Repository: prometheus/prometheus
File: util/httputil/cors.go (Go)

Code before:
// 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"

	"github.com/grafana/regexp"
)

var corsHeaders = map[string]string{
	"Access-Control-Allow-Headers":  "Accept, Authorization, Content-Type",
	"Access-Control-Allow-Methods":  "GET, POST",
	"Access-Control-Expose-Headers": "Date",
}

// SetCORS enables cross-origin script calls.
func SetCORS(w http.ResponseWriter, o *regexp.Regexp, r *http.Request) {
	w.Header().Add("Vary", "Origin")
	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)
	}
}


Review comment (suggestion):
I don't think removing `OPTIONS` in here is related to the change.
IIUC, this is not needed as Prometheus doesn't offer actual OPTIONS endpoints and I don't think CORS spec would require this chicken-and-egg setting for preflights to work.
So I agree it's not needed, but maybe let's do it in another PR instead of hiding it in here so those who think this may break something can speak out.


Code after:
// 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"

	"github.com/grafana/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",
}

// SetCORS enables cross-origin script calls.
func SetCORS(w http.ResponseWriter, o *regexp.Regexp, r *http.Request) {
	w.Header().Add("Vary", "Origin")
	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)
	}
}