+-----------------+      +----------------------+      +----------------+      +----------+
| User's Phone    |<---- | Twilio SMS Network   | <----| NestJS App     | ---> | Database |
| (Sends/Receives)| ---->| (Sends/Receives SMS) | ---->| (API/Webhook)  | <--- | (Prisma) |
+-----------------+      +----------------------+      +----------------+      +----------+
        ^                          |                            |
        | (Webhook POST)           | (API Call to Send)         |
        +--------------------------+----------------------------+

npm install -g @nestjs/cli
# or
yarn global add @nestjs/cli

nest new nestjs-twilio-sms
cd nestjs-twilio-sms

# Core dependencies
npm install @nestjs/config twilio prisma @prisma/client joi class-validator class-transformer @nestjs/throttler
# or
yarn add @nestjs/config twilio prisma @prisma/client joi class-validator class-transformer @nestjs/throttler

# Development dependencies
npm install -D @types/joi prisma
# or
yarn add -D @types/joi prisma

#.env

# Database
# Ensure correct quoting for your environment/parser if needed_ but often no outer quotes are necessary.
DATABASE_URL=postgresql://YOUR_DB_USER:YOUR_DB_PASSWORD@YOUR_DB_HOST:YOUR_DB_PORT/YOUR_DB_NAME?schema=public

# Twilio Credentials
TWILIO_ACCOUNT_SID=ACxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
TWILIO_AUTH_TOKEN=your_auth_token
TWILIO_PHONE_NUMBER=+15551234567 # Your Twilio phone number

# Application Settings
API_BASE_URL=http://localhost:3000 # Base URL for webhook validation (use ngrok URL for local dev)
PORT=3000

// src/app.module.ts
import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { PrismaModule } from './prisma/prisma.module';
import { TwilioModule } from './twilio/twilio.module';
import { MessagesModule } from './messages/messages.module';
import { WebhooksModule } from './webhooks/webhooks.module';
import { ThrottlerModule_ ThrottlerGuard } from '@nestjs/throttler';
import { APP_GUARD } from '@nestjs/core';

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true_ // Make ConfigService available globally
      envFilePath: '.env'_ // Specify the env file path
    })_
    // Rate Limiting Configuration (See Section 7)
    ThrottlerModule.forRoot([{
      ttl: 60000_ // Time-to-live in milliseconds (e.g._ 60 seconds)
      limit: 10_ // Max requests per TTL per IP
    }])_
    PrismaModule_
    TwilioModule_
    MessagesModule_
    WebhooksModule_
  ]_
  controllers: [AppController]_
  providers: [
    AppService_
    // Apply rate limiting globally
    {
      provide: APP_GUARD_
      useClass: ThrottlerGuard_
    }_
  ]_
})
export class AppModule {}

npx prisma init

// prisma/schema.prisma
generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

// Models will be defined in Section 3

nest generate module twilio
nest generate service twilio

// src/twilio/twilio.service.ts
import { Injectable_ Logger } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { Twilio } from 'twilio';
import * as twilio from 'twilio'; // Import twilio namespace for static methods

@Injectable()
export class TwilioService {
  private readonly logger = new Logger(TwilioService.name);
  private client: Twilio;
  public readonly twilioPhoneNumber: string; // Made public for easier access

  constructor(private configService: ConfigService) {
    const accountSid = this.configService.get<string&gt;('TWILIO_ACCOUNT_SID');
    const authToken = this.configService.get<string&gt;('TWILIO_AUTH_TOKEN');
    this.twilioPhoneNumber = this.configService.get<string&gt;('TWILIO_PHONE_NUMBER');

    if (!accountSid || !authToken || !this.twilioPhoneNumber) {
      this.logger.error('Twilio credentials are not configured in .env file');
      throw new Error('Twilio credentials are not configured.');
    }

    this.client = new Twilio(accountSid, authToken);
    this.logger.log('Twilio client initialized.');
  }

  async sendMessage(to: string, body: string): Promise<string&gt; {
    try {
      const message = await this.client.messages.create({
        body: body,
        from: this.twilioPhoneNumber,
        to: to, // Ensure 'to' number is in E.164 format
      });
      this.logger.log(`Message sent to ${to}. SID: ${message.sid}`);
      return message.sid;
    } catch (error) {
      this.logger.error(`Failed to send message to ${to}: ${error.message}`);
      // Consider rethrowing or handling specific Twilio errors (e.g., invalid number)
      throw error;
    }
  }

