Enum McpSessionIdError 

pub enum McpSessionIdError {
    Empty,
    NotVisibleAscii {
        index: usize,
        byte: u8,
        low: u8,
        high: u8,
    },
    WrongLength {
        expected: usize,
        found: usize,
    },
    NotHex {
        index: usize,
        character: char,
    },
    Unparsable {
        source: ParseIntError,
    },
}

Why a Mcp-Session-Id header is not an McpSessionId.

Four distinct refusals rather than one, because they are four different mistakes and a caller that gets one of them back needs to know which. A single “invalid” string would make the common case — a client that sent the wrong header name, or one that pre-dates the session concept — impossible to tell apart from a truncated value.

Deliberately not Copy, unlike the value types beside it: the last variant carries a ParseIntError, and Copy is only worth having on a type that lives on the request path. This one is produced once, on a refusal.

Variants

Empty

The value was nothing but optional whitespace.

NotVisibleAscii

A byte outside the visible-ASCII range reached the value.

Fields

index: usize

Byte offset within the trimmed value.

byte: u8

The offending byte.

low: u8

Lowest permitted byte, VISIBLE_ASCII_RANGE’s start.

high: u8

Highest permitted byte, VISIBLE_ASCII_RANGE’s end.

WrongLength

The value was not sixteen characters.

Fields

expected: usize

The fixed width, DIGITS.

found: usize

What arrived.

NotHex

A character in the value was not a hexadecimal digit.

Fields

index: usize

Byte offset within the trimmed value.

character: char

The offending character.

Unparsable

The digits were well-formed but did not denote a u64.

Fields

source: ParseIntError

The underlying conversion failure.

Implementations

impl McpSessionIdError

pub fn validate_opaque(value: &str) -> Result<&str, Self>

Checks a raw header value and returns its significant part.

Trimming first is not leniency for its own sake: RFC 9110 §5.5 allows optional whitespace around a field-value and an HTTP parser is entitled to hand the field with it still attached. Rejecting a legal header because of transport framing the client could not have avoided would be our bug, not theirs.

Interior whitespace is not tolerated even though field-value technically permits it, and the narrowing is deliberate: that allowance is for a human-typed Subject:, and a session id is a machine-carried identifier that no reader would expect to be trimmed. A value with a tab in the middle is refused as not visible ASCII, which is where a reader would look for it.

Errors

McpSessionIdError::Empty for a wholly blank value, and McpSessionIdError::NotVisibleAscii naming the first byte that is out of range. Only the first offender is reported: the value is a header, and a message listing every bad byte in a 4 KiB garbage string is noise.

This checks only what the specification requires of a session id: “The session ID MUST only contain visible ASCII characters”, and it is otherwise the server’s to shape. A client holds whatever id the server it dialled issued — a UUID, a JWT, a counter — so it must not insist on the sixteen-digit form this crate’s own server happens to write; validate is for the server side, which does.

pub fn validate(value: &str) -> Result<&str, Self>

Checks that a value is the form this crate’s own server issues.

Errors

Everything validate_opaque refuses, plus a value that is not sixteen hexadecimal digits.

Trait Implementations

impl Clone for McpSessionIdError

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for McpSessionIdError

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

Formats the value using the given formatter.

impl Display for McpSessionIdError

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

Formats the value using the given formatter.

impl Eq for McpSessionIdError

impl Error for McpSessionIdError

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 McpSessionIdError

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for McpSessionIdError