fix: allow updated domain names in federation (#11365)

additionally also disallow overlapping domain names

cmd/utils.go

@@ -665,37 +665,56 @@ func restQueries(keys ...string) []string {
 	return accumulator
 }
 
-// lcp finds the longest common prefix of the input strings.
-// It compares by bytes instead of runes (Unicode code points).
-// It's up to the caller to do Unicode normalization if desired
-// (e.g. see golang.org/x/text/unicode/norm).
-func lcp(l []string) string {
-	// Special cases first
-	switch len(l) {
-	case 0:
+// Suffix returns the longest common suffix of the provided strings
+func lcpSuffix(strs []string) string {
+	return lcp(strs, false)
+}
+
+func lcp(strs []string, pre bool) string {
+	// short-circuit empty list
+	if len(strs) == 0 {
 		return ""
-	case 1:
-		return l[0]
 	}
-	// LCP of min and max (lexigraphically)
-	// is the LCP of the whole set.
-	min, max := l[0], l[0]
-	for _, s := range l[1:] {
-		switch {
-		case s < min:
-			min = s
-		case s > max:
-			max = s
+	xfix := strs[0]
+	// short-circuit single-element list
+	if len(strs) == 1 {
+		return xfix
+	}
+	// compare first to rest
+	for _, str := range strs[1:] {
+		xfixl := len(xfix)
+		strl := len(str)
+		// short-circuit empty strings
+		if xfixl == 0 || strl == 0 {
+			return ""
+		}
+		// maximum possible length
+		maxl := xfixl
+		if strl < maxl {
+			maxl = strl
+		}
+		// compare letters
+		if pre {
+			// prefix, iterate left to right
+			for i := 0; i < maxl; i++ {
+				if xfix[i] != str[i] {
+					xfix = xfix[:i]
+					break
+				}
+			}
+		} else {
+			// suffix, iterate right to left
+			for i := 0; i < maxl; i++ {
+				xi := xfixl - i - 1
+				si := strl - i - 1
+				if xfix[xi] != str[si] {
+					xfix = xfix[xi+1:]
+					break
+				}
+			}
 		}
 	}
-	for i := 0; i < len(min) && i < len(max); i++ {
-		if min[i] != max[i] {
-			return min[:i]
-		}
-	}
-	// In the case where lengths are not equal but all bytes
-	// are equal, min is the answer ("foo" < "foobar").
-	return min
+	return xfix
 }
 
 // Returns the mode in which MinIO is running