  /**
   * Validates an incoming Twilio webhook request.
   * CRITICAL: Ensure the 'url' and 'params' accurately reflect what Twilio uses
   * to generate the signature. If using body-parsing middleware, you might need
   * access to the RAW request body for accurate validation.
   * @param signature The X-Twilio-Signature header value.
   * @param url The full URL (with protocol, host, and path) that Twilio requested.
   * @param params The request parameters (usually the parsed request body for POST).
   * @returns True if the signature is valid, false otherwise.
   */
  validateWebhookRequest(
    signature: string | string[],
    url: string, // The full request URL Twilio hit
    params: any, // The POST parameters
  ): boolean {
    const authToken = this.configService.get<string&gt;('TWILIO_AUTH_TOKEN');
    // The 'twilio' library's validator expects the full URL including protocol and host
    // Ensure the URL passed here matches exactly what Twilio used.
    // Example: `https://<your-ngrok-or-domain&gt;.io/webhooks/twilio/sms`

    // Ensure signature is a single string
    const sigHeader = Array.isArray(signature) ? signature[0] : signature;

    if (!sigHeader) {
        this.logger.warn('Missing X-Twilio-Signature header');
        return false;
    }

    this.logger.debug(`Validating webhook: Sig='${sigHeader}', URL='${url}', Params=${JSON.stringify(params)}`);

    try {
      // Use the library's validation function (accessed via namespace import)
      // IMPORTANT: If body-parsing middleware modified `params`, this might fail.
      // Consider using `twilio.validateRequestWithBody` if you have the raw body.
      return twilio.validateRequest(authToken, sigHeader, url, params);
    } catch (error) {
        this.logger.error(`Error during webhook validation: ${error.message}`);
        return false;
    }
  }
}

// src/twilio/twilio.module.ts
import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config'; // Ensure ConfigModule is available
import { TwilioService } from './twilio.service';

@Module({
  imports: [ConfigModule], // Import ConfigModule if not global or imported elsewhere
  providers: [TwilioService],
  exports: [TwilioService], // Export the service for other modules to use
})
export class TwilioModule {}

nest generate module prisma
nest generate service prisma --flat # Use --flat for no sub-directory

// src/prisma.service.ts
import { Injectable, OnModuleInit, INestApplication, Logger } from '@nestjs/common';
import { PrismaClient } from '@prisma/client';

@Injectable()
export class PrismaService extends PrismaClient implements OnModuleInit {
  private readonly logger = new Logger(PrismaService.name);

  async onModuleInit() {
    try {
      await this.$connect();
      this.logger.log('Database connection established.');
    } catch (error) {
      this.logger.error('Failed to connect to the database', error.stack);
      // Consider application exit strategy if DB connection fails on start
      // process.exit(1);
    }
  }

  async enableShutdownHooks(app: INestApplication) {
    // Prisma recommends listening to Prisma-specific signals if possible,
    // but NestJS hooks often suffice.
    // Correctly listen for 'beforeExit' on the process object
    process.on('beforeExit', async () => {
      this.logger.log('Closing database connection due to app shutdown...');
      // Ensure the app closes, which should trigger onModuleDestroy
      await app.close();
    });
  }

  // NestJS automatically calls onModuleDestroy on shutdown if enableShutdownHooks is called
  // async onModuleDestroy() {
  //   this.logger.log('Disconnecting Prisma client...');
  //   await this.$disconnect();
  // }
}

// src/prisma/prisma.module.ts
import { Global, Module } from '@nestjs/common';
import { PrismaService } from './prisma.service';

@Global() // Make PrismaService available globally without importing PrismaModule everywhere
@Module({
  providers: [PrismaService],
  exports: [PrismaService],
})
export class PrismaModule {}

// src/main.ts (example snippet)
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { PrismaService } from './prisma.service'; // Import PrismaService

async function bootstrap() {
  const app = await NestFactory.create(AppModule);

  // Get PrismaService instance (needed for shutdown hooks)
  const prismaService = app.get(PrismaService);
  await prismaService.enableShutdownHooks(app); // Call enableShutdownHooks

