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// Copyright 2014 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package metadata provides access to Google Compute Engine (GCE)
// metadata and API service accounts.
//
// This package is a wrapper around the GCE metadata service,
// as documented at https://developers.google.com/compute/docs/metadata.
package metadata
import (
"encoding/json"
"fmt"
"io/ioutil"
"net"
"net/http"
"net/url"
"os"
"runtime"
"strings"
"sync"
"time"
"golang.org/x/net/context"
"golang.org/x/net/context/ctxhttp"
"cloud.google.com/go/internal"
)
const (
// metadataIP is the documented metadata server IP address.
metadataIP = "169.254.169.254"
// metadataHostEnv is the environment variable specifying the
// GCE metadata hostname. If empty, the default value of
// metadataIP ("169.254.169.254") is used instead.
// This is variable name is not defined by any spec, as far as
// I know; it was made up for the Go package.
metadataHostEnv = "GCE_METADATA_HOST"
)
type cachedValue struct {
k string
trim bool
mu sync.Mutex
v string
}
var (
projID = &cachedValue{k: "project/project-id", trim: true}
projNum = &cachedValue{k: "project/numeric-project-id", trim: true}
instID = &cachedValue{k: "instance/id", trim: true}
)
var (
metaClient = &http.Client{
Transport: &internal.Transport{
Base: &http.Transport{
Dial: (&net.Dialer{
Timeout: 2 * time.Second,
KeepAlive: 30 * time.Second,
}).Dial,
ResponseHeaderTimeout: 2 * time.Second,
},
},
}
subscribeClient = &http.Client{
Transport: &internal.Transport{
Base: &http.Transport{
Dial: (&net.Dialer{
Timeout: 2 * time.Second,
KeepAlive: 30 * time.Second,
}).Dial,
},
},
}
)
// NotDefinedError is returned when requested metadata is not defined.
//
// The underlying string is the suffix after "/computeMetadata/v1/".
//
// This error is not returned if the value is defined to be the empty
// string.
type NotDefinedError string
func (suffix NotDefinedError) Error() string {
return fmt.Sprintf("metadata: GCE metadata %q not defined", string(suffix))
}
// Get returns a value from the metadata service.
// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
//
// If the GCE_METADATA_HOST environment variable is not defined, a default of
// 169.254.169.254 will be used instead.
//
// If the requested metadata is not defined, the returned error will
// be of type NotDefinedError.
func Get(suffix string) (string, error) {
val, _, err := getETag(metaClient, suffix)
return val, err
}
// getETag returns a value from the metadata service as well as the associated
// ETag using the provided client. This func is otherwise equivalent to Get.
func getETag(client *http.Client, suffix string) (value, etag string, err error) {
// Using a fixed IP makes it very difficult to spoof the metadata service in
// a container, which is an important use-case for local testing of cloud
// deployments. To enable spoofing of the metadata service, the environment
// variable GCE_METADATA_HOST is first inspected to decide where metadata
// requests shall go.
host := os.Getenv(metadataHostEnv)
if host == "" {
// Using 169.254.169.254 instead of "metadata" here because Go
// binaries built with the "netgo" tag and without cgo won't
// know the search suffix for "metadata" is
// ".google.internal", and this IP address is documented as
// being stable anyway.
host = metadataIP
}
url := "http://" + host + "/computeMetadata/v1/" + suffix
req, _ := http.NewRequest("GET", url, nil)
req.Header.Set("Metadata-Flavor", "Google")
res, err := client.Do(req)
if err != nil {
return "", "", err
}
defer res.Body.Close()
if res.StatusCode == http.StatusNotFound {
return "", "", NotDefinedError(suffix)
}
if res.StatusCode != 200 {
return "", "", fmt.Errorf("status code %d trying to fetch %s", res.StatusCode, url)
}
all, err := ioutil.ReadAll(res.Body)
if err != nil {
return "", "", err
}
return string(all), res.Header.Get("Etag"), nil
}
func getTrimmed(suffix string) (s string, err error) {
s, err = Get(suffix)
s = strings.TrimSpace(s)
return
}
func (c *cachedValue) get() (v string, err error) {
defer c.mu.Unlock()
c.mu.Lock()
if c.v != "" {
return c.v, nil
}
if c.trim {
v, err = getTrimmed(c.k)
} else {
v, err = Get(c.k)
}
if err == nil {
c.v = v
}
return
}
var (
onGCEOnce sync.Once
onGCE bool
)
// OnGCE reports whether this process is running on Google Compute Engine.
