Merge branch 'get-real-ip'

README.md

@@ -84,15 +84,23 @@ Middleware values are plain `func(http.Handler) http.Handler`, so any stdlib-com
 
 The `pkg/middleware` package ships:
 
-- **`Logger`** — emits a structured `http.request` record (method, path, status, duration) via [splinter](https://git.juancwu.dev/juancwu/splinter)'s default logger.
+- **`Logger`** — emits a structured `http.request` record (method, path, status, duration, client) via [splinter](https://git.juancwu.dev/juancwu/splinter)'s default logger. The `client` field is `r.RemoteAddr`, so pairing with `RealIP` makes it the resolved client IP.
 - **`LoggerWith(*splinter.Logger)`** — same, but routes records through the supplied splinter logger instead of the default.
 - **`Recoverer`** — catches panics inside handlers, wraps the value with [errx](https://git.juancwu.dev/juancwu/errx) under op `middleware.Recoverer`, logs it with the stack, and writes a 500 response.
+- **`RealIP`** — replaces `r.RemoteAddr` with the originating client IP from `CF-Connecting-IP`, `True-Client-IP`, `X-Real-IP`, or `X-Forwarded-For` (in that order). Always trusts these headers — only register it when the service sits behind a trusted proxy.
+- **`RealIPWith(trusted ...netip.Prefix)`** — same, but only honors the headers when the immediate peer's IP falls within one of the trusted prefixes. Requests from outside the allowlist pass through untouched.
 
 ```go
 custom := splinter.New(splinter.WithStream(...))
 mux.Use(middleware.Recoverer, middleware.LoggerWith(custom))
 ```
 
+When using `RealIP` together with `Logger`, register `RealIP` first so the logged `client` field is the resolved client IP rather than the proxy's peer address:
+
+```go
+mux.Use(middleware.RealIP, middleware.Logger)
+```
+
 ## Path parameters
 
 lightmux is a thin wrapper, so path parameters work the stdlib way:

pkg/middleware/logger.go

@@ -53,6 +53,7 @@ func loggerHandler(l *splinter.Logger, next http.Handler) http.Handler {
 				"path", r.URL.Path,
 				"status", rec.status,
 				"duration", time.Since(start),
+				"client", r.RemoteAddr,
 			)
 			return
 		}
@@ -61,6 +62,7 @@ func loggerHandler(l *splinter.Logger, next http.Handler) http.Handler {
 			"path", r.URL.Path,
 			"status", rec.status,
 			"duration", time.Since(start),
+			"client", r.RemoteAddr,
 		)
 	})
 }

pkg/middleware/logger_test.go

@@ -37,7 +37,7 @@ func TestLogger(t *testing.T) {
 		t.Errorf("status code = %d, want 418", rr.Code)
 	}
 	out := buf.String()
-	for _, want := range []string{`"method":"GET"`, `"path":"/foo"`, `"status":418`} {
+	for _, want := range []string{`"method":"GET"`, `"path":"/foo"`, `"status":418`, `"client":"192.0.2.1:1234"`} {
 		if !strings.Contains(out, want) {
 			t.Errorf("log output missing %s\nfull output: %s", want, out)
 		}

