traefik/pkg/middlewares/customerrors/custom_errors.go

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package customerrors
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import (
"bufio"
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"context"
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"fmt"
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"net"
"net/http"
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"net/url"
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"strconv"
"strings"
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"github.com/opentracing/opentracing-go/ext"
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"github.com/traefik/traefik/v3/pkg/config/dynamic"
"github.com/traefik/traefik/v3/pkg/middlewares"
"github.com/traefik/traefik/v3/pkg/tracing"
"github.com/traefik/traefik/v3/pkg/types"
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"github.com/vulcand/oxy/v2/utils"
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)
// Compile time validation that the response recorder implements http interfaces correctly.
var (
_ middlewares.Stateful = &codeModifier{}
_ middlewares.Stateful = &codeCatcher{}
)
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const typeName = "customError"
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type serviceBuilder interface {
BuildHTTP(ctx context.Context, serviceName string) (http.Handler, error)
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}
// customErrors is a middleware that provides the custom error pages..
type customErrors struct {
name string
next http.Handler
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backendHandler http.Handler
httpCodeRanges types.HTTPCodeRanges
backendQuery string
}
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// New creates a new custom error pages middleware.
func New(ctx context.Context, next http.Handler, config dynamic.ErrorPage, serviceBuilder serviceBuilder, name string) (http.Handler, error) {
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middlewares.GetLogger(ctx, name, typeName).Debug().Msg("Creating middleware")
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httpCodeRanges, err := types.NewHTTPCodeRanges(config.Status)
if err != nil {
return nil, err
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}
backend, err := serviceBuilder.BuildHTTP(ctx, config.Service)
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if err != nil {
return nil, err
}
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return &customErrors{
name: name,
next: next,
backendHandler: backend,
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httpCodeRanges: httpCodeRanges,
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backendQuery: config.Query,
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}, nil
}
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func (c *customErrors) GetTracingInformation() (string, ext.SpanKindEnum) {
return c.name, tracing.SpanKindNoneEnum
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}
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func (c *customErrors) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
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logger := middlewares.GetLogger(req.Context(), c.name, typeName)
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if c.backendHandler == nil {
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logger.Error().Msg("Error pages: no backend handler.")
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tracing.SetErrorWithEvent(req, "Error pages: no backend handler.")
c.next.ServeHTTP(rw, req)
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return
}
catcher := newCodeCatcher(rw, c.httpCodeRanges)
c.next.ServeHTTP(catcher, req)
if !catcher.isFilteredCode() {
return
}
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// check the recorder code against the configured http status code ranges
code := catcher.getCode()
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logger.Debug().Msgf("Caught HTTP Status Code %d, returning error page", code)
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var query string
if len(c.backendQuery) > 0 {
query = "/" + strings.TrimPrefix(c.backendQuery, "/")
query = strings.ReplaceAll(query, "{status}", strconv.Itoa(code))
query = strings.ReplaceAll(query, "{url}", url.QueryEscape(req.URL.String()))
}
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pageReq, err := newRequest("http://" + req.Host + query)
if err != nil {
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logger.Error().Err(err).Send()
http.Error(rw, http.StatusText(code), code)
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return
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}
utils.CopyHeaders(pageReq.Header, req.Header)
c.backendHandler.ServeHTTP(newCodeModifier(rw, code),
pageReq.WithContext(req.Context()))
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}
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func newRequest(baseURL string) (*http.Request, error) {
u, err := url.Parse(baseURL)
if err != nil {
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return nil, fmt.Errorf("error pages: error when parse URL: %w", err)
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}
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req, err := http.NewRequest(http.MethodGet, u.String(), nil)
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if err != nil {
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return nil, fmt.Errorf("error pages: error when create query: %w", err)
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}
req.RequestURI = u.RequestURI()
return req, nil
}
// codeCatcher is a response writer that detects as soon as possible whether the
// response is a code within the ranges of codes it watches for. If it is, it
// simply drops the data from the response. Otherwise, it forwards it directly to
// the original client (its responseWriter) without any buffering.
type codeCatcher struct {
headerMap http.Header
code int
httpCodeRanges types.HTTPCodeRanges
caughtFilteredCode bool
responseWriter http.ResponseWriter
headersSent bool
}
func newCodeCatcher(rw http.ResponseWriter, httpCodeRanges types.HTTPCodeRanges) *codeCatcher {
return &codeCatcher{
headerMap: make(http.Header),
code: http.StatusOK, // If backend does not call WriteHeader on us, we consider it's a 200.
