crank/apps/mcp-server/src/app.rs

use std::{sync::Arc, time::Duration};

use axum::{
    Json, Router,
    extract::State,
    http::{
        HeaderMap, HeaderValue, StatusCode,
        header::{self, ACCEPT},
    },
    response::{IntoResponse, Response},
    routing::get,
};
use mcpaas_registry::{PostgresRegistry, RegistryOperation};
use mcpaas_runtime::{RuntimeError, RuntimeExecutor, RuntimeOperation};
use serde::{Deserialize, Serialize};
use serde_json::{Value, json};

use crate::{
    catalog::PublishedToolCatalog,
    jsonrpc::{
        CURRENT_PROTOCOL_VERSION, DEFAULT_PROTOCOL_VERSION, is_notification, is_request,
        is_response, jsonrpc_error, jsonrpc_result, method_name, negotiated_protocol_version,
        params, request_id,
    },
    session::{SessionState, SessionStore},
};

const HEADER_MCP_SESSION_ID: &str = "MCP-Session-Id";
const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";

#[derive(Clone)]
pub struct AppState {
    catalog: PublishedToolCatalog,
    runtime: RuntimeExecutor,
    sessions: SessionStore,
    allowed_origins: AllowedOrigins,
}

#[derive(Clone)]
pub struct AllowedOrigins {
    public_origin: Option<String>,
}

#[derive(Debug, Serialize, Deserialize)]
struct InitializeParams {
    #[serde(rename = "protocolVersion")]
    protocol_version: String,
}

#[derive(Debug, Serialize, Deserialize)]
struct ToolCallParams {
    name: String,
    #[serde(default)]
    arguments: Value,
}

pub fn build_app(
    registry: PostgresRegistry,
    refresh_interval: Duration,
    public_base_url: Option<String>,
) -> Router {
    let state = Arc::new(AppState {
        catalog: PublishedToolCatalog::new(registry, refresh_interval),
        runtime: RuntimeExecutor::new(),
        sessions: SessionStore::new(),
        allowed_origins: AllowedOrigins::new(public_base_url),
    });

    Router::new()
        .route("/health", get(health))
        .route("/", get(mcp_get).post(mcp_post).delete(mcp_delete))
        .route("/mcp", get(mcp_get).post(mcp_post).delete(mcp_delete))
        .with_state(state)
}

async fn health() -> Json<Value> {
    Json(json!({
        "service": "mcp-server",
        "status": "ok"
    }))
}

async fn mcp_get() -> Response {
    StatusCode::METHOD_NOT_ALLOWED.into_response()
}

async fn mcp_delete(State(state): State<Arc<AppState>>, headers: HeaderMap) -> Response {
    match session_id_from_headers(&headers) {
        Ok(Some(session_id)) => {
            if state.sessions.delete(&session_id).await {
                StatusCode::NO_CONTENT.into_response()
            } else {
                StatusCode::NOT_FOUND.into_response()
            }
        }
        Ok(None) => StatusCode::BAD_REQUEST.into_response(),
        Err(status) => status.into_response(),
    }
}

async fn mcp_post(
    State(state): State<Arc<AppState>>,
    headers: HeaderMap,
    Json(message): Json<Value>,
) -> Response {
    if let Err(status) = validate_origin(&state.allowed_origins, &headers) {
        return status.into_response();
    }

    if let Err(status) = validate_accept_header(&headers) {
        return status.into_response();
    }

    if is_response(&message) || is_notification(&message) && method_name(&message).is_none() {
        return StatusCode::ACCEPTED.into_response();
    }

    let protocol_version = match protocol_version_from_headers(&headers) {
        Ok(value) => value,
        Err(status) => return status.into_response(),
    };

    match method_name(&message) {
        Some("initialize") if is_request(&message) => handle_initialize(state, &message).await,
        Some("notifications/initialized") if is_notification(&message) => {
            handle_initialized_notification(state, &headers).await
        }
        Some("ping") if is_request(&message) => {
            let session = match require_initialized_session(&state, &headers, &message).await {
                Ok(session) => session,
                Err(response) => return response,
            };

