consul/agent/http.go

package agent

import (
	"encoding/json"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/http/pprof"
	"net/url"
	"reflect"
	"regexp"
	"strconv"
	"strings"
	"sync/atomic"
	"time"

	"github.com/NYTimes/gziphandler"
	"github.com/armon/go-metrics"
	"github.com/hashicorp/consul/acl"
	"github.com/hashicorp/consul/agent/cache"
	"github.com/hashicorp/consul/agent/config"
	"github.com/hashicorp/consul/agent/consul"
	"github.com/hashicorp/consul/agent/structs"
	"github.com/hashicorp/consul/agent/uiserver"
	"github.com/hashicorp/consul/api"
	"github.com/hashicorp/consul/lib"
	"github.com/hashicorp/consul/logging"
	"github.com/hashicorp/go-cleanhttp"
	"github.com/mitchellh/mapstructure"
	"github.com/pkg/errors"
)

// MethodNotAllowedError should be returned by a handler when the HTTP method is not allowed.
type MethodNotAllowedError struct {
	Method string
	Allow  []string
}

func (e MethodNotAllowedError) Error() string {
	return fmt.Sprintf("method %s not allowed", e.Method)
}

// BadRequestError should be returned by a handler when parameters or the payload are not valid
type BadRequestError struct {
	Reason string
}

func (e BadRequestError) Error() string {
	return fmt.Sprintf("Bad request: %s", e.Reason)
}

// NotFoundError should be returned by a handler when a resource specified does not exist
type NotFoundError struct {
	Reason string
}

func (e NotFoundError) Error() string {
	return e.Reason
}

// CodeWithPayloadError allow returning non HTTP 200
// Error codes while not returning PlainText payload
type CodeWithPayloadError struct {
	Reason      string
	StatusCode  int
	ContentType string
}

func (e CodeWithPayloadError) Error() string {
	return e.Reason
}

type ForbiddenError struct {
}

func (e ForbiddenError) Error() string {
	return "Access is restricted"
}

// HTTPHandlers provides an HTTP api for an agent.
type HTTPHandlers struct {
	agent           *Agent
	denylist        *Denylist
	configReloaders []ConfigReloader
	h               http.Handler
	metricsProxyCfg atomic.Value
}

// endpoint is a Consul-specific HTTP handler that takes the usual arguments in
// but returns a response object and error, both of which are handled in a
// common manner by Consul's HTTP server.
type endpoint func(resp http.ResponseWriter, req *http.Request) (interface{}, error)

// unboundEndpoint is an endpoint method on a server.
type unboundEndpoint func(s *HTTPHandlers, resp http.ResponseWriter, req *http.Request) (interface{}, error)

// endpoints is a map from URL pattern to unbound endpoint.
var endpoints map[string]unboundEndpoint

// allowedMethods is a map from endpoint prefix to supported HTTP methods.
// An empty slice means an endpoint handles OPTIONS requests and MethodNotFound errors itself.
var allowedMethods map[string][]string = make(map[string][]string)

// registerEndpoint registers a new endpoint, which should be done at package
// init() time.
func registerEndpoint(pattern string, methods []string, fn unboundEndpoint) {
	if endpoints == nil {
		endpoints = make(map[string]unboundEndpoint)
	}
	if endpoints[pattern] != nil || allowedMethods[pattern] != nil {
		panic(fmt.Errorf("Pattern %q is already registered", pattern))
	}

	endpoints[pattern] = fn
	allowedMethods[pattern] = methods
}

// wrappedMux hangs on to the underlying mux for unit tests.
type wrappedMux struct {
	mux     *http.ServeMux
	handler http.Handler
}

// ServeHTTP implements the http.Handler interface.
func (w *wrappedMux) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
	w.handler.ServeHTTP(resp, req)
}

// ReloadConfig updates any internal state when the config is changed at
// runtime.
func (s *HTTPHandlers) ReloadConfig(newCfg *config.RuntimeConfig) error {
	for _, r := range s.configReloaders {
		if err := r(newCfg); err != nil {
			return err
		}
	}
	return nil
}

