Support parsing candidates with missing Foundation

Not RFC 8445 compliant but are currently emitted by Google.

Resolves #390

candidate_base.go

@@ -393,8 +393,13 @@ func (c *candidateBase) copy() (Candidate, error) {
 
 // Marshal returns the string representation of the ICECandidate
 func (c *candidateBase) Marshal() string {
-	val := fmt.Sprintf("%s %d %s %d %s %d typ %s",
-		c.Foundation(),
+	val := c.Foundation()
+	if val == " " {
+		val = ""
+	}
+
+	val = fmt.Sprintf("%s %d %s %d %s %d typ %s",
+		val,
 		c.Component(),
 		c.NetworkType().NetworkShort(),
 		c.Priority(),
@@ -419,7 +424,11 @@ func (c *candidateBase) Marshal() string {
 // UnmarshalCandidate creates a Candidate from its string representation
 func UnmarshalCandidate(raw string) (Candidate, error) {
 	split := strings.Fields(raw)
-	if len(split) < 8 {
+	switch {
+	// Foundation not specified: not RFC 8445 compliant but seen in the wild
+	case len(split) == 7 && raw[0] == ' ':
+		split = append([]string{" "}, split...)
+	case len(split) < 8:
 		return nil, fmt.Errorf("%w (%d)", errAttributeTooShortICECandidate, len(split))
 	}
 

candidate_test.go

@@ -294,6 +294,22 @@ func TestCandidateMarshal(t *testing.T) {
 			},
 			"1380287402 1 udp 2130706431 e2494022-4d9a-4c1e-a750-cc48d4f8d6ee.local 60542 typ host", false,
 		},
+		// Missing Foundation
+		{
+			&CandidateHost{
+				candidateBase{
+					networkType:        NetworkTypeUDP4,
+					candidateType:      CandidateTypeHost,
+					address:            "127.0.0.1",
+					port:               80,
+					priorityOverride:   500,
+					foundationOverride: " ",
+				},
+				"",
+			},
+			" 1 udp 500 127.0.0.1 80 typ host",
+			false,
+		},
 
 		// Invalid candidates
 		{nil, "", true},
@@ -321,3 +337,10 @@ func TestCandidateMarshal(t *testing.T) {
 		assert.Equal(t, test.marshaled, actualCandidate.Marshal())
 	}
 }
+
+func TestMissingCandidateFoundation(t *testing.T) {
+	// " 1 udp 2113939711 2607:f8b0:400e:c0a::7f 19305 typ host generation 0"
+	// " 1 tcp 2113939710 2607:f8b0:400e:c0a::7f 19305 typ host tcptype passive generation 0"
+	// " 1 udp 2113932031 172.253.117.127 19305 typ host generation 0"
+	// " 1 tcp 2113932030 172.253.117.127 19305 typ host tcptype passive generation 0"
+}