            json_response(
                StatusCode::OK,
                jsonrpc_result(
                    request_id(&message),
                    json!({ "protocolVersion": session.protocol_version }),
                ),
                None,
                Some(&protocol_version),
            )
        }
        Some("tools/list") if is_request(&message) => {
            let session = match require_initialized_session(&state, &headers, &message).await {
                Ok(session) => session,
                Err(response) => return response,
            };

            match state.catalog.list_tools().await {
                Ok(tools) => {
                    let definitions = tools.iter().map(tool_definition).collect::<Vec<_>>();

                    json_response(
                        StatusCode::OK,
                        jsonrpc_result(request_id(&message), json!({ "tools": definitions })),
                        None,
                        Some(&session.protocol_version),
                    )
                }
                Err(error) => internal_jsonrpc_error(&message, error),
            }
        }
        Some("tools/call") if is_request(&message) => {
            let session = match require_initialized_session(&state, &headers, &message).await {
                Ok(session) => session,
                Err(response) => return response,
            };
            let tool_call_params: ToolCallParams = match serde_json::from_value(params(&message)) {
                Ok(value) => value,
                Err(error) => {
                    return json_response(
                        StatusCode::OK,
                        jsonrpc_error(request_id(&message), -32602, error.to_string()),
                        None,
                        Some(&session.protocol_version),
                    );
                }
            };

            let arguments = if tool_call_params.arguments.is_null() {
                json!({})
            } else {
                tool_call_params.arguments
            };

            match state.catalog.get_tool(&tool_call_params.name).await {
                Ok(Some(operation)) => {
                    match state
                        .runtime
                        .execute(&RuntimeOperation::from(operation), &arguments)
                        .await
                    {
                        Ok(output) => json_response(
                            StatusCode::OK,
                            jsonrpc_result(
                                request_id(&message),
                                json!({
                                    "content": [
                                        {
                                            "type": "text",
                                            "text": serde_json::to_string_pretty(&output).unwrap_or_else(|_| "{}".to_owned())
                                        }
                                    ],
                                    "structuredContent": output,
                                    "isError": false
                                }),
                            ),
                            None,
                            Some(&session.protocol_version),
                        ),
                        Err(error) => json_response(
                            StatusCode::OK,
                            jsonrpc_result(
                                request_id(&message),
                                json!({
                                    "content": [
                                        {
                                            "type": "text",
                                            "text": error.to_string()
                                        }
                                    ],
                                    "structuredContent": {
                                        "error": {
                                            "code": runtime_error_code(&error),
                                            "message": error.to_string()
                                        }
                                    },
                                    "isError": true
                                }),
                            ),
                            None,
                            Some(&session.protocol_version),
                        ),
                    }
                }
                Ok(None) => json_response(
                    StatusCode::OK,
                    jsonrpc_error(
                        request_id(&message),
                        -32602,
                        format!("tool {} was not found", tool_call_params.name),
                    ),
                    None,
                    Some(&session.protocol_version),
                ),
                Err(error) => internal_jsonrpc_error(&message, error),
            }
        }
        Some(method) if is_notification(&message) => {
            let _ = method;
            StatusCode::ACCEPTED.into_response()
        }
        Some(method) => json_response(
            StatusCode::OK,
            jsonrpc_error(
                request_id(&message),
                -32601,
                format!("method {method} is not supported"),
            ),
            None,
            Some(&protocol_version),
        ),
        None => json_response(
            StatusCode::BAD_REQUEST,
            jsonrpc_error(Value::Null, -32600, "invalid JSON-RPC message"),
            None,
            Some(&protocol_version),
        ),
    }
}

async fn handle_initialize(state: Arc<AppState>, message: &Value) -> Response {
    let initialize_params: InitializeParams = match serde_json::from_value(params(message)) {
        Ok(value) => value,
        Err(error) => {
            return json_response(
                StatusCode::OK,
                jsonrpc_error(request_id(message), -32602, error.to_string()),
                None,
                Some(DEFAULT_PROTOCOL_VERSION),
            );
        }
    };
    let Some(protocol_version) = negotiated_protocol_version(&initialize_params.protocol_version)
    else {
        return json_response(
            StatusCode::OK,
            jsonrpc_error(
                request_id(message),
                -32602,
                format!(
                    "unsupported protocol version {}",
                    initialize_params.protocol_version
                ),
            ),
            None,
            Some(DEFAULT_PROTOCOL_VERSION),
        );
    };
    let session_id = state.sessions.create(protocol_version).await;