// handler is used to initialize the Handler. In agent code we only ever call
// this once during agent initialization so it was always intended as a single
// pass init method. However many test rely on it as a cheaper way to get a
// handler to call ServeHTTP against and end up calling it multiple times on a
// single agent instance. Until this method had to manage state that might be
// affected by a reload or otherwise vary over time that was not problematic
// although it was wasteful to redo all this setup work multiple times in one
// test.
//
// Now uiserver and possibly other components need to handle reloadable state
// having test randomly clobber the state with the original config again for
// each call gets confusing fast. So handler will memoize it's response - it's
// allowed to call it multiple times on the same agent, but it will only do the
// work the first time and return the same handler on subsequent calls.
//
// The `enableDebug` argument used in the first call will be effective and a
// later change will not do anything. The same goes for the initial config. For
// example if config is reloaded with UI enabled but it was not originally, the
// http.Handler returned will still have it disabled.
//
// The first call must not be concurrent with any other call. Subsequent calls
// may be concurrent with HTTP requests since no state is modified.
func (s *HTTPHandlers) handler(enableDebug bool) http.Handler {
	// Memoize multiple calls.
	if s.h != nil {
		return s.h
	}

	mux := http.NewServeMux()

	// handleFuncMetrics takes the given pattern and handler and wraps to produce
	// metrics based on the pattern and request.
	handleFuncMetrics := func(pattern string, handler http.HandlerFunc) {
		// Get the parts of the pattern. We omit any initial empty for the
		// leading slash, and put an underscore as a "thing" placeholder if we
		// see a trailing slash, which means the part after is parsed. This lets
		// us distinguish from things like /v1/query and /v1/query/<query id>.
		var parts []string
		for i, part := range strings.Split(pattern, "/") {
			if part == "" {
				if i == 0 {
					continue
				}
				part = "_"
			}
			parts = append(parts, part)
		}

		// Tranform the pattern to a valid label by replacing the '/' by '_'.
		// Omit the leading slash.
		// Distinguish thing like /v1/query from /v1/query/<query_id> by having
		// an extra underscore.
		path_label := strings.Replace(pattern[1:], "/", "_", -1)

		// Register the wrapper.
		wrapper := func(resp http.ResponseWriter, req *http.Request) {
			start := time.Now()
			handler(resp, req)

			labels := []metrics.Label{{Name: "method", Value: req.Method}, {Name: "path", Value: path_label}}
			metrics.MeasureSinceWithLabels([]string{"api", "http"}, start, labels)

			// DEPRECATED Emit pre-1.9 metric as `consul.http...` to maintain backwards compatibility. Enabled by
			// default. Users may set `telemetry { disable_compat_1.9 = true }`
			if !s.agent.config.Telemetry.DisableCompatOneNine {
				key := append([]string{"http", req.Method}, parts...)
				metrics.MeasureSince(key, start)
			}
		}

		var gzipHandler http.Handler
		minSize := gziphandler.DefaultMinSize
		if pattern == "/v1/agent/monitor" {
			minSize = 0
		}
		gzipWrapper, err := gziphandler.GzipHandlerWithOpts(gziphandler.MinSize(minSize))
		if err == nil {
			gzipHandler = gzipWrapper(http.HandlerFunc(wrapper))
		} else {
			gzipHandler = gziphandler.GzipHandler(http.HandlerFunc(wrapper))
		}
		mux.Handle(pattern, gzipHandler)
	}

	// handlePProf takes the given pattern and pprof handler
	// and wraps it to add authorization and metrics
	handlePProf := func(pattern string, handler http.HandlerFunc) {
		wrapper := func(resp http.ResponseWriter, req *http.Request) {
			var token string
			s.parseToken(req, &token)

			rule, err := s.agent.resolveToken(token)
			if err != nil {
				resp.WriteHeader(http.StatusForbidden)
				return
			}

			// If enableDebug is not set, and ACLs are disabled, write
			// an unauthorized response
			if !enableDebug {
				if s.checkACLDisabled(resp, req) {
					return
				}
			}

			// If the token provided does not have the necessary permissions,
			// write a forbidden response
			if rule != nil && rule.OperatorRead(nil) != acl.Allow {
				resp.WriteHeader(http.StatusForbidden)
				return
			}

			// Call the pprof handler
			handler(resp, req)
		}

		handleFuncMetrics(pattern, http.HandlerFunc(wrapper))
	}
	mux.HandleFunc("/", s.Index)
	for pattern, fn := range endpoints {
		thisFn := fn
		methods := allowedMethods[pattern]
		bound := func(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
			return thisFn(s, resp, req)
		}
		handleFuncMetrics(pattern, s.wrap(bound, methods))
	}

