Add tcp-mss support.

--- a/main.c
+++ b/main.c
@@ -44,7 +44,8 @@
 	signlen,
 	lsr_length = 0,
 	ssr_length = 0,
-	tcp_ack;
+	tcp_ack,
+	tcp_mss;
 
 
 unsigned short int
@@ -95,6 +96,7 @@
 	opt_tcpexitcode	= FALSE,
 	opt_badcksum	= FALSE,
 	opt_tr_keep_ttl = FALSE,
+	opt_tcp_mss	= FALSE,
 	opt_tcp_timestamp = FALSE,
 	opt_tr_stop	= FALSE,
 	opt_tr_no_rtt	= FALSE,
--- a/globals.h
+++ b/globals.h
@@ -32,7 +32,8 @@
 		tcp_seqnum,
 		set_ack,
 		ip_header_length,
-		tcp_ack;
+		tcp_ack,
+		tcp_mss;
 
 extern unsigned short int
 		data_size;
@@ -77,6 +78,7 @@
 		opt_tcpexitcode,
 		opt_badcksum,
 		opt_tr_keep_ttl,
+		opt_tcp_mss,
 		opt_tcp_timestamp,
 		opt_tr_stop,
 		opt_tr_no_rtt,
--- a/parseoptions.c
+++ b/parseoptions.c
@@ -31,7 +31,7 @@
 	OPT_RROUTE, OPT_IPPROTO, OPT_ICMP_IPVER, OPT_ICMP_IPHLEN,
 	OPT_ICMP_IPLEN, OPT_ICMP_IPID, OPT_ICMP_IPPROTO, OPT_ICMP_CKSUM,
 	OPT_ICMP_TS, OPT_ICMP_ADDR, OPT_TCPEXITCODE, OPT_FAST, OPT_TR_KEEP_TTL,
-	OPT_TCP_TIMESTAMP, OPT_TR_STOP, OPT_TR_NO_RTT, OPT_ICMP_HELP,
+	OPT_TCP_TIMESTAMP, OPT_TCP_MSS, OPT_TR_STOP, OPT_TR_NO_RTT, OPT_ICMP_HELP,
 	OPT_RAND_DEST, OPT_RAND_SOURCE, OPT_LSRR, OPT_SSRR, OPT_ROUTE_HELP,
 	OPT_ICMP_IPSRC, OPT_ICMP_IPDST, OPT_ICMP_SRCPORT, OPT_ICMP_DSTPORT,
 	OPT_ICMP_GW, OPT_FORCE_ICMP, OPT_APD_SEND, OPT_SCAN, OPT_FASTER,
@@ -124,6 +124,7 @@
 	{ '\0', "force-icmp",	OPT_FORCE_ICMP,		AGO_NOARG },
 	{ '\0', "beep",		OPT_BEEP,		AGO_NOARG },
 	{ '\0', "flood",	OPT_FLOOD,		AGO_NOARG },
+	{ '\0', "tcp-mss",	OPT_TCP_MSS,		AGO_NEEDARG|AGO_EXCEPT0 },
 	AGO_LIST_TERM
 };
 
@@ -556,6 +557,10 @@
 		case OPT_FLOOD:
 			opt_flood = TRUE;
 			break;
+		case OPT_TCP_MSS:
+			opt_tcp_mss = TRUE;
+			tcp_mss = strtoul(ago_optarg, NULL, 0);
+			break;
 		}
 	}
 
--- a/usage.c
+++ b/usage.c
@@ -87,6 +87,7 @@
 "  -X  --xmas       set X unused flag (0x40)\n"
 "  -Y  --ymas       set Y unused flag (0x80)\n"
 "  --tcpexitcode    use last tcp->th_flags as exit code\n"
+"  --tcp-mss        enable the TCP MSS option with the given value\n"
 "  --tcp-timestamp  enable the TCP timestamp option to guess the HZ/uptime\n"
 "Common\n"
 "  -d  --data       data size                    (default is 0)\n"
--- a/sendtcp.c
+++ b/sendtcp.c
@@ -28,10 +28,12 @@
 	char			*packet, *data;
 	struct mytcphdr		*tcp;
 	struct pseudohdr	*pseudoheader;
-	unsigned char		*tstamp;
+	unsigned char		*opts;
 
