transport_context

Transport-specific metadata attached to each inbound message.

TransportContext is the base; each transport defines its own subclass with whatever fields make sense (HTTP request id, ASGI scope, stdio process handle, etc.). The dispatcher passes it through opaquely; only the layers above the dispatcher (ServerRunner, Context, user handlers) read its concrete fields.

TransportContext `dataclass`

Base transport metadata for an inbound message.

Subclass per transport and add fields as needed. Instances are immutable.

Source code in src/mcp/shared/transport_context.py

@dataclass(kw_only=True, frozen=True)
class TransportContext:
    """Base transport metadata for an inbound message.

    Subclass per transport and add fields as needed. Instances are immutable.
    """

    kind: str
    """Short identifier for the transport (e.g. `"stdio"`, `"streamable-http"`)."""

    can_send_request: bool
    """Whether the transport can deliver server-initiated requests to the peer.

    `False` for stateless HTTP and HTTP with JSON response mode; `True` for
    stdio, SSE, and stateful streamable HTTP. When `False`,
    `DispatchContext.send_raw_request` raises `NoBackChannelError`.
    """

    headers: Mapping[str, str] | None = None
    """Request headers carried by this message, when the transport has them.

    Populated by HTTP-based transports; `None` on stdio. Handlers should
    None-check before use.
    """

kind `instance-attribute`

kind: str

Short identifier for the transport (e.g. "stdio", "streamable-http").

can_send_request `instance-attribute`

can_send_request: bool

Whether the transport can deliver server-initiated requests to the peer.

False for stateless HTTP and HTTP with JSON response mode; True for stdio, SSE, and stateful streamable HTTP. When False, DispatchContext.send_raw_request raises NoBackChannelError.

headers `class-attribute` `instance-attribute`

headers: Mapping[str, str] | None = None

Request headers carried by this message, when the transport has them.

Populated by HTTP-based transports; None on stdio. Handlers should None-check before use.

transport_context