Better trie implementations

dataset/dnstrie/name.go

@@ -0,0 +1,62 @@
+package dnstrie
+
+import (
+	"strings"
+	"unicode"
+)
+
+// isValidDomainName validates if the given string is a valid DNS hostname.
+// A valid hostname consists of a series of labels separated by dots.
+// Each label must:
+// - Be between 1 and 63 characters long.
+// - Consist only of ASCII letters ('a'-'z', 'A'-'Z'), digits ('0'-'9'), and hyphens ('-').
+// - Not start or end with a hyphen.
+// The total length of the hostname (including dots) must not exceed 253 characters.
+func isValidDomainName(host string) bool {
+	// 1. Check total length. The maximum length of a full hostname is 253 characters.
+	if len(host) > 253 {
+		return false
+	}
+
+	// An empty string is not a valid hostname.
+	if host == "" {
+		return false
+	}
+
+	// 2. Handle optional trailing dot for FQDNs.
+	// If the hostname ends with a dot, we remove it for validation purposes.
+	if strings.HasSuffix(host, ".") {
+		host = host[:len(host)-1]
+	}
+
+	// After removing a potential trailing dot, the string might be empty.
+	if host == "" {
+		return false
+	}
+
+	// 3. Split the hostname into labels.
+	labels := strings.Split(host, ".")
+
+	// 4. Validate each label.
+	for _, label := range labels {
+		// a. Check label length (1 to 63 characters).
+		if len(label) < 1 || len(label) > 63 {
+			return false
+		}
+
+		// b. Check if label starts or ends with a hyphen.
+		if strings.HasPrefix(label, "-") || strings.HasSuffix(label, "-") {
+			return false
+		}
+
+		// c. Check for allowed characters in the label.
+		for _, char := range label {
+			if !unicode.IsLetter(char) && !unicode.IsDigit(char) && char != '-' {
+				return false
+			}
+		}
+	}
+
+	// If all checks pass, the hostname is valid.
+	return true
+}