// 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" "crypto/rand" "encoding/base64" "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" "go.uber.org/zap/zapcore" "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. // `{http.reverse_proxy.retries}` | The number of retries actually performed to communicate with an upstream. 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. 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"` // 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"` // If set, the proxy will write very detailed logs about its // inner workings. Enable this only when debugging, as it // will produce a lot of output. // // EXPERIMENTAL: This feature is subject to change or removal. VerboseLogs bool `json:"verbose_logs,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) // 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)) } // websocket over http2, assuming backend doesn't support this, the request will be modified to http1.1 upgrade // TODO: once we can reliably detect backend support this, it can be removed for those backends if r.ProtoMajor == 2 && r.Method == http.MethodConnect && r.Header.Get(":protocol") != "" { clonedReq.Header.Del(":protocol") // keep the body for later use. http1.1 upgrade uses http.NoBody caddyhttp.SetVar(clonedReq.Context(), "h2_websocket_body", clonedReq.Body) clonedReq.Body = http.NoBody clonedReq.Method = http.MethodGet clonedReq.Header.Set("Upgrade", r.Header.Get(":protocol")) clonedReq.Header.Set("Connection", "Upgrade") key := make([]byte, 16) _, randErr := rand.Read(key) if randErr != nil { return randErr } clonedReq.Header["Sec-WebSocket-Key"] = []string{base64.StdEncoding.EncodeToString(key)} } // 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 { // if the request body was buffered (and only the entire body, hence no body // set to read from after the buffer), make reading from the body idempotent // and reusable, so if a backend partially or fully reads the body but then // produces an error, the request can be repeated to the next backend with // the full body (retries should only happen for idempotent requests) (see #6259) if reqBodyBuf, ok := r.Body.(bodyReadCloser); ok && reqBodyBuf.body == nil { r.Body = io.NopCloser(bytes.NewReader(reqBodyBuf.buf.Bytes())) } var done bool done, proxyErr = h.proxyLoopIteration(clonedReq, r, w, proxyErr, start, retries, repl, reqHeader, reqHost, next) if done { break } if h.VerboseLogs { var lbWait time.Duration if h.LoadBalancing != nil { lbWait = time.Duration(h.LoadBalancing.TryInterval) } if c := h.logger.Check(zapcore.DebugLevel, "retrying"); c != nil { c.Write(zap.Error(proxyErr), zap.Duration("after", lbWait)) } } retries++ } // number of retries actually performed repl.Set("http.reverse_proxy.retries", 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 { if c := h.logger.Check(zapcore.ErrorLevel, "failed getting dynamic upstreams; falling back to static upstreams"); c != nil { c.Write(zap.Error(err)) } } else { upstreams = dUpstreams for _, dUp := range dUpstreams { h.provisionUpstream(dUp) } if c := h.logger.Check(zapcore.DebugLevel, "provisioned dynamic upstreams"); c != nil { c.Write(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, errNoUpstream) } if !h.LoadBalancing.tryAgain(h.ctx, start, retries, proxyErr, r, h.logger) { 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) } if c := h.logger.Check(zapcore.DebugLevel, "selected upstream"); c != nil { c.Write( 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.(roundtripSucceededError); 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, h.logger) { return true, proxyErr } return false, proxyErr } // Mapping of the canonical form of the headers, to the RFC 6455 form, // i.e. `WebSocket` with uppercase 'S'. var websocketHeaderMapping = map[string]string{ "Sec-Websocket-Accept": "Sec-WebSocket-Accept", "Sec-Websocket-Extensions": "Sec-WebSocket-Extensions", "Sec-Websocket-Key": "Sec-WebSocket-Key", "Sec-Websocket-Protocol": "Sec-WebSocket-Protocol", "Sec-Websocket-Version": "Sec-WebSocket-Version", } // normalizeWebsocketHeaders ensures we use the standard casing as per // RFC 6455, i.e. `WebSocket` with uppercase 'S'. Most servers don't // care about this difference (read headers case insensitively), but // some do, so this maximizes compatibility with upstreams. // See https://github.com/caddyserver/caddy/pull/6621 func normalizeWebsocketHeaders(header http.Header) { for k, rk := range websocketHeaderMapping { if v, ok := header[k]; ok { delete(header, k) header[rk] = v } } } // 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 { var readBytes int64 req.Body, readBytes = h.bufferedBody(req.Body, h.RequestBuffers) if h.RequestBuffers == -1 { req.ContentLength = readBytes 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", "") } // Indicate if request has been conveyed in early data. // RFC 8470: "An intermediary that forwards a request prior to the // completion of the TLS handshake with its client MUST send it with // the Early-Data header field set to “1” (i.e., it adds it if not // present in the request). An intermediary MUST use the Early-Data // header field if the request might have been subject to a replay and // might already have been forwarded by it or another instance // (see Section 6.2)." if req.TLS != nil && !req.TLS.HandshakeComplete { req.Header.Set("Early-Data", "1") } 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) normalizeWebsocketHeaders(req.Header) } // 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 var ( roundTripMutex sync.Mutex roundTripDone bool ) trace := &httptrace.ClientTrace{ Got1xxResponse: func(code int, header textproto.MIMEHeader) error { roundTripMutex.Lock() defer roundTripMutex.Unlock() if roundTripDone { // If RoundTrip has returned, don't try to further modify // the ResponseWriter's header map. return nil } 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) clear(h) return nil }, } req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace)) // do the round-trip start := time.Now() res, err := h.Transport.RoundTrip(req) duration := time.Since(start) // record that the round trip is done for the 1xx response handler roundTripMutex.Lock() roundTripDone = true roundTripMutex.Unlock() // emit debug log with values we know are safe, // or if there is no error, emit fuller log entry 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 { if c := logger.Check(zapcore.DebugLevel, "upstream roundtrip"); c != nil { c.Write(zap.Error(err)) } return err } if c := logger.Check(zapcore.DebugLevel, "upstream roundtrip"); c != nil { c.Write( 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) if c := logger.Check(zapcore.DebugLevel, "handling response"); c != nil { c.Write(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 roundtripSucceededError so caller knows that // the roundtrip was successful and to not retry if routeErr != nil { return roundtripSucceededError{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 { var wg sync.WaitGroup h.handleUpgradeResponse(logger, &wg, rw, req, res) wg.Wait() 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) if h.VerboseLogs { logger.Debug("wrote header") } err := h.copyResponse(rw, res.Body, h.flushInterval(req, res), logger) errClose := res.Body.Close() // close now, instead of defer, to populate res.Trailer if h.VerboseLogs || errClose != nil { if c := logger.Check(zapcore.DebugLevel, "closed response body from upstream"); c != nil { c.Write(zap.Error(errClose)) } } 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; // we'll just log the error and abort the stream here and panic just as // the standard lib's proxy to propagate the stream error. // see issue https://github.com/caddyserver/caddy/issues/5951 if c := logger.Check(zapcore.WarnLevel, "aborting with incomplete response"); c != nil { c.Write(zap.Error(err)) } // no extra logging from stdlib panic(http.ErrAbortHandler) } 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) } } if h.VerboseLogs { logger.Debug("response finalized") } 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, logger *zap.Logger) 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, errNoUpstream)) { if lb.RetryMatch == nil && req.Method != "GET" { // by default, don't retry requests if they aren't GET return false } match, err := lb.RetryMatch.AnyMatchWithError(req) if err != nil { logger.Error("error matching request for retry", zap.Error(err)) return false } if !match { 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 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 && err != io.EOF) || 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 } // roundtripSucceededError is an error type that is returned if the // roundtrip succeeded, but an error occurred after-the-fact. type roundtripSucceededError 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 } // 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" // errNoUpstream occurs when there are no upstream available. var errNoUpstream = fmt.Errorf("no upstreams available") // Interface guards var ( _ caddy.Provisioner = (*Handler)(nil) _ caddy.CleanerUpper = (*Handler)(nil) _ caddyhttp.MiddlewareHandler = (*Handler)(nil) )