getMultipleHoldingRegisters() in Modbus-TCP Server causes a failure when returning a Promise

[romor]

According the TypeScript definitions, IServiceVector::getMultipleHoldingRegisters() support returning Promise<number[]>.

However, when this is used, the return length check in servertcp_handler.js::300 will always fail. The corresponding code part is:

        const values = vector.getMultipleHoldingRegisters(address, length, unitID);
        if (values.length === length) {

As values is Promise{[...]} its length check fails and this results in a Modbus exception sent to client instead of the provided read result.

When getMultipleHoldingRegisters() returns number[] directly, without a Promise, everything works as expected.

[modbus2mqtt]

I have the same problem
Workaround:
use callback function by wrapping the promise

  queueMultipleRegister( addr: number, length: number, unitID: number, cb: FCallbackVal<number[]>): void{
    yourPromise(
      addr,
      length,
      unitID
    ).then((value)=>{
        cb(null,value)
    }).catch(e=>{cb(e,[])})
  }

However, it would be nicer if it works. :-)

[volkmarnissen]

It's not only HoldingRegister which doesn't work with Promise, it's also Coils
Additionally the Promise.then method for writeRegister will not be called after successful execution

It's very hard to find these kind of issues.
So, they should either work properly or marked as "not working" in the documentation.

I replaced all calls with promisses to calls with callback. This is more reliable.