	// Register wrapped pprof handlers
	handlePProf("/debug/pprof/", pprof.Index)
	handlePProf("/debug/pprof/cmdline", pprof.Cmdline)
	handlePProf("/debug/pprof/profile", pprof.Profile)
	handlePProf("/debug/pprof/symbol", pprof.Symbol)
	handlePProf("/debug/pprof/trace", pprof.Trace)

	if s.IsUIEnabled() {
		// Note that we _don't_ support reloading ui_config.{enabled, content_dir,
		// content_path} since this only runs at initial startup.
		uiHandler := uiserver.NewHandler(
			s.agent.config,
			s.agent.logger.Named(logging.HTTP),
			s.uiTemplateDataTransform(),
		)
		s.configReloaders = append(s.configReloaders, uiHandler.ReloadConfig)

		// Wrap it to add the headers specified by the http_config.response_headers
		// user config
		uiHandlerWithHeaders := serveHandlerWithHeaders(
			uiHandler,
			s.agent.config.HTTPResponseHeaders,
		)
		mux.Handle(
			"/robots.txt",
			uiHandlerWithHeaders,
		)
		mux.Handle(
			s.agent.config.UIConfig.ContentPath,
			http.StripPrefix(
				s.agent.config.UIConfig.ContentPath,
				uiHandlerWithHeaders,
			),
		)
	}
	// Initialize (reloadable) metrics proxy config
	s.metricsProxyCfg.Store(s.agent.config.UIConfig.MetricsProxy)
	s.configReloaders = append(s.configReloaders, func(cfg *config.RuntimeConfig) error {
		s.metricsProxyCfg.Store(cfg.UIConfig.MetricsProxy)
		return nil
	})

	// Wrap the whole mux with a handler that bans URLs with non-printable
	// characters, unless disabled explicitly to deal with old keys that fail this
	// check.
	h := cleanhttp.PrintablePathCheckHandler(mux, nil)
	if s.agent.config.DisableHTTPUnprintableCharFilter {
		h = mux
	}
	h = s.enterpriseHandler(h)
	s.h = &wrappedMux{
		mux:     mux,
		handler: h,
	}
	return s.h
}

// nodeName returns the node name of the agent
func (s *HTTPHandlers) nodeName() string {
	return s.agent.config.NodeName
}

// aclEndpointRE is used to find old ACL endpoints that take tokens in the URL
// so that we can redact them. The ACL endpoints that take the token in the URL
// are all of the form /v1/acl/<verb>/<token>, and can optionally include query
// parameters which are indicated by a question mark. We capture the part before
// the token, the token, and any query parameters after, and then reassemble as
// $1<hidden>$3 (the token in $2 isn't used), which will give:
//
// /v1/acl/clone/foo           -> /v1/acl/clone/<hidden>
// /v1/acl/clone/foo?token=bar -> /v1/acl/clone/<hidden>?token=<hidden>
//
// The query parameter in the example above is obfuscated like any other, after
// this regular expression is applied, so the regular expression substitution
// results in:
//
// /v1/acl/clone/foo?token=bar -> /v1/acl/clone/<hidden>?token=bar
//                                ^---- $1 ----^^- $2 -^^-- $3 --^
//
// And then the loop that looks for parameters called "token" does the last
// step to get to the final redacted form.
var (
	aclEndpointRE = regexp.MustCompile("^(/v1/acl/(create|update|destroy|info|clone|list)/)([^?]+)([?]?.*)$")
)

// wrap is used to wrap functions to make them more convenient
func (s *HTTPHandlers) wrap(handler endpoint, methods []string) http.HandlerFunc {
	httpLogger := s.agent.logger.Named(logging.HTTP)
	return func(resp http.ResponseWriter, req *http.Request) {
		setHeaders(resp, s.agent.config.HTTPResponseHeaders)
		setTranslateAddr(resp, s.agent.config.TranslateWANAddrs)

