* Server to server lines can now be 16384 bytes in size when

`PROTOCTL BIGLINES` is set. This will allow us to do things more
  efficiently and possibly raise some other limits in the future.
  This 16k is the size of the complete line, including sender,
  message tags, content and \r\n. Also, in server-to-server traffic
  we now allow 30 parameters (MAXPARA*2).
  The original input size limits for non-servers remain the same: the
  complete line can be 4k+512, with the non-mtag portion limit set
  at 512 bytes (including \r\n), and MAXPARA is still 15 as well.
* I chose 16k because I don't want to first raise it to like 8k
  and then realize later that 16k would be better and raise it again.
* To receive BIGLINES in a command, you need to `CommandAdd()` with
  flags `CMD_BIGLINES`, without it you still get regular 512 max.
  This is so, because a lot of the code does not expect longer than
  512 bytes lines or in parameters, so we can gradually change that
  (where needed).

doc/RELEASE-NOTES.md

@@ -107,6 +107,22 @@ in progress and may not be a stable version.
 * The [`require module` block](https://www.unrealircd.org/docs/Require_module_block)
   was only checked of one side of the link, thus partially not working.
 
+### Developers and protocol:
+* Server to server lines can now be 16384 bytes in size when
+  `PROTOCTL BIGLINES` is set. This will allow us to do things more
+  efficiently and possibly raise some other limits in the future.
+  This 16k is the size of the complete line, including sender,
+  message tags, content and \r\n. Also, in server-to-server traffic
+  we now allow 30 parameters (MAXPARA*2).  
+  The original input size limits for non-servers remain the same: the
+  complete line can be 4k+512, with the non-mtag portion limit set
+  at 512 bytes (including \r\n), and MAXPARA is still 15 as well.
+* To receive BIGLINES in a command, you need to `CommandAdd()` with
+  flags `CMD_BIGLINES`, without it you still get regular 512 max.
+  This is so, because a lot of the code does not expect longer than
+  512 bytes lines or in parameters, so we can gradually change that
+  (where needed).
+
 UnrealIRCd 6.1.0
 -----------------
 This is UnrealIRCd 6.1.0 stable. It is the direct successor to 6.0.7, there

include/channel.h

@@ -33,8 +33,6 @@
  * before Dreamforge aren't safe with more than six. -Donwulff
  */
 #include "msg.h"
-#define	MAXMODEPARAMS	(MAXPARA-3)	/* Maximum modes processed */
-#define RESYNCMODES	12	/* Max modes per MODE in resync */
-#define MODEPARAMS	6	/* Max modes from user */
+#define	MAXMODEPARAMS	(MAXPARA_USER-3)	/* Maximum modes processed */
 
 #endif

include/msg.h

@@ -167,6 +167,7 @@
 
 #define MSG_MLOCK	"MLOCK"
 
-#define MAXPARA    	15
+#define MAXPARA    	30
+#define MAXPARA_USER	15
 
 #endif

include/struct.h

@@ -183,8 +183,9 @@ typedef OperPermission (*OperClassEntryEvalCallback)(OperClassACLEntryVar* varia
 #define LINKLEN		32
 #define	BUFSIZE		512	/* WARNING: *DONT* CHANGE THIS!!!! */
 #define MAXTAGSIZE	8192	/**< Maximum length of message tags (4K user + 4K server) */
-#define MAXLINELENGTH	(MAXTAGSIZE+BUFSIZE)	/**< Maximum length of a line on IRC: 4k client tags + 4k server tags + 512 bytes (IRCv3) */
-#define READBUFSIZE	MAXLINELENGTH	/* for the read buffer */
+#define MAXLINELENGTH_USER	(MAXTAGSIZE+BUFSIZE)	/**< Maximum length of a line on IRC (for non-servers): 4k client tags + 4k server tags + 512 bytes (IRCv3) */
+#define MAXLINELENGTH	16384			/**< Maximum length of a line on IRC: from servers is 16k */
+#define READBUFSIZE	MAXLINELENGTH	/**< for the read buffer */
 #define	MAXRECIPIENTS 	20
 #define	MAXSILELENGTH	NICKLEN+USERLEN+HOSTLEN+10
 #define IDLEN		12
@@ -449,6 +450,7 @@ typedef enum ClientStatus {
 #define PROTO_SJSBY	0x000020	/* SJOIN setby information (TS and nick) */
 #define PROTO_MTAGS	0x000040	/* Support message tags and big buffers */
 #define PROTO_NEXTBANS	0x000080	/* Server supports named extended bans */
+#define PROTO_BIGLINES	0x000100	/* BIGLINES support */
 
