From b5bdb8a32312072db13a2d0b21358118e4414060 Mon Sep 17 00:00:00 2001
From: everhardt <rob@everhardt.nl>
Date: Sat, 8 Jun 2024 09:08:20 +0200
Subject: [PATCH] fix: uncaught error in read device identification (#557)

* fix: uncaught exception

* fix: two interpretations of numOfObjects
---
 index.js | 100 ++++++++++++++++++++++++++++++-------------------------
 1 file changed, 54 insertions(+), 46 deletions(-)

diff --git a/index.js b/index.js
index b88fa58..5225496 100644
--- a/index.js
+++ b/index.js
@@ -268,7 +268,10 @@ function _readFC43(data, modbus, next) {
 
     let startAt = 8;
     const result = {};
-    for (let i = 0; i < numOfObjects; i++) {
+    // The modbus specification states that numOfObjects is the number of
+    // objects in the response, but the example on page 45 shows the total
+    // number over all responses. Therefore be careful about reading more data than available
+    for (let i = 0; i < numOfObjects && startAt < data.length; i++) {
         const objectId = parseInt(data.readUInt8(startAt));
         const objectLength = parseInt(data.readUInt8(startAt + 1));
         const startOfData = startAt + 2;
@@ -496,51 +499,56 @@ function _onReceive(data) {
 
     /* parse incoming data
      */
-
-    switch (code) {
-        case 1:
-        case 2:
-            // Read Coil Status (FC=01)
-            // Read Input Status (FC=02)
-            _readFC2(data, next);
-            break;
-        case 3:
-        case 4:
-            // Read Input Registers (FC=04)
-            // Read Holding Registers (FC=03)
-            if (modbus._enron && !(transaction.nextDataAddress >= modbus._enronTables.shortRange[0] && transaction.nextDataAddress <= modbus._enronTables.shortRange[1])) {
-                _readFC3or4Enron(data, next);
-            } else {
-                _readFC3or4(data, next);
-            }
-            break;
-        case 5:
-            // Force Single Coil
-            _readFC5(data, next);
-            break;
-        case 6:
-            // Preset Single Register
-            if (modbus._enron && !(transaction.nextDataAddress >= modbus._enronTables.shortRange[0] && transaction.nextDataAddress <= modbus._enronTables.shortRange[1])) {
-                _readFC6Enron(data, next);
-            } else {
-                _readFC6(data, next);
-            }
-            break;
-        case 15:
-        case 16:
-            // Force Multiple Coils
-            // Preset Multiple Registers
-            _readFC16(data, next);
-            break;
-        case 17:
-            _readFC17(data, next);
-            break;
-        case 20:
-            _readFC20(data, transaction.next);
-            break;
-        case 43:
-            // read device identification
-            _readFC43(data, modbus, next);
+    try {
+        switch (code) {
+            case 1:
+            case 2:
+                // Read Coil Status (FC=01)
+                // Read Input Status (FC=02)
+                _readFC2(data, next);
+                break;
+            case 3:
+            case 4:
+                // Read Input Registers (FC=04)
+                // Read Holding Registers (FC=03)
+                if (modbus._enron && !(transaction.nextDataAddress >= modbus._enronTables.shortRange[0] && transaction.nextDataAddress <= modbus._enronTables.shortRange[1])) {
+                    _readFC3or4Enron(data, next);
+                } else {
+                    _readFC3or4(data, next);
+                }
+                break;
+            case 5:
+                // Force Single Coil
+                _readFC5(data, next);
+                break;
+            case 6:
+                // Preset Single Register
+                if (modbus._enron && !(transaction.nextDataAddress >= modbus._enronTables.shortRange[0] && transaction.nextDataAddress <= modbus._enronTables.shortRange[1])) {
+                    _readFC6Enron(data, next);
+                } else {
+                    _readFC6(data, next);
+                }
+                break;
+            case 15:
+            case 16:
+                // Force Multiple Coils
+                // Preset Multiple Registers
+                _readFC16(data, next);
+                break;
+            case 17:
+                _readFC17(data, next);
+                break;
+            case 20:
+                _readFC20(data, transaction.next);
+                break;
+            case 43:
+                // read device identification
+                _readFC43(data, modbus, next);
+        }
+    } catch (e) {
+        if (transaction.next) {
+            next(e);
+        }
     }
 }