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.

1 files changed, 17 insertions, 3 deletions

diff --git a/modules/caddyhttp/fileserver/matcher.go b/modules/caddyhttp/fileserver/matcher.go
index 9144ca4..1844421 100644
--- a/modules/caddyhttp/fileserver/matcher.go
+++ b/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"