feat(client): add support for interfacing with, and acting as, a BBMD device

Author: adam-nielsen

README.md

@@ -56,6 +56,8 @@ following services are already supported at this point in time:
 | Unconfirmed Event Notification | yes¹                                                                                   | yes¹                                                                          |
 | Unconfirmed Private Transfer   | yes¹                                                                                   | yes¹                                                                          |
 | Confirmed Private Transfer     | yes¹                                                                                   | yes¹                                                                          |
+| Register Foreign Device        | no                                                                                     | yes¹                                                                          |
+| Distribute Broadcast to Network| no                                                                                     | yes¹                                                                          |
 
 ¹ Support implemented as Beta (untested, undocumented, breaking interface)
 

lib/apdu.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const baAsn1      = require('./asn1');
 const baEnum      = require('./enum');
 
 const getDecodedType = module.exports.getDecodedType = (buffer, offset) => {
@@ -153,6 +154,20 @@ module.exports.decodeSegmentAck = (buffer, offset) => {
   };
 };
 
+module.exports.encodeResult = (buffer, /* BvlcResultFormat */ resultCode) => {
+  baAsn1.encodeUnsigned(buffer, resultCode, 2);
+};
+
+module.exports.decodeResult = (buffer, offset) => {
+  const orgOffset = offset;
+  const decode = baAsn1.decodeUnsigned(buffer, offset, 2);
+  offset += decode.len;
+  return {
+    len: offset - orgOffset,
+    resultCode: decode.value, // BvlcResultFormat
+  };
+};
+
 module.exports.encodeError = (buffer, type, service, invokeId) => {
   buffer.buffer[buffer.offset++] = type;
   buffer.buffer[buffer.offset++] = invokeId;

lib/asn1.js

@@ -46,7 +46,7 @@ const getEncodingType = (encoding, decodingBuffer, decodingOffset) => {
   }
 };
 
-const encodeUnsigned = (buffer, value, length) => {
+const encodeUnsigned = module.exports.encodeUnsigned = (buffer, value, length) => {
   buffer.buffer.writeUIntBE(value, buffer.offset, length, true);
   buffer.offset += length;
 };

lib/bvlc.js

@@ -2,11 +2,36 @@
 
 const baEnum      = require('./enum');
 
-module.exports.encode = (buffer, func, msgLength) => {
+const DefaultBACnetPort = 47808;
+
+module.exports.encode = (buffer, func, msgLength, originatingIP) => {
   buffer[0] = baEnum.BVLL_TYPE_BACNET_IP;
   buffer[1] = func;
   buffer[2] = (msgLength & 0xFF00) >> 8;
   buffer[3] = (msgLength & 0x00FF) >> 0;
+  if (originatingIP) {
+    // This is always a FORWARDED_NPDU regardless of the 'func' parameter.
+    if (func !== baEnum.BvlcResultPurpose.FORWARDED_NPDU) {
+      throw new Error('Cannot specify originatingIP unless '
+        + 'BvlcResultPurpose.FORWARDED_NPDU is used.');
+    }
+    // Encode the IP address and optional port into bytes.
+    const [ipstr, portstr] = originatingIP.split(':');
+    const port = parseInt(portstr) || DefaultBACnetPort;
+    const ip = ipstr.split('.');
+    buffer[4] = parseInt(ip[0]);
+    buffer[5] = parseInt(ip[1]);
+    buffer[6] = parseInt(ip[2]);
+    buffer[7] = parseInt(ip[3]);
+    buffer[8] = (port & 0xFF00) >> 8;
+    buffer[9] = (port & 0x00FF) >> 0;
+    return 6 + baEnum.BVLC_HEADER_LENGTH;
+  } else {
+    if (func === baEnum.BvlcResultPurpose.FORWARDED_NPDU) {
+      throw new Error('Must specify originatingIP if '
+        + 'BvlcResultPurpose.FORWARDED_NPDU is used.');
+    }
+  }
   return baEnum.BVLC_HEADER_LENGTH;
 };
 
@@ -15,31 +40,47 @@ module.exports.decode = (buffer, offset) => {
   const func = buffer[1];
   const msgLength = (buffer[2] << 8) | (buffer[3] << 0);
   if (buffer[0] !== baEnum.BVLL_TYPE_BACNET_IP || buffer.length !== msgLength) return;
+  let originatingIP = null;
   switch (func) {
     case baEnum.BvlcResultPurpose.BVLC_RESULT:
     case baEnum.BvlcResultPurpose.ORIGINAL_UNICAST_NPDU:
     case baEnum.BvlcResultPurpose.ORIGINAL_BROADCAST_NPDU:
     case baEnum.BvlcResultPurpose.DISTRIBUTE_BROADCAST_TO_NETWORK:
-      len =  4;
-      break;
-    case baEnum.BvlcResultPurpose.FORWARDED_NPDU:
-      len = 10;
-      break;
     case baEnum.BvlcResultPurpose.REGISTER_FOREIGN_DEVICE:
     case baEnum.BvlcResultPurpose.READ_FOREIGN_DEVICE_TABLE:
     case baEnum.BvlcResultPurpose.DELETE_FOREIGN_DEVICE_TABLE_ENTRY:
     case baEnum.BvlcResultPurpose.READ_BROADCAST_DISTRIBUTION_TABLE:
     case baEnum.BvlcResultPurpose.WRITE_BROADCAST_DISTRIBUTION_TABLE:
     case baEnum.BvlcResultPurpose.READ_BROADCAST_DISTRIBUTION_TABLE_ACK:
     case baEnum.BvlcResultPurpose.READ_FOREIGN_DEVICE_TABLE_ACK:
+      len = 4;
+      break;
+    case baEnum.BvlcResultPurpose.FORWARDED_NPDU:
+      // Work out where the packet originally came from before the BBMD
+      // forwarded it to us, so we can tell the BBMD where to send any reply to.
+      const port = (buffer[8] << 8) | buffer[9];
+      originatingIP = buffer.slice(4, 8).join('.');
+
+      // Only add the port if it's not the usual one.
+      if (port != DefaultBACnetPort) {
+        originatingIP += ':' + port;
+      }
+
+      len = 10;
+      break;
     case baEnum.BvlcResultPurpose.SECURE_BVLL:
+      // unimplemented
       return;
     default:
       return;
   }
   return {
     len: len,
     func: func,
-    msgLength: msgLength
+    msgLength: msgLength,
+    // Originating IP is set to the IP address of the node that originally
+    // sent the packet, when it has been forwarded to us by a BBMD (since the
+    // BBMD's IP address will be in the sender field.
+    originatingIP: originatingIP,
   };
 };