Provide `Write` capability on `DeviceCharacteristic`

[BYEDUCK]

Is it possible for this library to provide Write method on DeviceCharacteristic (MacOS) ?
Some devices have disabled writeWithoutResponse and only enabled write on their characteristics.

[BYEDUCK]

Isn't

func (c DeviceCharacteristic) Write(p []byte) (n int, err error) {
	c.service.device.prph.WriteCharacteristic(p, c.characteristic, true)

	return len(p), nil
}

in gattc_darwin.go all that is needed ?

[aykevl]

I would suggest WriteRequest instead of Write.
If you want to make a pull request, please implement this for at least two different BLE stacks, and test it on both stacks. This makes sure the API is portable.

For example, here is an implementation for Linux I wrote a few days ago:

diff --git a/gattc_linux.go b/gattc_linux.go
index 4d3fcb5..7a5ec47 100644
--- a/gattc_linux.go
+++ b/gattc_linux.go
@@ -207,12 +207,20 @@ func (s *DeviceService) DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacter
        return chars, nil
 }
 
+func (c DeviceCharacteristic) WriteRequest(p []byte) (n int, err error) {
+       err = c.characteristic.WriteValue(p, map[string]interface{}{"type": "request"})
+       if err != nil {
+               return 0, err
+       }
+       return len(p), nil
+}
+
 // WriteWithoutResponse replaces the characteristic value with a new value. The
 // call will return before all data has been written. A limited number of such
 // writes can be in flight at any given time. This call is also known as a
 // "write command" (as opposed to a write request).
 func (c DeviceCharacteristic) WriteWithoutResponse(p []byte) (n int, err error) {
-       err = c.characteristic.WriteValue(p, nil)
+       err = c.characteristic.WriteValue(p, map[string]interface{}{"type": "command"})
        if err != nil {
                return 0, err
        }

[ansoni-san]

@aykevi I believe gattc_windows.go already uses Write to provide write with response.

Should that be changed as well? It may break compatibility unnecessarily. Although this is early days, so now is a better time to change it than later on 🤔

[aykevl]

@aykevi I believe gattc_windows.go already uses Write to provide write with response.

Hmm, yes, you are right. Write it is, then.

(Also, I realized there are two different ways of calling them, either "write"/"write without response" or "write request"/"write command" - perhaps it's best to not mix those two).

[BYEDUCK]

Yes, these are two separate concepts:

write === write request

write without response === write command

gate_windows.go indeed already has write capability

I've tested the code with changes I mentioned and everything seemed fine at the beginning but with two different sequential write requests when I read response for the second one I still got response for the first.

I didn't have time to investigate what is the problem.

I switched to bleak and can recommend it if you are not sticked to golang.

[Ziphone]

The suggestion of @BYEDUCK did the trick for me. Did an awful workaround using go mod vendor - rather than maintaining a fork.

My project uses the original Go compiler, but includes this library because it is the best option with regular maintenance.