		// Obfuscate any tokens from appearing in the logs
		formVals, err := url.ParseQuery(req.URL.RawQuery)
		if err != nil {
			httpLogger.Error("Failed to decode query",
				"from", req.RemoteAddr,
				"error", err,
			)
			resp.WriteHeader(http.StatusInternalServerError)
			return
		}
		logURL := req.URL.String()
		if tokens, ok := formVals["token"]; ok {
			for _, token := range tokens {
				if token == "" {
					logURL += "<hidden>"
					continue
				}
				logURL = strings.Replace(logURL, token, "<hidden>", -1)
			}
		}
		logURL = aclEndpointRE.ReplaceAllString(logURL, "$1<hidden>$4")

		if s.denylist.Block(req.URL.Path) {
			errMsg := "Endpoint is blocked by agent configuration"
			httpLogger.Error("Request error",
				"method", req.Method,
				"url", logURL,
				"from", req.RemoteAddr,
				"error", errMsg,
			)
			resp.WriteHeader(http.StatusForbidden)
			fmt.Fprint(resp, errMsg)
			return
		}

		isForbidden := func(err error) bool {
			if acl.IsErrPermissionDenied(err) || acl.IsErrNotFound(err) {
				return true
			}
			_, ok := err.(ForbiddenError)
			return ok
		}

		isMethodNotAllowed := func(err error) bool {
			_, ok := err.(MethodNotAllowedError)
			return ok
		}

		isBadRequest := func(err error) bool {
			_, ok := err.(BadRequestError)
			return ok
		}

		isNotFound := func(err error) bool {
			_, ok := err.(NotFoundError)
			return ok
		}

		isTooManyRequests := func(err error) bool {
			// Sadness net/rpc can't do nice typed errors so this is all we got
			return err.Error() == consul.ErrRateLimited.Error()
		}

		addAllowHeader := func(methods []string) {
			resp.Header().Add("Allow", strings.Join(methods, ","))
		}

		handleErr := func(err error) {
			httpLogger.Error("Request error",
				"method", req.Method,
				"url", logURL,
				"from", req.RemoteAddr,
				"error", err,
			)
			switch {
			case isForbidden(err):
				resp.WriteHeader(http.StatusForbidden)
				fmt.Fprint(resp, err.Error())
			case structs.IsErrRPCRateExceeded(err):
				resp.WriteHeader(http.StatusTooManyRequests)
			case isMethodNotAllowed(err):
				// RFC2616 states that for 405 Method Not Allowed the response
				// MUST include an Allow header containing the list of valid
				// methods for the requested resource.
				// https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
				addAllowHeader(err.(MethodNotAllowedError).Allow)
				resp.WriteHeader(http.StatusMethodNotAllowed) // 405
				fmt.Fprint(resp, err.Error())
			case isBadRequest(err):
				resp.WriteHeader(http.StatusBadRequest)
				fmt.Fprint(resp, err.Error())
			case isNotFound(err):
				resp.WriteHeader(http.StatusNotFound)
				fmt.Fprint(resp, err.Error())
			case isTooManyRequests(err):
				resp.WriteHeader(http.StatusTooManyRequests)
				fmt.Fprint(resp, err.Error())
			default:
				resp.WriteHeader(http.StatusInternalServerError)
				fmt.Fprint(resp, err.Error())
			}
		}

		start := time.Now()
		defer func() {
			httpLogger.Debug("Request finished",
				"method", req.Method,
				"url", logURL,
				"from", req.RemoteAddr,
				"latency", time.Since(start).String(),
			)
		}()

		var obj interface{}

		// if this endpoint has declared methods, respond appropriately to OPTIONS requests. Otherwise let the endpoint handle that.
		if req.Method == "OPTIONS" && len(methods) > 0 {
			addAllowHeader(append([]string{"OPTIONS"}, methods...))
			return
		}

		// if this endpoint has declared methods, check the request method. Otherwise let the endpoint handle that.
		methodFound := len(methods) == 0
		for _, method := range methods {
			if method == req.Method {
				methodFound = true
				break
			}
		}

		if !methodFound {
			err = MethodNotAllowedError{req.Method, append([]string{"OPTIONS"}, methods...)}
		} else {
			err = s.checkWriteAccess(req)

			if err == nil {
				// Invoke the handler
				obj, err = handler(resp, req)
			}
		}
		contentType := "application/json"
		httpCode := http.StatusOK
		if err != nil {
			if errPayload, ok := err.(CodeWithPayloadError); ok {
				httpCode = errPayload.StatusCode
				if errPayload.ContentType != "" {
					contentType = errPayload.ContentType
				}
				if errPayload.Reason != "" {
					resp.Header().Add("X-Consul-Reason", errPayload.Reason)
				}
			} else {
				handleErr(err)
				return
			}
		}
		if obj == nil {
			return
		}
		var buf []byte
		if contentType == "application/json" {
			buf, err = s.marshalJSON(req, obj)
			if err != nil {
				handleErr(err)
				return
			}
		} else {
			if strings.HasPrefix(contentType, "text/") {
				if val, ok := obj.(string); ok {
					buf = []byte(val)
				}
			}
		}
		resp.Header().Set("Content-Type", contentType)
		resp.WriteHeader(httpCode)
		resp.Write(buf)
	}
}