  // ... other configurations (pipes, etc.)

  await app.listen(3000); // Or use ConfigService for port
}
bootstrap();

// prisma/schema.prisma
generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model Conversation {
  id              String    @id @default(uuid())
  participantNumber String  @unique // The external participant's phone number (E.164 format recommended)
  twilioNumber    String    // The Twilio number involved in this conversation (E.164 format)
  createdAt       DateTime  @default(now())
  updatedAt       DateTime  @updatedAt
  messages        Message[] // Relation to messages in this conversation
}

model Message {
  id             String        @id @default(uuid())
  conversationId String
  conversation   Conversation  @relation(fields: [conversationId], references: [id], onDelete: Cascade)
  direction      Direction     // Incoming or Outgoing
  body           String
  twilioSid      String?       @unique // Twilio's message SID, unique identifier (important for idempotency)
  sentAt         DateTime      @default(now())
  status         String?       // Optional: Status from Twilio (e.g., sent, delivered, failed)

  @@index([conversationId]) // Index for faster message lookups by conversation
}

enum Direction {
  INCOMING
  OUTGOING
}

# Ensure your DATABASE_URL in .env is correctly pointing to your dev database
npx prisma migrate dev --name init-messaging-schema

// Example usage in another service (e.g., MessagesService if created)
import { Injectable } from '@nestjs/common';
import { PrismaService } from '../prisma.service'; // Auto-injectable due to @Global()
import { Direction } from '@prisma/client'; // Import generated enum

@Injectable()
export class SomeServiceUsingPrisma {
  constructor(private prisma: PrismaService) {}

  async findOrCreateConversation(participantNumber: string, twilioNumber: string) {
    // Use upsert to find existing or create new conversation
    return this.prisma.conversation.upsert({
      where: { participantNumber }, // Assumes participantNumber is unique constraint
      update: {}, // No update needed if found based on participantNumber
      create: { participantNumber, twilioNumber },
    });
  }

  async saveMessage(data: {
    conversationId: string;
    direction: Direction;
    body: string;
    twilioSid?: string;
    status?: string;
  }) {
    return this.prisma.message.create({ data });
  }
}

nest generate module messages
nest generate controller messages
# No separate service needed here, logic fits well in the controller

// src/messages/dto/send-message.dto.ts
import { IsNotEmpty, IsPhoneNumber, IsString, MaxLength } from 'class-validator';

export class SendMessageDto {
  @IsPhoneNumber(undefined, { message: 'Recipient phone number must be in E.164 format (e.g., +15551234567).' }) // Validates E.164 format
  @IsNotEmpty()
  to: string;

  @IsString()
  @IsNotEmpty()
  @MaxLength(1600, { message: 'Message body cannot exceed 1600 characters.' }) // Twilio SMS limit
  body: string;
}

// src/messages/messages.controller.ts
import { Controller, Post, Body, ValidationPipe, UsePipes, Logger, InternalServerErrorException } from '@nestjs/common';
import { TwilioService } from '../twilio/twilio.service'; // Injected via module imports
import { PrismaService } from '../prisma.service'; // Injected via @Global() PrismaModule
import { SendMessageDto } from './dto/send-message.dto';
import { Direction } from '@prisma/client';

@Controller('messages')
export class MessagesController {
  private readonly logger = new Logger(MessagesController.name);

  constructor(
    private readonly twilioService: TwilioService,
    private readonly prisma: PrismaService,
  ) {}

  @Post('send')
  // Use ValidationPipe to automatically validate the request body against SendMessageDto
  @UsePipes(new ValidationPipe({ transform: true, whitelist: true }))
  async sendMessage(@Body() sendMessageDto: SendMessageDto) {
    const { to, body } = sendMessageDto;
    // Access the configured Twilio number from the service
    const twilioNumber = this.twilioService.twilioPhoneNumber;

    try {
      // 1. Find or create the conversation based on the recipient number (using E.164 format)
      const conversation = await this.prisma.conversation.upsert({
        where: { participantNumber: to },
        update: {}, // No update needed if conversation exists
        create: { participantNumber: to, twilioNumber: twilioNumber },
      });

      // 2. Send the message via Twilio
      const messageSid = await this.twilioService.sendMessage(to, body);

