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Expose stop service advertisment on Windows #281

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Expose stop service advertisment on Windows #281

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40dfdeb
feat: add stop service advertisement for windows
Jul 25, 2024
3d41e77
chore: add StopServiceAdvertisement stub for linux
Jul 30, 2024
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3 changes: 3 additions & 0 deletions adapter_windows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ import (
"github.com/go-ole/go-ole"
"github.com/saltosystems/winrt-go"
"github.com/saltosystems/winrt-go/windows/devices/bluetooth/advertisement"
"github.com/saltosystems/winrt-go/windows/devices/bluetooth/genericattributeprofile"
"github.com/saltosystems/winrt-go/windows/foundation"
)

Expand All @@ -16,6 +17,8 @@ type Adapter struct {
connectHandler func(device Device, connected bool)

defaultAdvertisement *Advertisement

gattServiceProvider *genericattributeprofile.GattServiceProvider
}

// DefaultAdapter is the default adapter on the system.
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6 changes: 6 additions & 0 deletions gatts_linux.go
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Expand Up @@ -71,6 +71,12 @@ func (c *bluezChar) WriteValue(value []byte, options map[string]dbus.Variant) *d
return nil
}

func (a *Adapter) StopServiceAdvertisement() error {
// TODO: implement on linux

return nil
}

// AddService creates a new service with the characteristics listed in the
// Service struct.
func (a *Adapter) AddService(s *Service) error {
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6 changes: 6 additions & 0 deletions gatts_windows.go
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Expand Up @@ -49,6 +49,8 @@ func (a *Adapter) AddService(s *Service) error {
return err
}

a.gattServiceProvider = serviceProvider
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If I understood correctly each GATT service requires its own GattServiceProvider. So if someone adds two services this would only store the latest created.

Users should be able to add and stop the specific service they want.

I was thinking that a map with the UUID and the service provider could work, but the BLE spec allows UUIDs to be repeated (a problem already found on other ble libraries hbldh/bleak#362).

So maybe AddService() should return some handle to the created service to stop it?

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So maybe AddService() should return some handle to the created service to stop it?

That sounds like a very reasonable suggestion!


localService, err := serviceProvider.GetService()
if err != nil {
return err
Expand Down Expand Up @@ -237,6 +239,10 @@ func (a *Adapter) AddService(s *Service) error {
return serviceProvider.StartAdvertisingWithParameters(params)
}

func (a *Adapter) StopServiceAdvertisement() error {
return a.gattServiceProvider.StopAdvertising()
}
Comment on lines +242 to +244
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Wait - so normally after you call adapter.AddService the service is also included in the advertisement packet?
That's not how BLE normally works. The advertisement packet and the list of services that are actually available after connection may overlap, but this is normally the responsibility of the application developer to explicitly include.

Apparently Windows works differently. This is quite annoying.
To keep the API consistent (so the user doesn't need to know too much about platform differences), I would recommend the following:

  • Keep track of which service UUIDs are currently listed in the configured advertisement packet.
  • Also keep track of which services are currently enabled.
  • On every update to the advertisement packet, start/stop advertising the services according to the UUIDs in the advertisement packet.

So how this could work in practice:

  • When advertisement is started, go through the enabled services and start advertisements for the services with an UUID listed in AdvertisementOptions.ServiceUUIDs.
  • When advertisement is stopped, go through the enabled services and stop advertisement for all of them.
  • When a new service is added, check whether the UUID is part of AdvertisementOptions.ServiceUUIDs of the current advertisement and only call StartAdvertisingWithParameters if it's in there.

(We don't currently have a way to stop services, that would probably also be useful to add).


// Write replaces the characteristic value with a new value.
func (c *Characteristic) Write(p []byte) (n int, err error) {
length := len(p)
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