// marshalJSON marshals the object into JSON, respecting the user's pretty-ness
// configuration.
func (s *HTTPHandlers) marshalJSON(req *http.Request, obj interface{}) ([]byte, error) {
	if _, ok := req.URL.Query()["pretty"]; ok || s.agent.config.DevMode {
		buf, err := json.MarshalIndent(obj, "", "    ")
		if err != nil {
			return nil, err
		}
		buf = append(buf, "\n"...)
		return buf, nil
	}

	buf, err := json.Marshal(obj)
	if err != nil {
		return nil, err
	}
	return buf, nil
}

// Returns true if the UI is enabled.
func (s *HTTPHandlers) IsUIEnabled() bool {
	// Note that we _don't_ support reloading ui_config.{enabled,content_dir}
	// since this only runs at initial startup.
	return s.agent.config.UIConfig.Dir != "" || s.agent.config.UIConfig.Enabled
}

// Renders a simple index page
func (s *HTTPHandlers) Index(resp http.ResponseWriter, req *http.Request) {
	// Send special headers too since this endpoint isn't wrapped with something
	// that sends them.
	setHeaders(resp, s.agent.config.HTTPResponseHeaders)

	// Check if this is a non-index path
	if req.URL.Path != "/" {
		resp.WriteHeader(http.StatusNotFound)
		return
	}

	// Give them something helpful if there's no UI so they at least know
	// what this server is.
	if !s.IsUIEnabled() {
		fmt.Fprint(resp, "Consul Agent")
		return
	}

	// Redirect to the UI endpoint
	http.Redirect(
		resp,
		req,
		s.agent.config.UIConfig.ContentPath,
		http.StatusMovedPermanently,
	) // 301
}

func decodeBody(body io.Reader, out interface{}) error {
	return lib.DecodeJSON(body, out)
}

// decodeBodyDeprecated is deprecated, please ues decodeBody above.
// decodeBodyDeprecated is used to decode a JSON request body
func decodeBodyDeprecated(req *http.Request, out interface{}, cb func(interface{}) error) error {
	// This generally only happens in tests since real HTTP requests set
	// a non-nil body with no content. We guard against it anyways to prevent
	// a panic. The EOF response is the same behavior as an empty reader.
	if req.Body == nil {
		return io.EOF
	}

	var raw interface{}
	dec := json.NewDecoder(req.Body)
	if err := dec.Decode(&raw); err != nil {
		return err
	}

	// Invoke the callback prior to decode
	if cb != nil {
		if err := cb(raw); err != nil {
			return err
		}
	}

	decodeConf := &mapstructure.DecoderConfig{
		DecodeHook: mapstructure.ComposeDecodeHookFunc(
			mapstructure.StringToTimeDurationHookFunc(),
			mapstructure.StringToTimeHookFunc(time.RFC3339),
			stringToReadableDurationFunc(),
		),
		Result: &out,
	}

	decoder, err := mapstructure.NewDecoder(decodeConf)
	if err != nil {
		return err
	}

	return decoder.Decode(raw)
}

// stringToReadableDurationFunc is a mapstructure hook for decoding a string
// into an api.ReadableDuration for backwards compatibility.
func stringToReadableDurationFunc() mapstructure.DecodeHookFunc {
	return func(
		f reflect.Type,
		t reflect.Type,
		data interface{}) (interface{}, error) {
		var v api.ReadableDuration
		if t != reflect.TypeOf(v) {
			return data, nil
		}

		switch {
		case f.Kind() == reflect.String:
			if dur, err := time.ParseDuration(data.(string)); err != nil {
				return nil, err
			} else {
				v = api.ReadableDuration(dur)
			}
			return v, nil
		default:
			return data, nil
		}
	}
}

// setTranslateAddr is used to set the address translation header. This is only
// present if the feature is active.
func setTranslateAddr(resp http.ResponseWriter, active bool) {
	if active {
		resp.Header().Set("X-Consul-Translate-Addresses", "true")
	}
}

