438 lines
12 KiB
Go
438 lines
12 KiB
Go
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// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package metadata provides access to Google Compute Engine (GCE)
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// metadata and API service accounts.
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//
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// This package is a wrapper around the GCE metadata service,
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// as documented at https://developers.google.com/compute/docs/metadata.
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package metadata // import "cloud.google.com/go/compute/metadata"
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import (
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"encoding/json"
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"fmt"
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"io/ioutil"
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"net"
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"net/http"
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"net/url"
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"os"
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"runtime"
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"strings"
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"sync"
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"time"
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"golang.org/x/net/context"
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"golang.org/x/net/context/ctxhttp"
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)
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const (
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// metadataIP is the documented metadata server IP address.
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metadataIP = "169.254.169.254"
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// metadataHostEnv is the environment variable specifying the
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// GCE metadata hostname. If empty, the default value of
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// metadataIP ("169.254.169.254") is used instead.
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// This is variable name is not defined by any spec, as far as
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// I know; it was made up for the Go package.
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metadataHostEnv = "GCE_METADATA_HOST"
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userAgent = "gcloud-golang/0.1"
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)
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type cachedValue struct {
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k string
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trim bool
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mu sync.Mutex
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v string
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}
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var (
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projID = &cachedValue{k: "project/project-id", trim: true}
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projNum = &cachedValue{k: "project/numeric-project-id", trim: true}
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instID = &cachedValue{k: "instance/id", trim: true}
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)
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var (
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metaClient = &http.Client{
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Transport: &http.Transport{
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Dial: (&net.Dialer{
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Timeout: 2 * time.Second,
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KeepAlive: 30 * time.Second,
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}).Dial,
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ResponseHeaderTimeout: 2 * time.Second,
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},
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}
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subscribeClient = &http.Client{
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Transport: &http.Transport{
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Dial: (&net.Dialer{
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Timeout: 2 * time.Second,
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KeepAlive: 30 * time.Second,
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}).Dial,
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},
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}
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)
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// NotDefinedError is returned when requested metadata is not defined.
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//
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// The underlying string is the suffix after "/computeMetadata/v1/".
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//
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// This error is not returned if the value is defined to be the empty
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// string.
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type NotDefinedError string
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func (suffix NotDefinedError) Error() string {
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return fmt.Sprintf("metadata: GCE metadata %q not defined", string(suffix))
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}
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// Get returns a value from the metadata service.
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// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
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//
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// If the GCE_METADATA_HOST environment variable is not defined, a default of
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// 169.254.169.254 will be used instead.
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//
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// If the requested metadata is not defined, the returned error will
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// be of type NotDefinedError.
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func Get(suffix string) (string, error) {
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val, _, err := getETag(metaClient, suffix)
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return val, err
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}
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// getETag returns a value from the metadata service as well as the associated
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// ETag using the provided client. This func is otherwise equivalent to Get.
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func getETag(client *http.Client, suffix string) (value, etag string, err error) {
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// Using a fixed IP makes it very difficult to spoof the metadata service in
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// a container, which is an important use-case for local testing of cloud
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// deployments. To enable spoofing of the metadata service, the environment
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// variable GCE_METADATA_HOST is first inspected to decide where metadata
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// requests shall go.
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host := os.Getenv(metadataHostEnv)
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if host == "" {
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// Using 169.254.169.254 instead of "metadata" here because Go
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// binaries built with the "netgo" tag and without cgo won't
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// know the search suffix for "metadata" is
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// ".google.internal", and this IP address is documented as
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// being stable anyway.
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host = metadataIP
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}
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url := "http://" + host + "/computeMetadata/v1/" + suffix
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req, _ := http.NewRequest("GET", url, nil)
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req.Header.Set("Metadata-Flavor", "Google")
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req.Header.Set("User-Agent", userAgent)
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res, err := client.Do(req)
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if err != nil {
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return "", "", err
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}
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defer res.Body.Close()
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if res.StatusCode == http.StatusNotFound {
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return "", "", NotDefinedError(suffix)
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}
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if res.StatusCode != 200 {
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return "", "", fmt.Errorf("status code %d trying to fetch %s", res.StatusCode, url)
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}
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all, err := ioutil.ReadAll(res.Body)
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if err != nil {
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return "", "", err
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}
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return string(all), res.Header.Get("Etag"), nil
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}
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func getTrimmed(suffix string) (s string, err error) {
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s, err = Get(suffix)
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s = strings.TrimSpace(s)
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return
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}
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func (c *cachedValue) get() (v string, err error) {
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defer c.mu.Unlock()
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c.mu.Lock()
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if c.v != "" {
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return c.v, nil
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}
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if c.trim {
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v, err = getTrimmed(c.k)
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} else {
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v, err = Get(c.k)
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}
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if err == nil {
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c.v = v
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}
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return
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}
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var (
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onGCEOnce sync.Once
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onGCE bool
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)
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// OnGCE reports whether this process is running on Google Compute Engine.
