Add the value to the WriteSingleCoil response

Author: Abestanis

CHANGELOG.md

@@ -9,7 +9,8 @@
 - Merged `modbus_core::rtu::FrameLocation` and `modbus_core::tcp::FrameLocation` and moved it to `modbus_core::FrameLocation`
 - Return a `FrameLocation` in addition to the parsed frame in `rtu::server::decode_response`,
   `rtu::client::decode_response`, `tcp::server::decode_response` and `tcp::client::decode_request`
-- Added `FrameLocation::end` helper.
+- Added `FrameLocation::end` helper
+- Fix `WriteSingleCoil` responses not including the output value
 
 ## v0.2.0 (2025-09-30)
 

src/codec/mod.rs

@@ -189,7 +189,10 @@ impl<'r> TryFrom<&'r [u8]> for Response<'r> {
                     _ => unreachable!(),
                 }
             }
-            F::WriteSingleCoil => Self::WriteSingleCoil(BigEndian::read_u16(&bytes[1..])),
+            F::WriteSingleCoil => Self::WriteSingleCoil(
+                BigEndian::read_u16(&bytes[1..3]),
+                u16_coil_to_bool(BigEndian::read_u16(&bytes[3..5]))?,
+            ),
 
             F::WriteMultipleCoils | F::WriteSingleRegister | F::WriteMultipleRegisters => {
                 let addr = BigEndian::read_u16(&bytes[1..]);
@@ -304,8 +307,9 @@ impl Encode for Response<'_> {
                 buf[1] = (registers.len() * 2) as u8;
                 registers.copy_to(&mut buf[2..]);
             }
-            Self::WriteSingleCoil(address) => {
+            Self::WriteSingleCoil(address, value) => {
                 BigEndian::write_u16(&mut buf[1..], *address);
+                BigEndian::write_u16(&mut buf[3..], bool_to_u16_coil(*value));
             }
             Self::WriteMultipleCoils(address, payload)
             | Self::WriteMultipleRegisters(address, payload)
@@ -385,8 +389,10 @@ const fn min_response_pdu_len(fn_code: FunctionCode) -> usize {
         | F::ReadInputRegisters
         | F::ReadHoldingRegisters
         | F::ReadWriteMultipleRegisters => 2,
-        F::WriteSingleCoil => 3,
-        F::WriteMultipleCoils | F::WriteSingleRegister | F::WriteMultipleRegisters => 5,
+        F::WriteSingleCoil
+        | F::WriteMultipleCoils
+        | F::WriteSingleRegister
+        | F::WriteMultipleRegisters => 5,
         _ => 1,
     }
 }
@@ -444,7 +450,7 @@ mod tests {
         assert_eq!(min_response_pdu_len(ReadCoils), 2);
         assert_eq!(min_response_pdu_len(ReadDiscreteInputs), 2);
         assert_eq!(min_response_pdu_len(ReadInputRegisters), 2);
-        assert_eq!(min_response_pdu_len(WriteSingleCoil), 3);
+        assert_eq!(min_response_pdu_len(WriteSingleCoil), 5);
         assert_eq!(min_response_pdu_len(ReadHoldingRegisters), 2);
         assert_eq!(min_response_pdu_len(WriteSingleRegister), 5);
         assert_eq!(min_response_pdu_len(WriteMultipleCoils), 5);
@@ -806,12 +812,23 @@ mod tests {
 
         #[test]
         fn write_single_coil() {
-            let res = Response::WriteSingleCoil(0x33);
-            let bytes = &mut [0, 0, 0];
+            let res = Response::WriteSingleCoil(0x33, true);
+            let bytes = &mut [0, 0, 0, 0, 0];
+            res.encode(bytes).unwrap();
+            assert_eq!(bytes[0], 5);
+            assert_eq!(bytes[1], 0x00);
+            assert_eq!(bytes[2], 0x33);
+            assert_eq!(bytes[3], 0xFF);
+            assert_eq!(bytes[4], 0x00);
+
+            let res = Response::WriteSingleCoil(0x33, false);
+            let bytes = &mut [0, 0, 0, 0, 0];
             res.encode(bytes).unwrap();
             assert_eq!(bytes[0], 5);
             assert_eq!(bytes[1], 0x00);
             assert_eq!(bytes[2], 0x33);
+            assert_eq!(bytes[3], 0x00);
+            assert_eq!(bytes[4], 0x00);
         }
 
         #[test]
@@ -959,9 +976,13 @@ mod tests {
 
         #[test]
         fn write_single_coil() {
-            let bytes: &[u8] = &[5, 0x00, 0x33];
+            let bytes: &[u8] = &[5, 0x00, 0x33, 0xFF, 0x00];
+            let rsp = Response::try_from(bytes).unwrap();
+            assert_eq!(rsp, Response::WriteSingleCoil(0x33, true));
+
+            let bytes: &[u8] = &[5, 0x00, 0x33, 0x00, 0x00];
             let rsp = Response::try_from(bytes).unwrap();
-            assert_eq!(rsp, Response::WriteSingleCoil(0x33));
+            assert_eq!(rsp, Response::WriteSingleCoil(0x33, false));
 
             let broken_bytes: &[u8] = &[5, 0x00];
             assert!(Response::try_from(broken_bytes).is_err());

src/frame/mod.rs

@@ -244,7 +244,7 @@ type MessageCount = u16;
 pub enum Response<'r> {
     ReadCoils(Coils<'r>),
     ReadDiscreteInputs(Coils<'r>),
-    WriteSingleCoil(Address),
+    WriteSingleCoil(Address, Coil),
     WriteMultipleCoils(Address, Quantity),
     ReadInputRegisters(Data<'r>),
     ReadHoldingRegisters(Data<'r>),
@@ -309,7 +309,7 @@ impl<'r> From<Response<'r>> for FunctionCode {
         match r {
             R::ReadCoils(_) => Self::ReadCoils,
             R::ReadDiscreteInputs(_) => Self::ReadDiscreteInputs,
-            R::WriteSingleCoil(_) => Self::WriteSingleCoil,
+            R::WriteSingleCoil(_, _) => Self::WriteSingleCoil,
             R::WriteMultipleCoils(_, _) => Self::WriteMultipleCoils,
             R::ReadInputRegisters(_) => Self::ReadInputRegisters,
             R::ReadHoldingRegisters(_) => Self::ReadHoldingRegisters,
@@ -402,7 +402,7 @@ impl Response<'_> {
     pub const fn pdu_len(&self) -> usize {
         match *self {
             Self::ReadCoils(coils) | Self::ReadDiscreteInputs(coils) => 2 + coils.packed_len(),
-            Self::WriteSingleCoil(_) => 3,
+            Self::WriteSingleCoil(_, _) => 5,
             Self::WriteMultipleCoils(_, _)
             | Self::WriteMultipleRegisters(_, _)
             | Self::WriteSingleRegister(_, _) => 5,
@@ -505,7 +505,7 @@ mod tests {
                 }),
                 2,
             ),
-            (WriteSingleCoil(0x0), 5),
+            (WriteSingleCoil(0x0, false), 5),
             (WriteMultipleCoils(0x0, 0x0), 0x0F),
             (
                 ReadInputRegisters(Data {