// setIndex is used to set the index response header
func setIndex(resp http.ResponseWriter, index uint64) {
	// If we ever return X-Consul-Index of 0 blocking clients will go into a busy
	// loop and hammer us since ?index=0 will never block. It's always safe to
	// return index=1 since the very first Raft write is always an internal one
	// writing the raft config for the cluster so no user-facing blocking query
	// will ever legitimately have an X-Consul-Index of 1.
	if index == 0 {
		index = 1
	}
	resp.Header().Set("X-Consul-Index", strconv.FormatUint(index, 10))
}

// setKnownLeader is used to set the known leader header
func setKnownLeader(resp http.ResponseWriter, known bool) {
	s := "true"
	if !known {
		s = "false"
	}
	resp.Header().Set("X-Consul-KnownLeader", s)
}

func setConsistency(resp http.ResponseWriter, consistency string) {
	if consistency != "" {
		resp.Header().Set("X-Consul-Effective-Consistency", consistency)
	}
}

// setLastContact is used to set the last contact header
func setLastContact(resp http.ResponseWriter, last time.Duration) {
	if last < 0 {
		last = 0
	}
	lastMsec := uint64(last / time.Millisecond)
	resp.Header().Set("X-Consul-LastContact", strconv.FormatUint(lastMsec, 10))
}

// setMeta is used to set the query response meta data
func setMeta(resp http.ResponseWriter, m structs.QueryMetaCompat) {
	setIndex(resp, m.GetIndex())
	setLastContact(resp, m.GetLastContact())
	setKnownLeader(resp, m.GetKnownLeader())
	setConsistency(resp, m.GetConsistencyLevel())
}

// setCacheMeta sets http response headers to indicate cache status.
func setCacheMeta(resp http.ResponseWriter, m *cache.ResultMeta) {
	if m == nil {
		return
	}
	str := "MISS"
	if m.Hit {
		str = "HIT"
	}
	resp.Header().Set("X-Cache", str)
	if m.Hit {
		resp.Header().Set("Age", fmt.Sprintf("%.0f", m.Age.Seconds()))
	}
}

// setHeaders is used to set canonical response header fields
func setHeaders(resp http.ResponseWriter, headers map[string]string) {
	for field, value := range headers {
		resp.Header().Set(http.CanonicalHeaderKey(field), value)
	}
}

// serveHandlerWithHeaders is used to serve a http.Handler with the specified headers
func serveHandlerWithHeaders(h http.Handler, headers map[string]string) http.HandlerFunc {
	return func(resp http.ResponseWriter, req *http.Request) {
		setHeaders(resp, headers)
		h.ServeHTTP(resp, req)
	}
}

// parseWait is used to parse the ?wait and ?index query params
// Returns true on error
func parseWait(resp http.ResponseWriter, req *http.Request, b structs.QueryOptionsCompat) bool {
	query := req.URL.Query()
	if wait := query.Get("wait"); wait != "" {
		dur, err := time.ParseDuration(wait)
		if err != nil {
			resp.WriteHeader(http.StatusBadRequest)
			fmt.Fprint(resp, "Invalid wait time")
			return true
		}
		b.SetMaxQueryTime(dur)
	}
	if idx := query.Get("index"); idx != "" {
		index, err := strconv.ParseUint(idx, 10, 64)
		if err != nil {
			resp.WriteHeader(http.StatusBadRequest)
			fmt.Fprint(resp, "Invalid index")
			return true
		}
		b.SetMinQueryIndex(index)
	}
	return false
}

// parseCacheControl parses the CacheControl HTTP header value. So far we only
// support maxage directive.
func parseCacheControl(resp http.ResponseWriter, req *http.Request, b structs.QueryOptionsCompat) bool {
	raw := strings.ToLower(req.Header.Get("Cache-Control"))

	if raw == "" {
		return false
	}

	// Didn't want to import a full parser for this. While quoted strings are
	// allowed in some directives, max-age does not allow them per
	// https://tools.ietf.org/html/rfc7234#section-5.2.2.8 so we assume all
	// well-behaved clients use the exact token form of max-age=<delta-seconds>
	// where delta-seconds is a non-negative decimal integer.
	directives := strings.Split(raw, ",")

	parseDurationOrFail := func(raw string) (time.Duration, bool) {
		i, err := strconv.Atoi(raw)
		if err != nil {
			resp.WriteHeader(http.StatusBadRequest)
			fmt.Fprint(resp, "Invalid Cache-Control header.")
			return 0, true
		}
		return time.Duration(i) * time.Second, false
	}

	for _, d := range directives {
		d = strings.ToLower(strings.TrimSpace(d))

