caddy/modules/caddyhttp/reverseproxy/reverseproxy.go

1438 lines
52 KiB
Go

// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package reverseproxy
import (
"bytes"
"context"
"encoding/json"
"errors"
"fmt"
"io"
"net"
"net/http"
"net/http/httptrace"
"net/netip"
"net/textproto"
"net/url"
"strconv"
"strings"
"sync"
"time"
"go.uber.org/zap"
"golang.org/x/net/http/httpguts"
"github.com/caddyserver/caddy/v2"
"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
"github.com/caddyserver/caddy/v2/modules/caddyevents"
"github.com/caddyserver/caddy/v2/modules/caddyhttp"
"github.com/caddyserver/caddy/v2/modules/caddyhttp/headers"
"github.com/caddyserver/caddy/v2/modules/caddyhttp/rewrite"
)
func init() {
caddy.RegisterModule(Handler{})
}
// Handler implements a highly configurable and production-ready reverse proxy.
//
// Upon proxying, this module sets the following placeholders (which can be used
// both within and after this handler; for example, in response headers):
//
// Placeholder | Description
// ------------|-------------
// `{http.reverse_proxy.upstream.address}` | The full address to the upstream as given in the config
// `{http.reverse_proxy.upstream.hostport}` | The host:port of the upstream
// `{http.reverse_proxy.upstream.host}` | The host of the upstream
// `{http.reverse_proxy.upstream.port}` | The port of the upstream
// `{http.reverse_proxy.upstream.requests}` | The approximate current number of requests to the upstream
// `{http.reverse_proxy.upstream.max_requests}` | The maximum approximate number of requests allowed to the upstream
// `{http.reverse_proxy.upstream.fails}` | The number of recent failed requests to the upstream
// `{http.reverse_proxy.upstream.latency}` | How long it took the proxy upstream to write the response header.
// `{http.reverse_proxy.upstream.latency_ms}` | Same as 'latency', but in milliseconds.
// `{http.reverse_proxy.upstream.duration}` | Time spent proxying to the upstream, including writing response body to client.
// `{http.reverse_proxy.upstream.duration_ms}` | Same as 'upstream.duration', but in milliseconds.
// `{http.reverse_proxy.duration}` | Total time spent proxying, including selecting an upstream, retries, and writing response.
// `{http.reverse_proxy.duration_ms}` | Same as 'duration', but in milliseconds.
type Handler struct {
// Configures the method of transport for the proxy. A transport
// is what performs the actual "round trip" to the backend.
// The default transport is plaintext HTTP.
TransportRaw json.RawMessage `json:"transport,omitempty" caddy:"namespace=http.reverse_proxy.transport inline_key=protocol"`
// A circuit breaker may be used to relieve pressure on a backend
// that is beginning to exhibit symptoms of stress or latency.
// By default, there is no circuit breaker.
CBRaw json.RawMessage `json:"circuit_breaker,omitempty" caddy:"namespace=http.reverse_proxy.circuit_breakers inline_key=type"`
// Load balancing distributes load/requests between backends.
LoadBalancing *LoadBalancing `json:"load_balancing,omitempty"`
// Health checks update the status of backends, whether they are
// up or down. Down backends will not be proxied to.
HealthChecks *HealthChecks `json:"health_checks,omitempty"`
// Upstreams is the static list of backends to proxy to.
Upstreams UpstreamPool `json:"upstreams,omitempty"`
// A module for retrieving the list of upstreams dynamically. Dynamic
// upstreams are retrieved at every iteration of the proxy loop for
// each request (i.e. before every proxy attempt within every request).
// Active health checks do not work on dynamic upstreams, and passive
// health checks are only effective on dynamic upstreams if the proxy
// server is busy enough that concurrent requests to the same backends
// are continuous. Instead of health checks for dynamic upstreams, it
// is recommended that the dynamic upstream module only return available
// backends in the first place.
DynamicUpstreamsRaw json.RawMessage `json:"dynamic_upstreams,omitempty" caddy:"namespace=http.reverse_proxy.upstreams inline_key=source"`
// Adjusts how often to flush the response buffer. By default,
// no periodic flushing is done. A negative value disables
// response buffering, and flushes immediately after each
// write to the client. This option is ignored when the upstream's
// response is recognized as a streaming response, or if its
// content length is -1; for such responses, writes are flushed
// to the client immediately.
//
// Normally, a request will be canceled if the client disconnects
// before the response is received from the backend. If explicitly
// set to -1, client disconnection will be ignored and the request
// will be completed to help facilitate low-latency streaming.
FlushInterval caddy.Duration `json:"flush_interval,omitempty"`
// A list of IP ranges (supports CIDR notation) from which
// X-Forwarded-* header values should be trusted. By default,
// no proxies are trusted, so existing values will be ignored
// when setting these headers. If the proxy is trusted, then
// existing values will be used when constructing the final
// header values.
TrustedProxies []string `json:"trusted_proxies,omitempty"`
// Headers manipulates headers between Caddy and the backend.
// By default, all headers are passed-thru without changes,
// with the exceptions of special hop-by-hop headers.
//
// X-Forwarded-For, X-Forwarded-Proto and X-Forwarded-Host
// are also set implicitly.
Headers *headers.Handler `json:"headers,omitempty"`
// DEPRECATED: Do not use; will be removed. See request_buffers instead.
DeprecatedBufferRequests bool `json:"buffer_requests,omitempty"`
// DEPRECATED: Do not use; will be removed. See response_buffers instead.
DeprecatedBufferResponses bool `json:"buffer_responses,omitempty"`
// DEPRECATED: Do not use; will be removed. See request_buffers and response_buffers instead.
DeprecatedMaxBufferSize int64 `json:"max_buffer_size,omitempty"`
// If nonzero, the entire request body up to this size will be read
// and buffered in memory before being proxied to the backend. This
// should be avoided if at all possible for performance reasons, but
// could be useful if the backend is intolerant of read latency or
// chunked encodings.
RequestBuffers int64 `json:"request_buffers,omitempty"`
// If nonzero, the entire response body up to this size will be read
// and buffered in memory before being proxied to the client. This
// should be avoided if at all possible for performance reasons, but
// could be useful if the backend has tighter memory constraints.
