libtailscale: match close semantics, remove race

It is theoretically possible for separate calls to tailscale_close to
race and cause a mess, so move the load+delete under a single mutex
lock.

While here, give it the closer error semantics to tailscale_listener_close.

Signed-off-by: David Crawshaw <[email protected]>

Author: crawshaw

tailscale.go

@@ -121,18 +121,21 @@ func TsnetUp(sd C.int) C.int {
 
 //export TsnetClose
 func TsnetClose(sd C.int) C.int {
-	s, err := getServer(sd)
-	if err != nil {
-		return s.recErr(err)
-	}
-
 	servers.mu.Lock()
-	delete(servers.m, sd)
+	s := servers.m[sd]
+	if s != nil {
+		delete(servers.m, sd)
+	}
 	servers.mu.Unlock()
 
+	if s == nil {
+		return C.EBADF
+	}
+
 	// TODO: cancel Up
 	// TODO: close related listeners / conns.
 	if err := s.s.Close(); err != nil {
+		s.s.Logf("tailscale_close: failed with %v", err)
 		return -1
 	}
 

tailscale.h

@@ -41,7 +41,10 @@ extern int tailscale_up(tailscale sd);
 
 // tailscale_close shuts down the server.
 //
-// Returns zero on success or -1 on error. No error details are available.
+// Returns:
+// 	0     - success
+// 	EBADF - sd is not a valid tailscale
+// 	-1    - other error, details printed to the tsnet logger
 extern int tailscale_close(tailscale sd);
 
 // The following set tailscale configuration options.