		if d == "must-revalidate" {
			b.SetMustRevalidate(true)
		}

		if strings.HasPrefix(d, "max-age=") {
			d, failed := parseDurationOrFail(d[8:])
			if failed {
				return true
			}
			b.SetMaxAge(d)
			if d == 0 {
				// max-age=0 specifically means that we need to consider the cache stale
				// immediately however MaxAge = 0 is indistinguishable from the default
				// where MaxAge is unset.
				b.SetMustRevalidate(true)
			}
		}
		if strings.HasPrefix(d, "stale-if-error=") {
			d, failed := parseDurationOrFail(d[15:])
			if failed {
				return true
			}
			b.SetStaleIfError(d)
		}
	}

	return false
}

// parseConsistency is used to parse the ?stale and ?consistent query params.
// Returns true on error
func (s *HTTPHandlers) parseConsistency(resp http.ResponseWriter, req *http.Request, b structs.QueryOptionsCompat) bool {
	query := req.URL.Query()
	defaults := true
	if _, ok := query["stale"]; ok {
		b.SetAllowStale(true)
		defaults = false
	}
	if _, ok := query["consistent"]; ok {
		b.SetRequireConsistent(true)
		defaults = false
	}
	if _, ok := query["leader"]; ok {
		defaults = false
	}
	if _, ok := query["cached"]; ok {
		b.SetUseCache(true)
		defaults = false
	}
	if maxStale := query.Get("max_stale"); maxStale != "" {
		dur, err := time.ParseDuration(maxStale)
		if err != nil {
			resp.WriteHeader(http.StatusBadRequest)
			fmt.Fprintf(resp, "Invalid max_stale value %q", maxStale)
			return true
		}
		b.SetMaxStaleDuration(dur)
		if dur.Nanoseconds() > 0 {
			b.SetAllowStale(true)
			defaults = false
		}
	}
	// No specific Consistency has been specified by caller
	if defaults {
		path := req.URL.Path
		if strings.HasPrefix(path, "/v1/catalog") || strings.HasPrefix(path, "/v1/health") {
			if s.agent.config.DiscoveryMaxStale.Nanoseconds() > 0 {
				b.SetMaxStaleDuration(s.agent.config.DiscoveryMaxStale)
				b.SetAllowStale(true)
			}
		}
	}
	if b.GetAllowStale() && b.GetRequireConsistent() {
		resp.WriteHeader(http.StatusBadRequest)
		fmt.Fprint(resp, "Cannot specify ?stale with ?consistent, conflicting semantics.")
		return true
	}
	if b.GetUseCache() && b.GetRequireConsistent() {
		resp.WriteHeader(http.StatusBadRequest)
		fmt.Fprint(resp, "Cannot specify ?cached with ?consistent, conflicting semantics.")
		return true
	}
	return false
}

// parseDC is used to parse the ?dc query param
func (s *HTTPHandlers) parseDC(req *http.Request, dc *string) {
	if other := req.URL.Query().Get("dc"); other != "" {
		*dc = other
	} else if *dc == "" {
		*dc = s.agent.config.Datacenter
	}
}

// parseTokenInternal is used to parse the ?token query param or the X-Consul-Token header or
// Authorization Bearer token (RFC6750).
func (s *HTTPHandlers) parseTokenInternal(req *http.Request, token *string) {
	tok := ""
	if other := req.URL.Query().Get("token"); other != "" {
		tok = other
	} else if other := req.Header.Get("X-Consul-Token"); other != "" {
		tok = other
	} else if other := req.Header.Get("Authorization"); other != "" {
		// HTTP Authorization headers are in the format: <Scheme>[SPACE]<Value>
		// Ref. https://tools.ietf.org/html/rfc7236#section-3
		parts := strings.Split(other, " ")

		// Authorization Header is invalid if containing 1 or 0 parts, e.g.:
		// "" || "<Scheme><Value>" || "<Scheme>" || "<Value>"
		if len(parts) > 1 {
			scheme := parts[0]
			// Everything after "<Scheme>" is "<Value>", trimmed
			value := strings.TrimSpace(strings.Join(parts[1:], " "))

			// <Scheme> must be "Bearer"
			if strings.ToLower(scheme) == "bearer" {
				// Since Bearer tokens shouldn't contain spaces (rfc6750#section-2.1)
				// "value" is tokenized, only the first item is used
				tok = strings.TrimSpace(strings.Split(value, " ")[0])
			}
		}
	}

