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package internal
import (
"errors"
"fmt"
"log/slog"
"net"
"net/http"
"net/netip"
"strings"
"github.com/TecharoHQ/anubis"
"github.com/sebest/xff"
)
// TODO: move into config
type XFFComputePreferences struct {
StripPrivate bool
StripLoopback bool
StripCGNAT bool
StripLLU bool
Flatten bool
}
var CGNat = netip.MustParsePrefix("100.64.0.0/10")
// UnchangingCache sets the Cache-Control header to cache a response for 1 year if
// and only if the application is compiled in "release" mode by Docker.
func UnchangingCache(next http.Handler) http.Handler {
//goland:noinspection GoBoolExpressions
if anubis.Version == "devel" {
return next
}
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Cache-Control", "public, max-age=31536000")
next.ServeHTTP(w, r)
})
}
// RemoteXRealIP sets the X-Real-Ip header to the request's real IP if
// the setting is enabled by the user.
func RemoteXRealIP(useRemoteAddress bool, bindNetwork string, next http.Handler) http.Handler {
if !useRemoteAddress {
slog.Debug("skipping middleware, useRemoteAddress is empty")
return next
}
if bindNetwork == "unix" {
// For local sockets there is no real remote address but the localhost
// address should be sensible.
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
r.Header.Set("X-Real-Ip", "127.0.0.1")
next.ServeHTTP(w, r)
})
}
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
host, _, err := net.SplitHostPort(r.RemoteAddr)
if err != nil {
panic(err) // this should never happen
}
r.Header.Set("X-Real-Ip", host)
next.ServeHTTP(w, r)
})
}
// XForwardedForToXRealIP sets the X-Real-Ip header based on the contents
// of the X-Forwarded-For header.
func XForwardedForToXRealIP(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if xffHeader := r.Header.Get("X-Forwarded-For"); r.Header.Get("X-Real-Ip") == "" && xffHeader != "" {
ip := xff.Parse(xffHeader)
slog.Debug("setting x-real-ip", "val", ip)
r.Header.Set("X-Real-Ip", ip)
}
next.ServeHTTP(w, r)
})
}
// XForwardedForUpdate sets or updates the X-Forwarded-For header, adding
// the known remote address to an existing chain if present
func XForwardedForUpdate(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
defer next.ServeHTTP(w, r)
pref := XFFComputePreferences{
StripPrivate: true,
StripLoopback: true,
StripCGNAT: true,
Flatten: true,
StripLLU: true,
}
remoteAddr := r.RemoteAddr
origXFFHeader := r.Header.Get("X-Forwarded-For")
if remoteAddr == "@" {
// remote is a unix socket
// do not touch chain
return
}
xffHeaderString, err := computeXFFHeader(remoteAddr, origXFFHeader, pref)
if err != nil {
slog.Debug("computing X-Forwarded-For header failed", "err", err)
return
}
if len(xffHeaderString) == 0 {
r.Header.Del("X-Forwarded-For")
} else {
r.Header.Set("X-Forwarded-For", xffHeaderString)
}
})
}
var (
ErrCantSplitHostParse = errors.New("internal: unable to net.SplitHostParse")
ErrCantParseRemoteIP = errors.New("internal: unable to parse remote IP")
)
func computeXFFHeader(remoteAddr string, origXFFHeader string, pref XFFComputePreferences) (string, error) {
remoteIP, _, err := net.SplitHostPort(remoteAddr)
if err != nil {
return "", fmt.Errorf("%w: %w", ErrCantSplitHostParse, err)
}
parsedRemoteIP, err := netip.ParseAddr(remoteIP)
if err != nil {
return "", fmt.Errorf("%w: %w", ErrCantParseRemoteIP, err)
}
origForwardedList := make([]string, 0, 4)
if origXFFHeader != "" {
origForwardedList = strings.Split(origXFFHeader, ",")
}
origForwardedList = append(origForwardedList, parsedRemoteIP.String())
forwardedList := make([]string, 0, len(origForwardedList))
// this behavior is equivalent to
// ingress-nginx "compute-full-forwarded-for"
// https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/#compute-full-forwarded-for
//
// this would be the correct place to strip and/or flatten this list
//
// strip - iterate backwards and eliminate configured trusted IPs
// flatten - only return the last element to avoid spoofing confusion
//
// many applications handle this in different ways, but
// generally they'd be expected to do these two things on
// their own end to find the first non-spoofed IP
for i := len(origForwardedList) - 1; i >= 0; i-- {
segmentIP, err := netip.ParseAddr(origForwardedList[i])
if err != nil {
// can't assess this element, so the remainder of the chain
// can't be trusted. not a fatal error, since anyone can
// spoof an XFF header
slog.Debug("failed to parse XFF segment", "err", err)
break
}
if pref.StripPrivate && segmentIP.IsPrivate() {
continue
}
if pref.StripLoopback && segmentIP.IsLoopback() {
continue
}
if pref.StripLLU && segmentIP.IsLinkLocalUnicast() {
continue
}
if pref.StripCGNAT && CGNat.Contains(segmentIP) {
continue
}
forwardedList = append([]string{segmentIP.String()}, forwardedList...)
}
var xffHeaderString string
if len(forwardedList) == 0 {
xffHeaderString = ""
return xffHeaderString, nil
}
if pref.Flatten {
xffHeaderString = forwardedList[len(forwardedList)-1]
} else {
xffHeaderString = strings.Join(forwardedList, ",")
}
return xffHeaderString, nil
}
// NoStoreCache sets the Cache-Control header to no-store for the response.
func NoStoreCache(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Cache-Control", "no-store")
next.ServeHTTP(w, r)
})
}
// NoBrowsing prevents directory browsing by returning a 404 for any request that ends with a "/".
func NoBrowsing(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if strings.HasSuffix(r.URL.Path, "/") {
http.NotFound(w, r)
return
}
next.ServeHTTP(w, r)
})
}
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