Parse DTLS setup in SetRemoteDescription

Take into consideration if remote is running DTLS as a
client/server. Before we ignored this value and we could
enter cases where DTLS would never connect.

Resolves #494

dtlsrole.go

@@ -1,5 +1,9 @@
 package webrtc
 
+import (
+	"github.com/pion/sdp/v2"
+)
+
 // DTLSRole indicates the role of the DTLS transport.
 type DTLSRole byte
 
@@ -28,3 +32,29 @@ func (r DTLSRole) String() string {
 		return unknownStr
 	}
 }
+
+// Iterate a SessionDescription from a remote to determine if an explicit
+// role can been determined for local connection. The decision is made from the first role we we parse.
+// If no role can be found we return DTLSRoleAuto
+func dtlsRoleFromRemoteSDP(sessionDescription *sdp.SessionDescription) DTLSRole {
+	if sessionDescription == nil {
+		return DTLSRoleAuto
+	}
+
+	for _, mediaSection := range sessionDescription.MediaDescriptions {
+		for _, attribute := range mediaSection.Attributes {
+			if attribute.Key == "setup" {
+				switch attribute.Value {
+				case "active":
+					return DTLSRoleServer
+				case "passive":
+					return DTLSRoleClient
+				default:
+					return DTLSRoleAuto
+				}
+			}
+		}
+	}
+
+	return DTLSRoleAuto
+}

dtlsrole_test.go

@@ -1,8 +1,10 @@
 package webrtc
 
 import (
+	"fmt"
 	"testing"
 
+	"github.com/pion/sdp/v2"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -25,3 +27,56 @@ func TestDTLSRole_String(t *testing.T) {
 		)
 	}
 }
+
+func TestDTLSRoleFromRemoteSDP(t *testing.T) {
+	parseSDP := func(raw string) *sdp.SessionDescription {
+		parsed := &sdp.SessionDescription{}
+		if err := parsed.Unmarshal([]byte(raw)); err != nil {
+			panic(err)
+		}
+		return parsed
+	}
+
+	const noMedia = `v=0
+o=- 4596489990601351948 2 IN IP4 127.0.0.1
+s=-
+t=0 0
+`
+
+	const mediaNoSetup = `v=0
+o=- 4596489990601351948 2 IN IP4 127.0.0.1
+s=-
+t=0 0
+m=application 47299 DTLS/SCTP 5000
+c=IN IP4 192.168.20.129
+`
+
+	const mediaSetupDeclared = `v=0
+o=- 4596489990601351948 2 IN IP4 127.0.0.1
+s=-
+t=0 0
+m=application 47299 DTLS/SCTP 5000
+c=IN IP4 192.168.20.129
+a=setup:%s
+`
+
+	testCases := []struct {
+		test               string
+		sessionDescription *sdp.SessionDescription
+		expectedRole       DTLSRole
+	}{
+		{"nil SessionDescription", nil, DTLSRoleAuto},
+		{"No MediaDescriptions", parseSDP(noMedia), DTLSRoleAuto},
+		{"MediaDescription, no setup", parseSDP(mediaNoSetup), DTLSRoleAuto},
+		{"MediaDescription, setup:actpass", parseSDP(fmt.Sprintf(mediaSetupDeclared, "actpass")), DTLSRoleAuto},
+		{"MediaDescription, setup:passive", parseSDP(fmt.Sprintf(mediaSetupDeclared, "passive")), DTLSRoleClient},
+		{"MediaDescription, setup:active", parseSDP(fmt.Sprintf(mediaSetupDeclared, "active")), DTLSRoleServer},
+	}
+	for _, testCase := range testCases {
+		assert.Equal(t,
+			testCase.expectedRole,
+			dtlsRoleFromRemoteSDP(testCase.sessionDescription),
+			"TestDTLSRoleFromSDP (%s)", testCase.test,
+		)
+	}
+}

peerconnection.go

@@ -470,7 +470,7 @@ func (pc *PeerConnection) CreateOffer(options *OfferOptions) (SessionDescription
 	d = d.WithValueAttribute(sdp.AttrKeyGroup, bundleValue)
 
 	for _, m := range d.MediaDescriptions {
-		m.WithPropertyAttribute("setup:actpass")
+		m.WithValueAttribute(sdp.AttrKeyConnectionSetup, "actpass")
 	}
 
 	sdpBytes, err := d.Marshal()
@@ -968,7 +968,7 @@ func (pc *PeerConnection) SetRemoteDescription(desc SessionDescription) error {
 
 		// Start the dtls transport
 		err = pc.dtlsTransport.Start(DTLSParameters{
-			Role:         DTLSRoleAuto,
+			Role:         dtlsRoleFromRemoteSDP(desc.parsed),
 			Fingerprints: []DTLSFingerprint{{Algorithm: fingerprintHash, Value: fingerprint}},
 		})
 		if err != nil {
@@ -1656,7 +1656,7 @@ func (pc *PeerConnection) addTransceiverSDP(d *sdp.SessionDescription, midValue
 	// Use the first transceiver to generate the section attributes
 	t := transceivers[0]
 	media := sdp.NewJSEPMediaDescription(t.kind.String(), []string{}).
-		WithValueAttribute(sdp.AttrKeyConnectionSetup, dtlsRole.String()). // pion/webrtc#494
+		WithValueAttribute(sdp.AttrKeyConnectionSetup, dtlsRole.String()).
 		WithValueAttribute(sdp.AttrKeyMID, midValue).
 		WithICECredentials(iceParams.UsernameFragment, iceParams.Password).
 		WithPropertyAttribute(sdp.AttrKeyRTCPMux).
@@ -1718,7 +1718,7 @@ func (pc *PeerConnection) addDataMediaSection(d *sdp.SessionDescription, midValu
 			},
 		},
 	}).
-		WithValueAttribute(sdp.AttrKeyConnectionSetup, dtlsRole.String()). // pion/webrtc#494
+		WithValueAttribute(sdp.AttrKeyConnectionSetup, dtlsRole.String()).
 		WithValueAttribute(sdp.AttrKeyMID, midValue).
 		WithPropertyAttribute(RTPTransceiverDirectionSendrecv.String()).
 		WithPropertyAttribute("sctpmap:5000 webrtc-datachannel 1024").