Build Bulk SMS Broadcasting with Sinch and NestJS: Complete TypeScript Implementation Guide

Send SMS messages reliably and at scale for applications needing notifications, marketing outreach, or user verification. While numerous providers exist, integrate them efficiently with careful planning, robust error handling, and scalable architecture.

This guide provides a complete, step-by-step walkthrough for building a production-ready bulk SMS sending service using the NestJS framework and the Sinch SMS API. You'll learn everything from initial project setup and configuration to implementing core sending logic, handling API responses, ensuring security, and preparing for deployment.

By the end of this tutorial, you'll build a functional NestJS application capable of accepting requests to send SMS messages to multiple recipients via the Sinch API, complete with logging, validation, and error handling.

Project Overview and Goals

What You're Building

Create a dedicated NestJS microservice (or module within a larger application) that exposes a secure API endpoint. This endpoint accepts a list of recipient phone numbers and a message body, then utilizes the Sinch REST API to send the message to all specified recipients in a single batch request.

Problems You'll Solve

• Centralized SMS Logic: Encapsulate all Sinch interaction logic in one place, making it maintainable and reusable.
• Scalable Sending: Leverage Sinch's batch API for efficient bulk messaging.
• Simplified Integration: Provide a clean API interface for other services or frontends to trigger SMS sending without needing direct Sinch credentials or implementation details.
• Robustness: Include essential features like configuration management, validation, logging, and error handling.

Technologies Used

• NestJS: A progressive Node.js framework for building efficient, reliable, and scalable server-side applications. Its modular architecture, dependency injection (DI), and built-in support for features like configuration and validation make it ideal. Current stable version: v11.1.6 (released January 2025) includes improved ConsoleLogger, microservices enhancements, and performance improvements.
• Sinch SMS API: A powerful REST API for sending and managing SMS messages globally. Focus on its batch sending capabilities using the /xms/v1/{service_plan_id}/batches endpoint.
• Node.js: The underlying JavaScript runtime.
• TypeScript: Enhances JavaScript with static typing for better code quality and maintainability.
• Axios (via @nestjs/axios): For making HTTP requests to the Sinch API.
• @nestjs/config: For managing environment variables and configuration.
• class-validator & class-transformer: For robust request data validation.
• nestjs-throttler: For basic rate limiting.

System Architecture

graph LR
    Client[Client Application / API Consumer] -->|1. POST /messages/bulk (recipients, message)| NestJS_API[NestJS Bulk SMS Service];
    NestJS_API -->|2. Validate Request| NestJS_API;
    NestJS_API -->|3. Call SinchService.sendBulkSms| SinchService[Sinch Service Module];
    SinchService -->|4. POST /xms/v1/{servicePlanId}/batches (Sinch Payload)| SinchAPI[Sinch SMS REST API];
    SinchAPI -->|5. Batch Response (ID, Status)| SinchService;
    SinchService -->|6. Processed Response| NestJS_API;
    NestJS_API -->|7. API Response (Success/Error)| Client;

    subgraph NestJS Bulk SMS Service
        direction LR
        MessagingController[Messaging Controller] --> ValidationPipe[Validation Pipe]
        ValidationPipe --> SinchService
        SinchService --> |Uses| HttpService[Http Module (Axios)]
        SinchService --> |Uses| ConfigService[Config Module]
        SinchService --> |Uses| LoggerService[Logger Module]
    end

    style NestJS_API fill:#f9f,stroke:#333,stroke-width:2px
    style SinchAPI fill:#ccf,stroke:#333,stroke-width:2px

Prerequisites

• Node.js (v22 LTS recommended – Active LTS until October 2025, then Maintenance LTS until April 2027)
• npm or yarn package manager
• A Sinch account (https://dashboard.sinch.com/signup)
• A provisioned Sinch phone number or Alphanumeric Sender ID
• Your Sinch Service Plan ID and API Token
• A code editor (e.g., VS Code)
• Basic understanding of TypeScript, Node.js, REST APIs, and NestJS fundamentals

1. Set Up Your NestJS Project

Start by creating a new NestJS project using the Nest CLI.

