is_valid_hostname

Checks that hostname is a valid hostname (RFC 1035 and RFC 1123, ASCII only).

The rules: at most 253 octets, not counting one optional trailing dot; labels of 1 to 63 octets made of ASCII letters, digits and hyphens; no label starts or ends with a hyphen. A label may start with a digit, but the last label may not be a number (decimal like 1, or hexadecimal like 0x7f): RFC 1123 section 2.1 keeps the top-level label alphabetic so that a hostname is never mistaken for an address, and URL parsers do read 127.1, 2130706433 or 0x7f000001 as 127.0.0.1. Underscores are refused (they are not hostname characters), and so are non-ASCII characters: convert an internationalized name to its xn-- form first.

This checks syntax only. It is not an SSRF check: a name that passes can still resolve to a private address. To guard a server that fetches user-supplied URLs, parse the URL first, then check the address you will actually connect to with is_public_ip.

Import

use helpers4::net::is_valid_hostname;

Cargo feature net (enabled by default). To compile only this module:

cargo add helpers4 --no-default-features --features net

or in Cargo.toml:

[dependencies]
helpers4 = { version = "0.0.5", default-features = false, features = ["net"] }

Signature

pub fn is_valid_hostname(hostname: &str) -> Result<(), HostnameError>

Parameters

Parameter	Type	Description
hostname	&str	The hostname to validate.

Returns

Result<(), HostnameError> — Ok on success, otherwise an Err: see Errors.

Errors

A HostnameError naming the first rule that fails.

Examples

use helpers4::net::{is_valid_hostname, HostnameError};

assert!(is_valid_hostname("example.com").is_ok());
assert!(is_valid_hostname("localhost.").is_ok());
assert_eq!(is_valid_hostname("-bad.example"), Err(HostnameError::HyphenEdge));
assert_eq!(is_valid_hostname("a..b"), Err(HostnameError::EmptyLabel));
assert_eq!(is_valid_hostname("127.0.0.1"), Err(HostnameError::NumericLastLabel));

Error type: HostnameError

Why a string is not a valid hostname (see is_valid_hostname).

use helpers4::net::HostnameError;

#[non_exhaustive]
pub enum HostnameError {
    /// The string is empty.
    Empty,
    /// The name is longer than 253 octets (not counting an optional trailing dot).
    TooLong,
    /// A label is empty: a leading dot, two consecutive dots, or a lone `"."`.
    EmptyLabel,
    /// A label is longer than 63 octets.
    LabelTooLong,
    /// A character other than an ASCII letter, digit or hyphen.
    InvalidChar {
        /// Byte offset of the character in the input.
        index: usize,
        /// The offending character.
        found: char,
    },
    /// A label starts or ends with a hyphen.
    HyphenEdge,
    /// The last label is a number (`127.1`, `2130706433`, `0x7f`): URL parsers read such a name as
    /// an IPv4 address, not as a hostname.
    NumericLastLabel,
}

Source

src/net/is_valid_hostname.rs