ResponseBuffers int64 `json:"response_buffers,omitempty"`
// If nonzero, streaming requests such as WebSockets will be
// forcibly closed at the end of the timeout. Default: no timeout.
StreamTimeout caddy.Duration `json:"stream_timeout,omitempty"`
// If nonzero, streaming requests such as WebSockets will not be
// closed when the proxy config is unloaded, and instead the stream
// will remain open until the delay is complete. In other words,
// enabling this prevents streams from closing when Caddy's config
// is reloaded. Enabling this may be a good idea to avoid a thundering
// herd of reconnecting clients which had their connections closed
// by the previous config closing. Default: no delay.
StreamCloseDelay caddy.Duration `json:"stream_close_delay,omitempty"`
// If configured, rewrites the copy of the upstream request.
// Allows changing the request method and URI (path and query).
// Since the rewrite is applied to the copy, it does not persist
// past the reverse proxy handler.
// If the method is changed to `GET` or `HEAD`, the request body
// will not be copied to the backend. This allows a later request
// handler -- either in a `handle_response` route, or after -- to
// read the body.
// By default, no rewrite is performed, and the method and URI
// from the incoming request is used as-is for proxying.
Rewrite *rewrite.Rewrite `json:"rewrite,omitempty"`
// List of handlers and their associated matchers to evaluate
// after successful roundtrips. The first handler that matches
// the response from a backend will be invoked. The response
// body from the backend will not be written to the client;
// it is up to the handler to finish handling the response.
// If passive health checks are enabled, any errors from the
// handler chain will not affect the health status of the
// backend.
//
// Three new placeholders are available in this handler chain:
// - `{http.reverse_proxy.status_code}` The status code from the response
// - `{http.reverse_proxy.status_text}` The status text from the response
// - `{http.reverse_proxy.header.*}` The headers from the response
HandleResponse []caddyhttp.ResponseHandler `json:"handle_response,omitempty"`
Transport http.RoundTripper `json:"-"`
CB CircuitBreaker `json:"-"`
DynamicUpstreams UpstreamSource `json:"-"`
// Holds the parsed CIDR ranges from TrustedProxies
trustedProxies []netip.Prefix
// Holds the named response matchers from the Caddyfile while adapting
responseMatchers map[string]caddyhttp.ResponseMatcher
// Holds the handle_response Caddyfile tokens while adapting
handleResponseSegments []*caddyfile.Dispenser
// Stores upgraded requests (hijacked connections) for proper cleanup
connections map[io.ReadWriteCloser]openConnection
connectionsCloseTimer *time.Timer
connectionsMu *sync.Mutex
ctx caddy.Context
logger *zap.Logger
events *caddyevents.App
}
// CaddyModule returns the Caddy module information.
func (Handler) CaddyModule() caddy.ModuleInfo {
return caddy.ModuleInfo{
ID: "http.handlers.reverse_proxy",
New: func() caddy.Module { return new(Handler) },
}
}
// Provision ensures that h is set up properly before use.
func (h *Handler) Provision(ctx caddy.Context) error {
eventAppIface, err := ctx.App("events")
if err != nil {
return fmt.Errorf("getting events app: %v", err)
}
h.events = eventAppIface.(*caddyevents.App)
h.ctx = ctx
h.logger = ctx.Logger()
h.connections = make(map[io.ReadWriteCloser]openConnection)
h.connectionsMu = new(sync.Mutex)
// TODO: remove deprecated fields sometime after v2.6.4
if h.DeprecatedBufferRequests {
h.logger.Warn("DEPRECATED: buffer_requests: this property will be removed soon; use request_buffers instead (and set a maximum buffer size)")
}
if h.DeprecatedBufferResponses {
h.logger.Warn("DEPRECATED: buffer_responses: this property will be removed soon; use response_buffers instead (and set a maximum buffer size)")
}
if h.DeprecatedMaxBufferSize != 0 {
h.logger.Warn("DEPRECATED: max_buffer_size: this property will be removed soon; use request_buffers and/or response_buffers instead (and set maximum buffer sizes)")
}
// warn about unsafe buffering config
if h.RequestBuffers == -1 || h.ResponseBuffers == -1 {
h.logger.Warn("UNLIMITED BUFFERING: buffering is enabled without any cap on buffer size, which can result in OOM crashes")
}
// start by loading modules
if h.TransportRaw != nil {
mod, err := ctx.LoadModule(h, "TransportRaw")
if err != nil {
return fmt.Errorf("loading transport: %v", err)
}
h.Transport = mod.(http.RoundTripper)
}
if h.LoadBalancing != nil && h.LoadBalancing.SelectionPolicyRaw != nil {
mod, err := ctx.LoadModule(h.LoadBalancing, "SelectionPolicyRaw")
if err != nil {
return fmt.Errorf("loading load balancing selection policy: %s", err)
}
h.LoadBalancing.SelectionPolicy = mod.(Selector)
}
if h.CBRaw != nil {
mod, err := ctx.LoadModule(h, "CBRaw")
if err != nil {
return fmt.Errorf("loading circuit breaker: %s", err)
}
h.CB = mod.(CircuitBreaker)
}
if h.DynamicUpstreamsRaw != nil {
mod, err := ctx.LoadModule(h, "DynamicUpstreamsRaw")
if err != nil {
return fmt.Errorf("loading upstream source module: %v", err)
}
h.DynamicUpstreams = mod.(UpstreamSource)
}
// parse trusted proxy CIDRs ahead of time
for _, str := range h.TrustedProxies {
if strings.Contains(str, "/") {
ipNet, err := netip.ParsePrefix(str)
if err != nil {
return fmt.Errorf("parsing CIDR expression: '%s': %v", str, err)
}
h.trustedProxies = append(h.trustedProxies, ipNet)
} else {
ipAddr, err := netip.ParseAddr(str)
if err != nil {
return fmt.Errorf("invalid IP address: '%s': %v", str, err)
}
ipNew := netip.PrefixFrom(ipAddr, ipAddr.BitLen())
h.trustedProxies = append(h.trustedProxies, ipNew)
}
}
// ensure any embedded headers handler module gets provisioned