1. Install NestJS CLI: If you don't have it installed globally, run:

   bash

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

2. Create New Project: Navigate to your desired development directory in your terminal and run:

   bash

   nest new sinch-bulk-sms-service
   

   Choose your preferred package manager (npm or yarn) when prompted.

3. Navigate into Project Directory:

   bash

   cd sinch-bulk-sms-service
   

4. Initial Project Structure: The Nest CLI generates a standard project structure:

   sinch-bulk-sms-service/
   ├── node_modules/
   ├── src/
   │   ├── app.controller.spec.ts
   │   ├── app.controller.ts
   │   ├── app.module.ts
   │   ├── app.service.ts
   │   └── main.ts
   ├── test/
   ├── .eslintrc.js
   ├── .gitignore
   ├── .prettierrc
   ├── nest-cli.json
   ├── package.json
   ├── README.md
   ├── tsconfig.build.json
   └── tsconfig.json
   

   Build upon this structure by adding modules for configuration, Sinch integration, and messaging endpoints.

5. Install Necessary Dependencies: Install modules for configuration management, making HTTP requests, and validation.

   bash

   npm install @nestjs/config @nestjs/axios axios class-validator class-transformer nestjs-throttler
   # or
   yarn add @nestjs/config @nestjs/axios axios class-validator class-transformer nestjs-throttler
   

2. Configure Environment and Credentials

Proper configuration management is crucial, especially for handling sensitive API credentials. Use @nestjs/config to load environment variables from a .env file.

1. Create .env and .env.example files: In the project root directory, create two files:

   • .env: Store your actual secrets and configuration. Do not commit this file to Git.
   • .env.example: Serves as a template showing required variables. Commit this file.

   .env.example:

   bash

   # Sinch API Configuration
   # Regional base URLs: https://us.sms.api.sinch.com (US), https://eu.sms.api.sinch.com (EU)
   # Choose based on data residency requirements. Do NOT include /xms/v1/{service_plan_id} here.
   SINCH_API_URL=https://us.sms.api.sinch.com
   SINCH_SERVICE_PLAN_ID=
   SINCH_API_TOKEN=
   SINCH_FROM_NUMBER=
   
   # Application Configuration
   PORT=3000
   

   .env:

   bash

   # Sinch API Configuration
   # Regional base URLs: https://us.sms.api.sinch.com (US), https://eu.sms.api.sinch.com (EU)
   # Choose based on data residency requirements. Do NOT include /xms/v1/{service_plan_id} here.
   SINCH_API_URL=https://us.sms.api.sinch.com # Or eu.sms.api.sinch.com for EU region
   SINCH_SERVICE_PLAN_ID=YOUR_ACTUAL_SERVICE_PLAN_ID
   SINCH_API_TOKEN=YOUR_ACTUAL_API_TOKEN
   SINCH_FROM_NUMBER=YOUR_SINCH_VIRTUAL_NUMBER_OR_SENDER_ID # e.g., +12025550101
   
   # Application Configuration
   PORT=3000
   

2. Obtain Your Sinch Credentials:

   • Login: Go to the Sinch Customer Dashboard.
   • Navigate to SMS API: Find the SMS product section, often under "Products" > "SMS."
   • API Credentials: Look for "API Credentials," "REST API," or similar. Here you'll find:
     • Service Plan ID: A unique identifier for your service plan. Use this for the SINCH_SERVICE_PLAN_ID variable.
     • API Token: An authentication token (sometimes called API Secret or Auth Token). Generate one if needed. Treat this like a password. Use this for the SINCH_API_TOKEN variable.
   • Base URL: The base URL depends on your account's region and data residency requirements:
     • US region: https://us.sms.api.sinch.com
     • EU region: https://eu.sms.api.sinch.com
     • The base URL excludes the /xms/v1/ path and your Service Plan ID – your application code adds those parts. Select the region where your transactional data will be stored; you can send global traffic regardless of selection.
   • From Number: Navigate to "Numbers" in your dashboard to see active virtual numbers or configured Alphanumeric Sender IDs. Choose the one for sending messages. Ensure it's in E.164 format (E.164 is the international telephone numbering plan format, e.g., +12025550101 for numbers). Use this for the SINCH_FROM_NUMBER variable.
   • Reference: https://developers.sinch.com/docs/sms/api-reference/ (official 2024 documentation)

