traefik/middlewares/retry.go

220 lines
6.4 KiB
Go

package middlewares
import (
"bufio"
"bytes"
"context"
"io/ioutil"
"net"
"net/http"
"github.com/containous/traefik/log"
"github.com/vulcand/oxy/utils"
)
// Compile time validation responseRecorder implements http interfaces correctly.
var (
_ Stateful = &retryResponseRecorderWithCloseNotify{}
)
// Retry is a middleware that retries requests
type Retry struct {
attempts int
next http.Handler
listener RetryListener
}
// NewRetry returns a new Retry instance
func NewRetry(attempts int, next http.Handler, listener RetryListener) *Retry {
return &Retry{
attempts: attempts,
next: next,
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)
recorder := newRetryResponseRecorder(rw)
retry.next.ServeHTTP(recorder, r.WithContext(newCtx))
// It's a stream request and the body gets already sent to the client.
// Therefore we should not send the response a second time.
if recorder.IsStreamingResponseStarted() {
recorder.Flush()
break
}
if !netErrorOccurred || attempts >= retry.attempts {
utils.CopyHeaders(rw.Header(), recorder.Header())
rw.WriteHeader(recorder.GetCode())
rw.Write(recorder.GetBody().Bytes())
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
}
}
// 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)
}
}
type retryResponseRecorder interface {
http.ResponseWriter
http.Flusher
GetCode() int
GetBody() *bytes.Buffer
IsStreamingResponseStarted() bool
}
// newRetryResponseRecorder returns an initialized retryResponseRecorder.
func newRetryResponseRecorder(rw http.ResponseWriter) retryResponseRecorder {
recorder := &retryResponseRecorderWithoutCloseNotify{
HeaderMap: make(http.Header),
Body: new(bytes.Buffer),
Code: http.StatusOK,
responseWriter: rw,
}
if _, ok := rw.(http.CloseNotifier); ok {
return &retryResponseRecorderWithCloseNotify{recorder}
}
return recorder
}
// retryResponseRecorderWithoutCloseNotify is an implementation of http.ResponseWriter that
// records its mutations for later inspection.
type retryResponseRecorderWithoutCloseNotify struct {
Code int // the HTTP response code from WriteHeader
HeaderMap http.Header // the HTTP response headers
Body *bytes.Buffer // if non-nil, the bytes.Buffer to append written data to
responseWriter http.ResponseWriter
err error
streamingResponseStarted bool
}
type retryResponseRecorderWithCloseNotify struct {
*retryResponseRecorderWithoutCloseNotify
}
// CloseNotify returns a channel that receives at most a
// single value (true) when the client connection has gone
// away.
func (rw *retryResponseRecorderWithCloseNotify) CloseNotify() <-chan bool {
return rw.responseWriter.(http.CloseNotifier).CloseNotify()
}
// Header returns the response headers.
func (rw *retryResponseRecorderWithoutCloseNotify) Header() http.Header {
m := rw.HeaderMap
if m == nil {
m = make(http.Header)
rw.HeaderMap = m
}
return m
}
func (rw *retryResponseRecorderWithoutCloseNotify) GetCode() int {
return rw.Code
}
func (rw *retryResponseRecorderWithoutCloseNotify) GetBody() *bytes.Buffer {
return rw.Body
}
func (rw *retryResponseRecorderWithoutCloseNotify) IsStreamingResponseStarted() bool {
return rw.streamingResponseStarted
}
// Write always succeeds and writes to rw.Body, if not nil.
func (rw *retryResponseRecorderWithoutCloseNotify) Write(buf []byte) (int, error) {
if rw.err != nil {
return 0, rw.err
}
return rw.Body.Write(buf)
}
// WriteHeader sets rw.Code.
func (rw *retryResponseRecorderWithoutCloseNotify) WriteHeader(code int) {
rw.Code = code
}
// Hijack hijacks the connection
func (rw *retryResponseRecorderWithoutCloseNotify) Hijack() (net.Conn, *bufio.ReadWriter, error) {
return rw.responseWriter.(http.Hijacker).Hijack()
}
// Flush sends any buffered data to the client.
func (rw *retryResponseRecorderWithoutCloseNotify) Flush() {
if !rw.streamingResponseStarted {
utils.CopyHeaders(rw.responseWriter.Header(), rw.Header())
rw.responseWriter.WriteHeader(rw.Code)
rw.streamingResponseStarted = true
}
_, err := rw.responseWriter.Write(rw.Body.Bytes())
if err != nil {
log.Errorf("Error writing response in retryResponseRecorder: %s", err)
rw.err = err
}
rw.Body.Reset()
flusher, ok := rw.responseWriter.(http.Flusher)
if ok {
flusher.Flush()
}
}