func OnGCE() bool {
onGCEOnce.Do(initOnGCE)
return onGCE
}
func initOnGCE() {
onGCE = testOnGCE()
}
func testOnGCE() bool {
// The user explicitly said they're on GCE, so trust them.
if os.Getenv(metadataHostEnv) != "" {
return true
}
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
resc := make(chan bool, 2)
// Try two strategies in parallel.
// See https://github.com/GoogleCloudPlatform/google-cloud-go/issues/194
go func() {
res, err := ctxhttp.Get(ctx, metaClient, "http://"+metadataIP)
if err != nil {
resc <- false
return
}
defer res.Body.Close()
resc <- res.Header.Get("Metadata-Flavor") == "Google"
}()
go func() {
addrs, err := net.LookupHost("metadata.google.internal")
if err != nil || len(addrs) == 0 {
resc <- false
return
}
resc <- strsContains(addrs, metadataIP)
}()
tryHarder := systemInfoSuggestsGCE()
if tryHarder {
res := <-resc
if res {
// The first strategy succeeded, so let's use it.
return true
}
// Wait for either the DNS or metadata server probe to
// contradict the other one and say we are running on
// GCE. Give it a lot of time to do so, since the system
// info already suggests we're running on a GCE BIOS.
timer := time.NewTimer(5 * time.Second)
defer timer.Stop()
select {
case res = <-resc:
return res
case <-timer.C:
// Too slow. Who knows what this system is.
return false
}
}
// There's no hint from the system info that we're running on
// GCE, so use the first probe's result as truth, whether it's
// true or false. The goal here is to optimize for speed for
// users who are NOT running on GCE. We can't assume that
// either a DNS lookup or an HTTP request to a blackholed IP
// address is fast. Worst case this should return when the
// metaClient's Transport.ResponseHeaderTimeout or
// Transport.Dial.Timeout fires (in two seconds).
return <-resc
}
// systemInfoSuggestsGCE reports whether the local system (without
// doing network requests) suggests that we're running on GCE. If this
// returns true, testOnGCE tries a bit harder to reach its metadata
// server.
func systemInfoSuggestsGCE() bool {
if runtime.GOOS != "linux" {
// We don't have any non-Linux clues available, at least yet.
return false
}
slurp, _ := ioutil.ReadFile("/sys/class/dmi/id/product_name")
name := strings.TrimSpace(string(slurp))
return name == "Google" || name == "Google Compute Engine"
}
// Subscribe subscribes to a value from the metadata service.
// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
// The suffix may contain query parameters.
//
// Subscribe calls fn with the latest metadata value indicated by the provided
// suffix. If the metadata value is deleted, fn is called with the empty string
// and ok false. Subscribe blocks until fn returns a non-nil error or the value
// is deleted. Subscribe returns the error value returned from the last call to
// fn, which may be nil when ok == false.
func Subscribe(suffix string, fn func(v string, ok bool) error) error {
const failedSubscribeSleep = time.Second * 5
// First check to see if the metadata value exists at all.
val, lastETag, err := getETag(subscribeClient, suffix)
if err != nil {
return err
}
if err := fn(val, true); err != nil {
return err
}
ok := true
if strings.ContainsRune(suffix, '?') {
suffix += "&wait_for_change=true&last_etag="
} else {
suffix += "?wait_for_change=true&last_etag="
}
for {
val, etag, err := getETag(subscribeClient, suffix+url.QueryEscape(lastETag))
if err != nil {
if _, deleted := err.(NotDefinedError); !deleted {
time.Sleep(failedSubscribeSleep)
continue // Retry on other errors.