3. Update .gitignore: Ensure .env is listed in your .gitignore file to prevent accidentally committing secrets:

   .gitignore:

   # .gitignore
   node_modules
   dist
   .env
   

4. Load Configuration in AppModule: Modify src/app.module.ts to import and configure the ConfigModule.

   src/app.module.ts:

   typescript

   import { Module } from '@nestjs/common';
   import { ConfigModule } from '@nestjs/config';
   import { AppController } from './app.controller';
   import { AppService } from './app.service';
   // Import other modules here later
   
   @Module({
     imports: [
       ConfigModule.forRoot({
         isGlobal: true, // Makes ConfigModule available globally
         envFilePath: '.env', // Specifies the env file path
       }),
       // Add other modules (SinchModule, MessagingModule) here later
     ],
     controllers: [AppController], // Remove these later if not needed
     providers: [AppService], // Remove these later if not needed
   })
   export class AppModule {}
   

   Setting isGlobal: true means you don't need to import ConfigModule into other modules explicitly to use ConfigService.

3. Implement the Sinch Service

Create a dedicated module and service to handle all interactions with the Sinch API. This section covers the core integration, including authentication, request/response handling, and error management.

1. Generate Sinch Module and Service:

   bash

   nest g module sinch
   nest g service sinch
   

   This creates src/sinch/sinch.module.ts and src/sinch/sinch.service.ts.

2. Configure HttpModule: Use @nestjs/axios (which wraps Axios) to make HTTP calls. Configure it asynchronously within the SinchModule to inject the ConfigService and set the base regional URL and authentication headers dynamically.

   src/sinch/sinch.module.ts:

   typescript

   import { Module } from '@nestjs/common';
   import { ConfigModule, ConfigService } from '@nestjs/config';
   import { HttpModule } from '@nestjs/axios';
   import { SinchService } from './sinch.service';
   
   @Module({
     imports: [
       ConfigModule, // Import if not global, needed for ConfigService injection
       HttpModule.registerAsync({
         imports: [ConfigModule], // Import ConfigModule here too
         useFactory: async (configService: ConfigService) => ({
           baseURL: configService.get<string&gt;('SINCH_API_URL'), // Base regional URL from .env
           headers: {
             'Authorization': `Bearer ${configService.get<string&gt;('SINCH_API_TOKEN')}`, // Auth header
             'Content-Type': 'application/json',
           },
           timeout: 5000, // Optional: Set request timeout (5000 ms = 5 seconds)
         }),
         inject: [ConfigService], // Inject ConfigService into the factory
       }),
     ],
     providers: [SinchService],
     exports: [SinchService], // Export service to use in other modules
   })
   export class SinchModule {}
   
   • HttpModule.registerAsync: Allows dynamic configuration using dependencies like ConfigService.
   • baseURL: Sets the root regional URL (e.g., https://us.sms.api.sinch.com) for all requests made via this HttpModule instance. The specific API path (/xms/v1/...) is added in the service.
   • headers: Sets default headers, including the crucial Authorization bearer token.
   • exports: Makes SinchService available for injection into other modules (like your upcoming MessagingModule).

