Rework module system. Now modules/commands are defined in a single file each, with both the function executed by teh agent and the definition for server-side argument parsing.

src/agent/core/heartbeat.nim

@@ -0,0 +1,43 @@
+import times 
+
+import ../../common/[types, serialize, utils, crypto]
+
+proc createHeartbeat*(config: AgentConfig): Heartbeat = 
+    return Heartbeat(
+        header: Header(
+            magic: MAGIC,
+            version: VERSION, 
+            packetType: cast[uint8](MSG_HEARTBEAT),
+            flags: cast[uint16](FLAG_ENCRYPTED),
+            size: 0'u32,
+            agentId: uuidToUint32(config.agentId),
+            seqNr: 0'u64,
+            iv: generateIV(),
+            gmac: default(AuthenticationTag)
+        ), 
+        listenerId: uuidToUint32(config.listenerId),
+        timestamp: uint32(now().toTime().toUnix())
+    )
+
+proc serializeHeartbeat*(config: AgentConfig, request: var Heartbeat): seq[byte] =
+
+    var packer = initPacker()
+
+    # Serialize check-in / heartbeat request
+    packer 
+        .add(request.listenerId)
+        .add(request.timestamp)
+
+    let body = packer.pack()
+    packer.reset()
+
+    # Encrypt check-in / heartbeat request body 
+    let (encData, gmac) = encrypt(config.sessionKey, request.header.iv, body, request.header.seqNr)
+
+    # Set authentication tag (GMAC)
+    request.header.gmac = gmac
+
+    # Serialize header
+    let header = packer.packHeader(request.header, uint32(encData.len))
+
+    return header & encData