datasource/waagent: add support for WAAgent metadata

datasource/waagent/waagent.go

@@ -0,0 +1,108 @@
+package waagent
+
+import (
+	"encoding/json"
+	"encoding/xml"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"os"
+	"path"
+)
+
+type waagent struct {
+	root     string
+	readFile func(filename string) ([]byte, error)
+}
+
+func NewDatasource(root string) *waagent {
+	return &waagent{root, ioutil.ReadFile}
+}
+
+func (a *waagent) IsAvailable() bool {
+	_, err := os.Stat(path.Join(a.root, "provisioned"))
+	return !os.IsNotExist(err)
+}
+
+func (a *waagent) AvailabilityChanges() bool {
+	return true
+}
+
+func (a *waagent) ConfigRoot() string {
+	return a.root
+}
+
+func (a *waagent) FetchMetadata() ([]byte, error) {
+	metadataBytes, err := a.tryReadFile(path.Join(a.root, "SharedConfig.xml"))
+	if err != nil {
+		return nil, err
+	}
+	if len(metadataBytes) == 0 {
+		return metadataBytes, nil
+	}
+
+	type Instance struct {
+		Id             string `xml:"id,attr"`
+		Address        string `xml:"address,attr"`
+		InputEndpoints struct {
+			Endpoints []struct {
+				LoadBalancedPublicAddress string `xml:"loadBalancedPublicAddress,attr"`
+			} `xml:"Endpoint"`
+		}
+	}
+
+	type SharedConfig struct {
+		Incarnation struct {
+			Instance string `xml:"instance,attr"`
+		}
+		Instances struct {
+			Instances []Instance `xml:"Instance"`
+		}
+	}
+
+	var metadata SharedConfig
+	if err := xml.Unmarshal(metadataBytes, &metadata); err != nil {
+		return nil, err
+	}
+
+	var instance Instance
+	for _, i := range metadata.Instances.Instances {
+		if i.Id == metadata.Incarnation.Instance {
+			instance = i
+			break
+		}
+	}
+
+	attrs := map[string]string{
+		"local-ipv4": instance.Address,
+	}
+	for _, e := range instance.InputEndpoints.Endpoints {
+		host, _, err := net.SplitHostPort(e.LoadBalancedPublicAddress)
+		if err == nil {
+			attrs["public-ipv4"] = host
+			break
+		}
+	}
+	return json.Marshal(attrs)
+}
+
+func (a *waagent) FetchUserdata() ([]byte, error) {
+	return a.tryReadFile(path.Join(a.root, "CustomData"))
+}
+
+func (a *waagent) FetchNetworkConfig(filename string) ([]byte, error) {
+	return nil, nil
+}
+
+func (a *waagent) Type() string {
+	return "waagent"
+}
+
+func (a *waagent) tryReadFile(filename string) ([]byte, error) {
+	fmt.Printf("Attempting to read from %q\n", filename)
+	data, err := a.readFile(filename)
+	if os.IsNotExist(err) {
+		err = nil
+	}
+	return data, err
+}