feat: more elaborate XFF compute (#350)

* feat: more elaborate XFF compute

#328 followup

now featuring configuration and
defaults that shouldn't break most
setups.

fixes #344

* refactor: obvious condition eval order optimization

* feat: add StripLLU implementation

* chore: I'm sorry it's 7 AM

* test: add test environment for unix socket serving

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(unix-socket-xff): comment out the shell script more

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(internal): fix logic bug in XFF computation, add tests

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(internal): prevent panic in local testing

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(internal): shuffle around return values to flow better

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Co-authored-by: Xe Iaso <me@xeiaso.net>

test/cmd/unixhttpd/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"log/slog"
+	"net"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/TecharoHQ/anubis/internal"
+	"github.com/facebookgo/flagenv"
+)
+
+var (
+	dir        = flag.String("dir", ".", "directory to serve")
+	slogLevel  = flag.String("slog-level", "info", "logging level")
+	socketPath = flag.String("socket-path", "./unixhttpd.sock", "unix socket path to use")
+)
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage of %s:\n", filepath.Base(os.Args[0]))
+		fmt.Fprintf(os.Stderr, "  %s [--dir=.] [--socket-path=./unixhttpd.sock]\n\n", filepath.Base(os.Args[0]))
+		flag.PrintDefaults()
+		os.Exit(2)
+	}
+}
+
+func main() {
+	flagenv.Parse()
+	flag.Parse()
+
+	internal.InitSlog(*slogLevel)
+
+	if *dir == "" && *socketPath == "" {
+		flag.Usage()
+	}
+
+	slog.Info("starting up", "dir", *dir, "socketPath", *socketPath)
+
+	os.Remove(*socketPath)
+
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("/reqmeta", func(w http.ResponseWriter, r *http.Request) {
+		contains := strings.Contains(r.Header.Get("Accept"), "text/html")
+
+		if contains {
+			w.Header().Add("Content-Type", "text/html")
+			fmt.Fprint(w, "<pre id=\"main\"><code>")
+		}
+
+		r.Write(w)
+
+		if contains {
+			fmt.Fprintln(w, "</pre></code>")
+		}
+	})
+
+	mux.Handle("/", http.FileServer(http.Dir(*dir)))
+
+	server := http.Server{
+		Handler: mux,
+	}
+
+	unixListener, err := net.Listen("unix", *socketPath)
+	if err != nil {
+		panic(err)
+	}
+	log.Fatal(server.Serve(unixListener))
+}