Enum UsernameError 

#[non_exhaustive]
pub enum UsernameError {
    Empty,
    TooLong {
        len: usize,
        max: usize,
    },
    AddressShaped,
    ControlCharacter,
}

Why a username string was rejected by Username::from_str.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Empty

The username is empty, or is nothing but whitespace.

Whitespace-only is refused here rather than treated as a name: a claim nobody can type back, and that renders as nothing at all in every UI, is not a name. Note that normalization does not remove it — NFC discards nothing — so this is a screen, not a consequence of one.

TooLong

The normalized username exceeds Username::MAX_BYTES.

Measured after normalization, since that is the form that gets published, hashed and signed.

Fields

len: usize

Normalized length in bytes.

max: usize

The ceiling.

AddressShaped

The username has the shape of an Address.

Refused at the type rather than at publish time so no caller can skip the screen. Two namespaces that never share a spelling cannot be confused by a UI that renders both, and a claim on an address-shaped name has no legitimate use.

ControlCharacter

The username contains a control or format character.

A name that can contain a newline or a bidi override is a name that renders as something other than itself in every UI that displays it.

Both Unicode Cc (control) and Cf (format) are refused, and the second is the one that matters: char::is_control covers only Cc, so a screen built on it alone lets through U+202E RIGHT-TO-LEFT OVERRIDE and the zero-width joiners — exactly the characters that make a name display as something other than its own bytes. Confusables between scripts remain out of scope (see the module docs); characters whose entire function is to alter rendering are not.

Trait Implementations

impl Clone for UsernameError

fn clone(&self) -> UsernameError

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for UsernameError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for UsernameError

fn fmt(&self, __formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for UsernameError

impl Error for UsernameError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl PartialEq for UsernameError

fn eq(&self, other: &UsernameError) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for UsernameError