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/file/file_test.go

@@ -0,0 +1,106 @@
+package file
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/docker/docker/pkg/discovery"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInitialize(t *testing.T) {
+	d := &Discovery{}
+	d.Initialize("/path/to/file", 1000, 0)
+	assert.Equal(t, d.path, "/path/to/file")
+}
+
+func TestNew(t *testing.T) {
+	d, err := discovery.New("file:///path/to/file", 0, 0)
+	assert.NoError(t, err)
+	assert.Equal(t, d.(*Discovery).path, "/path/to/file")
+}
+
+func TestContent(t *testing.T) {
+	data := `
+1.1.1.[1:2]:1111
+2.2.2.[2:4]:2222
+`
+	ips := parseFileContent([]byte(data))
+	assert.Len(t, ips, 5)
+	assert.Equal(t, ips[0], "1.1.1.1:1111")
+	assert.Equal(t, ips[1], "1.1.1.2:1111")
+	assert.Equal(t, ips[2], "2.2.2.2:2222")
+	assert.Equal(t, ips[3], "2.2.2.3:2222")
+	assert.Equal(t, ips[4], "2.2.2.4:2222")
+}
+
+func TestRegister(t *testing.T) {
+	discovery := &Discovery{path: "/path/to/file"}
+	assert.Error(t, discovery.Register("0.0.0.0"))
+}
+
+func TestParsingContentsWithComments(t *testing.T) {
+	data := `
+### test ###
+1.1.1.1:1111 # inline comment
+# 2.2.2.2:2222
+      ### empty line with comment
+    3.3.3.3:3333
+### test ###
+`
+	ips := parseFileContent([]byte(data))
+	assert.Len(t, ips, 2)
+	assert.Equal(t, "1.1.1.1:1111", ips[0])
+	assert.Equal(t, "3.3.3.3:3333", ips[1])
+}
+
+func TestWatch(t *testing.T) {
+	data := `
+1.1.1.1:1111
+2.2.2.2:2222
+`
+	expected := discovery.Entries{
+		&discovery.Entry{Host: "1.1.1.1", Port: "1111"},
+		&discovery.Entry{Host: "2.2.2.2", Port: "2222"},
+	}
+
+	// Create a temporary file and remove it.
+	tmp, err := ioutil.TempFile(os.TempDir(), "discovery-file-test")
+	assert.NoError(t, err)
+	assert.NoError(t, tmp.Close())
+	assert.NoError(t, os.Remove(tmp.Name()))
+
+	// Set up file discovery.
+	d := &Discovery{}
+	d.Initialize(tmp.Name(), 1000, 0)
+	stopCh := make(chan struct{})
+	ch, errCh := d.Watch(stopCh)
+
+	// Make sure it fires errors since the file doesn't exist.
+	assert.Error(t, <-errCh)
+	// We have to drain the error channel otherwise Watch will get stuck.
+	go func() {
+		for range errCh {
+		}
+	}()
+
+	// Write the file and make sure we get the expected value back.
+	assert.NoError(t, ioutil.WriteFile(tmp.Name(), []byte(data), 0600))
+	assert.Equal(t, expected, <-ch)
+
+	// Add a new entry and look it up.
+	expected = append(expected, &discovery.Entry{Host: "3.3.3.3", Port: "3333"})
+	f, err := os.OpenFile(tmp.Name(), os.O_APPEND|os.O_WRONLY, 0600)
+	assert.NoError(t, err)
+	assert.NotNil(t, f)
+	_, err = f.WriteString("\n3.3.3.3:3333\n")
+	assert.NoError(t, err)
+	f.Close()
+	assert.Equal(t, expected, <-ch)
+
+	// Stop and make sure it closes all channels.
+	close(stopCh)
+	assert.Nil(t, <-ch)
+	assert.Nil(t, <-errCh)
+}