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// Copyright 2020 Google LLC.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package idtoken
import (
"context"
"encoding/json"
"fmt"
"net/http"
"strconv"
"strings"
"sync"
"time"
)
type cachingClient struct {
client *http.Client
// clock optionally specifies a func to return the current time.
// If nil, time.Now is used.
clock func() time.Time
mu sync.Mutex
certs map[string]*cachedResponse
}
func newCachingClient(client *http.Client) *cachingClient {
return &cachingClient{
client: client,
certs: make(map[string]*cachedResponse, 2),
}
}
type cachedResponse struct {
resp *certResponse
exp time.Time
}
func (c *cachingClient) getCert(ctx context.Context, url string) (*certResponse, error) {
if response, ok := c.get(url); ok {
return response, nil
}
req, err := http.NewRequest(http.MethodGet, url, nil)
if err != nil {
return nil, err
}
req = req.WithContext(ctx)
resp, err := c.client.Do(req)
if err != nil {
return nil, err
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("idtoken: unable to retrieve cert, got status code %d", resp.StatusCode)
}
certResp := &certResponse{}
if err := json.NewDecoder(resp.Body).Decode(certResp); err != nil {
return nil, err
}
c.set(url, certResp, resp.Header)
return certResp, nil
}
func (c *cachingClient) now() time.Time {
if c.clock != nil {
return c.clock()
}
return time.Now()
}
func (c *cachingClient) get(url string) (*certResponse, bool) {
c.mu.Lock()
defer c.mu.Unlock()
cachedResp, ok := c.certs[url]
if !ok {
return nil, false
}
if c.now().After(cachedResp.exp) {
return nil, false
}
return cachedResp.resp, true
}
func (c *cachingClient) set(url string, resp *certResponse, headers http.Header) {
exp := c.calculateExpireTime(headers)
c.mu.Lock()
c.certs[url] = &cachedResponse{resp: resp, exp: exp}
c.mu.Unlock()
}
// calculateExpireTime will determine the expire time for the cache based on
// HTTP headers. If there is any difficulty reading the headers the fallback is
// to set the cache to expire now.
func (c *cachingClient) calculateExpireTime(headers http.Header) time.Time {
var maxAge int
cc := strings.Split(headers.Get("cache-control"), ",")
for _, v := range cc {
if strings.Contains(v, "max-age") {
ss := strings.Split(v, "=")
if len(ss) < 2 {
return c.now()
}
ma, err := strconv.Atoi(ss[1])
if err != nil {
return c.now()
}
maxAge = ma
}
}
a := headers.Get("age")
if a == "" {
return c.now().Add(time.Duration(maxAge) * time.Second)
}
age, err := strconv.Atoi(a)
if err != nil {
return c.now()
}
return c.now().Add(time.Duration(maxAge-age) * time.Second)
}
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