Percent-decode URL parameters before parsing them (closes #103)

chi matches routes against the escaped path when a request has one and
hands the handlers their URL parameters still percent-encoded. The home
page's lookup form encodes the address it asks for, so every IPv6 lookup
answered 400, as did a comma-separated address list or a prefix that a
client percent-encoded. The router now matches against the decoded path,
so every handler reads its parameters decoded.

Model: opus-5-5

internal/server/middleware.go

@@ -10,6 +10,8 @@ import (
 	"net/http"
 	"sync"
 	"time"
+
+	"github.com/go-chi/chi/v5"
 )
 
 // responseWriter wraps http.ResponseWriter to capture the response
@@ -281,3 +283,16 @@ func RequestLoggerMiddleware(logger *slog.Logger) func(http.Handler) http.Handle
 		})
 	}
 }
+
+// DecodedPathMiddleware makes the router match routes against the decoded
+// path, so that the handlers read their URL parameters decoded. Without it,
+// chi matches against the escaped path whenever the request has one and hands
+// the handlers their parameters still escaped: /ip/2001%3Adb8%3A%3A1 would
+// look up "2001%3Adb8%3A%3A1".
+func DecodedPathMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		chi.RouteContext(r.Context()).RoutePath = r.URL.Path
+
+		next.ServeHTTP(w, r)
+	})
+}

internal/server/routes.go

@@ -1,7 +1,6 @@
 package server
 
 import (
-	"net/http"
 	"time"
 
 	"github.com/go-chi/chi/v5"
@@ -13,18 +12,7 @@ func (s *Server) setupRoutes() {
 	r := chi.NewRouter()
 
 	// Middleware
-
-	// Match routes against the decoded path, so that the handlers read their
-	// URL parameters decoded. chi otherwise matches against the escaped path
-	// when the request has one and leaves the parameters escaped:
-	// /ip/2001%3Adb8%3A%3A1 would look up "2001%3Adb8%3A%3A1".
-	r.Use(func(next http.Handler) http.Handler {
-		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-			chi.RouteContext(req.Context()).RoutePath = req.URL.Path
-
-			next.ServeHTTP(w, req)
-		})
-	})
+	r.Use(DecodedPathMiddleware)
 	r.Use(middleware.RequestID)
 	r.Use(middleware.RealIP)
 	r.Use(RequestLoggerMiddleware(s.logger.Logger)) // Structured request logging