[release-branch.go1.20] Revert "net/http: FileServer method check + minimal OPTIONS implementation"

This reverts https://go.dev/cl/413554

Reason for revert: Backwards-incompatible change in behavior.

For golang#53501
For golang#59375
Fixes golang#59469

Change-Id: Ic3f63b378f9c819599b32e5e6e410f6163849317
Reviewed-on: https://go-review.googlesource.com/c/go/+/482635
Reviewed-by: Tatiana Bradley <[email protected]>
Run-TryBot: Damien Neil <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
(cherry picked from commit c02fa75)
Reviewed-on: https://go-review.googlesource.com/c/go/+/488635
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: neild

src/net/http/fs.go

@@ -858,22 +858,12 @@ func FileServer(root FileSystem) Handler {
 }
 
 func (f *fileHandler) ServeHTTP(w ResponseWriter, r *Request) {
-	const options = MethodOptions + ", " + MethodGet + ", " + MethodHead
-
-	switch r.Method {
-	case MethodGet, MethodHead:
-		if !strings.HasPrefix(r.URL.Path, "/") {
-			r.URL.Path = "/" + r.URL.Path
-		}
-		serveFile(w, r, f.root, path.Clean(r.URL.Path), true)
-
-	case MethodOptions:
-		w.Header().Set("Allow", options)
-
-	default:
-		w.Header().Set("Allow", options)
-		Error(w, "read-only", StatusMethodNotAllowed)
+	upath := r.URL.Path
+	if !strings.HasPrefix(upath, "/") {
+		upath = "/" + upath
+		r.URL.Path = upath
 	}
+	serveFile(w, r, f.root, path.Clean(upath), true)
 }
 
 // httpRange specifies the byte range to be sent to the client.

src/net/http/fs_test.go

@@ -24,7 +24,6 @@ import (
 	"reflect"
 	"regexp"
 	"runtime"
-	"sort"
 	"strings"
 	"testing"
 	"time"
@@ -420,46 +419,6 @@ func testFileServerImplicitLeadingSlash(t *testing.T, mode testMode) {
 	}
 }
 
-func TestFileServerMethodOptions(t *testing.T) { run(t, testFileServerMethodOptions) }
-func testFileServerMethodOptions(t *testing.T, mode testMode) {
-	const want = "GET, HEAD, OPTIONS"
-	ts := newClientServerTest(t, mode, FileServer(Dir("."))).ts
-
-	tests := []struct {
-		method     string
-		wantStatus int
-	}{
-		{MethodOptions, StatusOK},
-
-		{MethodDelete, StatusMethodNotAllowed},
-		{MethodPut, StatusMethodNotAllowed},
-		{MethodPost, StatusMethodNotAllowed},
-	}
-
-	for _, test := range tests {
-		req, err := NewRequest(test.method, ts.URL, nil)
-		if err != nil {
-			t.Fatal(err)
-		}
-		res, err := ts.Client().Do(req)
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer res.Body.Close()
-
-		if res.StatusCode != test.wantStatus {
-			t.Errorf("%s got status %q, want code %d", test.method, res.Status, test.wantStatus)
-		}
-
-		a := strings.Split(res.Header.Get("Allow"), ", ")
-		sort.Strings(a)
-		got := strings.Join(a, ", ")
-		if got != want {
-			t.Errorf("%s got Allow header %q, want %q", test.method, got, want)
-		}
-	}
-}
-
 func TestDirJoin(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("skipping test on windows")