time and consistent success
+in trailing (and shooting) valid targets we are going to inform the
+server admin of suspicious behaviour.
+
+the system does not act on its own, it merely gives feedback and
+expects the host to act upon it.
+
+we can tally the feedback and create a score based on suspicious
+behaviour as a result. these results should ideally be made public
+to the other players so they themselves can make a choice
+
+technical deep dive:
+
+we accumulate the camera angle deltas over time to track
+the average mouse movement intensity over a short period of time.
+waiting a full second will actually remove a full 360 degrees
+of delta.
+then we also accumulate accuracy information, we increases a counter
+whenever the player is actively firing, while also aiming at an opposing
+player within an radius of less than 10 degrees (to compensate for rocket shots
+and othe projectile trails).
+whenever the player is firing and not aiming with that level of precision,
+the counter goes down.
+
+if the deltas together reach a high point together, that must mean that
+the player is having frantic mouse movements, combined with
+incredible hit accuracy.
+
+the high point calibration is taken from analyzing various demos
+of known pro players as well as some cheating incidents.
+
+limitations:
+
+when going through teleporters, the angle deltas may be high
+enough to trigger false positives.
+
+this is obviously not a perfect system, but it is to be used
+as a tool to assist in the decision making that goes into
+moderating a game server.
+*/
+
+void
+CheatersLament(NSClientPlayer playerEntity, vector absAngles, float buttons, float timeLength)
+{
+	vector angleDelta = playerEntity.pb_last_angles - absAngles; /* diff between old and new */
+
+	/* only decrement above 0 */
+	if (playerEntity.pb_angle_delta > 0.0)
+		playerEntity.pb_angle_delta -= timeLength * 360;
+	else
+		playerEntity.pb_angle_delta = 0.0f;
+
+	/* ditto */
+	if (playerEntity.pb_player_delta > 0.0)
+		playerEntity.pb_player_delta -= timeLength;
+	else
+		playerEntity.pb_player_delta = 0.0f;
+
+	/* if the player is firing, calculate the player delta */
+	if (buttons & INPUT_BUTTON0 || buttons & INPUT_BUTTON3) { /* primary & secondary fire counts */
+		vector deltaPosition;
+		float deltaDegrees;
+
+		makevectors( absAngles );
+		for (entity e = world; (e = find(e, ::classname, "player"));) {
+			deltaPosition = normalize( e.origin - playerEntity.origin );
+			deltaDegrees = deltaPosition * v_forward;
+
+			other = world;
+			traceline(e.origin, playerEntity.origin, MOVE_OTHERONLY, playerEntity);
+
+			if (trace_fraction == 1.0f && deltaDegrees >= 0.95) {
+				playerEntity.pb_player_delta += timeLength * 4.0f;
+			}
+		}
+	}
+
+	playerEntity.pb_last_angles = absAngles; /* set so we don't accumulate */
+
+	/* if our angle delta is less than 256, don't bother reporting */
+	if (vlen(angleDelta) < 256.0) {
+		return;
+	}
+
+	/* we will add the difference only if it is big enough from last frame */
+	playerEntity.pb_angle_delta += vlen(angleDelta);
+
+	/* if our delta is consistently above 1024 and we've been trailing a player for 2
+		whole second... suspect foul play */
+	if (playerEntity.pb_angle_delta > 1024.0 && playerEntity.pb_player_delta > 2.0) {
+		localcmd(sprintf("echo Lamenting %S (%s) with (a: %f p: %f)\n", playerEntity.netname, infokey(playerEntity, INFOKEY_P_IP), playerEntity.pb_angle_delta,  playerEntity.pb_player_delta));
+	}
+}

src/shared/NSClientPlayer.h

@@ -168,6 +168,10 @@ private:
 	float m_flPainTime;
 
 	entity last_used;
+
+	float pb_angle_delta;
+	float pb_player_delta;
+	vector pb_last_angles;
 #endif
 };