From e2da5769f56b8ee9e48033fc44ad38db0c03d802 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Fri, 17 Jan 2020 11:41:44 +0100
Subject: [PATCH] Improve OPTIONS handling

---
 internal/server.go | 13 ++++++++++---
 server.go          | 21 +++++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/internal/server.go b/internal/server.go
index bf5cf1d..e88aed2 100644
--- a/internal/server.go
+++ b/internal/server.go
@@ -1,10 +1,11 @@
 package internal
 
 import (
-	"net/http"
+	"encoding/xml"
 	"fmt"
 	"mime"
-	"encoding/xml"
+	"net/http"
+	"strings"
 )
 
 type HTTPError struct {
@@ -26,6 +27,7 @@ func (err *HTTPError) Error() string {
 }
 
 type Backend interface {
+	Options(r *http.Request) ([]string, error)
 	HeadGet(w http.ResponseWriter, r *http.Request) error
 	Propfind(r *http.Request, pf *Propfind, depth Depth) (*Multistatus, error)
 }
@@ -61,7 +63,12 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *Handler) handleOptions(w http.ResponseWriter, r *http.Request) error {
-	w.Header().Add("Allow", "OPTIONS, GET, HEAD, PROPFIND")
+	methods, err := h.Backend.Options(r)
+	if err != nil {
+		return err
+	}
+
+	w.Header().Add("Allow", strings.Join(methods, ", "))
 	w.Header().Add("DAV", "1, 3")
 	w.WriteHeader(http.StatusNoContent)
 	return nil
diff --git a/server.go b/server.go
index f9d84a9..f6ab544 100644
--- a/server.go
+++ b/server.go
@@ -37,6 +37,27 @@ type backend struct {
 	FileSystem FileSystem
 }
 
+func (b *backend) Options(r *http.Request) ([]string, error) {
+	f, err := b.FileSystem.Open(r.URL.Path)
+	if os.IsNotExist(err) {
+		return []string{http.MethodOptions}, nil
+	} else if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	fi, err := f.Stat()
+	if err != nil {
+		return nil, err
+	}
+
+	if fi.IsDir() {
+		return []string{http.MethodOptions, "PROPFIND"}, nil
+	} else {
+		return []string{http.MethodOptions, http.MethodHead, http.MethodGet, "PROPFIND"}, nil
+	}
+}
+
 func (b *backend) HeadGet(w http.ResponseWriter, r *http.Request) error {
 	f, err := b.FileSystem.Open(r.URL.Path)
 	if err != nil {