      // 3. Save the outgoing message to the database
      const savedMessage = await this.prisma.message.create({
        data: {
          conversationId: conversation.id,
          direction: Direction.OUTGOING,
          body: body,
          twilioSid: messageSid,
          status: 'sent', // Initial status; could be updated via status callbacks later
        },
      });

      this.logger.log(`Message initiated to ${to}, SID: ${messageSid}, DB ID: ${savedMessage.id}`);
      return { success: true, messageSid: messageSid, conversationId: conversation.id };

    } catch (error) {
      this.logger.error(`Failed to send message to ${to}: ${error.message}`, error.stack);
      // Consider more specific error handling based on Twilio or Prisma errors
      throw new InternalServerErrorException('Failed to send message.');
    }
  }
}

// src/messages/messages.module.ts
import { Module } from '@nestjs/common';
import { MessagesController } from './messages.controller';
// Import necessary modules that export services used by the controller
import { TwilioModule } from '../twilio/twilio.module'; // Provides TwilioService
// PrismaModule is global, so no need to import here

@Module({
  imports: [
    TwilioModule, // Makes TwilioService available for injection
  ],
  controllers: [MessagesController],
  providers: [], // No specific service for this module in this example
})
export class MessagesModule {}

curl -X POST http://localhost:3000/messages/send \
-H ""Content-Type: application/json"" \
-d '{
  ""to"": ""+15559876543"",
  ""body"": ""Hello from NestJS and Twilio!""
}'

nest generate module webhooks
nest generate controller webhooks/twilio --flat # Place controller directly in webhooks

// src/webhooks/twilio.controller.ts
import { Controller, Post, Body, Headers, Req, Res, Logger, ForbiddenException, InternalServerErrorException, BadRequestException } from '@nestjs/common';
import { Request, Response } from 'express'; // Use Express types for Req/Res
import { TwilioService } from '../twilio/twilio.service';
import { PrismaService } from '../prisma.service';
import { Direction, Prisma } from '@prisma/client'; // Import Prisma namespace for error codes
import { twiml } from 'twilio'; // For TwiML responses
import { ConfigService } from '@nestjs/config';

// Define a simple DTO for expected webhook payload fields
// This helps with basic structure validation if NestJS parses the body
// Note: Twilio sends PascalCase keys
class TwilioWebhookDto {
    From: string;
    To: string;
    Body: string;
    MessageSid: string;
    SmsStatus?: string; // Optional status field
    // Add other fields if needed (e.g., NumMedia)
}

@Controller('webhooks/twilio')
export class TwilioWebhookController {
  private readonly logger = new Logger(TwilioWebhookController.name);

  constructor(
    private readonly twilioService: TwilioService,
    private readonly prisma: PrismaService,
    private readonly configService: ConfigService,
  ) {}

  // Note: Twilio sends data as 'application/x-www-form-urlencoded'.
  // NestJS's default body parser handles this.
  // IMPORTANT: Validation requires the exact URL Twilio requested.
  @Post('sms') // Endpoint: /webhooks/twilio/sms
  async handleIncomingSms(
    @Headers('X-Twilio-Signature') signature: string,
    @Body() body: TwilioWebhookDto, // Use DTO, NestJS parses urlencoded body
    @Req() request: Request, // Inject original Express request
    @Res() response: Response, // Inject Express response for TwiML
  ) {
    this.logger.log(`Incoming SMS webhook received. SID: ${body.MessageSid}`);
    this.logger.debug(`Webhook Body: ${JSON.stringify(body)}`);

    // 1. Construct the full URL Twilio requested (needed for validation)
    // Ensure API_BASE_URL is correctly set (e.g., https://your-ngrok.io or https://your-domain.com)
    const baseUrl = this.configService.get<string&gt;('API_BASE_URL');
    if (!baseUrl) {
        this.logger.error('API_BASE_URL is not configured in environment variables.');
        // Don't send TwiML here, it's an internal configuration error.
        response.status(500).send('Internal server configuration error.');
        return;
    }
    const fullUrl = `${baseUrl}${request.originalUrl}`;

