From aa0221d87ca355d5021f81f8f65cf6a47bc93c38 Mon Sep 17 00:00:00 2001
From: Sadie Powell <sadie@witchery.services>
Date: Sun, 20 Dec 2020 04:04:19 +0000
Subject: Replace the SERVER stub command with something actually useful.

This will typically never be reached because the remote will wait
until it receives a CAPAB response before sending SERVER. Instead
replace it with a CAPAB stub command that quits servers with a
helpful message.
---
 make/template/config.h     |  3 +++
 src/coremods/core_stub.cpp | 62 ++++++++++++++++++++--------------------------
 2 files changed, 30 insertions(+), 35 deletions(-)

diff --git a/make/template/config.h b/make/template/config.h
index a4a21250a..034191893 100644
--- a/make/template/config.h
+++ b/make/template/config.h
@@ -43,6 +43,9 @@
 /** The default location that module files are stored in. */
 #define INSPIRCD_MODULE_PATH "@MODULE_DIR@"
 
+/** The URL of the InspIRCd docs site. */
+#define INSPIRCD_DOCS "https://docs.inspircd.org/@VERSION_MAJOR@/"
+
 #ifndef _WIN32
  %target include/config.h
 
diff --git a/src/coremods/core_stub.cpp b/src/coremods/core_stub.cpp
index 0b7cfaa32..0448067c0 100644
--- a/src/coremods/core_stub.cpp
+++ b/src/coremods/core_stub.cpp
@@ -28,6 +28,29 @@ enum
 	ERR_USERSDISABLED = 446
 };
 
+class CommandCapab : public Command
+{
+ public:
+	CommandCapab(Module* parent)
+		: Command(parent, "CAPAB")
+	{
+		works_before_reg = true;
+	}
+
+	CmdResult Handle(User* user, const Params& parameters) CXX11_OVERRIDE
+	{
+		if (user->registered == REG_NONE)
+		{
+			// The CAPAB command is used in the server protocol for negotiating
+			// the protocol version when initiating a server connection. There
+			// is no legitimate reason for a user to send this so we disconnect
+			// users who sent it in order to help out server admins who have
+			// misconfigured their server.
+			ServerInstance->Users->QuitUser(user, "You can not connect a server to a client port. Read " INSPIRCD_DOCS "modules/spanningtree for docs on how to link a server.");
+		}
+		return CMD_FAILURE;
+	}
+};
 
 /** Handle /CONNECT.
  */
@@ -83,38 +106,6 @@ class CommandLinks : public Command
 	}
 };
 
-/** Handle /SERVER.
- */
-class CommandServer : public Command
-{
- public:
-	/** Constructor for server.
-	 */
-	CommandServer(Module* parent)
-		: Command(parent, "SERVER")
-	{
-		works_before_reg = true;
-	}
-
-	/** Handle command.
-	 * @param parameters The parameters to the command
-	 * @param user The user issuing the command
-	 * @return A value from CmdResult to indicate command success or failure.
-	 */
-	CmdResult Handle(User* user, const Params& parameters) CXX11_OVERRIDE
-	{
-		if (user->registered == REG_ALL)
-		{
-			user->WriteNumeric(ERR_ALREADYREGISTERED, "You are already registered. (Perhaps your IRC client does not have a /SERVER command).");
-		}
-		else
-		{
-			user->WriteNumeric(ERR_NOTREGISTERED, "SERVER", "You may not register as a server (servers have separate ports from clients, change your config)");
-		}
-		return CMD_FAILURE;
-	}
-};
-
 /** Handle /SQUIT.
  */
 class CommandSquit : public Command
@@ -175,18 +166,19 @@ class CommandUsers
 
 class CoreModStub : public Module
 {
+ private:
+ 	CommandCapab cmdcapab;
 	CommandConnect cmdconnect;
 	CommandLinks cmdlinks;
-	CommandServer cmdserver;
 	CommandSquit cmdsquit;
 	CommandSummon cmdsummon;
 	CommandUsers cmdusers;
 
  public:
 	CoreModStub()
-		: cmdconnect(this)
+		: cmdcapab(this)
+		, cmdconnect(this)
 		, cmdlinks(this)
-		, cmdserver(this)
 		, cmdsquit(this)
 		, cmdsummon(this)
 		, cmdusers(this)
-- 
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