    json_response(
        StatusCode::OK,
        jsonrpc_result(
            request_id(message),
            json!({
                "protocolVersion": protocol_version,
                "capabilities": {
                    "tools": {
                        "listChanged": false
                    }
                },
                "serverInfo": {
                    "name": "rmcp-mcp-server",
                    "version": env!("CARGO_PKG_VERSION")
                }
            }),
        ),
        Some(&session_id),
        Some(protocol_version),
    )
}

async fn handle_initialized_notification(state: Arc<AppState>, headers: &HeaderMap) -> Response {
    match session_id_from_headers(headers) {
        Ok(Some(session_id)) => {
            if state.sessions.mark_initialized(&session_id).await {
                StatusCode::ACCEPTED.into_response()
            } else {
                StatusCode::NOT_FOUND.into_response()
            }
        }
        Ok(None) => StatusCode::BAD_REQUEST.into_response(),
        Err(status) => status.into_response(),
    }
}

async fn require_initialized_session(
    state: &Arc<AppState>,
    headers: &HeaderMap,
    message: &Value,
) -> Result<SessionState, Response> {
    let session_id = match session_id_from_headers(headers) {
        Ok(Some(session_id)) => session_id,
        Ok(None) => return Err(StatusCode::BAD_REQUEST.into_response()),
        Err(status) => return Err(status.into_response()),
    };

    let Some(session) = state.sessions.get(&session_id).await else {
        return Err(StatusCode::NOT_FOUND.into_response());
    };

    if !session.initialized {
        return Err(json_response(
            StatusCode::OK,
            jsonrpc_error(request_id(message), -32002, "session is not initialized"),
            None,
            Some(&session.protocol_version),
        ));
    }

    Ok(session)
}

fn validate_origin(
    allowed_origins: &AllowedOrigins,
    headers: &HeaderMap,
) -> Result<(), StatusCode> {
    let Some(origin) = headers.get(header::ORIGIN) else {
        return Ok(());
    };
    let Ok(origin) = origin.to_str() else {
        return Err(StatusCode::FORBIDDEN);
    };

    if allowed_origins.is_allowed(origin) {
        return Ok(());
    }

    Err(StatusCode::FORBIDDEN)
}

fn validate_accept_header(headers: &HeaderMap) -> Result<(), StatusCode> {
    let Some(accept) = headers.get(ACCEPT) else {
        return Err(StatusCode::BAD_REQUEST);
    };
    let Ok(accept) = accept.to_str() else {
        return Err(StatusCode::BAD_REQUEST);
    };
    let normalized = accept.to_ascii_lowercase();

    if normalized.contains("application/json") && normalized.contains("text/event-stream") {
        return Ok(());
    }

    Err(StatusCode::NOT_ACCEPTABLE)
}

fn protocol_version_from_headers(headers: &HeaderMap) -> Result<String, StatusCode> {
    let Some(version) = headers.get(HEADER_MCP_PROTOCOL_VERSION) else {
        return Ok(DEFAULT_PROTOCOL_VERSION.to_owned());
    };
    let Ok(version) = version.to_str() else {
        return Err(StatusCode::BAD_REQUEST);
    };

    if negotiated_protocol_version(version).is_some() {
        return Ok(version.to_owned());
    }

    Err(StatusCode::BAD_REQUEST)
}

fn session_id_from_headers(headers: &HeaderMap) -> Result<Option<String>, StatusCode> {
    let Some(session_id) = headers.get(HEADER_MCP_SESSION_ID) else {
        return Ok(None);
    };
    let Ok(session_id) = session_id.to_str() else {
        return Err(StatusCode::BAD_REQUEST);
    };

