traefik/middlewares/retry/retry.go
2019-02-13 17:26:04 +01:00

207 lines
5.6 KiB
Go

package retry
import (
"bufio"
"context"
"fmt"
"io/ioutil"
"net"
"net/http"
"net/http/httptrace"
"github.com/containous/traefik/config"
"github.com/containous/traefik/middlewares"
"github.com/containous/traefik/tracing"
"github.com/opentracing/opentracing-go/ext"
)
// Compile time validation that the response writer implements http interfaces correctly.
var _ middlewares.Stateful = &responseWriterWithCloseNotify{}
const (
typeName = "Retry"
)
// Listener is used to inform about retry attempts.
type Listener 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)
}
// Listeners is a convenience type to construct a list of Listener and notify
// each of them about a retry attempt.
type Listeners []Listener
// retry is a middleware that retries requests.
type retry struct {
attempts int
next http.Handler
listener Listener
name string
}
// New returns a new retry middleware.
func New(ctx context.Context, next http.Handler, config config.Retry, listener Listener, name string) (http.Handler, error) {
logger := middlewares.GetLogger(ctx, name, typeName)
logger.Debug("Creating middleware")
if config.Attempts <= 0 {
return nil, fmt.Errorf("incorrect (or empty) value for attempt (%d)", config.Attempts)
}
return &retry{
attempts: config.Attempts,
next: next,
listener: listener,
name: name,
}, nil
}
func (r *retry) GetTracingInformation() (string, ext.SpanKindEnum) {
return r.name, tracing.SpanKindNoneEnum
}
func (r *retry) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
// if we might make multiple attempts, swap the body for an ioutil.NopCloser
// cf https://github.com/containous/traefik/issues/1008
if r.attempts > 1 {
body := req.Body
defer body.Close()
req.Body = ioutil.NopCloser(body)
}
attempts := 1
for {
shouldRetry := attempts < r.attempts
retryResponseWriter := newResponseWriter(rw, shouldRetry)
// Disable retries when the backend already received request data
trace := &httptrace.ClientTrace{
WroteHeaders: func() {
retryResponseWriter.DisableRetries()
},
WroteRequest: func(httptrace.WroteRequestInfo) {
retryResponseWriter.DisableRetries()
},
}
newCtx := httptrace.WithClientTrace(req.Context(), trace)
r.next.ServeHTTP(retryResponseWriter, req.WithContext(newCtx))
if !retryResponseWriter.ShouldRetry() {
break
}
attempts++
logger := middlewares.GetLogger(req.Context(), r.name, typeName)
logger.Debugf("New attempt %d for request: %v", attempts, req.URL)
r.listener.Retried(req, attempts)
}
}
// Retried exists to implement the Listener interface. It calls Retried on each of its slice entries.
func (l Listeners) Retried(req *http.Request, attempt int) {
for _, listener := range l {
listener.Retried(req, attempt)
}
}
type responseWriter interface {
http.ResponseWriter
http.Flusher
ShouldRetry() bool
DisableRetries()
}
func newResponseWriter(rw http.ResponseWriter, shouldRetry bool) responseWriter {
responseWriter := &responseWriterWithoutCloseNotify{
responseWriter: rw,
headers: make(http.Header),
shouldRetry: shouldRetry,
}
if _, ok := rw.(http.CloseNotifier); ok {
return &responseWriterWithCloseNotify{
responseWriterWithoutCloseNotify: responseWriter,
}
}
return responseWriter
}
type responseWriterWithoutCloseNotify struct {
responseWriter http.ResponseWriter
headers http.Header
shouldRetry bool
written bool
}
func (r *responseWriterWithoutCloseNotify) ShouldRetry() bool {
return r.shouldRetry
}
func (r *responseWriterWithoutCloseNotify) DisableRetries() {
r.shouldRetry = false
}
func (r *responseWriterWithoutCloseNotify) Header() http.Header {
if r.written {
return r.responseWriter.Header()
}
return r.headers
}
func (r *responseWriterWithoutCloseNotify) Write(buf []byte) (int, error) {
if r.ShouldRetry() {
return len(buf), nil
}
return r.responseWriter.Write(buf)
}
func (r *responseWriterWithoutCloseNotify) WriteHeader(code int) {
if r.ShouldRetry() && code == http.StatusServiceUnavailable {
// We get a 503 HTTP Status Code when there is no backend server in the pool
// to which the request could be sent. Also, note that r.ShouldRetry()
// will never return true in case there was a connection established to
// the backend server and so we can be sure that the 503 was produced
// inside Traefik already and we don't have to retry in this cases.
r.DisableRetries()
}
if r.ShouldRetry() {
return
}
// In that case retry case is set to false which means we at least managed
// to write headers to the backend : we are not going to perform any further retry.
// So it is now safe to alter current response headers with headers collected during
// the latest try before writing headers to client.
headers := r.responseWriter.Header()
for header, value := range r.headers {
headers[header] = value
}
r.responseWriter.WriteHeader(code)
r.written = true
}
func (r *responseWriterWithoutCloseNotify) Hijack() (net.Conn, *bufio.ReadWriter, error) {
hijacker, ok := r.responseWriter.(http.Hijacker)
if !ok {
return nil, nil, fmt.Errorf("%T is not a http.Hijacker", r.responseWriter)
}
return hijacker.Hijack()
}
func (r *responseWriterWithoutCloseNotify) Flush() {
if flusher, ok := r.responseWriter.(http.Flusher); ok {
flusher.Flush()
}
}
type responseWriterWithCloseNotify struct {
*responseWriterWithoutCloseNotify
}
func (r *responseWriterWithCloseNotify) CloseNotify() <-chan bool {
return r.responseWriter.(http.CloseNotifier).CloseNotify()
}