// (see https://caddy.community/t/set-cookie-manipulation-in-reverse-proxy/7666?u=matt
// for what happens if we forget to provision it)
if h.Headers != nil {
err := h.Headers.Provision(ctx)
if err != nil {
return fmt.Errorf("provisioning embedded headers handler: %v", err)
}
}
if h.Rewrite != nil {
err := h.Rewrite.Provision(ctx)
if err != nil {
return fmt.Errorf("provisioning rewrite: %v", err)
}
}
// set up transport
if h.Transport == nil {
t := &HTTPTransport{}
err := t.Provision(ctx)
if err != nil {
return fmt.Errorf("provisioning default transport: %v", err)
}
h.Transport = t
}
// set up load balancing
if h.LoadBalancing == nil {
h.LoadBalancing = new(LoadBalancing)
}
if h.LoadBalancing.SelectionPolicy == nil {
h.LoadBalancing.SelectionPolicy = RandomSelection{}
}
if h.LoadBalancing.TryDuration > 0 && h.LoadBalancing.TryInterval == 0 {
// a non-zero try_duration with a zero try_interval
// will always spin the CPU for try_duration if the
// upstream is local or low-latency; avoid that by
// defaulting to a sane wait period between attempts
h.LoadBalancing.TryInterval = caddy.Duration(250 * time.Millisecond)
}
lbMatcherSets, err := ctx.LoadModule(h.LoadBalancing, "RetryMatchRaw")
if err != nil {
return err
}
err = h.LoadBalancing.RetryMatch.FromInterface(lbMatcherSets)
if err != nil {
return err
}
// set up upstreams
for _, u := range h.Upstreams {
h.provisionUpstream(u)
}
if h.HealthChecks != nil {
// set defaults on passive health checks, if necessary
if h.HealthChecks.Passive != nil {
h.HealthChecks.Passive.logger = h.logger.Named("health_checker.passive")
if h.HealthChecks.Passive.MaxFails == 0 {
h.HealthChecks.Passive.MaxFails = 1
}
}
// if active health checks are enabled, configure them and start a worker
if h.HealthChecks.Active != nil {
err := h.HealthChecks.Active.Provision(ctx, h)
if err != nil {
return err
}
if h.HealthChecks.Active.IsEnabled() {
go h.activeHealthChecker()
}
}
}
// set up any response routes
for i, rh := range h.HandleResponse {
err := rh.Provision(ctx)
if err != nil {
return fmt.Errorf("provisioning response handler %d: %v", i, err)
}
}
upstreamHealthyUpdater := newMetricsUpstreamsHealthyUpdater(h)
upstreamHealthyUpdater.Init()
return nil
}
// Cleanup cleans up the resources made by h.
func (h *Handler) Cleanup() error {
err := h.cleanupConnections()
// remove hosts from our config from the pool
for _, upstream := range h.Upstreams {
_, _ = hosts.Delete(upstream.String())
}
return err
}
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
// prepare the request for proxying; this is needed only once
clonedReq, err := h.prepareRequest(r, repl)
if err != nil {
return caddyhttp.Error(http.StatusInternalServerError,
fmt.Errorf("preparing request for upstream round-trip: %v", err))
}
// we will need the original headers and Host value if
// header operations are configured; this is so that each
// retry can apply the modifications, because placeholders
// may be used which depend on the selected upstream for
// their values
reqHost := clonedReq.Host
reqHeader := clonedReq.Header
start := time.Now()
defer func() {
// total proxying duration, including time spent on LB and retries
repl.Set("http.reverse_proxy.duration", time.Since(start))
repl.Set("http.reverse_proxy.duration_ms", time.Since(start).Seconds()*1e3) // multiply seconds to preserve decimal (see #4666)
}()
// in the proxy loop, each iteration is an attempt to proxy the request,
// and because we may retry some number of times, carry over the error
// from previous tries because of the nuances of load balancing & retries
var proxyErr error
var retries int
for {
var done bool
done, proxyErr = h.proxyLoopIteration(clonedReq, r, w, proxyErr, start, retries, repl, reqHeader, reqHost, next)
if done {
break
}
retries++
}
if proxyErr != nil {
return statusError(proxyErr)
}
return nil
}
// proxyLoopIteration implements an iteration of the proxy loop. Despite the enormous amount of local state
// that has to be passed in, we brought this into its own method so that we could run defer more easily.
// It returns true when the loop is done and should break; false otherwise. The error value returned should
// be assigned to the proxyErr value for the next iteration of the loop (or the error handled after break).
func (h *Handler) proxyLoopIteration(r *http.Request, origReq *http.Request, w http.ResponseWriter, proxyErr error, start time.Time, retries int,
repl *caddy.Replacer, reqHeader http.Header, reqHost string, next caddyhttp.Handler,
) (bool, error) {
// get the updated list of upstreams
upstreams := h.Upstreams
if h.DynamicUpstreams != nil {
dUpstreams, err := h.DynamicUpstreams.GetUpstreams(r)
if err != nil {
h.logger.Error("failed getting dynamic upstreams; falling back to static upstreams", zap.Error(err))
} else {
upstreams = dUpstreams
for _, dUp := range dUpstreams {
h.provisionUpstream(dUp)
}
h.logger.Debug("provisioned dynamic upstreams", zap.Int("count", len(dUpstreams)))
defer func() {
// these upstreams are dynamic, so they are only used for this iteration
// of the proxy loop; be sure to let them go away when we're done with them
for _, upstream := range dUpstreams {
_, _ = hosts.Delete(upstream.String())
}
}()
}
}
// choose an available upstream
upstream := h.LoadBalancing.SelectionPolicy.Select(upstreams, r, w)
if upstream == nil {
if proxyErr == nil {
proxyErr = caddyhttp.Error(http.StatusServiceUnavailable, noUpstreamsAvailable)
}
if !h.LoadBalancing.tryAgain(h.ctx, start, retries, proxyErr, r) {
return true, proxyErr
}
return false, proxyErr
}
// the dial address may vary per-request if placeholders are
// used, so perform those replacements here; the resulting
// DialInfo struct should have valid network address syntax
dialInfo, err := upstream.fillDialInfo(r)
if err != nil {
