Added CORS Origin flag (#5011)

Signed-off-by: Hrishikesh Barman <hrishikeshbman@gmail.com>

cmd/prometheus/main.go

@@ -26,6 +26,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"strings"
 	"sync"
@@ -50,6 +51,7 @@ import (
 	"github.com/prometheus/prometheus/discovery"
 	sd_config "github.com/prometheus/prometheus/discovery/config"
 	"github.com/prometheus/prometheus/notifier"
+	"github.com/prometheus/prometheus/pkg/relabel"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/rules"
 	"github.com/prometheus/prometheus/scrape"
@@ -100,6 +102,7 @@ func main() {
 		RemoteFlushDeadline model.Duration
 
 		prometheusURL   string
+		corsRegexString string
 
 		promlogConfig promlog.Config
 	}{
@@ -209,6 +212,9 @@ func main() {
 	a.Flag("query.max-samples", "Maximum number of samples a single query can load into memory. Note that queries will fail if they would load more samples than this into memory, so this also limits the number of samples a query can return.").
 		Default("50000000").IntVar(&cfg.queryMaxSamples)
 
+	a.Flag("web.cors.origin", `Regex for CORS origin. It is fully anchored. Eg. 'https?://(domain1|domain2)\.com'`).
+		Default(".*").StringVar(&cfg.corsRegexString)
+
 	promlogflag.AddFlags(a, &cfg.promlogConfig)
 
 	_, err := a.Parse(os.Args[1:])
@@ -224,6 +230,12 @@ func main() {
 		os.Exit(2)
 	}
 
+	cfg.web.CORSOrigin, err = compileCORSRegexString(cfg.corsRegexString)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, errors.Wrapf(err, "could not compile CORS regex string %q", cfg.corsRegexString))
+		os.Exit(2)
+	}
+
 	cfg.web.ReadTimeout = time.Duration(cfg.webTimeout)
 	// Default -web.route-prefix to path of -web.external-url.
 	if cfg.web.RoutePrefix == "" {
@@ -674,6 +686,15 @@ func startsOrEndsWithQuote(s string) bool {
 		strings.HasSuffix(s, "\"") || strings.HasSuffix(s, "'")
 }
 
+// compileCORSRegexString compiles given string and adds anchors
+func compileCORSRegexString(s string) (*regexp.Regexp, error) {
+	r, err := relabel.NewRegexp(s)
+	if err != nil {
+		return nil, err
+	}
+	return r.Regexp, nil
+}
+
 // computeExternalURL computes a sanitized external URL from a raw input. It infers unset
 // URL parts from the OS and the given listen address.
 func computeExternalURL(u, listenAddr string) (*url.URL, error) {

util/httputil/cors.go

@@ -0,0 +1,47 @@
+// Copyright 2013 The Prometheus 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 httputil
+
+import (
+	"net/http"
+	"regexp"
+)
+
+var corsHeaders = map[string]string{
+	"Access-Control-Allow-Headers":  "Accept, Authorization, Content-Type, Origin",
+	"Access-Control-Allow-Methods":  "GET, POST, OPTIONS",
+	"Access-Control-Expose-Headers": "Date",
+	"Vary":                          "Origin",
+}
+
+// Enables cross-site script calls.
+func SetCORS(w http.ResponseWriter, o *regexp.Regexp, r *http.Request) {
+	origin := r.Header.Get("Origin")
+	if origin == "" {
+		return
+	}
+
+	for k, v := range corsHeaders {
+		w.Header().Set(k, v)
+	}
+
+	if o.String() == ".*" {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		return
+	}
+
+	if o.MatchString(origin) {
+		w.Header().Set("Access-Control-Allow-Origin", origin)
+	}
+}

util/httputil/cors_test.go

@@ -0,0 +1,80 @@
+// Copyright 2016 The Prometheus 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 httputil
+
+import (
+	"net/http"
+	"regexp"
+	"testing"
+)
+
+func getCORSHandlerFunc() http.Handler {
+	hf := func(w http.ResponseWriter, r *http.Request) {
+		reg := regexp.MustCompile(`^https://foo\.com$`)
+		SetCORS(w, reg, r)
+		w.WriteHeader(http.StatusOK)
+	}
+	return http.HandlerFunc(hf)
+}
+
+func TestCORSHandler(t *testing.T) {
+	tearDown := setup()
+	defer tearDown()
+	client := &http.Client{}
+
+	ch := getCORSHandlerFunc()
+	mux.Handle("/any_path", ch)
+
+	dummyOrigin := "https://foo.com"
+
+	// OPTIONS with legit origin
+	req, err := http.NewRequest("OPTIONS", server.URL+"/any_path", nil)
+
+	if err != nil {
+		t.Error("could not create request")
+	}
+
+	req.Header.Set("Origin", dummyOrigin)
+	resp, err := client.Do(req)
+
+	if err != nil {
+		t.Error("client get failed with unexpected error")
+	}
+
+	AccessControlAllowOrigin := resp.Header.Get("Access-Control-Allow-Origin")
+
+	if AccessControlAllowOrigin != dummyOrigin {
+		t.Fatalf("%q does not match %q", dummyOrigin, AccessControlAllowOrigin)
+	}
+
+	// OPTIONS with bad origin
+	req, err = http.NewRequest("OPTIONS", server.URL+"/any_path", nil)
+
+	if err != nil {
+		t.Error("could not create request")
+	}
+
+	req.Header.Set("Origin", "https://not-foo.com")
+	resp, err = client.Do(req)
+
+	if err != nil {
+		t.Error("client get failed with unexpected error")
+	}
+
+	AccessControlAllowOrigin = resp.Header.Get("Access-Control-Allow-Origin")
+
+	if AccessControlAllowOrigin != "" {
+		t.Fatalf("Access-Control-Allow-Origin should not exist but it was set to: %q", AccessControlAllowOrigin)
+	}
+}

web/api/v1/api.go

@@ -23,6 +23,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"regexp"
 	"sort"
 	"strconv"
 	"time"
@@ -76,13 +77,6 @@ const (
 	errorNotFound    errorType = "not_found"
 )
 
