diff --git a/src/index.js b/src/index.js
index ffae389..794c502 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,109 +1,5 @@
 const net = require('net');
-const assert = require('assert');
-
-function chunkString(str, len) {
-  const size = Math.ceil(str.length/len)
-  const r = Array(size)
-  let offset = 0
-  
-  for (let i = 0; i < size; i++) {
-    r[i] = str.substr(offset, len)
-    offset += len
-  }
-  
-  return r
-}
-
-function logDataStream(data){  
-  const strs = chunkString(data.toString('hex'), 16);
-  return strs.map((str) => chunkString(str, 2).join(' ')).join('\n');
-}
-
-class TLV {
-  static fromBuffer(buf) {
-    const type = buf.slice(0, 2).readInt16BE(0);
-    const len = buf.slice(2, 4).readInt16BE(0)
-    const payload = buf.slice(4, 4 + len);
-
-    return new TLV(type, payload);
-  }
-
-  constructor(type, payload) {
-    this.type = type;
-    this.len = payload.length;
-    this.payload = payload;
-  }
-
-  toString() {
-    return `TLV(${this.type}, ${this.len}, ${this.payload.toString('ascii')})`;
-  }
-}
-
-class SNAC {
-  static fromBuffer(buf, payloadLength = 0) {
-    const family = buf.slice(0,2).readInt16BE(0);
-    const service = buf.slice(2,4).readInt16BE(0);
-    const flags = buf.slice(4, 6);
-    const requestID = buf.slice(6, 10).readInt32BE(0);
-    const payload = []; // SNACs can have multiple TLVs
-
-    let payloadIdx = 10;
-    let cb = 0, cbLimit = 10; //circuit breaker
-    while (payloadIdx < payloadLength && cb < cbLimit) {
-      const tlv = TLV.fromBuffer(buf.slice(payloadIdx));
-      payload.push(tlv);
-      payloadIdx += tlv.len + 4; // 4 bytes for TLV type + payload length
-      cb++;
-    }
-    if (cb === cbLimit) {
-      console.error('Application error, cb limit reached');
-      process.exit(1);
-    }
-    
-    return new SNAC(family, service, flags, requestID, payload);
-  }
-
-  constructor(family, service, flags, requestID, payload) {
-    this.family = family;
-    this.service = service;
-    this.flags = flags;
-    this.requestID = requestID;
-    this.payload = payload;
-  }
-
-  toString() {
-    return `SNAC(${this.family.toString(16)},${this.service.toString(16)}) #${this.requestID}\n  ${this.payload}`;
-  }
-}
-
-class FLAP {
-  static fromBuffer(buf) {
-    assert.equal(buf[0], 0x2a, 'Expected 0x2a FLAP header');
-    const channel = parseInt(buf[1], 16);
-    const datagramNumber = buf.slice(2,4).readInt16BE(0);
-    const payloadLength = buf.slice(4, 6).readInt16BE(0);
-    const payload = buf.slice(6, 6 + payloadLength);
-
-    return new FLAP(channel, datagramNumber, payload)
-  }
-
-  constructor(channel, datagramNumber, payload) {
-    this.channel = channel;
-    this.datagramNumber = datagramNumber;
-    this.payload = payload;
-    this.payloadLength = this.payload.length;
-
-    if (channel === 2) {
-      this.payload = SNAC.fromBuffer(this.payload, this.payloadLength);
-    }
-  }
-
-  toString() {
-    const hasSnac = this.payload instanceof SNAC;
-    const payload = hasSnac ? this.payload.toString() : logDataStream(this.payload).split('\n').join('\n  ');
-    return `ch:${this.channel}, dn: ${this.datagramNumber}, len: ${this.payloadLength}, payload:\n  ${payload}`
-  }
-}
+const { logDataStream } = require('./util');
 
 const server = net.createServer((socket) => {
   console.log('client connected...');
@@ -115,6 +11,7 @@ const server = net.createServer((socket) => {
 
   socket.on('data', (data) => {
     const flap = FLAP.fromBuffer(Buffer.from(data, 'hex'));
+    console.log(logDataStream(flap.toBuffer()));
     console.log('RECV', flap.toString());
   });
 
