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aan: use sync messages as keep alives

both server and client need to be convinced that the connection
is broken for a connection reestablishment to happen as the server
will only start looking for incoming clients when the connection
already broke. so use the 8 second interval sync messages
to check for connection lifeness. if we miss two syncs in time,
we declare the connecton to be broken and will try to reconnect.

--- a/sys/src/cmd/aan.c

+++ b/sys/src/cmd/aan.c

@@ -21,14 +21,6 @@

 	Hdrsz = 3*4,

 };

-typedef struct Endpoints Endpoints;

-struct Endpoints {

-	char	*lsys;

-	char	*lserv;

-	char	*rsys;

-	char	*rserv;

-};

-

 typedef struct {

 	uchar	nb[4];		// Number of data bytes in this message

 	uchar	msg[4];		// Message number

@@ -35,7 +27,7 @@

 	uchar	acked[4];	// Number of messages acked

 } Hdr;

-typedef struct t_Buf {

+typedef struct {

 	Hdr	hdr;

 	uchar	buf[Bufsize];

 } Buf;

@@ -52,6 +44,8 @@

 static int	maxto = Maxto;

 static char	*Logname = "aan";

 static int	client;

+static int	reader = -1;

+static int	lostsync;

 static Alt a[] = {

 	/*	c	v	 op   */

@@ -62,7 +56,7 @@

 static void		fromnet(void*);

 static void		fromclient(void*);

-static void		reconnect(int);

+static int		reconnect(int);

 static void		synchronize(void);

 static int 		sendcommand(ulong, ulong);

 static void		showmsg(int, char *, Buf *);

@@ -77,6 +71,7 @@

 	exits("usage");

 }

+ 

 static int

 catch(void *, char *s)

 {

@@ -107,6 +102,7 @@

 	vlong synctime;

 	int i, n, failed;

 	Channel *timer;

+	Hdr hdr;

 	Buf *b;

 	ARGBEGIN {

@@ -151,8 +147,7 @@

 	 * long if there is some general connection problem

 	 * (like NAT).

 	 */

-	netfd = -1;

-	reconnect(60);

+	netfd = reconnect(60);

 	unsent = chancreate(sizeof(Buf *), Nbuf);

 	unacked = chancreate(sizeof(Buf *), Nbuf);

@@ -164,7 +159,8 @@

 	for (i = 0; i < Nbuf; i++)

 		sendp(empty, emalloc(sizeof(Buf)));

-	if (proccreate(fromnet, nil, Stacksize) < 0)

+	reader = proccreate(fromnet, nil, Stacksize);

+	if (reader < 0)

 		sysfatal("Cannot start fromnet; %r");

 	if (proccreate(fromclient, nil, Stacksize) < 0)

@@ -177,24 +173,29 @@

 	a[Unsent].c = unsent;

 	a[Unsent].v = &b;

+Restart:

 	synctime = nsec() + Synctime;

 	failed = 0;

+	lostsync = 0;

 	while (!done) {

 		if (failed) {

 			// Wait for the netreader to die.

 			while (netfd >= 0) {

 				dmessage(1, "main; waiting for netreader to die\n");

+				threadint(reader);

 				sleep(1000);

 			}

 			// the reader died; reestablish the world.

-			reconnect(maxto);

+			netfd = reconnect(maxto);

 			synchronize();

-			failed = 0;

+			goto Restart;

 		}

-		if (nsec() >= synctime) {

-			Hdr hdr;

+		switch (alt(a)) {

+		case Timer:

+			if (netfd < 0 || nsec() < synctime)

+				break;

 			PBIT32(hdr.nb, 0);

 			PBIT32(hdr.acked, inmsg);

@@ -205,11 +206,13 @@

 				failed = 1;

 				continue;

 			}

-			synctime = nsec() + Synctime;

-		}

-		switch (alt(a)) {

-		case Timer:

+			if(++lostsync > 2){

+				dmessage(2, "main; lost sync\n");

+				failed = 1;

+				continue;

+			}

+			synctime = nsec() + Synctime;

 			break;

 		case Unsent:

@@ -268,10 +271,13 @@

 static void

 fromnet(void*)

 {

+	extern void _threadnote(void *, char *);

 	static int lastacked;

 	int n, m, len, acked;

 	Buf *b;

+	notify(_threadnote);

+

 	threadsetname("fromnet");

 	b = emalloc(sizeof(Buf));

@@ -294,6 +300,7 @@

 			netfd = -1;

 			continue;

 		}

+		lostsync = 0;	// reset timeout

 		n = GBIT32(b->hdr.nb);

 		m = GBIT32(b->hdr.msg);

 		acked = GBIT32(b->hdr.acked);

@@ -353,7 +360,7 @@

 	done = 1;

 }

-static void

+static int

 reconnect(int secs)

 {

 	NetConnInfo *nci;

@@ -395,9 +402,8 @@

 		freenetconninfo(nci);

 	} else

 		syslog(0, Logname, "connected");

-	

-	// Wakes up the netreader.

-	netfd = fd;

+

+	return fd;

 }

 static void