responseWriter: rw,
httpCodeRanges: httpCodeRanges,
}
}
func (cc *codeCatcher) Header() http.Header {
if cc.headerMap == nil {
cc.headerMap = make(http.Header)
}
return cc.headerMap
}
func (cc *codeCatcher) getCode() int {
return cc.code
}
// isFilteredCode returns whether the codeCatcher received a response code among the ones it is watching,
// and for which the response should be deferred to the error handler.
func (cc *codeCatcher) isFilteredCode() bool {
return cc.caughtFilteredCode
}
func (cc *codeCatcher) Write(buf []byte) (int, error) {
// If WriteHeader was already called from the caller, this is a NOOP.
// Otherwise, cc.code is actually a 200 here.
cc.WriteHeader(cc.code)
if cc.caughtFilteredCode {
// We don't care about the contents of the response,
// since we want to serve the ones from the error page,
// so we just drop them.
return len(buf), nil
}
return cc.responseWriter.Write(buf)
}
func (cc *codeCatcher) WriteHeader(code int) {
if cc.headersSent || cc.caughtFilteredCode {
return
}
cc.code = code
for _, block := range cc.httpCodeRanges {
if cc.code >= block[0] && cc.code <= block[1] {
cc.caughtFilteredCode = true
// it will be up to the caller to send the headers,
// so it is out of our hands now.
return
}
}
utils.CopyHeaders(cc.responseWriter.Header(), cc.Header())
cc.responseWriter.WriteHeader(cc.code)
cc.headersSent = true
}
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// Hijack hijacks the connection.
func (cc *codeCatcher) Hijack() (net.Conn, *bufio.ReadWriter, error) {
if hj, ok := cc.responseWriter.(http.Hijacker); ok {
return hj.Hijack()
}
return nil, nil, fmt.Errorf("%T is not a http.Hijacker", cc.responseWriter)
}
// Flush sends any buffered data to the client.
func (cc *codeCatcher) Flush() {
// If WriteHeader was already called from the caller, this is a NOOP.
// Otherwise, cc.code is actually a 200 here.
cc.WriteHeader(cc.code)
// We don't care about the contents of the response,
// since we want to serve the ones from the error page,
// so we just don't flush.
// (e.g., To prevent superfluous WriteHeader on request with a
// `Transfert-Encoding: chunked` header).
if cc.caughtFilteredCode {
return
}
if flusher, ok := cc.responseWriter.(http.Flusher); ok {
flusher.Flush()
}
}
// codeModifier forwards a response back to the client,
// while enforcing a given response code.
type codeModifier struct {
code int // the code enforced in the response.
// headerSent is whether the headers have already been sent,
// either through Write or WriteHeader.
headerSent bool
headerMap http.Header // the HTTP response headers from the backend.
responseWriter http.ResponseWriter
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}
// newCodeModifier returns a codeModifier that enforces the given code.
func newCodeModifier(rw http.ResponseWriter, code int) *codeModifier {
return &codeModifier{
headerMap: make(http.Header),
code: code,
responseWriter: rw,
}
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}
// Header returns the response headers.
func (r *codeModifier) Header() http.Header {
if r.headerMap == nil {
r.headerMap = make(http.Header)
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}
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return r.headerMap
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}
// Write calls WriteHeader to send the enforced code,
// then writes the data directly to r.responseWriter.
func (r *codeModifier) Write(buf []byte) (int, error) {
r.WriteHeader(r.code)
return r.responseWriter.Write(buf)
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}
// WriteHeader sends the headers, with the enforced code (the code in argument
// is always ignored), if it hasn't already been done.
func (r *codeModifier) WriteHeader(_ int) {
if r.headerSent {
return
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}
utils.CopyHeaders(r.responseWriter.Header(), r.Header())
r.responseWriter.WriteHeader(r.code)
r.headerSent = true
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}
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// Hijack hijacks the connection.
func (r *codeModifier) 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()
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}
// Flush sends any buffered data to the client.
func (r *codeModifier) Flush() {
r.WriteHeader(r.code)
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if flusher, ok := r.responseWriter.(http.Flusher); ok {
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flusher.Flush()
}
}