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]>

1 files changed, 19 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)