-var corsHeaders = map[string]string{
-	"Access-Control-Allow-Headers":  "Accept, Authorization, Content-Type, Origin",
-	"Access-Control-Allow-Methods":  "GET, OPTIONS",
-	"Access-Control-Allow-Origin":   "*",
-	"Access-Control-Expose-Headers": "Date",
-}
-
 var remoteReadQueries = prometheus.NewGauge(prometheus.GaugeOpts{
 	Namespace: namespace,
 	Subsystem: subsystem,
@@ -129,13 +123,6 @@ type apiFuncResult struct {
 	finalizer func()
 }
 
-// Enables cross-site script calls.
-func setCORS(w http.ResponseWriter) {
-	for h, v := range corsHeaders {
-		w.Header().Set(h, v)
-	}
-}
-
 type apiFunc func(r *http.Request) apiFuncResult
 
 // TSDBAdmin defines the tsdb interfaces used by the v1 API for admin operations.
@@ -165,6 +152,7 @@ type API struct {
 	logger                log.Logger
 	remoteReadSampleLimit int
 	remoteReadGate        *gate.Gate
+	CORSOrigin            *regexp.Regexp
 }
 
 func init() {
@@ -187,6 +175,7 @@ func NewAPI(
 	rr rulesRetriever,
 	remoteReadSampleLimit int,
 	remoteReadConcurrencyLimit int,
+	CORSOrigin *regexp.Regexp,
 ) *API {
 	return &API{
 		QueryEngine:           qe,
@@ -204,6 +193,7 @@ func NewAPI(
 		remoteReadSampleLimit: remoteReadSampleLimit,
 		remoteReadGate:        gate.New(remoteReadConcurrencyLimit),
 		logger:                logger,
+		CORSOrigin:            CORSOrigin,
 	}
 }
 
@@ -211,7 +201,7 @@ func NewAPI(
 func (api *API) Register(r *route.Router) {
 	wrap := func(f apiFunc) http.HandlerFunc {
 		hf := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			setCORS(w)
+			httputil.SetCORS(w, api.CORSOrigin, r)
 			result := f(r)
 			if result.err != nil {
 				api.respondError(w, result.err, result.data)

web/api/v1/api_test.go

@@ -1416,12 +1416,6 @@ func TestOptionsMethod(t *testing.T) {
 	if resp.StatusCode != http.StatusNoContent {
 		t.Fatalf("Expected status %d, got %d", http.StatusNoContent, resp.StatusCode)
 	}
-
-	for h, v := range corsHeaders {
-		if resp.Header.Get(h) != v {
-			t.Fatalf("Expected %q for header %q, got %q", v, h, resp.Header.Get(h))
-		}
-	}
 }
 
 func TestRespond(t *testing.T) {

web/web.go

@@ -28,6 +28,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"sort"
 	"strings"
@@ -173,6 +174,7 @@ type Options struct {
 	Flags         map[string]string
 
 	ListenAddress              string
+	CORSOrigin                 *regexp.Regexp
 	ReadTimeout                time.Duration
 	MaxConnections             int
 	ExternalURL                *url.URL
@@ -259,6 +261,7 @@ func New(logger log.Logger, o *Options) *Handler {
 		h.ruleManager,
 		h.options.RemoteReadSampleLimit,
 		h.options.RemoteReadConcurrencyLimit,
+		h.options.CORSOrigin,
 	)
 
 	if o.RoutePrefix != "/" {
@@ -340,20 +343,6 @@ func New(logger log.Logger, o *Options) *Handler {
 	return h
 }
 
-var corsHeaders = map[string]string{
-	"Access-Control-Allow-Headers":  "Accept, Authorization, Content-Type, Origin",
-	"Access-Control-Allow-Methods":  "GET, OPTIONS",
-	"Access-Control-Allow-Origin":   "*",
-	"Access-Control-Expose-Headers": "Date",
-}
-
-// Enables cross-site script calls.
-func setCORS(w http.ResponseWriter) {
-	for h, v := range corsHeaders {
-		w.Header().Set(h, v)
-	}
-}
-
 func serveDebug(w http.ResponseWriter, req *http.Request) {
 	ctx := req.Context()
 	subpath := route.Param(ctx, "subpath")
@@ -474,7 +463,7 @@ func (h *Handler) Run(ctx context.Context) error {
 
 	mux.Handle(apiPath+"/", http.StripPrefix(apiPath,
 		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			setCORS(w)
+			httputil.SetCORS(w, h.options.CORSOrigin, r)
 			hhFunc(w, r)
 		}),
 	))