/*
 * MinIO Cloud Storage, (C) 2018 MinIO, Inc.
 *
 * 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 handlers

import (
	"net"
	"net/http"
	"regexp"
	"strings"
)

var (
	// De-facto standard header keys.
	xForwardedFor    = http.CanonicalHeaderKey("X-Forwarded-For")
	xForwardedHost   = http.CanonicalHeaderKey("X-Forwarded-Host")
	xForwardedPort   = http.CanonicalHeaderKey("X-Forwarded-Port")
	xForwardedProto  = http.CanonicalHeaderKey("X-Forwarded-Proto")
	xForwardedScheme = http.CanonicalHeaderKey("X-Forwarded-Scheme")
	xRealIP          = http.CanonicalHeaderKey("X-Real-IP")
)

var (
	// RFC7239 defines a new "Forwarded: " header designed to replace the
	// existing use of X-Forwarded-* headers.
	// e.g. Forwarded: for=192.0.2.60;proto=https;by=203.0.113.43
	forwarded = http.CanonicalHeaderKey("Forwarded")
	// Allows for a sub-match of the first value after 'for=' to the next
	// comma, semi-colon or space. The match is case-insensitive.
	forRegex = regexp.MustCompile(`(?i)(?:for=)([^(;|,| )]+)(.*)`)
	// Allows for a sub-match for the first instance of scheme (http|https)
	// prefixed by 'proto='. The match is case-insensitive.
	protoRegex = regexp.MustCompile(`(?i)^(;|,| )+(?:proto=)(https|http)`)
)

// GetSourceScheme retrieves the scheme from the X-Forwarded-Proto and RFC7239
// Forwarded headers (in that order).
func GetSourceScheme(r *http.Request) string {
	var scheme string

	// Retrieve the scheme from X-Forwarded-Proto.
	if proto := r.Header.Get(xForwardedProto); proto != "" {
		scheme = strings.ToLower(proto)
	} else if proto = r.Header.Get(xForwardedScheme); proto != "" {
		scheme = strings.ToLower(proto)
	} else if proto := r.Header.Get(forwarded); proto != "" {
		// match should contain at least two elements if the protocol was
		// specified in the Forwarded header. The first element will always be
		// the 'for=', which we ignore, subsequently we proceed to look for
		// 'proto=' which should precede right after `for=` if not
		// we simply ignore the values and return empty. This is in line
		// with the approach we took for returning first ip from multiple
		// params.
		if match := forRegex.FindStringSubmatch(proto); len(match) > 1 {
			if match = protoRegex.FindStringSubmatch(match[2]); len(match) > 1 {
				scheme = strings.ToLower(match[2])
			}
		}
	}

	return scheme
}

// GetSourceIPFromHeaders retrieves the IP from the X-Forwarded-For, X-Real-IP
// and RFC7239 Forwarded headers (in that order)
func GetSourceIPFromHeaders(r *http.Request) string {
	var addr string

	if fwd := r.Header.Get(xForwardedFor); fwd != "" {
		// Only grab the first (client) address. Note that '192.168.0.1,
		// 10.1.1.1' is a valid key for X-Forwarded-For where addresses after
		// the first may represent forwarding proxies earlier in the chain.
		s := strings.Index(fwd, ", ")
		if s == -1 {
			s = len(fwd)
		}
		addr = fwd[:s]
	} else if fwd := r.Header.Get(xRealIP); fwd != "" {
		// X-Real-IP should only contain one IP address (the client making the
		// request).
		addr = fwd
	} else if fwd := r.Header.Get(forwarded); fwd != "" {
		// match should contain at least two elements if the protocol was
		// specified in the Forwarded header. The first element will always be
		// the 'for=' capture, which we ignore. In the case of multiple IP
		// addresses (for=8.8.8.8, 8.8.4.4, 172.16.1.20 is valid) we only
		// extract the first, which should be the client IP.
		if match := forRegex.FindStringSubmatch(fwd); len(match) > 1 {
			// IPv6 addresses in Forwarded headers are quoted-strings. We strip
			// these quotes.
			addr = strings.Trim(match[1], `"`)
		}
	}

	return addr
}

// GetSourceIP retrieves the IP from the request headers
// and falls back to r.RemoteAddr when necessary.
func GetSourceIP(r *http.Request) string {
	addr := GetSourceIPFromHeaders(r)
	if addr != "" {
		return addr
	}

	// Default to remote address if headers not set.
	addr, _, _ = net.SplitHostPort(r.RemoteAddr)
	return addr
}