Enum TransportKind 

pub enum TransportKind {
    Stdio,
    LegacySse,
    StreamableHttp,
    StatelessHttp,
}

A transport the specification defines.

Ordered by the revision that introduced it, so the declaration order is chronological and Ord is derived rather than written. See tests::derived_ordering_agrees_in_both_directions.

Variants

Stdio

Newline-delimited JSON over a child process’s standard streams.

Defined by every revision, 2024-11-05 through the newest. It predates the HTTP transports and is not a lifecycle the protocol version changes.

LegacySse

HTTP+SSE as defined for 2024-11-05, where the client opened a GET stream and the server held a single POST endpoint.

Removed in 2025-03-26. Kept as a distinct variant rather than folded into StreamableHttp because a bridge that receives a message from one of these has to be able to say so, and because it is the only revision that can require this branch to exist.

StreamableHttp

The stateful Streamable HTTP transport introduced in 2025-03-26: a single endpoint that upgrades to SSE, with an Mcp-Session-Id header tying calls together.

StatelessHttp

The stateless lifecycle introduced in 2026-07-28.

Distinct from StreamableHttp rather than a mode of it, because the two differ in what the session tracks: this one has no protocol-level session at all, every request carries its version and capabilities in _meta, and there is no initialize handshake. Code that caches per session cannot treat them alike.

Implementations

impl TransportKind

pub const ALL: [Self; 4]

Every transport, in the order the revisions introduced them.

pub const fn as_str(self) -> &'static str

The transport’s short name, for logs, errors and CLI arguments.

These are this project’s own vocabulary rather than the specification’s — the spec never names its transports in a versioned field — so StreamableHttp is http and StatelessHttp is http-stateless. The CLI surfaces the same spellings, and changing one means changing both.

Trait Implementations

impl Clone for TransportKind

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for TransportKind

impl Debug for TransportKind

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

Formats the value using the given formatter.

impl Display for TransportKind

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

Formats the value using the given formatter.

impl Eq for TransportKind

impl Hash for TransportKind

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for TransportKind

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

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

Restrict a value to a certain range.

impl PartialEq for TransportKind

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

Equality operator ==.

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

Inequality operator !=.

impl PartialOrd for TransportKind

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for TransportKind