Struct Extension 

pub struct Extension<T>(pub T);

Extract typed data from router extensions.

This extractor retrieves data that was added to the router via crate::McpRouter::with_state() or crate::McpRouter::with_extension(), or inserted by middleware into the request context’s extensions.

Example

use std::sync::Arc;
use tower_mcp::{McpRouter, ToolBuilder, CallToolResult};
use tower_mcp::extract::{Extension, Json};
use schemars::JsonSchema;
use serde::Deserialize;

#[derive(Clone)]
struct DatabasePool {
    url: String,
}

#[derive(Deserialize, JsonSchema)]
struct QueryInput {
    sql: String,
}

let pool = Arc::new(DatabasePool { url: "postgres://...".into() });

let tool = ToolBuilder::new("query")
    .description("Run a query")
    .extractor_handler_typed::<_, _, _, QueryInput>(
        (),
        |Extension(db): Extension<Arc<DatabasePool>>, Json(input): Json<QueryInput>| async move {
            Ok(CallToolResult::text(format!("Query on {}: {}", db.url, input.sql)))
        },
    )
    .build()
    .unwrap();

let router = McpRouter::new()
    .with_state(pool)
    .tool(tool);

Rejection

Returns an ExtensionRejection if the requested type is not found in the extensions. The rejection contains the type name of the missing extension.

Tuple Fields

0: T

Trait Implementations

impl<T: Clone> Clone for Extension<T>

fn clone(&self) -> Extension<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Extension<T>

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

Formats the value using the given formatter.

impl<T> Deref for Extension<T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<S, T> FromToolRequest<S> for Extension<T>

where T: Clone + Send + Sync + 'static,

type Rejection = ExtensionRejection

The rejection type returned when extraction fails.

fn from_tool_request( ctx: &RequestContext, _state: &S, _args: &Value, ) -> Result<Self, Self::Rejection>

Extract this type from the tool request.