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fix(darwin): WriteWithoutResponse checks CanSendWriteWithoutResponse before request #386

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fix(darwin): WriteWithoutResponse checks CanSendWriteWithoutResponse before request #386

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fe363b9
feat(gattc): add CanSendWriteWithoutResponse for darwin
acouvreur Oct 4, 2025
6b21611
fix doc
acouvreur Oct 4, 2025
319250f
WriteWithoutResponse checks if it can send write without response req…
acouvreur Oct 21, 2025
0e87cf5
remove mutex
acouvreur Oct 23, 2025
281cb3f
remove unused named return params
acouvreur Oct 23, 2025
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5 changes: 5 additions & 0 deletions gattc.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
package bluetooth

import "errors"

var ErrCannotSendWriteWithoutResponse = errors.New("cannot send write without response")
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@gen2thomas gen2thomas Oct 26, 2025

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It seems all other implementations already have its error handling (e.g. gattc_hci.go), so we should move this variable to "gattc_darwin.go". We need it exposed to use it in user code for checks, like you already demonstrated in your small example. (IMO unexposed variants in the other implementations are not that powerful, but this is another story.)

18 changes: 15 additions & 3 deletions gattc_darwin.go
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Expand Up @@ -199,9 +199,13 @@ func (c DeviceCharacteristic) Write(p []byte) (n int, err error) {

// 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) {
// writes can be in flight at any given time.
// If the client is not ready to send write without response requests at this time, ErrCannotSendWriteWithoutResponse is returned.
func (c DeviceCharacteristic) WriteWithoutResponse(p []byte) (int, error) {
if !c.service.device.prph.CanSendWriteWithoutResponse() {
return 0, ErrCannotSendWriteWithoutResponse
}

c.service.device.prph.WriteCharacteristic(p, c.characteristic, false)

return len(p), nil
Expand All @@ -227,6 +231,14 @@ func (c DeviceCharacteristic) GetMTU() (uint16, error) {
return uint16(c.service.device.prph.MaximumWriteValueLength(false)), nil
}

// CanSendWriteWithoutResponse returns whether a WriteWithoutResponse can be sent
// at this time. If this returns false, you must wait for some time before
// sending another WriteWithoutResponse. This is typically because the internal
// buffer is full.
func (c DeviceCharacteristic) CanSendWriteWithoutResponse() bool {
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@deadprogram deadprogram Nov 11, 2025

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Since this function does not exist in any of the other platforms, I am hesitant to include it. Can just checking in the WriteWithoutResponse() function as you do above be enough the address the issue?

return c.service.device.prph.CanSendWriteWithoutResponse()
}

// Read reads the current characteristic value.
func (c *deviceCharacteristic) Read(data []byte) (n int, err error) {
c.readChan = make(chan error)
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