 /* For client capabilities: */
 #define CAP_INVERT	1L
@@ -614,6 +616,7 @@ typedef enum ClientStatus {
 #define SupportCLK(x)		(CHECKSERVERPROTO(x, PROTO_CLK))
 #define SupportMTAGS(x)		(CHECKSERVERPROTO(x, PROTO_MTAGS))
 #define SupportNEXTBANS(x)	(CHECKSERVERPROTO(x, PROTO_NEXTBANS))
+#define SupportBIGLINES(x)	(CHECKSERVERPROTO(x, PROTO_BIGLINES))
 
 #define SetVL(x)		((x)->local->proto |= PROTO_VL)
 #define SetSJSBY(x)		((x)->local->proto |= PROTO_SJSBY)
@@ -621,6 +624,7 @@ typedef enum ClientStatus {
 #define SetCLK(x)		((x)->local->proto |= PROTO_CLK)
 #define SetMTAGS(x)		((x)->local->proto |= PROTO_MTAGS)
 #define SetNEXTBANS(x)		((x)->local->proto |= PROTO_NEXTBANS)
+#define SetBIGLINES(x)		((x)->local->proto |= PROTO_BIGLINES)
 
 /* Dcc deny types (see src/s_extra.c) */
 #define DCCDENY_HARD	0
@@ -917,6 +921,8 @@ struct SWhois {
 #define CMD_OPER		0x0200
 /** Command is for control channel only (unrealircd.ctl socket) */
 #define CMD_CONTROL		0x0400
+/** Command is able to receive BIG lines */
+#define CMD_BIGLINES		0x0800
 
 /** Command function - used by all command handlers.
  * This is used in the code like <pre>CMD_FUNC(cmd_yourcmd)</pre> as a function definition.

src/modules/protoctl.c

@@ -122,6 +122,10 @@ CMD_FUNC(cmd_protoctl)
 		{
 			SetNEXTBANS(client);
 		}
+		else if (!strcmp(name, "BIGLINES"))
+		{
+			SetBIGLINES(client);
+		}
 		else if (!strcmp(name, "NICKCHARS") && value)
 		{
 			if (!IsServer(client) && !IsEAuth(client) && !IsHandshake(client))

src/parse.c

@@ -251,12 +251,13 @@ void parse(Client *cptr, char *buffer, int length)
  *               	the message has a sender, eg :xyz PRIVMSG ..
  * @param mtags  	Message tags received for this message.
  * @param mtags_bytes	The length of all message tags.
- * @param ch		The incoming line received (buffer), excluding message tags.
+ * @param line		The incoming line received (buffer), excluding message tags.
  */
-static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_bytes, char *ch)
+static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_bytes, char *line)
 {
 	Client *from = cptr;
 	char *s;
+	char *ch = line;
 	int len, i, numeric = 0, paramcount;
 #ifdef DEBUGMODE
 	time_t then, ticks;
@@ -267,14 +268,14 @@ static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_
 
