do not change other classes

examples/go.sum

@@ -1,5 +1,7 @@
 github.com/blackjack/webcam v0.0.0-20220329180758-ba064708e165 h1:QsIbRyO2tn5eSJZ/skuDqSTo0GWI5H4G1AT7Mm2H0Nw=
 github.com/blackjack/webcam v0.0.0-20220329180758-ba064708e165/go.mod h1:G0X+rEqYPWSq0dG8OMf8M446MtKytzpPjgS3HbdOJZ4=
+github.com/blackjack/webcam v0.0.0-20230411204030-32744c21431f h1:qBxp6Oz8y0AfeqjrYcHaYdfWQf+vUXAwgZ+GWnTtd/E=
+github.com/blackjack/webcam v0.0.0-20230411204030-32744c21431f/go.mod h1:G0X+rEqYPWSq0dG8OMf8M446MtKytzpPjgS3HbdOJZ4=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 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=
@@ -111,8 +113,11 @@ golang.org/x/image v0.0.0-20191009234506-e7c1f5e7dbb8/go.mod h1:FeLwcggjj3mMvU+o
 golang.org/x/image v0.0.0-20200927104501-e162460cd6b5/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/image v0.5.0 h1:5JMiNunQeQw++mMOz48/ISeNu3Iweh/JaZU8ZLqHRrI=
 golang.org/x/image v0.5.0/go.mod h1:FVC7BI/5Ym8R25iw5OLsgshdUBbT1h5jZTpA+mvAdZ4=
+golang.org/x/image v0.7.0 h1:gzS29xtG1J5ybQlv0PuyfE3nmc6R4qB73m6LUUmvFuw=
+golang.org/x/image v0.7.0/go.mod h1:nd/q4ef1AKKYl/4kft7g+6UyGbdiqWqTP1ZAbRoV7Rg=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
+golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
@@ -130,6 +135,7 @@ golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -152,6 +158,8 @@ golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.4.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0 h1:MUK/U/4lj1t1oPg0HfuXDN/Z1wv31ZJ/YcPiGccS4DU=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.7.0 h1:3jlCCIQZPdOYu1h8BkNvLz8Kgwtae2cagcG/VamtZRU=
+golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20191110171634-ad39bd3f0407/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
@@ -165,10 +173,12 @@ golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/text v0.4.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/text v0.6.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20201224043029-2b0845dc783e/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
+golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

pkg/driver/availability/error.go

@@ -0,0 +1,25 @@
+package availability
+
+import (
+	"errors"
+)
+
+type Error interface {
+	Error() string
+}
+
+var ErrUnimplemented Error = errors.New("not implemented")
+var ErrBusy Error = errors.New("device or resource busy")
+var ErrNoDevice Error = errors.New("no such device")
+
+type errorString struct {
+	s string
+}
+
+func NewError(text string) Error {
+	return &errorString{text}
+}
+
+func (e *errorString) Error() string {
+	return e.s
+}

pkg/driver/camera/camera_linux.go

@@ -6,12 +6,14 @@ import "C"
 import (
 	"context"
 	"errors"
+	"github.com/pion/mediadevices/pkg/driver/availability"
 	"image"
 	"io"
 	"os"
 	"path/filepath"
 	"strconv"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/blackjack/webcam"
@@ -350,3 +352,36 @@ func (c *camera) Properties() []prop.Media {
 	}
 	return properties
 }
+
+func (c *camera) IsAvailable() (bool, availability.Error) {
+	var err error
+
+	// close the opened file descriptor as quickly as possible and in all cases, including panics
+	func() {
+		var cam *webcam.Webcam
+		if cam, err = webcam.Open(c.path); err == nil {
+			defer cam.Close()
+			var index int32
+			// "Drivers must implement all the input ioctls when the device has one or more inputs..."
+			// Source: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/video.html?highlight=vidioc_enuminput
+			if index, err = cam.GetInput(); err == nil {
+				err = cam.SelectInput(uint32(index))
+			}
+		}
+	}()
+
+	var errno syscall.Errno
+	errors.As(err, &errno)
+
+	// See https://man7.org/linux/man-pages/man3/errno.3.html
+	switch {
+	case err == nil:
+		return true, nil
+	case errno == syscall.EBUSY:
+		return false, availability.ErrBusy
+	case errno == syscall.ENODEV || errno == syscall.ENOENT:
+		return false, availability.ErrNoDevice
+	default:
+		return false, availability.NewError(errno.Error())
+	}
+}

