traefik/middlewares/retry.go

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package middlewares
import (
"bufio"
"bytes"
"io/ioutil"
"net"
"net/http"
"github.com/containous/traefik/log"
"github.com/vulcand/oxy/utils"
)
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// Compile time validation responseRecorder implements http interfaces correctly.
var (
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_ Stateful = &retryResponseRecorder{}
)
// 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 {
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recorder := newRetryResponseRecorder()
recorder.responseWriter = rw
retry.next.ServeHTTP(recorder, r)
if !isNetworkError(recorder.Code) || attempts >= retry.attempts {
utils.CopyHeaders(rw.Header(), recorder.Header())
rw.WriteHeader(recorder.Code)
rw.Write(recorder.Body.Bytes())
break
}
attempts++
log.Debugf("New attempt %d for request: %v", attempts, r.URL)
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retry.listener.Retried(attempts)
}
}
func isNetworkError(status int) bool {
return status == http.StatusBadGateway || status == http.StatusGatewayTimeout
}
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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(attempt int)
}
// retryResponseRecorder is an implementation of http.ResponseWriter that
// records its mutations for later inspection.
type retryResponseRecorder 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
}
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// newRetryResponseRecorder returns an initialized retryResponseRecorder.
func newRetryResponseRecorder() *retryResponseRecorder {
return &retryResponseRecorder{
HeaderMap: make(http.Header),
Body: new(bytes.Buffer),
Code: 200,
}
}
// Header returns the response headers.
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func (rw *retryResponseRecorder) Header() http.Header {
m := rw.HeaderMap
if m == nil {
m = make(http.Header)
rw.HeaderMap = m
}
return m
}
// Write always succeeds and writes to rw.Body, if not nil.
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func (rw *retryResponseRecorder) Write(buf []byte) (int, error) {
if rw.err != nil {
return 0, rw.err
}
return rw.Body.Write(buf)
}
// WriteHeader sets rw.Code.
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func (rw *retryResponseRecorder) WriteHeader(code int) {
rw.Code = code
}
// Hijack hijacks the connection
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func (rw *retryResponseRecorder) Hijack() (net.Conn, *bufio.ReadWriter, error) {
return rw.responseWriter.(http.Hijacker).Hijack()
}
// CloseNotify returns a channel that receives at most a
// single value (true) when the client connection has gone
// away.
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func (rw *retryResponseRecorder) CloseNotify() <-chan bool {
return rw.responseWriter.(http.CloseNotifier).CloseNotify()
}
// Flush sends any buffered data to the client.
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func (rw *retryResponseRecorder) Flush() {
_, err := rw.responseWriter.Write(rw.Body.Bytes())
if err != nil {
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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()
}
}