🐛 fix bug in recvfrom

std/udp.nas

@@ -0,0 +1,49 @@
+use module.libsock;
+
+var udp_server = func(hostname, port, retry_delay = 5) {
+    var socket = libsock.socket;
+    var server = socket.socket(socket.AF_INET, socket.SOCK_DGRAM);
+    while(socket.bind(server, hostname, port) < 0){
+        println("[", os.time(), "] failed to bind socket "~server~" at ", hostname, ":", port, ".");
+        unix.sleep(retry_delay);
+        println("[", os.time(), "] retrying...");
+    }
+
+    return {
+        sendto: func(ip, port, message) {
+            var res = socket.sendto(server, ip, port, message);
+            println("[", os.time(), "] send message to ", ip, ":", port, " ", res, " byte(s)");
+            return res;
+        },
+        recvfrom: func(length = 1024) {
+            var message = socket.recvfrom(server, length);
+            println("[", os.time(), "] get message \"", message.str, "\" from ", message.fromip, ":", message.port);
+            return message;
+        }
+    }
+}
+
+var udp_client = func(hostname = "", port = -1, retry_delay = 5) {
+    var socket = libsock.socket;
+    var client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM);
+    if (port > 0 and size(hostname) != 0) {
+        while(socket.bind(client, hostname, port)<0){
+            println("[",os.time(),"] failed to bind socket "~client~" at ", hostname, ":", port, ".");
+            unix.sleep(retry_delay);
+            println("[",os.time(),"] retrying...");
+        }
+    }
+
+    return {
+        sendto: func(ip, port, message) {
+            var res = socket.sendto(client, ip, port, message);
+            println("[", os.time(), "] send message to ", ip, ":", port, " ", res, " byte(s)");
+            return res;
+        },
+        recvfrom: func(length = 1024) {
+            var message = socket.recvfrom(client, length);
+            println("[", os.time(), "] get message \"", message.str, "\" from ", message.fromip, ":", message.port);
+            return message;
+        }
+    }
+}