pkg/driver/driver.go

@@ -1,6 +1,7 @@
 package driver
 
 import (
+	"github.com/pion/mediadevices/pkg/driver/availability"
 	"github.com/pion/mediadevices/pkg/io/audio"
 	"github.com/pion/mediadevices/pkg/io/video"
 	"github.com/pion/mediadevices/pkg/prop"
@@ -45,3 +46,14 @@ type Driver interface {
 	Info() Info
 	Status() State
 }
+
+type AvailabilityAdapter interface {
+	IsAvailable() (bool, availability.Error)
+}
+
+func IsAvailable(d Driver) (bool, availability.Error) {
+	if aa, ok := d.(AvailabilityAdapter); ok {
+		return aa.IsAvailable()
+	}
+	return false, availability.ErrUnimplemented
+}

pkg/driver/wrapper.go

@@ -2,6 +2,7 @@ package driver
 
 import (
 	"github.com/google/uuid"
+	"github.com/pion/mediadevices/pkg/driver/availability"
 	"github.com/pion/mediadevices/pkg/io/audio"
 	"github.com/pion/mediadevices/pkg/io/video"
 	"github.com/pion/mediadevices/pkg/prop"
@@ -21,22 +22,28 @@ func wrapAdapter(a Adapter, info Info) Driver {
 		state:   StateClosed,
 	}
 
+	if aa, ok := a.(AvailabilityAdapter); ok {
+		d.isAvailable = aa.IsAvailable
+	}
+
 	switch v := a.(type) {
 	case VideoRecorder:
 		// Only expose Driver and VideoRecorder interfaces
 		d.VideoRecorder = v
 		r := &struct {
 			Driver
 			VideoRecorder
-		}{d, d}
+			AvailabilityAdapter
+		}{d, d, d}
 		return r
 	case AudioRecorder:
 		// Only expose Driver and AudioRecorder interfaces
 		d.AudioRecorder = v
 		return &struct {
 			Driver
 			AudioRecorder
-		}{d, d}
+			AvailabilityAdapter
+		}{d, d, d}
 	default:
 		panic("adapter has to be either VideoRecorder/AudioRecorder")
 	}
@@ -46,9 +53,10 @@ type adapterWrapper struct {
 	Adapter
 	VideoRecorder
 	AudioRecorder
-	id    string
-	info  Info
-	state State
+	id          string
+	info        Info
+	state       State
+	isAvailable func() (bool, availability.Error)
 }
 
 func (w *adapterWrapper) ID() string {
@@ -104,3 +112,10 @@ func (w *adapterWrapper) AudioRecord(p prop.Media) (r audio.Reader, err error) {
 	}
 	return
 }
+
+func (w *adapterWrapper) IsAvailable() (bool, availability.Error) {
+	if w.isAvailable == nil {
+		return false, availability.ErrUnimplemented
+	}
+	return w.isAvailable()
+}

pkg/driver/wrapper_test.go

@@ -2,6 +2,7 @@ package driver
 
 import (
 	"fmt"
+	"github.com/pion/mediadevices/pkg/driver/availability"
 	"testing"
 
 	"github.com/pion/mediadevices/pkg/io/audio"
@@ -39,6 +40,10 @@ func (a *audioAdapterBrokenMock) AudioRecord(p prop.Media) (r audio.Reader, err
 	return nil, recordErr
 }
 
+type availabilityAdapterMock struct{ videoAdapterMock }
+
+func (a *availabilityAdapterMock) IsAvailable() (bool, availability.Error) { return true, nil }
+
 func TestVideoWrapperState(t *testing.T) {
 	var a videoAdapterMock
 	d := wrapAdapter(&a, Info{})
@@ -136,3 +141,38 @@ func TestAudioWrapperWithBrokenRecorderState(t *testing.T) {
 		t.Errorf("expected the status to be %v, but got %v", StateClosed, d.Status())
 	}
 }
+
+func TestWrapperAvailabilityAdapter(t *testing.T) {
+	var aa availabilityAdapterMock
+	d := wrapAdapter(&aa, Info{})
+
+	ok, err := IsAvailable(d)
+	if err != nil {
+		t.Errorf("expected nil, but got %v", err)
+	}
+	if !ok {
+		t.Errorf("expected true, but got %v", ok)
+	}
+
+	var v videoAdapterMock
+	d = wrapAdapter(&v, Info{})
+
+	ok, err = IsAvailable(d)
+	if err == nil {
+		t.Errorf("expected err, but got %v", err)
+	}
+	if ok {
+		t.Errorf("expected false, but got %v", ok)
+	}
+
+	var a audioAdapterMock
+	d = wrapAdapter(&a, Info{})
+
+	ok, err = IsAvailable(d)
+	if err == nil {
+		t.Errorf("expected err, but got %v", err)
+	}
+	if ok {
+		t.Errorf("expected false, but got %v", ok)
+	}
+}