Struct StatelessRequestMeta 

pub struct StatelessRequestMeta {
    pub progress_token: Option<ProgressToken>,
    pub protocol_version: Option<String>,
    pub client_info: Option<Implementation>,
    pub client_capabilities: Option<ClientCapabilities>,
    pub log_level: Option<LogLevel>,
}

Per-request metadata carried in JSON-RPC _meta per SEP-2575.

In the 2026-07-28 protocol every request is self-contained – there is no initialize handshake and no session. The fields previously negotiated at init time (protocol version, client identity, client capabilities) ride on each request via the _meta object. The MCP-defined keys are reverse-DNS namespaced under io.modelcontextprotocol/.

Wire shape (per the FINAL spec):

"_meta": {
  "progressToken": "...",
  "io.modelcontextprotocol/protocolVersion": "2026-07-28",
  "io.modelcontextprotocol/clientInfo": { "name": "...", "version": "..." },
  "io.modelcontextprotocol/clientCapabilities": { ... },
  "io.modelcontextprotocol/logLevel": "info"
}

protocolVersion and clientCapabilities are REQUIRED per the spec. clientInfo is a SHOULD – clients are expected to send it on every request unless specifically configured not to, but a server MUST NOT reject a request for lacking it. All three are typed as Option<_> here so deserialization stays tolerant of partial/transitional clients; server-side validation should reject requests that lack the two required fields.

Fields

progress_token: Option<ProgressToken>

Progress token for receiving progress notifications.

protocol_version: Option<String>

The MCP protocol version this request targets.

For HTTP this MUST match the MCP-Protocol-Version header. On stdio and custom JSON-RPC bindings, this field independently selects the request lifecycle. Spec key: io.modelcontextprotocol/protocolVersion.

client_info: Option<Implementation>

Identifies the client software making this request. Clients SHOULD include this on every request unless specifically configured not to (SEP-2575, final – earlier SEP-2575 drafts had this as REQUIRED; the upstream schema demoted it before finalization). Self-reported and unverified: servers SHOULD NOT use it for behavior or security decisions, only display/logging/debugging.

client_capabilities: Option<ClientCapabilities>

Capabilities the client advertises for this specific request. REQUIRED per SEP-2575.

log_level: Option<LogLevel>

Optional per-request log-level override.

Implementations

impl StatelessRequestMeta

pub fn from_params(params: &Value) -> Option<Self>

Extract stateless request metadata from JSON-RPC request params.

The metadata is expected in the _meta field of the params object.

pub fn has_client_capabilities(&self) -> bool

Check if this request includes client capabilities.

pub fn has_client_info(&self) -> bool

Check if this request includes client identity.

Trait Implementations

impl Clone for StatelessRequestMeta

fn clone(&self) -> StatelessRequestMeta

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for StatelessRequestMeta

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

Formats the value using the given formatter.

impl Default for StatelessRequestMeta

fn default() -> StatelessRequestMeta

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for StatelessRequestMeta

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for StatelessRequestMeta

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.