Add FilterHTTPMethod and FilteringHTTPHandler

1 files changed, 48 insertions, 0 deletions

diff --git a/http.go b/http.go
new file mode 100644
index 0000000..83a6830
--- /dev/null
+++ b/http.go
@@ -0,0 +1,48 @@
+// SPDX-FileCopyrightText: © 2022 Grégoire Duchêne <gduchene@awhk.org>
+// SPDX-License-Identifier: ISC
+
+package core
+
+import (
+	"net/http"
+	"sort"
+	"strings"
+)
+
+// FilteringHTTPHandler returns a handler that will check that a request
+// was not filtered before handing it over to the passed handler.
+func FilteringHTTPHandler(handler http.Handler, filters ...HTTPFilterFunc) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		for _, filter := range filters {
+			if filter(w, req) {
+				return
+			}
+		}
+		handler.ServeHTTP(w, req)
+	})
+}
+
+// HTTPFilterFunc describes a filtering function for HTTP headers. The
+// filtering function must return true if a request should be filtered
+// and false otherwise. The filtering function may only call functions
+// on the http.ResponseWriter or change the http.Request if a request is
+// filtered.
+type HTTPFilterFunc func(http.ResponseWriter, *http.Request) bool
+
+// FilterHTTPMethod is an HTTPFilterFunc that filters requests based on
+// the HTTP methods passed. Requests that do not have a matching method
+// will be filtered.
+func FilterHTTPMethod(methods ...string) HTTPFilterFunc {
+	sort.Strings(methods)
+	allowed := strings.Join(methods, ", ")
+	return func(w http.ResponseWriter, req *http.Request) bool {
+		for _, method := range methods {
+			if method == req.Method {
+				return false
+			}
+		}
+		w.Header().Set("Allowed", allowed)
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		return true
+	}
+}