fileserver: Don't assume len(str) == len(ToLower(str)) (fix #3623)

We can't use a positional index on an original string that we got from
its lower-cased equivalent. Implement our own IndexFold() function b/c
the std lib does not have one.

modules/caddyhttp/fileserver/matcher.go

@@ -117,11 +117,13 @@ func (m *MatchFile) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 					return d.ArgErr()
 				}
 				m.TryPolicy = d.Val()
-			case "split":
+			case "split_path":
 				m.SplitPath = d.RemainingArgs()
 				if len(m.SplitPath) == 0 {
 					return d.ArgErr()
 				}
+			default:
+				return d.Errf("unrecognized subdirective: %s", d.Val())
 			}
 		}
 	}
@@ -279,9 +281,8 @@ func strictFileExists(file string) bool {
 // in the split value. Returns the path as-is if the
 // path cannot be split.
 func (m MatchFile) firstSplit(path string) string {
-	lowerPath := strings.ToLower(path)
 	for _, split := range m.SplitPath {
-		if idx := strings.Index(lowerPath, strings.ToLower(split)); idx > -1 {
+		if idx := indexFold(path, split); idx > -1 {
 			pos := idx + len(split)
 			// skip the split if it's not the final part of the filename
 			if pos != len(path) && !strings.HasPrefix(path[pos:], "/") {
@@ -293,6 +294,19 @@ func (m MatchFile) firstSplit(path string) string {
 	return path
 }
 
+// There is no strings.IndexFold() function like there is strings.EqualFold(),
+// but we can use strings.EqualFold() to build our own case-insensitive
+// substring search (as of Go 1.14).
+func indexFold(haystack, needle string) int {
+	nlen := len(needle)
+	for i := 0; i+nlen < len(haystack); i++ {
+		if strings.EqualFold(haystack[i:i+nlen], needle) {
+			return i
+		}
+	}
+	return -1
+}
+
 const (
 	tryPolicyFirstExist      = "first_exist"
 	tryPolicyLargestSize     = "largest_size"

modules/caddyhttp/fileserver/matcher_test.go

@@ -22,69 +22,84 @@ import (
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
 )
 
-func TestPhpFileMatcher(t *testing.T) {
-
+func TestPHPFileMatcher(t *testing.T) {
 	for i, tc := range []struct {
-		path string
+		path         string
 		expectedPath string
-		matched bool
+		matched      bool
 	}{
 		{
-			path: "/index.php",
+			path:         "/index.php",
 			expectedPath: "/index.php",
-			matched: true,
+			matched:      true,
 		},
 		{
-			path: "/index.php/somewhere",
+			path:         "/index.php/somewhere",
 			expectedPath: "/index.php",
-			matched: true,
+			matched:      true,
 		},
 		{
-			path: "/remote.php",
+			path:         "/remote.php",
 			expectedPath: "/remote.php",
-			matched: true,
+			matched:      true,
 		},
 		{
-			path: "/remote.php/somewhere",
+			path:         "/remote.php/somewhere",
 			expectedPath: "/remote.php",
-			matched: true,
+			matched:      true,
 		},
 		{
-			path: "/missingfile.php",
+			path:    "/missingfile.php",
 			matched: false,
 		},
 		{
-			path: "/notphp.php.txt",
+			path:         "/notphp.php.txt",
 			expectedPath: "/notphp.php.txt",
-			matched: true,
+			matched:      true,
 		},
 		{
-			path: "/notphp.php.txt/",
+			path:         "/notphp.php.txt/",
 			expectedPath: "/notphp.php.txt",
-			matched: true,
+			matched:      true,
 		},
 		{
-			path: "/notphp.php.txt.suffixed",
+			path:    "/notphp.php.txt.suffixed",
 			matched: false,
 		},
 		{
-			path: "/foo.php.php/index.php",
+			path:         "/foo.php.php/index.php",
 			expectedPath: "/foo.php.php/index.php",
-			matched: true,
+			matched:      true,
+		},
+		{
+			path:         "/foo.php.PHP/index.php",
+			expectedPath: "/foo.php.PHP/index.php",
+			matched:      true,
+		},
+		{
+			// See https://github.com/caddyserver/caddy/issues/3623
+			path:         "/%E2%C3",
+			expectedPath: "/%E2%C3",
+			matched:      false,
 		},
 	} {
 		m := &MatchFile{
 			Root:      "./testdata",
-			TryFiles:  []string{"{http.request.uri.path}"},
+			TryFiles:  []string{"{http.request.uri.path}", "{http.request.uri.path}/index.php"},
 			SplitPath: []string{".php"},
 		}
 
-		req := &http.Request{URL: &url.URL{Path: tc.path}}
+		u, err := url.Parse(tc.path)
+		if err != nil {
+			t.Fatalf("Test %d: parsing path: %v", i, err)
+		}
+
+		req := &http.Request{URL: u}
 		repl := caddyhttp.NewTestReplacer(req)
 
 		result := m.Match(req)
 		if result != tc.matched {
-			t.Fatalf("Test %d: match bool result: %v, expected: %v", i, result, tc.matched)
+			t.Fatalf("Test %d: expected match=%t, got %t", i, tc.matched, result)
 		}
 
 		rel, ok := repl.Get("http.matchers.file.relative")
@@ -99,4 +114,4 @@ func TestPhpFileMatcher(t *testing.T) {
 			t.Fatalf("Test %d: actual path: %v, expected: %v", i, rel, tc.expectedPath)
 		}
 	}
-}
+}