add tcp echo bot example

examples/tcp_echo_bot.js

@@ -0,0 +1,83 @@
+import TCPConnection from "../src/connection/tcp_connection.js";
+import BufferUtils from "../src/buffer_utils.js";
+import Constants from "../src/constants.js";
+
+// create tcp connection
+const connection = new TCPConnection("10.1.0.226", 5000);
+
+// wait until connected
+connection.on("connected", async () => {
+
+    // we are now connected
+    console.log(`Connected to: [${connection.host}:${connection.port}]`);
+
+    // send flood advert when connected
+    await connection.sendFloodAdvert();
+
+});
+
+// listen for new messages
+connection.on(Constants.PushCodes.MsgWaiting, async () => {
+    await syncMessages();
+});
+
+async function syncMessages() {
+    try {
+        while(true){
+
+            // sync messages until no more returned
+            const message = await connection.syncNextMessage();
+            if(!message){
+                break;
+            }
+
+            // handle received message
+            if(message.contactMessage){
+                await onContactMessageReceived(message.contactMessage);
+            } else if(message.channelMessage) {
+                await onChannelMessageReceived(message.channelMessage);
+            }
+
+        }
+    } catch(e) {
+        console.log(e);
+    }
+}
+
+async function findContactByPubKeyPrefix(pubKeyPrefix) {
+
+    // get contacts
+    const contacts = await connection.getContacts();
+
+    // find first contact matching pub key prefix
+    return contacts.find((contact) => {
+        const contactPubKeyPrefix = contact.publicKey.subarray(0, pubKeyPrefix.length);
+        return BufferUtils.areBuffersEqual(pubKeyPrefix, contactPubKeyPrefix);
+    });
+
+}
+
+async function onContactMessageReceived(message) {
+
+    console.log("Received contact message", message);
+
+    // find first contact matching pub key prefix
+    const contact = await findContactByPubKeyPrefix(message.pubKeyPrefix);
+    if(!contact){
+        console.log("Did not find contact for received message");
+        return;
+    }
+
+    // send it back
+    await connection.sendTextMessage(contact.publicKey, message.text, Constants.TxtTypes.Plain);
+
+}
+
+async function onChannelMessageReceived(message) {
+    console.log(`Received channel message`, message);
+}
+
+// todo auto reconnect on disconnect
+
+// connect to meshcore device
+await connection.connect();