From cd08819ea333e5aa86326d72bcfd169d1beb4c76 Mon Sep 17 00:00:00 2001
From: Steffen Pohle <steffen@gulpe.de>
Date: Fri, 8 Nov 2024 22:04:57 +0100
Subject: [PATCH] fixed single word/coil write fc5/fc6

---
 Changelog    |  3 +++
 Makefile     |  2 +-
 modbussrv.cc | 59 +++++++++++-----------------------------------------
 3 files changed, 16 insertions(+), 48 deletions(-)

diff --git a/Changelog b/Changelog
index 6bc44d9..30b454b 100644
--- a/Changelog
+++ b/Changelog
@@ -1,3 +1,6 @@
+2024-11-08:
+- fixed single coil / word write. Response was not correct.
+
 2024-08-07:
 - fixed compile on windows. stdint.h was not included
 
diff --git a/Makefile b/Makefile
index 92745c3..3e02600 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 .SILENT: help
-VERSION = 1.0.3
+VERSION = 1.0.4
 
 -include Makefile.rules
 
diff --git a/modbussrv.cc b/modbussrv.cc
index c0bc240..e4237ca 100644
--- a/modbussrv.cc
+++ b/modbussrv.cc
@@ -254,8 +254,6 @@ void ModbusSrv::ServerThread() {
 					else if (mbindata->fc == 5 || mbindata->fc == 6) {
 						if (WorkerAndEncodeWriteSingle(mbindata, mboutdata)) {
 							clients[slot]->Write(mboutdata->buffer, mboutdata->bufferlen);
-							delete clients[slot];
-							clients[slot] = NULL;
 						}
 						else {
 							char *txt = (char*)malloc(255);
@@ -456,33 +454,10 @@ int ModbusSrv::WorkerAndEncodeWriteSingle(struct modbus_data *mbin, struct modbu
 
 	// transaction
 	mbout->transactionid = mbin->transactionid;
-	i16 = htons((uint16_t)mbin->transactionid);
-	memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-	pos += sizeof (i16);
-
-	// protocolid
 	mbout->protoolid = mbin->protoolid;
-	i16 = htons((uint16_t)mbin->protoolid);
-	memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-	pos += sizeof (i16);
-
-	// length  3 + number of registers
-	mbout->length = 3;
-	mbout->length += mbin->regcnt * 2;		// 16bit = 2Bytes
-	i16 = htons((uint16_t)mbout->length);
-	memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-	pos += sizeof (i16);
-
-	// device id
+	mbout->length = 0;
 	mbout->unitid = mbin->unitid;
-	memcpy (mbout->buffer+pos, &mbout->unitid, sizeof(uint8_t));
-	pos += sizeof (uint8_t);
-
-	// fc
 	mbout->fc = mbin->fc;
-	memcpy (mbout->buffer+pos, &mbout->fc, sizeof(uint8_t));
-	pos += sizeof (uint8_t);
-
 	mbout->direction = 1;
 
 	if (mbin->fc == 5) {
@@ -492,33 +467,17 @@ int ModbusSrv::WorkerAndEncodeWriteSingle(struct modbus_data *mbin, struct modbu
 			else 							mbarray[FC1][mbin->regstart].value = 0;
 		}
 		else error = 1;
-
-		// return register and value
-		i16 = htons((uint16_t)mbin->regstart);
-		memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-		pos += sizeof (i16);
-
-		i16 = htons((uint16_t)mbin->regcnt);
-		memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-		pos += sizeof (i16);
 	}
 	if (mbin->fc == 6) {
 		mbarray[FC3][mbin->regstart].requested |= 2;
 		if (mbarray[FC3][mbin->regstart].enabled)
 			mbarray[FC3][mbin->regstart].value = mbin->regcnt;
 		else error = 1;
-
-		// return register and value
-		i16 = htons((uint16_t)mbin->regstart);
-		memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-		pos += sizeof (i16);
-
-		i16 = htons((uint16_t)mbin->regcnt);
-		memcpy (mbout->buffer+pos, &i16, sizeof(i16));
-		pos += sizeof (i16);
 	}
 
-	mbout->bufferlen = pos;
+	// mirror the output
+	memcpy (mbout->buffer, mbin->buffer, mbin->bufferlen);
+	mbout->bufferlen = mbin->bufferlen;
 
 	//
 	// inform the application about the modbus values change
@@ -672,8 +631,8 @@ int ModbusSrv::Decode(struct modbus_data *mbdata) {
 	int ret = 1;
 
 	mbdata->fc = 0;
-	mbdata->regcnt = -1;
-	mbdata->regstart = -1;
+	mbdata->regcnt = 0;
+	mbdata->regstart =-1;
 	mbdata->unitid = 0;
 	mbdata->length = 0;
 	mbdata->direction = 0;
@@ -716,6 +675,12 @@ int ModbusSrv::Decode(struct modbus_data *mbdata) {
 	pos += sizeof(i16);
 	mbdata->regstart = ntohs(i16);
 
+	// not needed for single write
+	if (mbdata->fc == 5 || mbdata->fc == 6) {
+		mbdata->regcnt = 0;
+		mbdata->bytecnt = 0;
+	}
+
 	// number of registers
 	if (mbdata->length < pos-6) ret = 0;
 	memcpy (&i16, mbdata->buffer+pos, sizeof(i16));