Add pkg/discovery for nodes discovery

Absorb Swarm's discovery package in order to provide a common node
discovery mechanism to be used by both Swarm and networking code.

Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>

discovery/generator_test.go

@@ -0,0 +1,55 @@
+package discovery
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGeneratorNotGenerate(t *testing.T) {
+	ips := Generate("127.0.0.1")
+	assert.Equal(t, len(ips), 1)
+	assert.Equal(t, ips[0], "127.0.0.1")
+}
+
+func TestGeneratorWithPortNotGenerate(t *testing.T) {
+	ips := Generate("127.0.0.1:8080")
+	assert.Equal(t, len(ips), 1)
+	assert.Equal(t, ips[0], "127.0.0.1:8080")
+}
+
+func TestGeneratorMatchFailedNotGenerate(t *testing.T) {
+	ips := Generate("127.0.0.[1]")
+	assert.Equal(t, len(ips), 1)
+	assert.Equal(t, ips[0], "127.0.0.[1]")
+}
+
+func TestGeneratorWithPort(t *testing.T) {
+	ips := Generate("127.0.0.[1:11]:2375")
+	assert.Equal(t, len(ips), 11)
+	assert.Equal(t, ips[0], "127.0.0.1:2375")
+	assert.Equal(t, ips[1], "127.0.0.2:2375")
+	assert.Equal(t, ips[2], "127.0.0.3:2375")
+	assert.Equal(t, ips[3], "127.0.0.4:2375")
+	assert.Equal(t, ips[4], "127.0.0.5:2375")
+	assert.Equal(t, ips[5], "127.0.0.6:2375")
+	assert.Equal(t, ips[6], "127.0.0.7:2375")
+	assert.Equal(t, ips[7], "127.0.0.8:2375")
+	assert.Equal(t, ips[8], "127.0.0.9:2375")
+	assert.Equal(t, ips[9], "127.0.0.10:2375")
+	assert.Equal(t, ips[10], "127.0.0.11:2375")
+}
+
+func TestGenerateWithMalformedInputAtRangeStart(t *testing.T) {
+	malformedInput := "127.0.0.[x:11]:2375"
+	ips := Generate(malformedInput)
+	assert.Equal(t, len(ips), 1)
+	assert.Equal(t, ips[0], malformedInput)
+}
+
+func TestGenerateWithMalformedInputAtRangeEnd(t *testing.T) {
+	malformedInput := "127.0.0.[1:x]:2375"
+	ips := Generate(malformedInput)
+	assert.Equal(t, len(ips), 1)
+	assert.Equal(t, ips[0], malformedInput)
+}