}
ok = false
}
lastETag = etag
if err := fn(val, ok); err != nil || !ok {
return err
}
}
}
// ProjectID returns the current instance's project ID string.
func ProjectID() (string, error) { return projID.get() }
// NumericProjectID returns the current instance's numeric project ID.
func NumericProjectID() (string, error) { return projNum.get() }
// InternalIP returns the instance's primary internal IP address.
func InternalIP() (string, error) {
return getTrimmed("instance/network-interfaces/0/ip")
}
// ExternalIP returns the instance's primary external (public) IP address.
func ExternalIP() (string, error) {
return getTrimmed("instance/network-interfaces/0/access-configs/0/external-ip")
}
// Hostname returns the instance's hostname. This will be of the form
// "<instanceID>.c.<projID>.internal".
func Hostname() (string, error) {
return getTrimmed("instance/hostname")
}
// InstanceTags returns the list of user-defined instance tags,
// assigned when initially creating a GCE instance.
func InstanceTags() ([]string, error) {
var s []string
j, err := Get("instance/tags")
if err != nil {
return nil, err
}
if err := json.NewDecoder(strings.NewReader(j)).Decode(&s); err != nil {
return nil, err
}
return s, nil
}
// InstanceID returns the current VM's numeric instance ID.
func InstanceID() (string, error) {
return instID.get()
}
// InstanceName returns the current VM's instance ID string.
func InstanceName() (string, error) {
host, err := Hostname()
if err != nil {
return "", err
}
return strings.Split(host, ".")[0], nil
}
// Zone returns the current VM's zone, such as "us-central1-b".
func Zone() (string, error) {
zone, err := getTrimmed("instance/zone")
// zone is of the form "projects/<projNum>/zones/<zoneName>".
if err != nil {
return "", err
}
return zone[strings.LastIndex(zone, "/")+1:], nil
}
// InstanceAttributes returns the list of user-defined attributes,
// assigned when initially creating a GCE VM instance. The value of an
// attribute can be obtained with InstanceAttributeValue.
func InstanceAttributes() ([]string, error) { return lines("instance/attributes/") }
// ProjectAttributes returns the list of user-defined attributes
// applying to the project as a whole, not just this VM. The value of
// an attribute can be obtained with ProjectAttributeValue.
func ProjectAttributes() ([]string, error) { return lines("project/attributes/") }
func lines(suffix string) ([]string, error) {
j, err := Get(suffix)
if err != nil {
return nil, err
}
s := strings.Split(strings.TrimSpace(j), "\n")
for i := range s {
s[i] = strings.TrimSpace(s[i])
}
return s, nil
}
// InstanceAttributeValue returns the value of the provided VM
// instance attribute.
//
// If the requested attribute is not defined, the returned error will
// be of type NotDefinedError.
//
// InstanceAttributeValue may return ("", nil) if the attribute was
// defined to be the empty string.
func InstanceAttributeValue(attr string) (string, error) {
return Get("instance/attributes/" + attr)
}
// ProjectAttributeValue returns the value of the provided
// project attribute.
//
// If the requested attribute is not defined, the returned error will
// be of type NotDefinedError.
//
// ProjectAttributeValue may return ("", nil) if the attribute was
// defined to be the empty string.
func ProjectAttributeValue(attr string) (string, error) {
return Get("project/attributes/" + attr)
}
// Scopes returns the service account scopes for the given account.
// The account may be empty or the string "default" to use the instance's
// main account.
func Scopes(serviceAccount string) ([]string, error) {
if serviceAccount == "" {
serviceAccount = "default"
}
return lines("instance/service-accounts/" + serviceAccount + "/scopes")
}
func strsContains(ss []string, s string) bool {
for _, v := range ss {
if v == s {
return true
}
}
return false
}