	*token = tok
	return
}

// parseTokenWithDefault passes through to parseTokenInternal and optionally resolves proxy tokens to real ACL tokens.
// If the token is invalid or not specified it will populate the token with the agents UserToken (acl_token in the
// consul configuration)
func (s *HTTPHandlers) parseTokenWithDefault(req *http.Request, token *string) {
	s.parseTokenInternal(req, token) // parseTokenInternal modifies *token
	if token != nil && *token == "" {
		*token = s.agent.tokens.UserToken()
		return
	}
	return
}

// parseToken is used to parse the ?token query param or the X-Consul-Token header or
// Authorization Bearer token header (RFC6750). This function is used widely in Consul's endpoints
func (s *HTTPHandlers) parseToken(req *http.Request, token *string) {
	s.parseTokenWithDefault(req, token)
}

func sourceAddrFromRequest(req *http.Request) string {
	xff := req.Header.Get("X-Forwarded-For")
	forwardHosts := strings.Split(xff, ",")
	if len(forwardHosts) > 0 {
		forwardIp := net.ParseIP(strings.TrimSpace(forwardHosts[0]))
		if forwardIp != nil {
			return forwardIp.String()
		}
	}

	host, _, err := net.SplitHostPort(req.RemoteAddr)
	if err != nil {
		return ""
	}

	ip := net.ParseIP(host)
	if ip != nil {
		return ip.String()
	} else {
		return ""
	}
}

// parseSource is used to parse the ?near=<node> query parameter, used for
// sorting by RTT based on a source node. We set the source's DC to the target
// DC in the request, if given, or else the agent's DC.
func (s *HTTPHandlers) parseSource(req *http.Request, source *structs.QuerySource) {
	s.parseDC(req, &source.Datacenter)
	source.Ip = sourceAddrFromRequest(req)
	if node := req.URL.Query().Get("near"); node != "" {
		if node == "_agent" {
			source.Node = s.agent.config.NodeName
		} else {
			source.Node = node
		}
	}
}

// parseMetaFilter is used to parse the ?node-meta=key:value query parameter, used for
// filtering results to nodes with the given metadata key/value
func (s *HTTPHandlers) parseMetaFilter(req *http.Request) map[string]string {
	if filterList, ok := req.URL.Query()["node-meta"]; ok {
		filters := make(map[string]string)
		for _, filter := range filterList {
			key, value := parseMetaPair(filter)
			filters[key] = value
		}
		return filters
	}
	return nil
}

func parseMetaPair(raw string) (string, string) {
	pair := strings.SplitN(raw, ":", 2)
	if len(pair) == 2 {
		return pair[0], pair[1]
	}
	return pair[0], ""
}

// parseInternal is a convenience method for endpoints that need
// to use both parseWait and parseDC.
func (s *HTTPHandlers) parseInternal(resp http.ResponseWriter, req *http.Request, dc *string, b structs.QueryOptionsCompat) bool {
	s.parseDC(req, dc)
	var token string
	s.parseTokenWithDefault(req, &token)
	b.SetToken(token)
	var filter string
	s.parseFilter(req, &filter)
	b.SetFilter(filter)
	if s.parseConsistency(resp, req, b) {
		return true
	}
	if parseCacheControl(resp, req, b) {
		return true
	}
	return parseWait(resp, req, b)
}

// parse is a convenience method for endpoints that need
// to use both parseWait and parseDC.
func (s *HTTPHandlers) parse(resp http.ResponseWriter, req *http.Request, dc *string, b structs.QueryOptionsCompat) bool {
	return s.parseInternal(resp, req, dc, b)
}

func (s *HTTPHandlers) checkWriteAccess(req *http.Request) error {
	if req.Method == http.MethodGet || req.Method == http.MethodHead || req.Method == http.MethodOptions {
		return nil
	}

	allowed := s.agent.config.AllowWriteHTTPFrom
	if len(allowed) == 0 {
		return nil
	}

	ipStr, _, err := net.SplitHostPort(req.RemoteAddr)
	if err != nil {
		return errors.Wrap(err, "unable to parse remote addr")
	}

	ip := net.ParseIP(ipStr)

	for _, n := range allowed {
		if n.Contains(ip) {
			return nil
		}
	}

	return ForbiddenError{}
}

func (s *HTTPHandlers) parseFilter(req *http.Request, filter *string) {
	if other := req.URL.Query().Get("filter"); other != "" {
		*filter = other
	}
}