    // 2. Validate Twilio Request (CRITICAL FOR SECURITY)
    // Pass the parsed body (params). If validation fails due to body parsing,
    // you might need to access the raw body BEFORE NestJS parses it.
    // This typically involves configuring `bodyParser: false` for the route
    // and using a library like `raw-body`. For simplicity, we assume default parsing works.
    const isValid = this.twilioService.validateWebhookRequest(
      signature,
      fullUrl, // Use the reconstructed full URL
      body,    // Pass the parsed body as parameters
    );

    if (!isValid) {
      this.logger.warn(`Invalid Twilio signature for URL: ${fullUrl}. Request rejected.`);
      // Respond with 403 Forbidden. DO NOT process further.
      // Avoid sending TwiML here; just send HTTP status.
      response.status(403).send('Invalid Twilio signature.');
      return; // Stop execution
    }

    this.logger.log('Twilio signature validated successfully.');

    // 3. Extract required fields (already partially validated by DTO structure)
    const fromNumber = body.From; // Sender's number (E.164)
    const twilioNumber = body.To; // Your Twilio number (E.164)
    const messageBody = body.Body;
    const messageSid = body.MessageSid;

    // Optional: Add more robust validation if needed
    if (!fromNumber || !twilioNumber || typeof messageBody === 'undefined' || !messageSid) {
        this.logger.error('Webhook payload missing required fields after parsing.');
        // Send a simple error response back to Twilio. Avoid TwiML if it's a bad request format.
        response.status(400).send('Missing required fields.');
        return;
    }

    try {
      // 4. Find or Create Conversation (use normalized E.164 numbers)
      const conversation = await this.prisma.conversation.upsert({
        where: { participantNumber: fromNumber },
        update: {}, // No update needed if found
        create: { participantNumber: fromNumber, twilioNumber: twilioNumber },
      });

      // 5. Save Incoming Message (use unique constraint on twilioSid for idempotency)
      try {
        await this.prisma.message.create({
            data: {
            conversationId: conversation.id,
            direction: Direction.INCOMING,
            body: messageBody,
            twilioSid: messageSid,
            status: body.SmsStatus ?? 'received', // Capture status if provided
            },
        });
         this.logger.log(`Incoming message from ${fromNumber} saved. SID: ${messageSid}`);
      } catch (error) {
          // Handle potential unique constraint violation (duplicate webhook) gracefully
          if (error instanceof Prisma.PrismaClientKnownRequestError && error.code === 'P2002') {
              this.logger.warn(`Duplicate message received (SID: ${messageSid}). Ignoring.`);
              // Respond to Twilio successfully as we've already processed this SID
          } else {
              throw error; // Re-throw other database errors
          }
      }

      // 6. Prepare and Send TwiML Response
      // TwiML (Twilio Markup Language) is an XML-based language to instruct Twilio.
      const twimlResponse = new twiml.MessagingResponse();

      // Example: A simple auto-reply
      twimlResponse.message('Thanks for your message! We received it.');

      // If you need complex logic: Check messageBody, query APIs, etc., *before* sending response.
      // Keep webhook handlers fast. Offload long tasks to background jobs if needed.

      // Send the TwiML response back to Twilio
      response.type('text/xml');
      response.send(twimlResponse.toString());
      this.logger.log(`Sent TwiML acknowledgement to Twilio for SID: ${messageSid}`);

    } catch (error) {
      this.logger.error(`Error processing incoming SMS from ${fromNumber} (SID: ${messageSid}): ${error.message}`, error.stack);

      // Strategy: Send a TwiML error message back to Twilio so it knows something went wrong.
      // Avoid leaking sensitive details in the message.
      const twimlError = new twiml.MessagingResponse();
      twimlError.message('Sorry, we encountered an error processing your message. Please try again later.');
      response.type('text/xml');
      response.status(500).send(twimlError.toString());

      // Alternative: If the error should propagate internally and not send TwiML error:
      // throw new InternalServerErrorException('Failed to process incoming message.');
    }
  }
}

// src/webhooks/webhooks.module.ts
import { Module } from '@nestjs/common';
import { TwilioWebhookController } from './twilio.controller';
import { TwilioModule } from '../twilio/twilio.module'; // Provides TwilioService for validation
import { ConfigModule } from '@nestjs/config'; // Needed for API_BASE_URL
// PrismaModule is global

@Module({
  imports: [
    TwilioModule,
    ConfigModule, // Import ConfigModule to access ConfigService
  ],
  controllers: [TwilioWebhookController],
})
export class WebhooksModule {}