return true, fmt.Errorf("making dial info: %v", err)
}
h.logger.Debug("selected upstream",
zap.String("dial", dialInfo.Address),
zap.Int("total_upstreams", len(upstreams)))
// attach to the request information about how to dial the upstream;
// this is necessary because the information cannot be sufficiently
// or satisfactorily represented in a URL
caddyhttp.SetVar(r.Context(), dialInfoVarKey, dialInfo)
// set placeholders with information about this upstream
repl.Set("http.reverse_proxy.upstream.address", dialInfo.String())
repl.Set("http.reverse_proxy.upstream.hostport", dialInfo.Address)
repl.Set("http.reverse_proxy.upstream.host", dialInfo.Host)
repl.Set("http.reverse_proxy.upstream.port", dialInfo.Port)
repl.Set("http.reverse_proxy.upstream.requests", upstream.Host.NumRequests())
repl.Set("http.reverse_proxy.upstream.max_requests", upstream.MaxRequests)
repl.Set("http.reverse_proxy.upstream.fails", upstream.Host.Fails())
// mutate request headers according to this upstream;
// because we're in a retry loop, we have to copy
// headers (and the r.Host value) from the original
// so that each retry is identical to the first
if h.Headers != nil && h.Headers.Request != nil {
r.Header = make(http.Header)
copyHeader(r.Header, reqHeader)
r.Host = reqHost
h.Headers.Request.ApplyToRequest(r)
}
// proxy the request to that upstream
proxyErr = h.reverseProxy(w, r, origReq, repl, dialInfo, next)
if proxyErr == nil || errors.Is(proxyErr, context.Canceled) {
// context.Canceled happens when the downstream client
// cancels the request, which is not our failure
return true, nil
}
// if the roundtrip was successful, don't retry the request or
// ding the health status of the upstream (an error can still
// occur after the roundtrip if, for example, a response handler
// after the roundtrip returns an error)
if succ, ok := proxyErr.(roundtripSucceeded); ok {
return true, succ.error
}
// remember this failure (if enabled)
h.countFailure(upstream)
// if we've tried long enough, break
if !h.LoadBalancing.tryAgain(h.ctx, start, retries, proxyErr, r) {
return true, proxyErr
}
return false, proxyErr
}
// prepareRequest clones req so that it can be safely modified without
// changing the original request or introducing data races. It then
// modifies it so that it is ready to be proxied, except for directing
// to a specific upstream. This method adjusts headers and other relevant
// properties of the cloned request and should be done just once (before
// proxying) regardless of proxy retries. This assumes that no mutations
// of the cloned request are performed by h during or after proxying.
func (h Handler) prepareRequest(req *http.Request, repl *caddy.Replacer) (*http.Request, error) {
req = cloneRequest(req)
// if enabled, perform rewrites on the cloned request; if
// the method is GET or HEAD, prevent the request body
// from being copied to the upstream
if h.Rewrite != nil {
changed := h.Rewrite.Rewrite(req, repl)
if changed && (h.Rewrite.Method == "GET" || h.Rewrite.Method == "HEAD") {
req.ContentLength = 0
req.Body = nil
}
}
// if enabled, buffer client request; this should only be
// enabled if the upstream requires it and does not work
// with "slow clients" (gunicorn, etc.) - this obviously
// has a perf overhead and makes the proxy at risk of
// exhausting memory and more susceptible to slowloris
// attacks, so it is strongly recommended to only use this
// feature if absolutely required, if read timeouts are
// set, and if body size is limited
if h.RequestBuffers != 0 && req.Body != nil {
req.Body, req.ContentLength = h.bufferedBody(req.Body, h.RequestBuffers)
req.Header.Set("Content-Length", strconv.FormatInt(req.ContentLength, 10))
}
if req.ContentLength == 0 {
req.Body = nil // Issue golang/go#16036: nil Body for http.Transport retries
}
req.Close = false
// if User-Agent is not set by client, then explicitly
// disable it so it's not set to default value by std lib
if _, ok := req.Header["User-Agent"]; !ok {
req.Header.Set("User-Agent", "")
}
reqUpType := upgradeType(req.Header)
removeConnectionHeaders(req.Header)
// Remove hop-by-hop headers to the backend. Especially
// important is "Connection" because we want a persistent
// connection, regardless of what the client sent to us.
// Issue golang/go#46313: don't skip if field is empty.
for _, h := range hopHeaders {
// Issue golang/go#21096: tell backend applications that care about trailer support
// that we support trailers. (We do, but we don't go out of our way to
// advertise that unless the incoming client request thought it was worth
// mentioning.)
if h == "Te" && httpguts.HeaderValuesContainsToken(req.Header["Te"], "trailers") {
req.Header.Set("Te", "trailers")
continue
}
req.Header.Del(h)
}
// After stripping all the hop-by-hop connection headers above, add back any
// necessary for protocol upgrades, such as for websockets.
if reqUpType != "" {
req.Header.Set("Connection", "Upgrade")
req.Header.Set("Upgrade", reqUpType)
}
// Set up the PROXY protocol info
address := caddyhttp.GetVar(req.Context(), caddyhttp.ClientIPVarKey).(string)
addrPort, err := netip.ParseAddrPort(address)
if err != nil {
// OK; probably didn't have a port
addr, err := netip.ParseAddr(address)
if err != nil {
// Doesn't seem like a valid ip address at all
} else {
// Ok, only the port was missing
addrPort = netip.AddrPortFrom(addr, 0)
}
}
proxyProtocolInfo := ProxyProtocolInfo{AddrPort: addrPort}
caddyhttp.SetVar(req.Context(), proxyProtocolInfoVarKey, proxyProtocolInfo)
// Add the supported X-Forwarded-* headers
err = h.addForwardedHeaders(req)
if err != nil {
return nil, err
}
return req, nil
}
// addForwardedHeaders adds the de-facto standard X-Forwarded-*
// headers to the request before it is sent upstream.
