traefik/pkg/middlewares/headers/responsewriter.go

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package headers
import (
"bufio"
"fmt"
"net"
"net/http"
"github.com/containous/traefik/v2/pkg/log"
)
type responseModifier struct {
r *http.Request
w http.ResponseWriter
headersSent bool // whether headers have already been sent
code int // status code, must default to 200
modifier func(*http.Response) error // can be nil
modified bool // whether modifier has already been called for the current request
modifierErr error // returned by modifier call
}
// modifier can be nil.
func newResponseModifier(w http.ResponseWriter, r *http.Request, modifier func(*http.Response) error) *responseModifier {
return &responseModifier{
r: r,
w: w,
modifier: modifier,
code: http.StatusOK,
}
}
func (w *responseModifier) WriteHeader(code int) {
if w.headersSent {
return
}
defer func() {
w.code = code
w.headersSent = true
}()
if w.modifier == nil || w.modified {
w.w.WriteHeader(code)
return
}
resp := http.Response{
Header: w.w.Header(),
Request: w.r,
}
if err := w.modifier(&resp); err != nil {
w.modifierErr = err
// we are propagating when we are called in Write, but we're logging anyway,
// because we could be called from another place which does not take care of
// checking w.modifierErr.
log.WithoutContext().Errorf("Error when applying response modifier: %v", err)
w.w.WriteHeader(http.StatusInternalServerError)
return
}
w.modified = true
w.w.WriteHeader(code)
}
func (w *responseModifier) Header() http.Header {
return w.w.Header()
}
func (w *responseModifier) Write(b []byte) (int, error) {
w.WriteHeader(w.code)
if w.modifierErr != nil {
return 0, w.modifierErr
}
return w.w.Write(b)
}
// Hijack hijacks the connection.
func (w *responseModifier) Hijack() (net.Conn, *bufio.ReadWriter, error) {
if h, ok := w.w.(http.Hijacker); ok {
return h.Hijack()
}
return nil, nil, fmt.Errorf("not a hijacker: %T", w.w)
}
// Flush sends any buffered data to the client.
func (w *responseModifier) Flush() {
if flusher, ok := w.w.(http.Flusher); ok {
flusher.Flush()
}
}