    Ok(Some(session_id.to_owned()))
}

fn internal_jsonrpc_error(message: &Value, error: impl std::fmt::Display) -> Response {
    json_response(
        StatusCode::INTERNAL_SERVER_ERROR,
        jsonrpc_error(request_id(message), -32603, error.to_string()),
        None,
        Some(DEFAULT_PROTOCOL_VERSION),
    )
}

fn runtime_error_code(error: &RuntimeError) -> &'static str {
    match error {
        RuntimeError::Schema(_) => "schema_validation_error",
        RuntimeError::Mapping(_) => "mapping_error",
        RuntimeError::GraphqlAdapter(_) => "adapter_execution_error",
        RuntimeError::GrpcAdapter(_) => "adapter_execution_error",
        RuntimeError::RestAdapter(_) => "adapter_execution_error",
        RuntimeError::UnsupportedProtocol { .. } => "unsupported_protocol",
        RuntimeError::InvalidPreparedRequest { .. } => "runtime_error",
    }
}

fn json_response(
    status: StatusCode,
    payload: Value,
    session_id: Option<&str>,
    protocol_version: Option<&str>,
) -> Response {
    let mut response = (status, Json(payload)).into_response();

    if let Some(session_id) = session_id {
        response.headers_mut().insert(
            HEADER_MCP_SESSION_ID,
            HeaderValue::from_str(session_id)
                .unwrap_or_else(|_| HeaderValue::from_static("invalid")),
        );
    }

    if let Some(protocol_version) = protocol_version {
        response.headers_mut().insert(
            HEADER_MCP_PROTOCOL_VERSION,
            HeaderValue::from_str(protocol_version)
                .unwrap_or_else(|_| HeaderValue::from_static(CURRENT_PROTOCOL_VERSION)),
        );
    }

    response
}

fn tool_definition(operation: &RegistryOperation) -> Value {
    json!({
        "name": operation.name,
        "title": operation.tool_description.title,
        "description": operation.tool_description.description,
        "inputSchema": schema_to_json_schema(&operation.input_schema)
    })
}

fn schema_to_json_schema(schema: &mcpaas_schema::Schema) -> Value {
    match schema.kind {
        mcpaas_schema::SchemaKind::Object => {
            let mut properties = serde_json::Map::new();
            let mut required = Vec::new();

            for (field_name, field_schema) in &schema.fields {
                properties.insert(field_name.clone(), schema_to_json_schema(field_schema));

                if field_schema.required {
                    required.push(Value::String(field_name.clone()));
                }
            }

            json!({
                "type": "object",
                "properties": properties,
                "required": required
            })
        }
        mcpaas_schema::SchemaKind::Array => json!({
            "type": "array",
            "items": schema
                .items
                .as_deref()
                .map(schema_to_json_schema)
                .unwrap_or_else(|| json!({}))
        }),
        mcpaas_schema::SchemaKind::String => json!({ "type": "string" }),
        mcpaas_schema::SchemaKind::Integer => json!({ "type": "integer" }),
        mcpaas_schema::SchemaKind::Number => json!({ "type": "number" }),
        mcpaas_schema::SchemaKind::Boolean => json!({ "type": "boolean" }),
        mcpaas_schema::SchemaKind::Enum => json!({
            "type": "string",
            "enum": schema.enum_values
        }),
        mcpaas_schema::SchemaKind::Null => json!({ "type": "null" }),
        mcpaas_schema::SchemaKind::Oneof => json!({
            "anyOf": schema.variants.iter().map(schema_to_json_schema).collect::<Vec<_>>()
        }),
    }
}

impl AllowedOrigins {
    fn new(public_base_url: Option<String>) -> Self {
        Self {
            public_origin: public_base_url.and_then(|value| extract_origin(&value)),
        }
    }

    fn is_allowed(&self, origin: &str) -> bool {
        if origin.starts_with("http://localhost")
            || origin.starts_with("http://127.0.0.1")
            || origin.starts_with("https://localhost")
            || origin.starts_with("https://127.0.0.1")
        {
            return true;
        }

        match &self.public_origin {
            Some(public_origin) => public_origin == origin,
            None => false,
        }
    }
}

fn extract_origin(url: &str) -> Option<String> {
    let mut parts = url.split('/');
    let scheme = parts.next()?;
    let empty = parts.next()?;
    let authority = parts.next()?;

    if empty.is_empty() {
        return Some(format!("{scheme}//{authority}"));
    }

    None
}