libc: provide netmkaddrbuf() function avoiding the static buffer

We need a reentrant version for netmkaddr() that
can be used in multithreaded programs.

sys/include/libc.h

@@ -543,6 +543,7 @@ extern	void	setnetmtpt(char*, int, char*);
 extern	int	hangup(int);
 extern	int	listen(char*, char*);
 extern	char*	netmkaddr(char*, char*, char*);
+extern	char*	netmkaddrbuf(char*, char*, char*, char*, int);
 extern	int	reject(int, char*, char*);
 
 /*

sys/man/2/dial

@@ -1,6 +1,6 @@
 .TH DIAL 2
 .SH NAME
-dial, hangup, announce, listen, accept, reject, netmkaddr, setnetmtpt, getnetconninfo, freenetconninfo \- make and break network connections
+dial, hangup, announce, listen, accept, reject, netmkaddr, netmkaddrbuf, setnetmtpt, getnetconninfo, freenetconninfo \- make and break network connections
 .SH SYNOPSIS
 .B #include <u.h>
 .br
@@ -25,7 +25,12 @@ int   accept(int ctl, char *dir)
 int   reject(int ctl, char *dir, char *cause)
 .PP
 .B
-char* netmkaddr(char *addr, char *defnet, char *defservice)
+char* netmkaddr(char *addr, char *defnet, char *defsrv)
+.PP
+.B
+char* netmkaddrbuf(char *addr, char *defnet, char *defsrv,
+.br
+	char *buf, int len)
 .PP
 .B
 void  setnetmtpt(char *to, int tolen, char *from)
@@ -171,10 +176,19 @@ returns a file descriptor for the data file opened
 .BR ORDWR .
 .PP
 .I Netmkaddr
-makes an address suitable for dialing or announcing.
+and
-It takes an address along with a default network and service to use
+.I netmkaddrbuf
+make an address suitable for dialing or announcing.
+They take an address along with a default network and service to use
 if they are not specified in the address.
-It returns a pointer to static data holding the actual address to use.
+.I Netmkaddrbuf
+stores the resulting dialstring in
+.I buf
+up to a maximum length of
+.I len
+and returns a pointer to it.
+.I Netmkaddr
+returns a pointer to a static buffer.
 .PP
 .I Getnetconninfo
 returns a structure containing information about a

sys/src/libc/port/netmkaddr.c

@@ -6,47 +6,48 @@
  *  make an address, add the defaults
  */
 char *
-netmkaddr(char *linear, char *defnet, char *defsrv)
+netmkaddrbuf(char *addr, char *defnet, char *defsrv, char *buf, int len)
 {
-	static char addr[256];
 	char *cp;
 
+	cp = strchr(addr, '!');
+	if(cp == nil){
 		/*
 		 *  dump network name
 		 */
-	cp = strchr(linear, '!');
+		if(defnet == nil){
-	if(cp == 0){
+			if(defsrv != nil)
-		if(defnet==0){
+				snprint(buf, len, "net!%s!%s", addr, defsrv);
-			if(defsrv)
-				snprint(addr, sizeof(addr), "net!%s!%s",
-					linear, defsrv);
 			else
-				snprint(addr, sizeof(addr), "net!%s", linear);
+				snprint(buf, len, "net!%s", addr);
 		}
 		else {
-			if(defsrv)
+			if(defsrv != nil)
-				snprint(addr, sizeof(addr), "%s!%s!%s", defnet,
+				snprint(buf, len, "%s!%s!%s", defnet, addr, defsrv);
-					linear, defsrv);
 			else
-				snprint(addr, sizeof(addr), "%s!%s", defnet,
+				snprint(buf, len, "%s!%s", defnet, addr);
-					linear);
 		}
-		return addr;
+	} else {
-	}
-
-	/*
-	 *  if there is already a service, use it
-	 */
 		cp = strchr(cp+1, '!');
-	if(cp)
+		if(cp != nil || defsrv == nil){
-		return linear;
+			/*
-
+			 *  if there is already a service or no defsrv given
+			 */
+			snprint(buf, len, "%s", addr);
+		} else {
 			/*
 			 *  add default service
 			 */
-	if(defsrv == 0)
+			snprint(buf, len,"%s!%s", addr, defsrv);
-		return linear;
+		}
-	snprint(addr, sizeof(addr), "%s!%s", linear, defsrv);
+	}
-
+	return buf;
-	return addr;
+}
+
+char *
+netmkaddr(char *addr, char *defnet, char *defsrv)
+{
+	static char buf[256];
+
+	return netmkaddrbuf(addr, defnet, defsrv, buf, sizeof(buf));
 }