pkg/middleware/realip.go

@@ -0,0 +1,86 @@
+package middleware
+
+import (
+	"net"
+	"net/http"
+	"net/netip"
+	"strings"
+)
+
+var realIPHeaders = []string{
+	"CF-Connecting-IP",
+	"True-Client-IP",
+	"X-Real-IP",
+	"X-Forwarded-For",
+}
+
+// RealIP rewrites r.RemoteAddr with the originating client IP found in common
+// reverse-proxy headers (Cloudflare, nginx). It always trusts these headers —
+// only register it when the service sits behind a trusted proxy. Use
+// RealIPWith for an allowlist-gated variant.
+func RealIP(next http.Handler) http.Handler {
+	return realIPHandler(nil, next)
+}
+
+// RealIPWith returns a RealIP middleware that only honors the proxy headers
+// when the immediate peer (parsed from r.RemoteAddr) falls within one of the
+// trusted prefixes. Requests from outside the allowlist are passed through
+// untouched.
+func RealIPWith(trusted ...netip.Prefix) Middleware {
+	if trusted == nil {
+		trusted = []netip.Prefix{}
+	}
+	return func(next http.Handler) http.Handler {
+		return realIPHandler(trusted, next)
+	}
+}
+
+func realIPHandler(trusted []netip.Prefix, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if trusted != nil && !peerTrusted(r.RemoteAddr, trusted) {
+			next.ServeHTTP(w, r)
+			return
+		}
+		if ip := extractRealIP(r); ip != "" {
+			r2 := *r
+			r2.RemoteAddr = ip
+			next.ServeHTTP(w, &r2)
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+func extractRealIP(r *http.Request) string {
+	for _, h := range realIPHeaders {
+		v := r.Header.Get(h)
+		if v == "" {
+			continue
+		}
+		if i := strings.IndexByte(v, ','); i >= 0 {
+			v = v[:i]
+		}
+		v = strings.TrimSpace(v)
+		if net.ParseIP(v) != nil {
+			return v
+		}
+	}
+	return ""
+}
+
+func peerTrusted(remoteAddr string, trusted []netip.Prefix) bool {
+	var peer netip.Addr
+	if ap, err := netip.ParseAddrPort(remoteAddr); err == nil {
+		peer = ap.Addr()
+	} else if a, err2 := netip.ParseAddr(remoteAddr); err2 == nil {
+		peer = a
+	} else {
+		return false
+	}
+	for _, p := range trusted {
+		if p.Contains(peer) {
+			return true
+		}
+	}
+	return false
+}