 	*fromptr = cptr; /* The default, unless a source is specified (and permitted) */
 
-	/* The remaining part should never be more than 510 bytes
-	 * (that is 512 minus CR LF, as specified in RFC1459 section 2.3).
+	/* In client-to-server traffic, the remaining part should
+	 * never be more than 510 bytes (that is 512 minus CR LF,
+	 * as specified in RFC1459 section 2.3).
 	 * If it is too long, then we cut it off here.
+	 * Note that there is a second check later for the IsServer() case.
 	 */
-	if (strlen(ch) > 510)
-	{
+	if (!IsServer(cptr) && (strlen(ch) > 510))
 		ch[510] = '\0';
-	}
 
 	para[0] = (char *)DEADBEEF_ADDR; /* helps us catch bugs :) */
 
@@ -355,6 +356,20 @@ static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_
 	s = strchr(ch, ' ');	/* s -> End of the command code */
 	len = (s) ? (s - ch) : 0;
 
+	/* An early "guard": check for oversized command name
+	 * (not parameters, the actual command name being 512+ chars),
+	 * just in case... especially for BIGLINES.
+	 */
+	if (len > 512)
+	{
+		ch[510] = '\0';
+		sendto_one(from, NULL, ":%s %d %s %s :Unknown command",
+				       me.name, ERR_UNKNOWNCOMMAND,
+				       from->name, ch);
+		ircstats.is_unco++;
+		return;
+	}
+
 	if (len == 3 && isdigit(*ch) && isdigit(*(ch + 1)) && isdigit(*(ch + 2)))
 	{
 		/* Numeric (eg: 311) */
@@ -462,11 +477,26 @@ static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_
 	   ** (about same effect as ":" has...) --msa
 	 */
 
+	/* The high MAXPARA is only for servers, so readjust here for clients... */
+	if (!IsServer(from) && (paramcount > MAXPARA_USER))
+		paramcount = MAXPARA_USER;
+
 	/* Note initially true: s==NULL || *(s-1) == '\0' !! */
 
 	i = 0;
 	if (s)
 	{
+		if (IsServer(cptr) && (!cmptr || !(cmptr->flags & CMD_BIGLINES)))
+		{
+			int slen = strlen(s);
+			if ((s-line)+slen > 510)
+			{
+				ch[510] = '\0'; /* same as check at beginning of this function */
+				if (slen > 510)
+					s[510] = '\0'; /* just in case the earlier cut was like mid-sender instead of in parameters */
+			}
+		}
+
 		/*
 		if (paramcount > MAXPARA)
 			paramcount = MAXPARA;

src/send.c

@@ -253,11 +253,33 @@ static int sendbufto_one_prepare_line(Client *to, char *msg)
 	len = strlen(p);
 	if (!len || (p[len - 1] != '\n'))
 	{
-		if (len > 510)
-			len = 510;
-		p[len++] = '\r';
-		p[len++] = '\n';
-		p[len] = '\0';
+		if (!IsServer(to) || !SupportBIGLINES(to->direction))
+		{
+			/* Normal case */
+			if (len > 510)
+				len = 510;
+			p[len++] = '\r';
+			p[len++] = '\n';
+			p[len] = '\0';
+		} else {
+			/* BIGLINES case:
+			 * - first 'if' is about the total line length,
+			 *   this is basically an optimized strlen(msg)
+			 * - the 'else' applies to non-mtags part,
+			 *   like in the 'Normal case' from above.
+			 */
+			if ((p - msg) + len > MAXLINELENGTH-3)
+			{
+				len = MAXLINELENGTH-3;
+				msg[len++] = '\r';
+				msg[len++] = '\n';
+				msg[len] = '\0';
+			} else {
+				p[len++] = '\r';
+				p[len++] = '\n';
+				p[len] = '\0';
+			}
+		}
 	}
 
 	/* Return length, that is:

src/serv.c

@@ -264,7 +264,7 @@ void send_proto(Client *client, ConfigItem_link *aconf)
 		me.id, (long long)TStime());
 
 	/* Third line */
-	sendto_one(client, NULL, "PROTOCTL NICKCHARS=%s CHANNELCHARS=%s",
+	sendto_one(client, NULL, "PROTOCTL NICKCHARS=%s CHANNELCHARS=%s BIGLINES",
 		charsys_get_current_languages(),
 		allowed_channelchars_valtostr(iConf.allowed_channelchars));
 }