//
// These headers are security sensitive, so care is taken to only
// use existing values for these headers from the incoming request
// if the client IP is trusted (i.e. coming from a trusted proxy
// sitting in front of this server). If the request didn't have
// the headers at all, then they will be added with the values
// that we can glean from the request.
func (h Handler) addForwardedHeaders(req *http.Request) error {
// Parse the remote IP, ignore the error as non-fatal,
// but the remote IP is required to continue, so we
// just return early. This should probably never happen
// though, unless some other module manipulated the request's
// remote address and used an invalid value.
clientIP, _, err := net.SplitHostPort(req.RemoteAddr)
if err != nil {
// Remove the `X-Forwarded-*` headers to avoid upstreams
// potentially trusting a header that came from the client
req.Header.Del("X-Forwarded-For")
req.Header.Del("X-Forwarded-Proto")
req.Header.Del("X-Forwarded-Host")
return nil
}
// Client IP may contain a zone if IPv6, so we need
// to pull that out before parsing the IP
clientIP, _, _ = strings.Cut(clientIP, "%")
ipAddr, err := netip.ParseAddr(clientIP)
if err != nil {
return fmt.Errorf("invalid IP address: '%s': %v", clientIP, err)
}
// Check if the client is a trusted proxy
trusted := caddyhttp.GetVar(req.Context(), caddyhttp.TrustedProxyVarKey).(bool)
for _, ipRange := range h.trustedProxies {
if ipRange.Contains(ipAddr) {
trusted = true
break
}
}
// If we aren't the first proxy, and the proxy is trusted,
// retain prior X-Forwarded-For information as a comma+space
// separated list and fold multiple headers into one.
clientXFF := clientIP
prior, ok, omit := allHeaderValues(req.Header, "X-Forwarded-For")
if trusted && ok && prior != "" {
clientXFF = prior + ", " + clientXFF
}
if !omit {
req.Header.Set("X-Forwarded-For", clientXFF)
}
// Set X-Forwarded-Proto; many backend apps expect this,
// so that they can properly craft URLs with the right
// scheme to match the original request
proto := "https"
if req.TLS == nil {
proto = "http"
}
prior, ok, omit = lastHeaderValue(req.Header, "X-Forwarded-Proto")
if trusted && ok && prior != "" {
proto = prior
}
if !omit {
req.Header.Set("X-Forwarded-Proto", proto)
}
// Set X-Forwarded-Host; often this is redundant because
// we pass through the request Host as-is, but in situations
// where we proxy over HTTPS, the user may need to override
// Host themselves, so it's helpful to send the original too.
host := req.Host
prior, ok, omit = lastHeaderValue(req.Header, "X-Forwarded-Host")
if trusted && ok && prior != "" {
host = prior
}
if !omit {
req.Header.Set("X-Forwarded-Host", host)
}
return nil
}
// reverseProxy performs a round-trip to the given backend and processes the response with the client.
// (This method is mostly the beginning of what was borrowed from the net/http/httputil package in the
// Go standard library which was used as the foundation.)
func (h *Handler) reverseProxy(rw http.ResponseWriter, req *http.Request, origReq *http.Request, repl *caddy.Replacer, di DialInfo, next caddyhttp.Handler) error {
_ = di.Upstream.Host.countRequest(1)
//nolint:errcheck
defer di.Upstream.Host.countRequest(-1)
// point the request to this upstream
h.directRequest(req, di)
server := req.Context().Value(caddyhttp.ServerCtxKey).(*caddyhttp.Server)
shouldLogCredentials := server.Logs != nil && server.Logs.ShouldLogCredentials
// Forward 1xx status codes, backported from https://github.com/golang/go/pull/53164
trace := &httptrace.ClientTrace{
Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
h := rw.Header()
copyHeader(h, http.Header(header))
rw.WriteHeader(code)
// Clear headers coming from the backend
// (it's not automatically done by ResponseWriter.WriteHeader() for 1xx responses)
for k := range header {
delete(h, k)
}
return nil
},
}
req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
// if FlushInterval is explicitly configured to -1 (i.e. flush continuously to achieve
// low-latency streaming), don't let the transport cancel the request if the client
// disconnects: user probably wants us to finish sending the data to the upstream
// regardless, and we should expect client disconnection in low-latency streaming
// scenarios (see issue #4922)
if h.FlushInterval == -1 {
req = req.WithContext(ignoreClientGoneContext{req.Context()})
}
// do the round-trip; emit debug log with values we know are
// safe, or if there is no error, emit fuller log entry
start := time.Now()
res, err := h.Transport.RoundTrip(req)
duration := time.Since(start)
logger := h.logger.With(
zap.String("upstream", di.Upstream.String()),
zap.Duration("duration", duration),
zap.Object("request", caddyhttp.LoggableHTTPRequest{
Request: req,
ShouldLogCredentials: shouldLogCredentials,
}),
)
if err != nil {
logger.Debug("upstream roundtrip", zap.Error(err))
return err
}
logger.Debug("upstream roundtrip",
zap.Object("headers", caddyhttp.LoggableHTTPHeader{
Header: res.Header,
ShouldLogCredentials: shouldLogCredentials,
}),
zap.Int("status", res.StatusCode))
// duration until upstream wrote response headers (roundtrip duration)
repl.Set("http.reverse_proxy.upstream.latency", duration)
repl.Set("http.reverse_proxy.upstream.latency_ms", duration.Seconds()*1e3) // multiply seconds to preserve decimal (see #4666)
// update circuit breaker on current conditions
if di.Upstream.cb != nil {
di.Upstream.cb.RecordMetric(res.StatusCode, duration)
}
// perform passive health checks (if enabled)
if h.HealthChecks != nil && h.HealthChecks.Passive != nil {
// strike if the status code matches one that is "bad"
for _, badStatus := range h.HealthChecks.Passive.UnhealthyStatus {
if caddyhttp.StatusCodeMatches(res.StatusCode, badStatus) {
h.countFailure(di.Upstream)
}
}
// strike if the roundtrip took too long
if h.HealthChecks.Passive.UnhealthyLatency > 0 &&
duration >= time.Duration(h.HealthChecks.Passive.UnhealthyLatency) {
h.countFailure(di.Upstream)
}
}
// if enabled, buffer the response body
if h.ResponseBuffers != 0 {
res.Body, _ = h.bufferedBody(res.Body, h.ResponseBuffers)
}
// see if any response handler is configured for this response from the backend
for i, rh := range h.HandleResponse {
if rh.Match != nil && !rh.Match.Match(res.StatusCode, res.Header) {
continue
}
// if configured to only change the status code,
// do that then continue regular proxy response
if statusCodeStr := rh.StatusCode.String(); statusCodeStr != "" {
statusCode, err := strconv.Atoi(repl.ReplaceAll(statusCodeStr, ""))
if err != nil {
return caddyhttp.Error(http.StatusInternalServerError, err)
}
if statusCode != 0 {
res.StatusCode = statusCode
}
break
}
// set up the replacer so that parts of the original response can be
// used for routing decisions
for field, value := range res.Header {
repl.Set("http.reverse_proxy.header."+field, strings.Join(value, ","))
}
repl.Set("http.reverse_proxy.status_code", res.StatusCode)
repl.Set("http.reverse_proxy.status_text", res.Status)
logger.Debug("handling response", zap.Int("handler", i))
// we make some data available via request context to child routes
// so that they may inherit some options and functions from the
// handler, and be able to copy the response.
