Struct MiddlewareStack 

pub struct MiddlewareStack { /* private fields */ }

Ordered collection of middleware with execution logic

The stack executes middleware in two phases:

1. Before dispatch: Middleware execute in registration order

   • First error stops the chain
   • Session injections accumulate across all middleware

2. After dispatch: Middleware execute in reverse registration order

   • Allows proper cleanup/finalization
   • Errors replace the result

Examples

use turul_http_mcp_server::middleware::{MiddlewareStack, McpMiddleware, RequestContext, SessionInjection, MiddlewareError};
use turul_mcp_session_storage::SessionView;
use async_trait::async_trait;
use std::sync::Arc;

struct LoggingMiddleware;

#[async_trait]
impl McpMiddleware for LoggingMiddleware {
    async fn before_dispatch(
        &self,
        ctx: &mut RequestContext<'_>,
        _session: Option<&dyn SessionView>,
        _injection: &mut SessionInjection,
    ) -> Result<(), MiddlewareError> {
        println!("Request: {}", ctx.method());
        Ok(())
    }
}

let mut stack = MiddlewareStack::new();
stack.push(Arc::new(LoggingMiddleware));

assert_eq!(stack.len(), 1);

Implementations

impl MiddlewareStack

pub fn new() -> Self

Create an empty middleware stack

pub fn push(&mut self, middleware: Arc<dyn McpMiddleware>)

Add middleware to the end of the stack

Parameters

• middleware: Middleware implementation (must be Arc-wrapped for sharing)

Execution Order

• Before dispatch: First added executes first
• After dispatch: First added executes last (reverse order)

pub fn len(&self) -> usize

Get the number of middleware in the stack

pub fn is_empty(&self) -> bool

Check if the stack is empty

pub async fn execute_before( &self, ctx: &mut RequestContext<'_>, session: Option<&dyn SessionView>, ) -> Result<SessionInjection, MiddlewareError>

Execute all middleware before dispatch

Parameters

• ctx: Mutable request context
• session: Optional read-only session view
  • None for initialize (session doesn’t exist yet)
  • Some(session) for all other methods

Returns

• Ok(SessionInjection): All middleware succeeded, contains accumulated injections
• Err(MiddlewareError): First middleware that failed

Execution

1. Execute each middleware in registration order
2. Accumulate session injections from all middleware
3. Stop on first error

pub async fn execute_after( &self, ctx: &RequestContext<'_>, result: &mut DispatcherResult, ) -> Result<(), MiddlewareError>

Execute all middleware after dispatch

Parameters

• ctx: Read-only request context
• result: Mutable dispatcher result

Returns

• Ok(()): All middleware succeeded
• Err(MiddlewareError): First middleware that failed

Execution

1. Execute each middleware in reverse registration order
2. Stop on first error
3. Allow middleware to modify result

Trait Implementations

impl Clone for MiddlewareStack

fn clone(&self) -> MiddlewareStack

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Default for MiddlewareStack

fn default() -> MiddlewareStack

Returns the “default value” for a type.