pkg/middleware/realip_test.go

@@ -0,0 +1,198 @@
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"testing"
+)
+
+const defaultTestRemoteAddr = "192.0.2.1:1234"
+
+func captureRemoteAddr(got *string) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		*got = r.RemoteAddr
+	})
+}
+
+func TestRealIP(t *testing.T) {
+	cases := []struct {
+		name    string
+		headers map[string]string
+		want    string
+	}{
+		{
+			name: "no headers",
+			want: defaultTestRemoteAddr,
+		},
+		{
+			name:    "CF-Connecting-IP",
+			headers: map[string]string{"CF-Connecting-IP": "203.0.113.5"},
+			want:    "203.0.113.5",
+		},
+		{
+			name:    "True-Client-IP",
+			headers: map[string]string{"True-Client-IP": "203.0.113.6"},
+			want:    "203.0.113.6",
+		},
+		{
+			name:    "X-Real-IP",
+			headers: map[string]string{"X-Real-IP": "203.0.113.7"},
+			want:    "203.0.113.7",
+		},
+		{
+			name:    "X-Forwarded-For single",
+			headers: map[string]string{"X-Forwarded-For": "203.0.113.8"},
+			want:    "203.0.113.8",
+		},
+		{
+			name:    "X-Forwarded-For list",
+			headers: map[string]string{"X-Forwarded-For": "203.0.113.9, 10.0.0.1, 10.0.0.2"},
+			want:    "203.0.113.9",
+		},
+		{
+			name:    "X-Forwarded-For with spaces",
+			headers: map[string]string{"X-Forwarded-For": "  203.0.113.10 , 10.0.0.1"},
+			want:    "203.0.113.10",
+		},
+		{
+			name: "precedence CF over XFF",
+			headers: map[string]string{
+				"CF-Connecting-IP": "203.0.113.11",
+				"X-Forwarded-For":  "198.51.100.1",
+			},
+			want: "203.0.113.11",
+		},
+		{
+			name: "invalid then valid",
+			headers: map[string]string{
+				"CF-Connecting-IP": "not-an-ip",
+				"X-Real-IP":        "203.0.113.12",
+			},
+			want: "203.0.113.12",
+		},
+		{
+			name:    "IPv6",
+			headers: map[string]string{"X-Real-IP": "2001:db8::1"},
+			want:    "2001:db8::1",
+		},
+		{
+			name:    "all invalid falls through",
+			headers: map[string]string{"CF-Connecting-IP": "garbage"},
+			want:    defaultTestRemoteAddr,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			var got string
+			h := RealIP(captureRemoteAddr(&got))
+
+			req := httptest.NewRequest(http.MethodGet, "/", nil)
+			for k, v := range tc.headers {
+				req.Header.Set(k, v)
+			}
+			h.ServeHTTP(httptest.NewRecorder(), req)
+
+			if got != tc.want {
+				t.Errorf("r.RemoteAddr = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestRealIPDoesNotMutateCallerRequest(t *testing.T) {
+	var seen string
+	h := RealIP(captureRemoteAddr(&seen))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Header.Set("X-Real-IP", "203.0.113.13")
+	original := req.RemoteAddr
+
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if seen != "203.0.113.13" {
+		t.Errorf("handler saw r.RemoteAddr = %q, want %q", seen, "203.0.113.13")
+	}
+	if req.RemoteAddr != original {
+		t.Errorf("caller's request was mutated: RemoteAddr = %q, want %q", req.RemoteAddr, original)
+	}
+}
+
+func TestRealIPWithTrustedPeer(t *testing.T) {
+	var got string
+	h := RealIPWith(netip.MustParsePrefix("10.0.0.0/8"))(captureRemoteAddr(&got))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.RemoteAddr = "10.1.2.3:55555"
+	req.Header.Set("X-Real-IP", "203.0.113.20")
+
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if got != "203.0.113.20" {
+		t.Errorf("trusted peer header not honored: r.RemoteAddr = %q, want %q", got, "203.0.113.20")
+	}
+}
+
+func TestRealIPWithUntrustedPeer(t *testing.T) {
+	var got string
+	h := RealIPWith(netip.MustParsePrefix("10.0.0.0/8"))(captureRemoteAddr(&got))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.RemoteAddr = "203.0.113.99:55555"
+	req.Header.Set("X-Real-IP", "198.51.100.1")
+
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if got != "203.0.113.99:55555" {
+		t.Errorf("untrusted peer should not have header honored: r.RemoteAddr = %q, want %q", got, "203.0.113.99:55555")
+	}
+}
+
+func TestRealIPWithMultiplePrefixesIPv6(t *testing.T) {
+	var got string
+	h := RealIPWith(
+		netip.MustParsePrefix("10.0.0.0/8"),
+		netip.MustParsePrefix("2001:db8::/32"),
+	)(captureRemoteAddr(&got))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.RemoteAddr = "[2001:db8::abcd]:55555"
+	req.Header.Set("X-Real-IP", "203.0.113.30")
+
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if got != "203.0.113.30" {
+		t.Errorf("IPv6 peer match should honor header: r.RemoteAddr = %q, want %q", got, "203.0.113.30")
+	}
+}
+
+func TestRealIPWithZeroPrefixesNoOp(t *testing.T) {
+	var got string
+	h := RealIPWith()(captureRemoteAddr(&got))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Header.Set("CF-Connecting-IP", "203.0.113.40")
+	original := req.RemoteAddr
+
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if got != original {
+		t.Errorf("RealIPWith() with no prefixes should be a no-op: r.RemoteAddr = %q, want %q", got, original)
+	}
+}
+
+func TestRealIPWithUnparseableRemoteAddr(t *testing.T) {
+	var got string
+	h := RealIPWith(netip.MustParsePrefix("10.0.0.0/8"))(captureRemoteAddr(&got))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.RemoteAddr = "not-an-addr"
+	req.Header.Set("CF-Connecting-IP", "203.0.113.50")
+
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if got != "not-an-addr" {
+		t.Errorf("unparseable RemoteAddr should pass through unchanged: got %q", got)
+	}
+}

pkg/router/mux_test.go

@@ -166,4 +166,3 @@ func TestConflictingPatternsPanic(t *testing.T) {
 	}()
 	m.Get("/x", func(w http.ResponseWriter, r *http.Request) {})
 }
-

pkg/router/pattern_test.go

@@ -4,8 +4,8 @@ import "testing"
 
 func TestSplitPattern(t *testing.T) {
 	cases := []struct {
-		in                       string
+		in                 string
-		method, host, path       string
+		method, host, path string
 	}{
 		{"/foo", "", "", "/foo"},
 		{"GET /foo", "GET", "", "/foo"},