3. Implement SinchService Logic: Now, we implement the core method to send bulk SMS messages.

   src/sinch/sinch.service.ts:

   typescript

   import { Injectable, Logger, InternalServerErrorException } from '@nestjs/common';
   import { ConfigService } from '@nestjs/config';
   import { HttpService } from '@nestjs/axios';
   import { firstValueFrom, map, catchError } from 'rxjs';
   import { AxiosError } from 'axios';
   
   // Interface matching the expected Sinch API response for batch send
   // NOTE: Verify this against the official Sinch API documentation for the /batches endpoint.
   interface SinchBatchResponse {
     id: string;
     to: string[];
     from: string;
     canceled: boolean;
     body: string;
     type: string;
     created_at: string;
     modified_at: string;
     delivery_report: string;
     // Add other relevant fields from Sinch docs if needed
   }
   
   @Injectable()
   export class SinchService {
     private readonly logger = new Logger(SinchService.name);
     private readonly sinchFromNumber: string;
     private readonly servicePlanId: string;
     private readonly sinchApiUrl: string;
   
     constructor(
       private readonly httpService: HttpService,
       private readonly configService: ConfigService,
     ) {
       // Fetch config values once during instantiation
       this.sinchFromNumber = this.configService.get<string&gt;('SINCH_FROM_NUMBER');
       this.servicePlanId = this.configService.get<string&gt;('SINCH_SERVICE_PLAN_ID');
       this.sinchApiUrl = this.configService.get<string&gt;('SINCH_API_URL'); // Base URL
   
       if (!this.sinchFromNumber || !this.servicePlanId || !this.sinchApiUrl) {
          this.logger.error('Sinch configuration incomplete. Check SINCH_FROM_NUMBER, SINCH_SERVICE_PLAN_ID, and SINCH_API_URL environment variables.');
          // Use specific NestJS exception
          throw new InternalServerErrorException('Sinch configuration is incomplete. Check environment variables.');
       }
     }
   
     /**
      * Sends a bulk SMS message using the Sinch batch API.
      * @param recipients - Array of phone numbers in E.164 format (e.g., +12025550101).
      * @param messageBody - The text content of the SMS.
      * @returns The Sinch batch response upon successful submission.
      * @throws Error (or specific NestJS Exception) if the API call fails or configuration is missing.
      */
     async sendBulkSms(recipients: string[], messageBody: string): Promise<SinchBatchResponse&gt; {
       if (!recipients || recipients.length === 0) {
         // Consider throwing BadRequestException if called directly from controller context,
         // but generic Error is okay for service layer internal validation.
         throw new Error('Recipient list cannot be empty.');
       }
       if (!messageBody) {
           throw new Error('Message body cannot be empty.');
       }
   
       const payload = {
         from: this.sinchFromNumber,
         to: recipients,
         body: messageBody,
         // Add other optional parameters here if needed, e.g.:
         // delivery_report: 'summary',
         // type: 'mt_text', // Default for text messages
       };
   
       // Construct the full path including the service plan ID
       const endpointPath = `/xms/v1/${this.servicePlanId}/batches`;
       const fullUrl = `${this.sinchApiUrl}${endpointPath}`; // For logging
   
       this.logger.log(`Sending bulk SMS to ${recipients.length} recipients via Sinch`);
       this.logger.debug(`Sinch API Endpoint: ${fullUrl}`);
       this.logger.debug(`Sinch Payload: ${JSON.stringify(payload)}`);
   
       try {
           // Use firstValueFrom to convert Observable to Promise
           const response = await firstValueFrom(
               // Make POST request to the dynamically constructed path
               this.httpService.post<SinchBatchResponse&gt;(endpointPath, payload).pipe(
                   map((axiosResponse) =&gt; {
                       this.logger.log(`Sinch API call successful. Batch ID: ${axiosResponse.data.id}`);
                       return axiosResponse.data; // Return the data part of the response
                   }),
                   catchError((error: AxiosError) =&gt; {
                       this.logger.error(`Sinch API Error: ${error.message}`, error.stack);
                       this.logger.error(`Sinch Response Status: ${error.response?.status}`);
                       this.logger.error(`Sinch Response Data: ${JSON.stringify(error.response?.data)}`);
   
