Fix MacOS deadlock during BLE scan

The MacOS BLE Scan() method blocks until all queued instances of the
callback function finish. This created a deadlock, since the callback
function would try to write a matching advertisement to an unbuffered
channel, and the unbuffered channel would not be read until Scan()
completed.

To fix the problem, this commit makes the channel buffered, allowing the
callback function to succeed on the first match. The callback handles
subsequent matches by detecting that the scan context has been
canceled and returning.

This commit also uprevs the BLE package. This was previously impossible
because we relied on the device.Connect method, which is broken
upstream on MacOS.

Author: Seth Terashima

go.mod

@@ -5,7 +5,7 @@ go 1.23
 require (
 	github.com/99designs/keyring v1.2.2
 	github.com/cronokirby/saferith v0.33.0
-	github.com/go-ble/ble v0.0.0-20220207185428-60d1eecf2633
+	github.com/go-ble/ble v0.0.0-20240122180141-8c5522f54333
 	github.com/golang-jwt/jwt/v5 v5.2.1
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
 	golang.org/x/term v0.5.0

go.sum

@@ -13,8 +13,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dvsekhvalnov/jose2go v1.6.0 h1:Y9gnSnP4qEI0+/uQkHvFXeD2PLPJeXEL+ySMEA2EjTY=
 github.com/dvsekhvalnov/jose2go v1.6.0/go.mod h1:QsHjhyTlD/lAVqn/NSbVZmSCGeDehTB/mPZadG+mhXU=
-github.com/go-ble/ble v0.0.0-20220207185428-60d1eecf2633 h1:ZrzoZQz1CF33SPHLkjRpnVuZwr9cO1lTEc4Js7SgBos=
-github.com/go-ble/ble v0.0.0-20220207185428-60d1eecf2633/go.mod h1:fFJl/jD/uyILGBeD5iQ8tYHrPlJafyqCJzAyTHNJ1Uk=
+github.com/go-ble/ble v0.0.0-20240122180141-8c5522f54333 h1:bQK6D51cNzMSTyAf0HtM30V2IbljHTDam7jru9JNlJA=
+github.com/go-ble/ble v0.0.0-20240122180141-8c5522f54333/go.mod h1:fFJl/jD/uyILGBeD5iQ8tYHrPlJafyqCJzAyTHNJ1Uk=
 github.com/godbus/dbus v0.0.0-20190726142602-4481cbc300e2 h1:ZpnhV/YsD2/4cESfV5+Hoeu/iUR3ruzNvZ+yQfO03a0=
 github.com/godbus/dbus v0.0.0-20190726142602-4481cbc300e2/go.mod h1:bBOAhwG1umN6/6ZUMtDFBMQR8jRg9O75tm9K00oMsK4=
 github.com/golang-jwt/jwt/v5 v5.2.1 h1:OuVbFODueb089Lh128TAcimifWaLhJwVflnrgM17wHk=

pkg/connector/ble/ble.go

@@ -5,6 +5,7 @@ package ble
 import (
 	"context"
 	"crypto/sha1"
+	"errors"
 	"fmt"
 	"strings"
 	"sync"
@@ -169,16 +170,28 @@ func ScanVehicleBeacon(ctx context.Context, vin string) (Advertisement, error) {
 func scanVehicleBeacon(ctx context.Context, localName string) (Advertisement, error) {
 	var err error
 	ctx2, cancel := context.WithCancel(ctx)
+	defer cancel()
 
-	ch := make(chan Advertisement)
+	ch := make(chan Advertisement, 1)
 	fn := func(a Advertisement) {
 		if a.LocalName() != localName {
 			return
 		}
-		cancel()
-		ch <- a
+		select {
+		case ch <- a:
+			cancel() // Notify device.Scan() that we found a match
+		case <-ctx2.Done():
+			// Another goroutine already found a matching advertisement. We need to return so that
+			// the MacOS implementation of device.Scan(...) unblocks.
+		}
+	}
+
+	if err = device.Scan(ctx2, false, fn); !errors.Is(err, context.Canceled) {
+		// If ctx rather than ctx2 was canceled, we'll pick that error up below. This is a bit
+		// hacky, but unfortunately device.Scan() _always_ returns an error on MacOS because it does
+		// not terminate until the provided context is canceled.
+		return nil, err
 	}
-	err = device.Scan(ctx2, false, fn)
 
 	select {
 	case a, ok := <-ch:
@@ -187,8 +200,8 @@ func scanVehicleBeacon(ctx context.Context, localName string) (Advertisement, er
 			return nil, fmt.Errorf("scan channel closed")
 		}
 		return a, nil
-	default:
-		return nil, err
+	case <-ctx.Done():
+		return nil, ctx.Err()
 	}
 }