Add EnableDataChannelBlockWrite to SettingEngine

The settingengine can enabled block write if
datachannel is detached, makes it working like
a normal net.Conn.

datachannel.go

@@ -450,6 +450,12 @@ func (d *DataChannel) ensureOpen() error {
 // pion/datachannel documentation for the correct way to handle the
 // resulting DataChannel object.
 func (d *DataChannel) Detach() (datachannel.ReadWriteCloser, error) {
+	return d.DetachWithDeadline()
+}
+
+// DetachWithDeadline allows you to detach the underlying datachannel.
+// It is the same as Detach but returns a ReadWriteCloserDeadliner.
+func (d *DataChannel) DetachWithDeadline() (datachannel.ReadWriteCloserDeadliner, error) {
 	d.mu.Lock()
 
 	if !d.api.settingEngine.detach.DataChannels {

sctptransport.go

@@ -98,7 +98,7 @@ func (r *SCTPTransport) GetCapabilities() SCTPCapabilities {
 // Start the SCTPTransport. Since both local and remote parties must mutually
 // create an SCTPTransport, SCTP SO (Simultaneous Open) is used to establish
 // a connection over SCTP.
-func (r *SCTPTransport) Start(SCTPCapabilities) error {
+func (r *SCTPTransport) Start(_ SCTPCapabilities) error {
 	if r.isStarted {
 		return nil
 	}
@@ -114,6 +114,7 @@ func (r *SCTPTransport) Start(SCTPCapabilities) error {
 		EnableZeroChecksum:   r.api.settingEngine.sctp.enableZeroChecksum,
 		LoggerFactory:        r.api.settingEngine.LoggerFactory,
 		RTOMax:               float64(r.api.settingEngine.sctp.rtoMax) / float64(time.Millisecond),
+		BlockWrite:           r.api.settingEngine.detach.DataChannels && r.api.settingEngine.dataChannelBlockWrite,
 	})
 	if err != nil {
 		return err

settingengine.go

@@ -103,6 +103,7 @@ type SettingEngine struct {
 	iceMaxBindingRequests                     *uint16
 	fireOnTrackBeforeFirstRTP                 bool
 	disableCloseByDTLS                        bool
+	dataChannelBlockWrite                     bool
 }
 
 // getReceiveMTU returns the configured MTU. If SettingEngine's MTU is configured to 0 it returns the default
@@ -121,6 +122,12 @@ func (e *SettingEngine) DetachDataChannels() {
 	e.detach.DataChannels = true
 }
 
+// EnableDataChannelBlockWrite allows data channels to block on write,
+// it only works if DetachDataChannels is enabled
+func (e *SettingEngine) EnableDataChannelBlockWrite(nonblockWrite bool) {
+	e.dataChannelBlockWrite = nonblockWrite
+}
+
 // SetSRTPProtectionProfiles allows the user to override the default SRTP Protection Profiles
 // The default srtp protection profiles are provided by the function `defaultSrtpProtectionProfiles`
 func (e *SettingEngine) SetSRTPProtectionProfiles(profiles ...dtls.SRTPProtectionProfile) {

settingengine_test.go

@@ -12,6 +12,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/pion/datachannel"
 	"github.com/pion/dtls/v3/pkg/crypto/elliptic"
 	"github.com/pion/dtls/v3/pkg/protocol/handshake"
 	"github.com/pion/ice/v4"
@@ -417,3 +418,45 @@ func TestDisableCloseByDTLS(t *testing.T) {
 	assert.True(t, offer.ConnectionState() == PeerConnectionStateConnected)
 	assert.NoError(t, offer.Close())
 }
+
+func TestEnableDataChannelBlockWrite(t *testing.T) {
+	lim := test.TimeOut(time.Second * 30)
+	defer lim.Stop()
+
+	report := test.CheckRoutines(t)
+	defer report()
+
+	s := SettingEngine{}
+	s.DetachDataChannels()
+	s.EnableDataChannelBlockWrite(true)
+	s.SetSCTPMaxReceiveBufferSize(1500)
+
+	offer, answer, err := NewAPI(WithSettingEngine(s)).newPair(Configuration{})
+	assert.NoError(t, err)
+
+	dc, err := offer.CreateDataChannel("data", nil)
+	assert.NoError(t, err)
+	detachChan := make(chan datachannel.ReadWriteCloserDeadliner, 1)
+	dc.OnOpen(func() {
+		detached, err1 := dc.DetachWithDeadline()
+		assert.NoError(t, err1)
+		detachChan <- detached
+	})
+
+	assert.NoError(t, signalPair(offer, answer))
+	untilConnectionState(PeerConnectionStateConnected, offer, answer).Wait()
+
+	// write should block and return deadline exceeded since the receiver is not reading
+	// and the buffer size is 1500 bytes
+	rawDC := <-detachChan
+	assert.NoError(t, rawDC.SetWriteDeadline(time.Now().Add(time.Second)))
+	buf := make([]byte, 1000)
+	for i := 0; i < 10; i++ {
+		_, err = rawDC.Write(buf)
+		if err != nil {
+			break
+		}
+	}
+	assert.ErrorIs(t, err, context.DeadlineExceeded)
+	closePairNow(t, offer, answer)
+}