121 lines
4.5 KiB
Go
121 lines
4.5 KiB
Go
package handlers
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import (
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"net/http"
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"regexp"
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"strings"
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)
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var (
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// De-facto standard header keys.
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xForwardedFor = http.CanonicalHeaderKey("X-Forwarded-For")
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xForwardedHost = http.CanonicalHeaderKey("X-Forwarded-Host")
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xForwardedProto = http.CanonicalHeaderKey("X-Forwarded-Proto")
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xForwardedScheme = http.CanonicalHeaderKey("X-Forwarded-Scheme")
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xRealIP = http.CanonicalHeaderKey("X-Real-IP")
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)
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var (
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// RFC7239 defines a new "Forwarded: " header designed to replace the
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// existing use of X-Forwarded-* headers.
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// e.g. Forwarded: for=192.0.2.60;proto=https;by=203.0.113.43.
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forwarded = http.CanonicalHeaderKey("Forwarded")
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// Allows for a sub-match of the first value after 'for=' to the next
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// comma, semi-colon or space. The match is case-insensitive.
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forRegex = regexp.MustCompile(`(?i)(?:for=)([^(;|,| )]+)`)
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// Allows for a sub-match for the first instance of scheme (http|https)
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// prefixed by 'proto='. The match is case-insensitive.
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protoRegex = regexp.MustCompile(`(?i)(?:proto=)(https|http)`)
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)
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// ProxyHeaders inspects common reverse proxy headers and sets the corresponding
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// fields in the HTTP request struct. These are X-Forwarded-For and X-Real-IP
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// for the remote (client) IP address, X-Forwarded-Proto or X-Forwarded-Scheme
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// for the scheme (http|https), X-Forwarded-Host for the host and the RFC7239
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// Forwarded header, which may include both client IPs and schemes.
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//
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// NOTE: This middleware should only be used when behind a reverse
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// proxy like nginx, HAProxy or Apache. Reverse proxies that don't (or are
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// configured not to) strip these headers from client requests, or where these
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// headers are accepted "as is" from a remote client (e.g. when Go is not behind
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// a proxy), can manifest as a vulnerability if your application uses these
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// headers for validating the 'trustworthiness' of a request.
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func ProxyHeaders(h http.Handler) http.Handler {
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fn := func(w http.ResponseWriter, r *http.Request) {
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// Set the remote IP with the value passed from the proxy.
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if fwd := getIP(r); fwd != "" {
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r.RemoteAddr = fwd
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}
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// Set the scheme (proto) with the value passed from the proxy.
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if scheme := getScheme(r); scheme != "" {
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r.URL.Scheme = scheme
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}
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// Set the host with the value passed by the proxy
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if r.Header.Get(xForwardedHost) != "" {
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r.Host = r.Header.Get(xForwardedHost)
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}
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// Call the next handler in the chain.
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h.ServeHTTP(w, r)
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}
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return http.HandlerFunc(fn)
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}
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// getIP retrieves the IP from the X-Forwarded-For, X-Real-IP and RFC7239
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// Forwarded headers (in that order).
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func getIP(r *http.Request) string {
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var addr string
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switch {
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case r.Header.Get(xForwardedFor) != "":
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fwd := r.Header.Get(xForwardedFor)
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// Only grab the first (client) address. Note that '192.168.0.1,
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// 10.1.1.1' is a valid key for X-Forwarded-For where addresses after
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// the first may represent forwarding proxies earlier in the chain.
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s := strings.Index(fwd, ", ")
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if s == -1 {
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s = len(fwd)
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}
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addr = fwd[:s]
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case r.Header.Get(xRealIP) != "":
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addr = r.Header.Get(xRealIP)
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case r.Header.Get(forwarded) != "":
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// match should contain at least two elements if the protocol was
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// specified in the Forwarded header. The first element will always be
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// the 'for=' capture, which we ignore. In the case of multiple IP
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// addresses (for=8.8.8.8, 8.8.4.4,172.16.1.20 is valid) we only
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// extract the first, which should be the client IP.
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if match := forRegex.FindStringSubmatch(r.Header.Get(forwarded)); len(match) > 1 {
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// IPv6 addresses in Forwarded headers are quoted-strings. We strip
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// these quotes.
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addr = strings.Trim(match[1], `"`)
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}
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}
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return addr
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}
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// getScheme retrieves the scheme from the X-Forwarded-Proto and RFC7239
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// Forwarded headers (in that order).
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func getScheme(r *http.Request) string {
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var scheme string
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// Retrieve the scheme from X-Forwarded-Proto.
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if proto := r.Header.Get(xForwardedProto); proto != "" {
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scheme = strings.ToLower(proto)
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} else if proto = r.Header.Get(xForwardedScheme); proto != "" {
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scheme = strings.ToLower(proto)
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} else if proto = r.Header.Get(forwarded); proto != "" {
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// match should contain at least two elements if the protocol was
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// specified in the Forwarded header. The first element will always be
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// the 'proto=' capture, which we ignore. In the case of multiple proto
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// parameters (invalid) we only extract the first.
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if match := protoRegex.FindStringSubmatch(proto); len(match) > 1 {
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scheme = strings.ToLower(match[1])
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}
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}
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return scheme
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}
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