Support DataChannel messages larger then MaxUint16

SCTP now internally can handle larger messages

Resolves #2712

settingengine.go

@@ -83,6 +83,7 @@ type SettingEngine struct {
 		maxReceiveBufferSize uint32
 		enableZeroChecksum   bool
 		rtoMax               time.Duration
+		maxMessageSize       uint32
 	}
 	sdpMediaLevelFingerprints                 bool
 	answeringDTLSRole                         DTLSRole
@@ -106,6 +107,14 @@ type SettingEngine struct {
 	dataChannelBlockWrite                     bool
 }
 
+func (e *SettingEngine) getSCTPMaxMessageSize() uint32 {
+	if e.sctp.maxMessageSize != 0 {
+		return e.sctp.maxMessageSize
+	}
+
+	return defaultMaxSCTPMessageSize
+}
+
 // getReceiveMTU returns the configured MTU. If SettingEngine's MTU is configured to 0 it returns the default.
 func (e *SettingEngine) getReceiveMTU() uint {
 	if e.receiveMTU != 0 {
@@ -467,6 +476,12 @@ func (e *SettingEngine) EnableSCTPZeroChecksum(isEnabled bool) {
 	e.sctp.enableZeroChecksum = isEnabled
 }
 
+// SetSCTPMaxMessageSize sets the largest message we are willing to accept.
+// Leave this 0 for the default max message size.
+func (e *SettingEngine) SetSCTPMaxMessageSize(maxMessageSize uint32) {
+	e.sctp.maxMessageSize = maxMessageSize
+}
+
 // SetDTLSCustomerCipherSuites allows the user to specify a list of DTLS CipherSuites.
 // This allow usage of Ciphers that are reserved for private usage.
 func (e *SettingEngine) SetDTLSCustomerCipherSuites(customCipherSuites func() []dtls.CipherSuite) {