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package aws
import (
"math"
"net"
"net/http"
"time"
)
type RetryableFunc func(*http.Request, *http.Response, error) bool
type WaitFunc func(try int)
type DeadlineFunc func() time.Time
type ResilientTransport struct {
// Timeout is the maximum amount of time a dial will wait for
// a connect to complete.
//
// The default is no timeout.
//
// With or without a timeout, the operating system may impose
// its own earlier timeout. For instance, TCP timeouts are
// often around 3 minutes.
DialTimeout time.Duration
// MaxTries, if non-zero, specifies the number of times we will retry on
// failure. Retries are only attempted for temporary network errors or known
// safe failures.
MaxTries int
Deadline DeadlineFunc
ShouldRetry RetryableFunc
Wait WaitFunc
transport *http.Transport
}
// Convenience method for creating an http client
func NewClient(rt *ResilientTransport) *http.Client {
rt.transport = &http.Transport{
Dial: func(netw, addr string) (net.Conn, error) {
c, err := net.DialTimeout(netw, addr, rt.DialTimeout)
if err != nil {
return nil, err
}
c.SetDeadline(rt.Deadline())
return c, nil
},
Proxy: http.ProxyFromEnvironment,
}
// TODO: Would be nice is ResilientTransport allowed clients to initialize
// with http.Transport attributes.
return &http.Client{
Transport: rt,
}
}
var retryingTransport = &ResilientTransport{
Deadline: func() time.Time {
return time.Now().Add(5 * time.Second)
},
DialTimeout: 10 * time.Second,
MaxTries: 3,
ShouldRetry: awsRetry,
Wait: ExpBackoff,
}
// Exported default client
var RetryingClient = NewClient(retryingTransport)
func (t *ResilientTransport) RoundTrip(req *http.Request) (*http.Response, error) {
return t.tries(req)
}
// Retry a request a maximum of t.MaxTries times.
// We'll only retry if the proper criteria are met.
// If a wait function is specified, wait that amount of time
// In between requests.
func (t *ResilientTransport) tries(req *http.Request) (res *http.Response, err error) {
for try := 0; try < t.MaxTries; try += 1 {
res, err = t.transport.RoundTrip(req)
if !t.ShouldRetry(req, res, err) {
break
}
if res != nil {
res.Body.Close()
}
if t.Wait != nil {
t.Wait(try)
}
}
return
}
func ExpBackoff(try int) {
time.Sleep(100 * time.Millisecond *
time.Duration(math.Exp2(float64(try))))
}
func LinearBackoff(try int) {
time.Sleep(time.Duration(try*100) * time.Millisecond)
}
// Decide if we should retry a request.
// In general, the criteria for retrying a request is described here
// http://docs.aws.amazon.com/general/latest/gr/api-retries.html
func awsRetry(req *http.Request, res *http.Response, err error) bool {
retry := false
// Retry if there's a temporary network error.
if neterr, ok := err.(net.Error); ok {
if neterr.Temporary() {
retry = true
}
}
// Retry if we get a 5xx series error.
if res != nil {
if res.StatusCode >= 500 && res.StatusCode < 600 {
retry = true
}
}
return retry
}
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