// we use the original request here, so that any routes from 'next'
// see the original request rather than the proxy cloned request.
hrc := &handleResponseContext{
handler: h,
response: res,
start: start,
logger: logger,
}
ctx := origReq.Context()
ctx = context.WithValue(ctx, proxyHandleResponseContextCtxKey, hrc)
// pass the request through the response handler routes
routeErr := rh.Routes.Compile(next).ServeHTTP(rw, origReq.WithContext(ctx))
// close the response body afterwards, since we don't need it anymore;
// either a route had 'copy_response' which already consumed the body,
// or some other terminal handler ran which doesn't need the response
// body after that point (e.g. 'file_server' for X-Accel-Redirect flow),
// or we fell through to subsequent handlers past this proxy
// (e.g. forward auth's 2xx response flow).
if !hrc.isFinalized {
res.Body.Close()
}
// wrap any route error in roundtripSucceeded so caller knows that
// the roundtrip was successful and to not retry
if routeErr != nil {
return roundtripSucceeded{routeErr}
}
// we're done handling the response, and we don't want to
// fall through to the default finalize/copy behaviour
return nil
}
// copy the response body and headers back to the upstream client
return h.finalizeResponse(rw, req, res, repl, start, logger)
}
// finalizeResponse prepares and copies the response.
func (h *Handler) finalizeResponse(
rw http.ResponseWriter,
req *http.Request,
res *http.Response,
repl *caddy.Replacer,
start time.Time,
logger *zap.Logger,
) error {
// deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
if res.StatusCode == http.StatusSwitchingProtocols {
h.handleUpgradeResponse(logger, rw, req, res)
return nil
}
removeConnectionHeaders(res.Header)
for _, h := range hopHeaders {
res.Header.Del(h)
}
// apply any response header operations
if h.Headers != nil && h.Headers.Response != nil {
if h.Headers.Response.Require == nil ||
h.Headers.Response.Require.Match(res.StatusCode, res.Header) {
h.Headers.Response.ApplyTo(res.Header, repl)
}
}
copyHeader(rw.Header(), res.Header)
// The "Trailer" header isn't included in the Transport's response,
// at least for *http.Transport. Build it up from Trailer.
announcedTrailers := len(res.Trailer)
if announcedTrailers > 0 {
trailerKeys := make([]string, 0, len(res.Trailer))
for k := range res.Trailer {
trailerKeys = append(trailerKeys, k)
}
rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
}
rw.WriteHeader(res.StatusCode)
err := h.copyResponse(rw, res.Body, h.flushInterval(req, res))
res.Body.Close() // close now, instead of defer, to populate res.Trailer
if err != nil {
// we're streaming the response and we've already written headers, so
// there's nothing an error handler can do to recover at this point;
// the standard lib's proxy panics at this point, but we'll just log
// the error and abort the stream here
logger.Error("aborting with incomplete response", zap.Error(err))
return nil
}
if len(res.Trailer) > 0 {
// Force chunking if we saw a response trailer.
// This prevents net/http from calculating the length for short
// bodies and adding a Content-Length.
//nolint:bodyclose
http.NewResponseController(rw).Flush()
}
// total duration spent proxying, including writing response body
repl.Set("http.reverse_proxy.upstream.duration", time.Since(start))
repl.Set("http.reverse_proxy.upstream.duration_ms", time.Since(start).Seconds()*1e3)
if len(res.Trailer) == announcedTrailers {
copyHeader(rw.Header(), res.Trailer)
return nil
}
for k, vv := range res.Trailer {
k = http.TrailerPrefix + k
for _, v := range vv {
rw.Header().Add(k, v)
}
}
return nil
}
// tryAgain takes the time that the handler was initially invoked,
// the amount of retries already performed, as well as any error
// currently obtained, and the request being tried, and returns
// true if another attempt should be made at proxying the request.
// If true is returned, it has already blocked long enough before
// the next retry (i.e. no more sleeping is needed). If false is
// returned, the handler should stop trying to proxy the request.
func (lb LoadBalancing) tryAgain(ctx caddy.Context, start time.Time, retries int, proxyErr error, req *http.Request) bool {
// no retries are configured
if lb.TryDuration == 0 && lb.Retries == 0 {
return false
}
// if we've tried long enough, break
if lb.TryDuration > 0 && time.Since(start) >= time.Duration(lb.TryDuration) {
return false
}
// if we've reached the retry limit, break
if lb.Retries > 0 && retries >= lb.Retries {
return false
}
// if the error occurred while dialing (i.e. a connection
// could not even be established to the upstream), then it
// should be safe to retry, since without a connection, no
// HTTP request can be transmitted; but if the error is not
// specifically a dialer error, we need to be careful
if proxyErr != nil {
_, isDialError := proxyErr.(DialError)
herr, isHandlerError := proxyErr.(caddyhttp.HandlerError)
// if the error occurred after a connection was established,
// we have to assume the upstream received the request, and
// retries need to be carefully decided, because some requests
// are not idempotent
if !isDialError && !(isHandlerError && errors.Is(herr, noUpstreamsAvailable)) {
if lb.RetryMatch == nil && req.Method != "GET" {
// by default, don't retry requests if they aren't GET
return false
}
if !lb.RetryMatch.AnyMatch(req) {
return false
}
}
}
// fast path; if the interval is zero, we don't need to wait
if lb.TryInterval == 0 {
return true
}
// otherwise, wait and try the next available host
timer := time.NewTimer(time.Duration(lb.TryInterval))
select {
case <-timer.C:
return true
case <-ctx.Done():
if !timer.Stop() {
// if the timer has been stopped then read from the channel
<-timer.C
}
return false
}
}
// directRequest modifies only req.URL so that it points to the upstream
// in the given DialInfo. It must modify ONLY the request URL.
