caddyhttp: add http.request.local{,.host,.port} placeholder (#6182)

* caddyhttp: add `http.request.local{,.host,.port}` placeholder

This is the counterpart of `http.request.remote{,.host,.port}`.

`http.request.remote` operates on the remote client's address, while
`http.request.local` operates on the address the connection arrived on.

Take the following example:

- Caddy serving on `203.0.113.1:80`
- Client on `203.0.113.2`

`http.request.remote.host` would return `203.0.113.2` (client IP)

`http.request.local.host` would return `203.0.113.1` (server IP)
`http.request.local.port` would return `80` (server port)

I find this helpful for debugging setups with multiple servers and/or
multiple network paths (multiple IPs, AnyIP, Anycast).

Co-authored-by: networkException <[email protected]>

* caddyhttp: add unit test for `http.request.local{,.host,.port}`

* caddyhttp: add integration test for `http.request.local.port`

* caddyhttp: fix `http.request.local.host` placeholder handling with unix sockets

The implementation matches the one of `http.request.remote.host` now and
returns the unix socket path (just like `http.request.local` already did)
instead of an empty string.

---------

Co-authored-by: networkException <[email protected]>

4 files changed, 64 insertions, 0 deletions

diff --git a/caddytest/integration/caddyfile_test.go b/caddytest/integration/caddyfile_test.go
index 628363a52..11ffc08ae 100644
--- a/caddytest/integration/caddyfile_test.go
+++ b/caddytest/integration/caddyfile_test.go
@@ -517,6 +517,25 @@ func TestUriOps(t *testing.T) {
 	tester.AssertGetResponse("http://localhost:9080/endpoint?foo=bar0&baz=buz&taz=nottest&changethis=val", 200, "changed=val&foo=bar0&foo=bar&key%3Dvalue=example&taz=test")
 }
 
+// Tests the `http.request.local.port` placeholder.
+// We don't test the very similar `http.request.local.host` placeholder,
+// because depending on the host the test is running on, localhost might
+// refer to 127.0.0.1 or ::1.
+// TODO: Test each http version separately (especially http/3)
+func TestHttpRequestLocalPortPlaceholder(t *testing.T) {
+	tester := caddytest.NewTester(t)
+
+	tester.InitServer(`
+	{
+		admin localhost:2999
+		http_port     9080
+	}
+	:9080
+	respond "{http.request.local.port}"`, "caddyfile")
+
+	tester.AssertGetResponse("http://localhost:9080/", 200, "9080")
+}
+
 func TestSetThenAddQueryParams(t *testing.T) {
 	tester := caddytest.NewTester(t)
 
diff --git a/modules/caddyhttp/app.go b/modules/caddyhttp/app.go
index cdb368c4f..f46c891f3 100644
--- a/modules/caddyhttp/app.go
+++ b/modules/caddyhttp/app.go
@@ -68,6 +68,9 @@ func init() {
 // `{http.request.orig_uri.query}` | The request's original query string (without `?`)
 // `{http.request.port}` | The port part of the request's Host header
 // `{http.request.proto}` | The protocol of the request
+// `{http.request.local.host}` | The host (IP) part of the local address the connection arrived on
+// `{http.request.local.port}` | The port part of the local address the connection arrived on
+// `{http.request.local}` | The local address the connection arrived on
 // `{http.request.remote.host}` | The host (IP) part of the remote client's address
 // `{http.request.remote.port}` | The port part of the remote client's address
 // `{http.request.remote}` | The address of the remote client
diff --git a/modules/caddyhttp/replacer.go b/modules/caddyhttp/replacer.go
index 10258da01..1cf3ec474 100644
--- a/modules/caddyhttp/replacer.go
+++ b/modules/caddyhttp/replacer.go
@@ -119,11 +119,38 @@ func addHTTPVarsToReplacer(repl *caddy.Replacer, req *http.Request, w http.Respo
 				return port, true
 			case "http.request.hostport":
 				return req.Host, true
+			case "http.request.local":
+				localAddr, _ := req.Context().Value(http.LocalAddrContextKey).(net.Addr)
+				return localAddr.String(), true
+			case "http.request.local.host":
+				localAddr, _ := req.Context().Value(http.LocalAddrContextKey).(net.Addr)
+				host, _, err := net.SplitHostPort(localAddr.String())
+				if err != nil {
+					// localAddr is host:port for tcp and udp sockets and /unix/socket.path
+					// for unix sockets. net.SplitHostPort only operates on tcp and udp sockets,
+					// not unix sockets and will fail with the latter.
+					// We assume when net.SplitHostPort fails, localAddr is a unix socket and thus
+					// already "split" and save to return.
+					return localAddr, true
+				}
+				return host, true
+			case "http.request.local.port":
+				localAddr, _ := req.Context().Value(http.LocalAddrContextKey).(net.Addr)
+				_, port, _ := net.SplitHostPort(localAddr.String())
+				if portNum, err := strconv.Atoi(port); err == nil {
+					return portNum, true
+				}
+				return port, true
 			case "http.request.remote":
 				return req.RemoteAddr, true
 			case "http.request.remote.host":
 				host, _, err := net.SplitHostPort(req.RemoteAddr)
 				if err != nil {
+					// req.RemoteAddr is host:port for tcp and udp sockets and /unix/socket.path
+					// for unix sockets. net.SplitHostPort only operates on tcp and udp sockets,
+					// not unix sockets and will fail with the latter.
+					// We assume when net.SplitHostPort fails, req.RemoteAddr is a unix socket
+					// and thus already "split" and save to return.
 					return req.RemoteAddr, true
 				}
 				return host, true
diff --git a/modules/caddyhttp/replacer_test.go b/modules/caddyhttp/replacer_test.go
index 44c6f2a89..50a2e8c62 100644
--- a/modules/caddyhttp/replacer_test.go
+++ b/modules/caddyhttp/replacer_test.go
@@ -19,6 +19,7 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/pem"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -29,7 +30,9 @@ import (
 func TestHTTPVarReplacement(t *testing.T) {
 	req, _ := http.NewRequest(http.MethodGet, "/foo/bar.tar.gz", nil)
 	repl := caddy.NewReplacer()
+	localAddr, _ := net.ResolveTCPAddr("tcp", "192.168.159.1:80")
 	ctx := context.WithValue(req.Context(), caddy.ReplacerCtxKey, repl)
+	ctx = context.WithValue(ctx, http.LocalAddrContextKey, localAddr)
 	req = req.WithContext(ctx)
 	req.Host = "example.com:80"
 	req.RemoteAddr = "192.168.159.32:1234"
@@ -96,6 +99,18 @@ eqp31wM9il1n+guTNyxJd+FzVAH+hCZE5K+tCgVDdVFUlDEHHbS/wqb2PSIoouLV
 			expect: "example.com:80",
 		},
 		{
+			get:    "http.request.local.host",
+			expect: "192.168.159.1",
+		},
+		{
+			get:    "http.request.local.port",
+			expect: "80",
+		},
+		{
+			get:    "http.request.local",
+			expect: "192.168.159.1:80",
+		},
+		{
 			get:    "http.request.remote.host",
 			expect: "192.168.159.32",
 		},