Function is_valid_hostname 

pub fn is_valid_hostname(hostname: &str) -> bool

Validates if a string is a valid hostname according to RFC 1035.

A valid hostname must:

• Be between 1 and 253 characters in length
• Not use reserved top-level domains (.localhost, .internal, .arpa, .local)
• Not be an IPv4 or IPv6 address
• Contain only valid hostname characters (letters, digits, hyphens, dots)
• Have valid DNS labels (no leading/trailing hyphens, max 63 chars per label)

Arguments

• hostname - The hostname string to validate

Returns

true if the hostname is valid according to RFC 1035, false otherwise

Examples

use atproto_identity::validation::is_valid_hostname;

// Valid hostnames
assert!(is_valid_hostname("example.com"));
assert!(is_valid_hostname("sub.example.com"));
assert!(is_valid_hostname("test-host.example.com"));
assert!(is_valid_hostname("localhost"));

// Invalid hostnames
assert!(!is_valid_hostname("192.168.1.1")); // IPv4 address
assert!(!is_valid_hostname("example.localhost")); // Reserved TLD
assert!(!is_valid_hostname("example..com")); // Double dot
assert!(!is_valid_hostname("-example.com")); // Leading hyphen