func (Handler) directRequest(req *http.Request, di DialInfo) {
// we need a host, so set the upstream's host address
reqHost := di.Address
// if the port equates to the scheme, strip the port because
// it's weird to make a request like http://example.com:80/.
if (req.URL.Scheme == "http" && di.Port == "80") ||
(req.URL.Scheme == "https" && di.Port == "443") {
reqHost = di.Host
}
req.URL.Host = reqHost
}
func (h Handler) provisionUpstream(upstream *Upstream) {
// create or get the host representation for this upstream
upstream.fillHost()
// give it the circuit breaker, if any
upstream.cb = h.CB
// if the passive health checker has a non-zero UnhealthyRequestCount
// but the upstream has no MaxRequests set (they are the same thing,
// but the passive health checker is a default value for for upstreams
// without MaxRequests), copy the value into this upstream, since the
// value in the upstream (MaxRequests) is what is used during
// availability checks
if h.HealthChecks != nil &&
h.HealthChecks.Passive != nil &&
h.HealthChecks.Passive.UnhealthyRequestCount > 0 &&
upstream.MaxRequests == 0 {
upstream.MaxRequests = h.HealthChecks.Passive.UnhealthyRequestCount
}
// upstreams need independent access to the passive
// health check policy because passive health checks
// run without access to h.
if h.HealthChecks != nil {
upstream.healthCheckPolicy = h.HealthChecks.Passive
}
}
// bufferedBody reads originalBody into a buffer with maximum size of limit (-1 for unlimited),
// then returns a reader for the buffer along with how many bytes were buffered. Always close
// the return value when done with it, just like if it was the original body! If limit is 0
// (which it shouldn't be), this function returns its input; i.e. is a no-op, for safety.
func (h Handler) bufferedBody(originalBody io.ReadCloser, limit int64) (io.ReadCloser, int64) {
if limit == 0 {
return originalBody, 0
}
var written int64
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
if limit > 0 {
n, err := io.CopyN(buf, originalBody, limit)
if err != nil || n == limit {
return bodyReadCloser{
Reader: io.MultiReader(buf, originalBody),
buf: buf,
body: originalBody,
}, n
}
} else {
written, _ = io.Copy(buf, originalBody)
}
originalBody.Close() // no point in keeping it open
return bodyReadCloser{
Reader: buf,
buf: buf,
}, written
}
// cloneRequest makes a semi-deep clone of origReq.
//
// Most of this code is borrowed from the Go stdlib reverse proxy,
// but we make a shallow-ish clone the request (deep clone only
// the headers and URL) so we can avoid manipulating the original
// request when using it to proxy upstream. This prevents request
// corruption and data races.
func cloneRequest(origReq *http.Request) *http.Request {
req := new(http.Request)
*req = *origReq
if origReq.URL != nil {
newURL := new(url.URL)
*newURL = *origReq.URL
if origReq.URL.User != nil {
newURL.User = new(url.Userinfo)
*newURL.User = *origReq.URL.User
}
// sanitize the request URL; we expect it to not contain the
// scheme and host since those should be determined by r.TLS
// and r.Host respectively, but some clients may include it
// in the request-line, which is technically valid in HTTP,
// but breaks reverseproxy behaviour, overriding how the
// dialer will behave. See #4237 for context.
newURL.Scheme = ""
newURL.Host = ""
req.URL = newURL
}
if origReq.Header != nil {
req.Header = origReq.Header.Clone()
}
if origReq.Trailer != nil {
req.Trailer = origReq.Trailer.Clone()
}
return req
}
func copyHeader(dst, src http.Header) {
for k, vv := range src {
for _, v := range vv {
dst.Add(k, v)
}
}
}
// allHeaderValues gets all values for a given header field,
// joined by a comma and space if more than one is set. If the
// header field is nil, then the omit is true, meaning some
// earlier logic in the server wanted to prevent this header from
// getting written at all. If the header is empty, then ok is
// false. Callers should still check that the value is not empty
// (the header field may be set but have an empty value).
func allHeaderValues(h http.Header, field string) (value string, ok bool, omit bool) {
values, ok := h[http.CanonicalHeaderKey(field)]
if ok && values == nil {
return "", true, true
}
if len(values) == 0 {
return "", false, false
}
return strings.Join(values, ", "), true, false
}
// lastHeaderValue gets the last value for a given header field
// if more than one is set. If the header field is nil, then
// the omit is true, meaning some earlier logic in the server
// wanted to prevent this header from getting written at all.
// If the header is empty, then ok is false. Callers should
// still check that the value is not empty (the header field
// may be set but have an empty value).
func lastHeaderValue(h http.Header, field string) (value string, ok bool, omit bool) {
values, ok := h[http.CanonicalHeaderKey(field)]
if ok && values == nil {
return "", true, true
}
if len(values) == 0 {
return "", false, false
}
return values[len(values)-1], true, false
}
func upgradeType(h http.Header) string {
if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
return ""
}
return strings.ToLower(h.Get("Upgrade"))
}
// removeConnectionHeaders removes hop-by-hop headers listed in the "Connection" header of h.
// See RFC 7230, section 6.1
func removeConnectionHeaders(h http.Header) {
for _, f := range h["Connection"] {
for _, sf := range strings.Split(f, ",") {
if sf = textproto.TrimString(sf); sf != "" {
h.Del(sf)
}
}
}
}
// statusError returns an error value that has a status code.
func statusError(err error) error {
// errors proxying usually mean there is a problem with the upstream(s)
statusCode := http.StatusBadGateway
// timeout errors have a standard status code (see issue #4823)
if err, ok := err.(net.Error); ok && err.Timeout() {
statusCode = http.StatusGatewayTimeout
}
// if the client canceled the request (usually this means they closed
// the connection, so they won't see any response), we can report it
// as a client error (4xx) and not a server error (5xx); unfortunately
// the Go standard library, at least at time of writing in late 2020,
// obnoxiously wraps the exported, standard context.Canceled error with
// an unexported garbage value that we have to do a substring check for:
// https://github.com/golang/go/blob/6965b01ea248cabb70c3749fd218b36089a21efb/src/net/net.go#L416-L430
if errors.Is(err, context.Canceled) || strings.Contains(err.Error(), "operation was canceled") {
// regrettably, there is no standard error code for "client closed connection", but
// for historical reasons we can use a code that a lot of people are already using;
// using 5xx is problematic for users; see #3748
statusCode = 499
}
return caddyhttp.Error(statusCode, err)
}
// LoadBalancing has parameters related to load balancing.
type LoadBalancing struct {
// A selection policy is how to choose an available backend.