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func OnGCE() bool {
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onGCEOnce.Do(initOnGCE)
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return onGCE
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}
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func initOnGCE() {
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onGCE = testOnGCE()
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}
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func testOnGCE() bool {
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// The user explicitly said they're on GCE, so trust them.
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if os.Getenv(metadataHostEnv) != "" {
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return true
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}
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ctx, cancel := context.WithCancel(context.Background())
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defer cancel()
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resc := make(chan bool, 2)
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// Try two strategies in parallel.
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// See https://github.com/GoogleCloudPlatform/google-cloud-go/issues/194
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go func() {
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req, _ := http.NewRequest("GET", "http://"+metadataIP, nil)
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req.Header.Set("User-Agent", userAgent)
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res, err := ctxhttp.Do(ctx, metaClient, req)
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if err != nil {
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resc <- false
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return
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}
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defer res.Body.Close()
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resc <- res.Header.Get("Metadata-Flavor") == "Google"
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}()
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go func() {
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addrs, err := net.LookupHost("metadata.google.internal")
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if err != nil || len(addrs) == 0 {
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resc <- false
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return
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}
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resc <- strsContains(addrs, metadataIP)
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}()
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tryHarder := systemInfoSuggestsGCE()
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if tryHarder {
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res := <-resc
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if res {
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// The first strategy succeeded, so let's use it.
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return true
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}
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// Wait for either the DNS or metadata server probe to
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// contradict the other one and say we are running on
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// GCE. Give it a lot of time to do so, since the system
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// info already suggests we're running on a GCE BIOS.
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timer := time.NewTimer(5 * time.Second)
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defer timer.Stop()
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select {
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case res = <-resc:
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return res
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case <-timer.C:
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// Too slow. Who knows what this system is.
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return false
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}
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}
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// There's no hint from the system info that we're running on
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// GCE, so use the first probe's result as truth, whether it's
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// true or false. The goal here is to optimize for speed for
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// users who are NOT running on GCE. We can't assume that
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// either a DNS lookup or an HTTP request to a blackholed IP
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// address is fast. Worst case this should return when the
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// metaClient's Transport.ResponseHeaderTimeout or
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// Transport.Dial.Timeout fires (in two seconds).
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return <-resc
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}
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// systemInfoSuggestsGCE reports whether the local system (without
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// doing network requests) suggests that we're running on GCE. If this
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// returns true, testOnGCE tries a bit harder to reach its metadata
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// server.
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func systemInfoSuggestsGCE() bool {
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if runtime.GOOS != "linux" {
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// We don't have any non-Linux clues available, at least yet.
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return false
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}
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slurp, _ := ioutil.ReadFile("/sys/class/dmi/id/product_name")
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name := strings.TrimSpace(string(slurp))
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return name == "Google" || name == "Google Compute Engine"
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}
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// Subscribe subscribes to a value from the metadata service.
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// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
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// The suffix may contain query parameters.
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//
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// Subscribe calls fn with the latest metadata value indicated by the provided
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// suffix. If the metadata value is deleted, fn is called with the empty string
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// and ok false. Subscribe blocks until fn returns a non-nil error or the value
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// is deleted. Subscribe returns the error value returned from the last call to
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// fn, which may be nil when ok == false.
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func Subscribe(suffix string, fn func(v string, ok bool) error) error {
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const failedSubscribeSleep = time.Second * 5
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// First check to see if the metadata value exists at all.
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val, lastETag, err := getETag(subscribeClient, suffix)
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if err != nil {
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return err
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}
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if err := fn(val, true); err != nil {
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return err
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}
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ok := true
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if strings.ContainsRune(suffix, '?') {
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suffix += "&wait_for_change=true&last_etag="
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} else {
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suffix += "?wait_for_change=true&last_etag="
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}
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for {
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val, etag, err := getETag(subscribeClient, suffix+url.QueryEscape(lastETag))
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if err != nil {
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if _, deleted := err.(NotDefinedError); !deleted {
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time.Sleep(failedSubscribeSleep)
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continue // Retry on other errors.
