Merge pull request #1 from sethterashima/fix-blocking-scan-goroutine

Fix MacOS deadlock during BLE scan

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()
 	}
 }