// The default policy is random selection.
SelectionPolicyRaw json.RawMessage `json:"selection_policy,omitempty" caddy:"namespace=http.reverse_proxy.selection_policies inline_key=policy"`
// How many times to retry selecting available backends for each
// request if the next available host is down. If try_duration is
// also configured, then retries may stop early if the duration
// is reached. By default, retries are disabled (zero).
Retries int `json:"retries,omitempty"`
// How long to try selecting available backends for each request
// if the next available host is down. Clients will wait for up
// to this long while the load balancer tries to find an available
// upstream host. If retries is also configured, tries may stop
// early if the maximum retries is reached. By default, retries
// are disabled (zero duration).
TryDuration caddy.Duration `json:"try_duration,omitempty"`
// How long to wait between selecting the next host from the pool.
// Default is 250ms if try_duration is enabled, otherwise zero. Only
// relevant when a request to an upstream host fails. Be aware that
// setting this to 0 with a non-zero try_duration can cause the CPU
// to spin if all backends are down and latency is very low.
TryInterval caddy.Duration `json:"try_interval,omitempty"`
// A list of matcher sets that restricts with which requests retries are
// allowed. A request must match any of the given matcher sets in order
// to be retried if the connection to the upstream succeeded but the
// subsequent round-trip failed. If the connection to the upstream failed,
// a retry is always allowed. If unspecified, only GET requests will be
// allowed to be retried. Note that a retry is done with the next available
// host according to the load balancing policy.
RetryMatchRaw caddyhttp.RawMatcherSets `json:"retry_match,omitempty" caddy:"namespace=http.matchers"`
SelectionPolicy Selector `json:"-"`
RetryMatch caddyhttp.MatcherSets `json:"-"`
}
// Selector selects an available upstream from the pool.
type Selector interface {
Select(UpstreamPool, *http.Request, http.ResponseWriter) *Upstream
}
// UpstreamSource gets the list of upstreams that can be used when
// proxying a request. Returned upstreams will be load balanced and
// health-checked. This should be a very fast function -- instant
// if possible -- and the return value must be as stable as possible.
// In other words, the list of upstreams should ideally not change much
// across successive calls. If the list of upstreams changes or the
// ordering is not stable, load balancing will suffer. This function
// may be called during each retry, multiple times per request, and as
// such, needs to be instantaneous. The returned slice will not be
// modified.
type UpstreamSource interface {
GetUpstreams(*http.Request) ([]*Upstream, error)
}
// Hop-by-hop headers. These are removed when sent to the backend.
// As of RFC 7230, hop-by-hop headers are required to appear in the
// Connection header field. These are the headers defined by the
// obsoleted RFC 2616 (section 13.5.1) and are used for backward
// compatibility.
var hopHeaders = []string{
"Alt-Svc",
"Connection",
"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
"Keep-Alive",
"Proxy-Authenticate",
"Proxy-Authorization",
"Te", // canonicalized version of "TE"
"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
"Transfer-Encoding",
"Upgrade",
}
// DialError is an error that specifically occurs
// in a call to Dial or DialContext.
type DialError struct{ error }
// TLSTransport is implemented by transports
// that are capable of using TLS.
type TLSTransport interface {
// TLSEnabled returns true if the transport
// has TLS enabled, false otherwise.
TLSEnabled() bool
// EnableTLS enables TLS within the transport
// if it is not already, using the provided
// value as a basis for the TLS config.
EnableTLS(base *TLSConfig) error
}
// roundtripSucceeded is an error type that is returned if the
// roundtrip succeeded, but an error occurred after-the-fact.
type roundtripSucceeded struct{ error }
// bodyReadCloser is a reader that, upon closing, will return
// its buffer to the pool and close the underlying body reader.
type bodyReadCloser struct {
io.Reader
buf *bytes.Buffer
body io.ReadCloser
}
func (brc bodyReadCloser) Close() error {
bufPool.Put(brc.buf)
if brc.body != nil {
return brc.body.Close()
}
return nil
}
// bufPool is used for buffering requests and responses.
var bufPool = sync.Pool{
New: func() any {
return new(bytes.Buffer)
},
}
// handleResponseContext carries some contextual information about the
// current proxy handling.
type handleResponseContext struct {
// handler is the active proxy handler instance, so that
// routes like copy_response may inherit some config
// options and have access to handler methods.
handler *Handler
// response is the actual response received from the proxy
// roundtrip, to potentially be copied if a copy_response
// handler is in the handle_response routes.
response *http.Response
// start is the time just before the proxy roundtrip was
// performed, used for logging.
start time.Time
// logger is the prepared logger which is used to write logs
// with the request, duration, and selected upstream attached.
logger *zap.Logger
// isFinalized is whether the response has been finalized,
// i.e. copied and closed, to make sure that it doesn't
// happen twice.
isFinalized bool
}
// ignoreClientGoneContext is a special context.Context type
// intended for use when doing a RoundTrip where you don't
// want a client disconnection to cancel the request during
// the roundtrip.
// This context clears cancellation, error, and deadline methods,
// but still allows values to pass through from its embedded
// context.
//
// TODO: This can be replaced with context.WithoutCancel once
// the minimum required version of Go is 1.21.
type ignoreClientGoneContext struct {
context.Context
}
func (c ignoreClientGoneContext) Deadline() (deadline time.Time, ok bool) {
return
}
func (c ignoreClientGoneContext) Done() <-chan struct{} {
return nil
}
func (c ignoreClientGoneContext) Err() error {
return nil
}
// proxyHandleResponseContextCtxKey is the context key for the active proxy handler
// so that handle_response routes can inherit some config options
// from the proxy handler.
const proxyHandleResponseContextCtxKey caddy.CtxKey = "reverse_proxy_handle_response_context"
var noUpstreamsAvailable = fmt.Errorf("no upstreams available")
// Interface guards
var (
_ caddy.Provisioner = (*Handler)(nil)
_ caddy.CleanerUpper = (*Handler)(nil)
_ caddyhttp.MiddlewareHandler = (*Handler)(nil)
)