@@ -127,8 +24,11 @@ const server = net.createServer((socket) => {
     console.log('client disconnected...');
   });
 
-  const hello = Buffer.from(new Uint8Array([0x2a, 0x01, 0, 0x01, 0, 0x04, 0x00, 0x00, 0x00, 0x01]));
-  socket.write(hello);
+  // const hello = Buffer.from(new Uint8Array([0x2a, 0x01, 0, 0x01, 0, 0x04, 0x00, 0x00, 0x00, 0x01]));
+
+  const hello = new FLAP(0x01, 0, Buffer.from([0x00, 0x00, 0x00, 0x01]));
+  // console.log(logDataStream(hello.toBuffer()));
+  socket.write(hello.toBuffer());
 
   /* 1. on connection, server sends
 
diff --git a/src/structures.js b/src/structures.js
new file mode 100644
index 0000000..63bc5a7
--- /dev/null
+++ b/src/structures.js
@@ -0,0 +1,133 @@
+const assert = require('assert');
+
+const { logDataStream } = require('./util');
+
+class TLV {
+  static fromBuffer(buf) {
+    const type = buf.slice(0, 2).readInt16BE(0);
+    const len = buf.slice(2, 4).readInt16BE(0)
+    const payload = buf.slice(4, 4 + len);
+
+    return new TLV(type, payload);
+  }
+
+  constructor(type, payload) {
+    this.type = type;
+    this.len = payload.length;
+    this.payload = payload;
+  }
+
+  toString() {
+    return `TLV(${this.type}, ${this.len}, ${this.payload.toString('ascii')})`;
+  }
+
+  toBuffer() {
+    const TLVHeader = Buffer.alloc(4, 0, 'hex');
+    TLVHeader.writeUInt16BE(this.type);
+    TLVHeader.writeUInt16BE(this.len, 2);
+    return Buffer.concat([TLVHeader, this.payload]);
+  }
+}
+
+class SNAC {
+  static fromBuffer(buf, payloadLength = 0) {
+    const family = buf.slice(0,2).readInt16BE(0);
+    const service = buf.slice(2,4).readInt16BE(0);
+    const flags = buf.slice(4, 6);
+    const requestID = buf.slice(6, 10).readInt32BE(0);
+    const payload = []; // SNACs can have multiple TLVs
+
+    let payloadIdx = 10;
+    let cb = 0, cbLimit = 10; //circuit breaker
+    while (payloadIdx < payloadLength && cb < cbLimit) {
+      const tlv = TLV.fromBuffer(buf.slice(payloadIdx));
+      payload.push(tlv);
+      payloadIdx += tlv.len + 4; // 4 bytes for TLV type + payload length
+      cb++;
+    }
+    if (cb === cbLimit) {
+      console.error('Application error, cb limit reached');
+      process.exit(1);
+    }
+    
+    return new SNAC(family, service, flags, requestID, payload);
+  }
+
+  constructor(family, service, flags, requestID, payload) {
+    this.family = family;
+    this.service = service;
+    this.flags = flags;
+    this.requestID = requestID;
+    this.payload = payload;
+  }
+
+  toString() {
+    return `SNAC(${this.family.toString(16)},${this.service.toString(16)}) #${this.requestID}\n  ${this.payload}`;
+  }
+
+  toBuffer() {
+    const SNACHeader = Buffer.alloc(10, 0, 'hex');
+    SNACHeader.writeUInt16BE(this.family);
+    SNACHeader.writeUInt16BE(this.service, 2);
+    SNACHeader.writeUInt16BE(this.flags, 4);
+    SNACHeader.writeUInt32BE(this.requestID, 6);
+
+    const payload = this.payload.map((tlv) => tlv.toBuffer());
+    return Buffer.concat([SNACHeader, ...payload]);
+  }
