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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package google
import (
"sort"
"strings"
"sync"
"time"
"golang.org/x/net/context"
"golang.org/x/oauth2"
)
// Set at init time by appenginevm_hook.go. If true, we are on App Engine Managed VMs.
var appengineVM bool
// Set at init time by appengine_hook.go. If nil, we're not on App Engine.
var appengineTokenFunc func(c context.Context, scopes ...string) (token string, expiry time.Time, err error)
// AppEngineTokenSource returns a token source that fetches tokens
// issued to the current App Engine application's service account.
// If you are implementing a 3-legged OAuth 2.0 flow on App Engine
// that involves user accounts, see oauth2.Config instead.
//
// The provided context must have come from appengine.NewContext.
func AppEngineTokenSource(ctx context.Context, scope ...string) oauth2.TokenSource {
if appengineTokenFunc == nil {
panic("google: AppEngineTokenSource can only be used on App Engine.")
}
scopes := append([]string{}, scope...)
sort.Strings(scopes)
return &appEngineTokenSource{
ctx: ctx,
scopes: scopes,
key: strings.Join(scopes, " "),
}
}
// aeTokens helps the fetched tokens to be reused until their expiration.
var (
aeTokensMu sync.Mutex
aeTokens = make(map[string]*tokenLock) // key is space-separated scopes
)
type tokenLock struct {
mu sync.Mutex // guards t; held while fetching or updating t
t *oauth2.Token
}
type appEngineTokenSource struct {
ctx context.Context
scopes []string
key string // to aeTokens map; space-separated scopes
}
func (ts *appEngineTokenSource) Token() (*oauth2.Token, error) {
if appengineTokenFunc == nil {
panic("google: AppEngineTokenSource can only be used on App Engine.")
}
aeTokensMu.Lock()
tok, ok := aeTokens[ts.key]
if !ok {
tok = &tokenLock{}
aeTokens[ts.key] = tok
}
aeTokensMu.Unlock()
tok.mu.Lock()
defer tok.mu.Unlock()
if tok.t.Valid() {
return tok.t, nil
}
access, exp, err := appengineTokenFunc(ts.ctx, ts.scopes...)
if err != nil {
return nil, err
}
tok.t = &oauth2.Token{
AccessToken: access,
Expiry: exp,
}
return tok.t, nil
}
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