+	if (opt_tcp_mss)
+		tcp_opt_size += 4;
 	if (opt_tcp_timestamp)
-		tcp_opt_size = 12;
+		tcp_opt_size += 12;
 
 	packet_size = TCPHDR_SIZE + tcp_opt_size + data_size;
 	packet = malloc(PSEUDOHDR_SIZE + packet_size);
@@ -41,7 +43,7 @@
 	}
 	pseudoheader = (struct pseudohdr*) packet;
 	tcp =  (struct mytcphdr*) (packet+PSEUDOHDR_SIZE);
-	tstamp = (unsigned char*) (packet+PSEUDOHDR_SIZE+TCPHDR_SIZE);
+	opts = (unsigned char*) (packet+PSEUDOHDR_SIZE+TCPHDR_SIZE);
 	data = (char*) (packet+PSEUDOHDR_SIZE+TCPHDR_SIZE+tcp_opt_size);
 	
 	memset(packet, 0, PSEUDOHDR_SIZE+packet_size);
@@ -64,14 +66,24 @@
 	tcp->th_win	= htons(src_winsize);
 	tcp->th_flags	= tcp_th_flags;
 
+	/* tcp MSS option */
+	if (opt_tcp_mss) {
+		opts[0] = 2;
+		opts[1] = 4;  /* 4 bytes, kind+len+MSS */
+		opts[2] = tcp_mss >> 8;
+		opts[3] = tcp_mss & 0xff;
+		opts += 4;
+	}
+
 	/* tcp timestamp option */
 	if (opt_tcp_timestamp) {
 		__u32 randts = rand() ^ (rand() << 16);
-		tstamp[0] = tstamp[1] = 1; /* NOOP */
-		tstamp[2] = 8;
-		tstamp[3] = 10; /* 10 bytes, kind+len+T1+T2 */
-		memcpy(tstamp+4, &randts, 4); /* random */
-		memset(tstamp+8, 0, 4); /* zero */
+		opts[0] = opts[1] = 1; /* NOOP */
+		opts[2] = 8;
+		opts[3] = 10; /* 10 bytes, kind+len+T1+T2 */
+		memcpy(opts+4, &randts, 4); /* random */
+		memset(opts+8, 0, 4); /* zero */
+		opts += 12;
 	}
 
 	/* data */
--- a/docs/hping3.8
+++ b/docs/hping3.8
@@ -98,6 +98,8 @@
 ] [
 .B \-\-tcpexitcode
 ] [
+.B \-\-tcp-mss
+] [
 .B \-\-tcp-timestamp
 ] [
 .B \-\-tr-stop
@@ -510,6 +512,9 @@
 .I -b --badcksum
 Send packets with a bad UDP/TCP checksum.
 .TP
+.I --tcp-mss
+Enable the TCP MSS option and set it to the given value.
+.TP
 .I --tcp-timestamp
 Enable the TCP timestamp option, and try to guess the timestamp update
 frequency and the remote system uptime.
--- a/docs/french/hping2-fr.8
+++ b/docs/french/hping2-fr.8
@@ -99,6 +99,8 @@
 ] [
 .B \-\-tcpexitcode
 ] [
+.B \-\-tcp-mss
+] [
 .B \-\-tcp-timestamp
 ] [
 .B \-\-tr-stop
@@ -549,6 +551,9 @@
 .I -b --badcksum
 Envoie des paquets avec une mauvaise somme de contrôle UDP/TCP
 .TP
+.I --tcp-mss
+Active l'option TCP MSS et la fixe avec la valeur donnée.
+.TP
 .I --tcp-timestamp
 Active l'option TCP timestamp, et essaye de deviner la fréquence de mise à
 jour du timestamp et l'uptime du système distant.