joshi-chinmay-016/AgentProof

When to Use

Use this skill when implementing request validation, authorization checks, response mapping, logging, error handling, or performance tracking on NitroStack tool methods.

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1. Guards (Guard and @UseGuards)

Guards determine if a request should be processed by a tool handler based on authentication, authorization, or other conditions.

Interface:

import { Guard, ExecutionContext } from '@nitrostack/core';

export interface Guard {
  canActivate(context: ExecutionContext): boolean | Promise<boolean>;
}

Example:

import { Guard, ExecutionContext, Injectable } from '@nitrostack/core';

@Injectable()
export class RolesGuard implements Guard {
  async canActivate(context: ExecutionContext): Promise<boolean> {
    const userRoles = context.clientMetadata?.roles || [];
    return userRoles.includes('admin');
  }
}

Apply the guard using @UseGuards(...):

import { Tool, UseGuards, z } from '@nitrostack/core';
import { RolesGuard } from './roles.guard.js';

export class AdminTools {
  @Tool({
    name: 'delete_system_logs',
    description: 'Delete all system logs from the server.',
    inputSchema: z.object({}),
  })
  @UseGuards(RolesGuard)
  async deleteLogs() {
    return { success: true };
  }
}

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2. Interceptors (InterceptorInterface and @UseInterceptors)

Interceptors can transform/intercept input arguments or mapped output from a tool method execution.

Interface:

import { ExecutionContext } from '@nitrostack/core';

export interface InterceptorInterface {
  intercept(context: ExecutionContext, next: () => Promise<unknown>): Promise<unknown>;
}

Example:

import { InterceptorInterface, ExecutionContext, Injectable } from '@nitrostack/core';

@Injectable()
export class TimingInterceptor implements InterceptorInterface {
  async intercept(context: ExecutionContext, next: () => Promise<unknown>): Promise<unknown> {
    const start = Date.now();
    const result = await next();
    const duration = Date.now() - start;
    context.logger.info(`Execution took ${duration}ms`);
    return {
      ...result,
      _meta: { durationMs: duration }
    };
  }
}

---

3. Exception Filters (ExceptionFilterInterface and @UseFilters)

Exception filters catch any errors thrown within guards, interceptors, or the tool handlers themselves, mapping them into user-friendly JSON payloads.

Interface:

import { ExecutionContext } from '@nitrostack/core';

export interface ExceptionFilterInterface {
  catch(exception: unknown, context: ExecutionContext): unknown | Promise<unknown>;
}

Example:

import { ExceptionFilterInterface, ExecutionContext, Injectable } from '@nitrostack/core';

@Injectable()
export class CustomExceptionFilter implements ExceptionFilterInterface {
  catch(exception: unknown, context: ExecutionContext) {
    const message = exception instanceof Error ? exception.message : 'Unknown error';
    return {
      error: true,
      message,
      timestamp: new Date().toISOString()
    };
  }
}

Apply the filter using @UseFilters(...) on a tool method:

import { Tool, UseFilters, z } from '@nitrostack/core';
import { CustomExceptionFilter } from './custom-exception.filter.js';

export class LoggingTools {
  @Tool({
    name: 'generate_report',
    description: 'Generates system usage reports.',
    inputSchema: z.object({}),
  })
  @UseFilters(CustomExceptionFilter)
  async generateReport() {
    throw new Error('Report generation is not implemented yet.');
  }
}

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4. Middleware (MiddlewareInterface, @Middleware and @UseMiddleware)

Middleware executes before the request reaches the tool handler, and can wrap the handler execution by invoking next().

Interface:

import { ExecutionContext } from '@nitrostack/core';

export interface MiddlewareInterface {
  use(context: ExecutionContext, next: () => Promise<unknown>): Promise<unknown>;
}

Example:

import { Middleware, MiddlewareInterface, ExecutionContext } from '@nitrostack/core';

@Middleware()
export class LoggingMiddleware implements MiddlewareInterface {
  async use(context: ExecutionContext, next: () => Promise<unknown>): Promise<unknown> {
    context.logger.info(`Entering tool: ${context.toolName}`);
    try {
      const result = await next();
      context.logger.info(`Exiting tool: ${context.toolName}`);
      return result;
    } catch (error) {
      context.logger.error(`Error in tool: ${error}`);
      throw error;
    }
  }
}

Apply the middleware using @UseMiddleware(...) on a tool method:

import { Tool, UseMiddleware, z } from '@nitrostack/core';
import { LoggingMiddleware } from './logging.middleware.js';

export class StationTools {
  @Tool({
    name: 'fetch_logs',
    description: 'Fetch station operations logs.',
    inputSchema: z.object({}),
  })
  @UseMiddleware(LoggingMiddleware)
  async fetchLogs() {
    return { status: 'operational' };
  }
}

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5. Pipes (PipeInterface, @Pipe and @UsePipes)

Pipes are used to transform or validate input arguments before they reach the tool handler method.

Interface:

import { ArgumentMetadata } from '@nitrostack/core';

export interface PipeInterface<T = unknown, R = unknown> {
  transform(value: T, metadata: ArgumentMetadata): R | Promise<R>;
}

Example:

import { Pipe, PipeInterface, ArgumentMetadata } from '@nitrostack/core';

@Pipe()
export class TrimPipe implements PipeInterface<Record<string, unknown>, Record<string, unknown>> {
  transform(value: Record<string, unknown>, metadata: ArgumentMetadata) {
    const trimmed: Record<string, unknown> = {};
    for (const [key, val] of Object.entries(value)) {
      trimmed[key] = typeof val === 'string' ? val.trim() : val;
    }
    return trimmed;
  }
}

Apply the pipe using @UsePipes(...) on a tool method:

import { Tool, UsePipes, z } from '@nitrostack/core';
import { TrimPipe } from './trim.pipe.js';

export class MessagingTools {
  @Tool({
    name: 'send_message',
    description: 'Send a message to other stations.',
    inputSchema: z.object({ text: z.string() }),
  })
  @UsePipes(TrimPipe)
  async sendMessage(input: { text: string }) {
    return { sentText: input.text };
  }
}