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}
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ok = false
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}
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lastETag = etag
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if err := fn(val, ok); err != nil || !ok {
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return err
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}
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}
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}
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// ProjectID returns the current instance's project ID string.
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func ProjectID() (string, error) { return projID.get() }
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// NumericProjectID returns the current instance's numeric project ID.
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func NumericProjectID() (string, error) { return projNum.get() }
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// InternalIP returns the instance's primary internal IP address.
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func InternalIP() (string, error) {
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return getTrimmed("instance/network-interfaces/0/ip")
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}
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// ExternalIP returns the instance's primary external (public) IP address.
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func ExternalIP() (string, error) {
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return getTrimmed("instance/network-interfaces/0/access-configs/0/external-ip")
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}
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// Hostname returns the instance's hostname. This will be of the form
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// "<instanceID>.c.<projID>.internal".
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func Hostname() (string, error) {
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return getTrimmed("instance/hostname")
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}
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// InstanceTags returns the list of user-defined instance tags,
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// assigned when initially creating a GCE instance.
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func InstanceTags() ([]string, error) {
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var s []string
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j, err := Get("instance/tags")
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if err != nil {
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return nil, err
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}
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if err := json.NewDecoder(strings.NewReader(j)).Decode(&s); err != nil {
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return nil, err
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}
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return s, nil
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}
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// InstanceID returns the current VM's numeric instance ID.
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func InstanceID() (string, error) {
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return instID.get()
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}
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// InstanceName returns the current VM's instance ID string.
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func InstanceName() (string, error) {
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host, err := Hostname()
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if err != nil {
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return "", err
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}
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return strings.Split(host, ".")[0], nil
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}
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// Zone returns the current VM's zone, such as "us-central1-b".
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func Zone() (string, error) {
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zone, err := getTrimmed("instance/zone")
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// zone is of the form "projects/<projNum>/zones/<zoneName>".
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if err != nil {
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return "", err
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}
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return zone[strings.LastIndex(zone, "/")+1:], nil
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}
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// InstanceAttributes returns the list of user-defined attributes,
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// assigned when initially creating a GCE VM instance. The value of an
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// attribute can be obtained with InstanceAttributeValue.
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func InstanceAttributes() ([]string, error) { return lines("instance/attributes/") }
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// ProjectAttributes returns the list of user-defined attributes
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// applying to the project as a whole, not just this VM. The value of
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// an attribute can be obtained with ProjectAttributeValue.
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func ProjectAttributes() ([]string, error) { return lines("project/attributes/") }
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func lines(suffix string) ([]string, error) {
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j, err := Get(suffix)
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if err != nil {
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return nil, err
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}
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s := strings.Split(strings.TrimSpace(j), "\n")
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for i := range s {
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s[i] = strings.TrimSpace(s[i])
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}
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return s, nil
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}
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// InstanceAttributeValue returns the value of the provided VM
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// instance attribute.
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//
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// If the requested attribute is not defined, the returned error will
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// be of type NotDefinedError.
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//
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// InstanceAttributeValue may return ("", nil) if the attribute was
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// defined to be the empty string.
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func InstanceAttributeValue(attr string) (string, error) {
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return Get("instance/attributes/" + attr)
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}
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// ProjectAttributeValue returns the value of the provided
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// project attribute.
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//
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// If the requested attribute is not defined, the returned error will
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// be of type NotDefinedError.
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//
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// ProjectAttributeValue may return ("", nil) if the attribute was
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// defined to be the empty string.
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func ProjectAttributeValue(attr string) (string, error) {
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return Get("project/attributes/" + attr)
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}
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// Scopes returns the service account scopes for the given account.
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// The account may be empty or the string "default" to use the instance's
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// main account.
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func Scopes(serviceAccount string) ([]string, error) {
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if serviceAccount == "" {
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serviceAccount = "default"
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}
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return lines("instance/service-accounts/" + serviceAccount + "/scopes")
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}
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func strsContains(ss []string, s string) bool {
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for _, v := range ss {
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if v == s {
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return true
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}
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}
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return false
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}
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