+}
+
+class FLAP {
+  static fromBuffer(buf) {
+    assert.equal(buf[0], 0x2a, 'Expected 0x2a FLAP header');
+    const channel = parseInt(buf[1], 16);
+    const datagramNumber = buf.slice(2,4).readInt16BE(0);
+    const payloadLength = buf.slice(4, 6).readInt16BE(0);
+    const payload = buf.slice(6, 6 + payloadLength);
+
+    return new FLAP(channel, datagramNumber, payload)
+  }
+
+  constructor(channel, datagramNumber, payload) {
+    this.channel = channel;
+    this.datagramNumber = datagramNumber;
+
+    this.payload = payload;
+    this.payloadLength = this.payload.length;
+
+    if (payload instanceof SNAC) {
+      this.payloadLength = payload.toBuffer().length;
+    }
+
+    if (channel === 2 && !(payload instanceof SNAC)) {
+      this.payload = SNAC.fromBuffer(this.payload, this.payloadLength);
+    }
+  }
+
+  toString() {
+    const hasSnac = this.payload instanceof SNAC;
+    const payload = hasSnac ? this.payload.toString() : logDataStream(this.payload).split('\n').join('\n  ');
+    return `ch:${this.channel}, dn: ${this.datagramNumber}, len: ${this.payloadLength}, payload:\n  ${payload}`
+  }
+
+  toBuffer() {
+    const FLAPHeader = Buffer.alloc(6, 0, 'hex');
+    FLAPHeader.writeInt8(0x2a, 0);
+    FLAPHeader.writeInt8(this.channel, 1);
+    FLAPHeader.writeInt16BE(this.datagramNumber, 2);
+    FLAPHeader.writeInt16BE(this.payloadLength, 4);
+
+    let payload = this.payload;
+    if (payload instanceof SNAC) {
+      payload = payload.toBuffer();
+    }
+
+    return Buffer.concat([FLAPHeader, payload]);
+  }
+}
+
+module.exports = {
+  TLV,
+  SNAC,
+  FLAP,
+};
diff --git a/src/util.js b/src/util.js
new file mode 100644
index 0000000..477d0c7
--- /dev/null
+++ b/src/util.js
@@ -0,0 +1,21 @@
+function chunkString(str, len) {
+  const size = Math.ceil(str.length/len)
+  const r = Array(size)
+  let offset = 0
+  
+  for (let i = 0; i < size; i++) {
+    r[i] = str.substr(offset, len)
+    offset += len
+  }
+  
+  return r
+}
+
+function logDataStream(data){  
+  const strs = chunkString(data.toString('hex'), 16);
+  return strs.map((str) => chunkString(str, 2).join(' ')).join('\n');
+}
+
+module.exports = {
+  logDataStream,
+};
diff --git a/tests/data-structures.js b/tests/data-structures.js
new file mode 100644
index 0000000..25b5f06
--- /dev/null
+++ b/tests/data-structures.js
@@ -0,0 +1,20 @@
+const assert = require('assert');
+
+const { FLAP, SNAC, TLV } = require('../src/structures');
+
+const tests = [
+  () => {
+    // Construct and test a CLI_AUTH_REQUEST
+    const md5_auth_req = new FLAP(0x02, 0, new SNAC(0x17, 0x06, 0x0000, 0, [new TLV(0x0001, Buffer.from("toof"))]));
+    assert(md5_auth_req.channel === 2);
+    assert(md5_auth_req.payload instanceof SNAC);
+    assert(md5_auth_req.payload.family === 23);
+    assert(md5_auth_req.payload.service === 6);
+    assert(md5_auth_req.payload.payload.length === 1);
+    assert(md5_auth_req.payload.payload[0].len === 4);
+  }
+];
+
+tests.forEach((testFn) => {
+  testFn();
+});