Add MulticastDNSHostName to AgentConfig

Allow users to pass in a static MulticastDNSHostName, this can be used to
connect peers in a LAN without signaling. If you set a static uFrag/uPwd
on either side and have a static hostname you can gather without knowing
an IP Address on either side.

agent.go

@@ -199,6 +199,9 @@ type AgentConfig struct {
 	// MulticastDNSMode controls mDNS behavior for the ICE agent
 	MulticastDNSMode MulticastDNSMode
 
+	// MulticastDNSHostName controls the hostname for this agent. If none is specified a random one will be generated
+	MulticastDNSHostName string
+
 	// ConnectionTimeout defaults to 30 seconds when this property is nil.
 	// If the duration is 0, we will never timeout this connection.
 	ConnectionTimeout *time.Duration
@@ -313,6 +316,7 @@ func createMulticastDNS(mDNSMode MulticastDNSMode, mDNSName string, log logging.
 
 // NewAgent creates a new Agent
 func NewAgent(config *AgentConfig) (*Agent, error) {
+	var err error
 	if config.PortMax < config.PortMin {
 		return nil, ErrPort
 	}
@@ -337,9 +341,15 @@ func NewAgent(config *AgentConfig) (*Agent, error) {
 		localPwd = config.LocalPwd
 	}
 
-	mDNSName, err := generateMulticastDNSName()
-	if err != nil {
-		return nil, err
+	mDNSName := config.MulticastDNSHostName
+	if mDNSName == "" {
+		if mDNSName, err = generateMulticastDNSName(); err != nil {
+			return nil, err
+		}
+	}
+
+	if !strings.HasSuffix(mDNSName, ".local") || len(strings.Split(mDNSName, ".")) != 2 {
+		return nil, ErrInvalidMulticastDNSHostName
 	}
 
 	mDNSMode := config.MulticastDNSMode

errors.go

@@ -94,4 +94,7 @@ var (
 	// ErrIneffectiveNAT1To1IPMappingSrflx indicates that 1:1 NAT IP mapping for srflx candidate is
 	// requested, but the srflx candidate type is disabled.
 	ErrIneffectiveNAT1To1IPMappingSrflx = errors.New("1:1 NAT IP mapping for srflx candidate ineffective")
+
+	// ErrInvalidMulticastDNSHostName indicates an invalid MulticastDNSHostName
+	ErrInvalidMulticastDNSHostName = errors.New("invalid mDNS HostName, must end with .local and can only contain a single '.'")
 )

go.sum

@@ -31,6 +31,7 @@ github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81P
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/net v0.0.0-20190619014844-b5b0513f8c1b h1:lkjdUzSyJ5P1+eal9fxXX9Xg2BTfswsonKUse48C0uE=
 golang.org/x/net v0.0.0-20190619014844-b5b0513f8c1b/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20191126235420-ef20fe5d7933 h1:e6HwijUxhDe+hPNjZQQn9bA5PW3vNmnN64U2ZW759Lk=
 golang.org/x/net v0.0.0-20191126235420-ef20fe5d7933/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

mdns_test.go

@@ -1,6 +1,7 @@
 package ice
 
 import (
+	"context"
 	"testing"
 	"time"
 
@@ -93,3 +94,39 @@ func TestMulticastDNSMixedConnection(t *testing.T) {
 	assert.NoError(t, aAgent.Close())
 	assert.NoError(t, bAgent.Close())
 }
+
+func TestMulticastDNSStaticHostName(t *testing.T) {
+	lim := test.TimeOut(time.Second * 30)
+	defer lim.Stop()
+
+	report := test.CheckRoutines(t)
+	defer report()
+
+	_, err := NewAgent(&AgentConfig{
+		NetworkTypes:         []NetworkType{NetworkTypeUDP4},
+		CandidateTypes:       []CandidateType{CandidateTypeHost},
+		MulticastDNSMode:     MulticastDNSModeQueryAndGather,
+		MulticastDNSHostName: "invalidHostName",
+	})
+	assert.Equal(t, err, ErrInvalidMulticastDNSHostName)
+
+	agent, err := NewAgent(&AgentConfig{
+		Trickle:              true,
+		NetworkTypes:         []NetworkType{NetworkTypeUDP4},
+		CandidateTypes:       []CandidateType{CandidateTypeHost},
+		MulticastDNSMode:     MulticastDNSModeQueryAndGather,
+		MulticastDNSHostName: "validName.local",
+	})
+	assert.NoError(t, err)
+
+	correctHostName, resolveFunc := context.WithCancel(context.Background())
+	assert.NoError(t, agent.OnCandidate(func(c Candidate) {
+		if c.Address() == "validName.local" {
+			resolveFunc()
+		}
+	}))
+
+	assert.NoError(t, agent.GatherCandidates())
+	<-correctHostName.Done()
+	assert.NoError(t, agent.Close())
+}