traefik/middlewares/retry.go

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package middlewares
import (
"bufio"
"context"
"io/ioutil"
"net"
"net/http"
"github.com/containous/traefik/log"
)
// Compile time validation that the response writer implements http interfaces correctly.
var _ Stateful = &retryResponseWriterWithCloseNotify{}
// Retry is a middleware that retries requests
type Retry struct {
attempts int
next http.Handler
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listener RetryListener
}
// NewRetry returns a new Retry instance
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func NewRetry(attempts int, next http.Handler, listener RetryListener) *Retry {
return &Retry{
attempts: attempts,
next: next,
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listener: listener,
}
}
func (retry *Retry) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
// if we might make multiple attempts, swap the body for an ioutil.NopCloser
// cf https://github.com/containous/traefik/issues/1008
if retry.attempts > 1 {
body := r.Body
defer body.Close()
r.Body = ioutil.NopCloser(body)
}
attempts := 1
for {
netErrorOccurred := false
// We pass in a pointer to netErrorOccurred so that we can set it to true on network errors
// when proxying the HTTP requests to the backends. This happens in the custom RecordingErrorHandler.
newCtx := context.WithValue(r.Context(), defaultNetErrCtxKey, &netErrorOccurred)
retryResponseWriter := newRetryResponseWriter(rw, attempts >= retry.attempts, &netErrorOccurred)
retry.next.ServeHTTP(retryResponseWriter, r.WithContext(newCtx))
if !retryResponseWriter.ShouldRetry() {
break
}
attempts++
log.Debugf("New attempt %d for request: %v", attempts, r.URL)
retry.listener.Retried(r, attempts)
}
}
// netErrorCtxKey is a custom type that is used as key for the context.
type netErrorCtxKey string
// defaultNetErrCtxKey is the actual key which value is used to record network errors.
var defaultNetErrCtxKey netErrorCtxKey = "NetErrCtxKey"
// NetErrorRecorder is an interface to record net errors.
type NetErrorRecorder interface {
// Record can be used to signal the retry middleware that an network error happened
// and therefore the request should be retried.
Record(ctx context.Context)
}
// DefaultNetErrorRecorder is the default NetErrorRecorder implementation.
type DefaultNetErrorRecorder struct{}
// Record is recording network errors by setting the context value for the defaultNetErrCtxKey to true.
func (DefaultNetErrorRecorder) Record(ctx context.Context) {
val := ctx.Value(defaultNetErrCtxKey)
if netErrorOccurred, isBoolPointer := val.(*bool); isBoolPointer {
*netErrorOccurred = true
}
}
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// RetryListener is used to inform about retry attempts.
type RetryListener interface {
// Retried will be called when a retry happens, with the request attempt passed to it.
// For the first retry this will be attempt 2.
Retried(req *http.Request, attempt int)
}
// RetryListeners is a convenience type to construct a list of RetryListener and notify
// each of them about a retry attempt.
type RetryListeners []RetryListener
// Retried exists to implement the RetryListener interface. It calls Retried on each of its slice entries.
func (l RetryListeners) Retried(req *http.Request, attempt int) {
for _, retryListener := range l {
retryListener.Retried(req, attempt)
}
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}
type retryResponseWriter interface {
http.ResponseWriter
http.Flusher
ShouldRetry() bool
}
func newRetryResponseWriter(rw http.ResponseWriter, attemptsExhausted bool, netErrorOccured *bool) retryResponseWriter {
responseWriter := &retryResponseWriterWithoutCloseNotify{
responseWriter: rw,
attemptsExhausted: attemptsExhausted,
netErrorOccured: netErrorOccured,
}
if _, ok := rw.(http.CloseNotifier); ok {
return &retryResponseWriterWithCloseNotify{responseWriter}
}
return responseWriter
}
type retryResponseWriterWithoutCloseNotify struct {
responseWriter http.ResponseWriter
attemptsExhausted bool
netErrorOccured *bool
}
func (rr *retryResponseWriterWithoutCloseNotify) ShouldRetry() bool {
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return *rr.netErrorOccured && !rr.attemptsExhausted
}
func (rr *retryResponseWriterWithoutCloseNotify) Header() http.Header {
if rr.ShouldRetry() {
return make(http.Header)
}
return rr.responseWriter.Header()
}
func (rr *retryResponseWriterWithoutCloseNotify) Write(buf []byte) (int, error) {
if rr.ShouldRetry() {
return 0, nil
}
return rr.responseWriter.Write(buf)
}
func (rr *retryResponseWriterWithoutCloseNotify) WriteHeader(code int) {
if rr.ShouldRetry() {
return
}
rr.responseWriter.WriteHeader(code)
}
func (rr *retryResponseWriterWithoutCloseNotify) Hijack() (net.Conn, *bufio.ReadWriter, error) {
return rr.responseWriter.(http.Hijacker).Hijack()
}
func (rr *retryResponseWriterWithoutCloseNotify) Flush() {
if flusher, ok := rr.responseWriter.(http.Flusher); ok {
flusher.Flush()
}
}
type retryResponseWriterWithCloseNotify struct {
*retryResponseWriterWithoutCloseNotify
}
func (rr *retryResponseWriterWithCloseNotify) CloseNotify() <-chan bool {
return rr.responseWriter.(http.CloseNotifier).CloseNotify()
}