                       // Throw a NestJS exception for better handling upstream
                       const status = error.response?.status || 500;
                       const errorMessage = `Sinch API request failed with status ${status}: ${JSON.stringify(error.response?.data || error.message)}`;
   
                       // Map specific statuses (401, 403 etc.) to specific exceptions if needed
                       // For now, wrap in InternalServerErrorException
                       throw new InternalServerErrorException(errorMessage);
                   }),
               ),
           );
           return response;
       } catch (error) {
           // Log if the error wasn't already logged in catchError (e.g., input validation errors)
           if (!(error instanceof InternalServerErrorException)) {
                this.logger.error(`Failed to send bulk SMS (Pre-request or unexpected): ${error.message}`, error.stack);
           }
           // Ensure the error propagates up (controller catches it)
           throw error;
       }
     }
   }
   
   • Logger: Uses NestJS's built-in Logger.
   • Constructor: Injects HttpService and ConfigService. Fetches required config values (SINCH_FROM_NUMBER, SINCH_SERVICE_PLAN_ID, SINCH_API_URL) early and throws InternalServerErrorException if any are missing.
   • sendBulkSms Method:
     • Takes recipients array and message body.
     • Performs basic input checks (throwing generic Error here is acceptable as the controller catches it).
     • Constructs the payload object.
     • Constructs the API endpointPath dynamically using the servicePlanId fetched in the constructor (/xms/v1/${this.servicePlanId}/batches).
     • Uses this.httpService.post with the relative endpointPath. The base URL (SINCH_API_URL) is automatically prepended by the HttpModule.
     • Uses firstValueFrom to convert the RxJS Observable to a Promise.
     • Uses .pipe() with RxJS operators:
       • map: Extracts the data from the successful Axios response.
       • catchError: Handles Axios errors. Logs detailed information and throws a NestJS InternalServerErrorException wrapping the Sinch error details.
     • Includes a final catch block to handle errors thrown before the HTTP call (like input validation) or other unexpected issues.

4. Import SinchModule into AppModule: Make the SinchModule (and thus SinchService) available to the application.

   src/app.module.ts:

   typescript

   import { Module } from '@nestjs/common';
   import { ConfigModule } from '@nestjs/config';
   import { AppController } from './app.controller';
   import { AppService } from './app.service';
   import { SinchModule } from './sinch/sinch.module'; // Import SinchModule
   // Import other modules here later
   
   @Module({
     imports: [
       ConfigModule.forRoot({
         isGlobal: true,
         envFilePath: '.env',
       }),
       SinchModule, // Add SinchModule here
       // Add MessagingModule later
     ],
     controllers: [AppController],
     providers: [AppService],
   })
   export class AppModule {}
   

4. Building the API Layer

Now, let's create the controller and DTO (Data Transfer Object) to expose an endpoint for triggering the bulk SMS send.

1. Generate Messaging Module and Controller:

   bash

   nest g module messaging
   nest g controller messaging
   

   This creates src/messaging/messaging.module.ts and src/messaging/messaging.controller.ts.

2. Create Bulk SMS DTO: Data Transfer Objects define the expected shape of request bodies and enable automatic validation using class-validator.

   Create a file src/messaging/dto/bulk-sms.dto.ts:

   src/messaging/dto/bulk-sms.dto.ts:

   typescript

   import {
     IsArray,
     ArrayNotEmpty,
     ArrayMinSize,
     IsString,
     IsPhoneNumber, // Validates E.164 format (approximately)
     MinLength,
     MaxLength,
   } from 'class-validator';
   
   export class BulkSmsDto {
     @IsArray()
     @ArrayNotEmpty()
     @ArrayMinSize(1)
     @IsPhoneNumber(undefined, { each: true, message: 'Each recipient must be a valid E.164 phone number (e.g., +12025550101)' })
     recipients: string[];
   
     @IsString()
     @MinLength(1, { message: 'Message body cannot be empty.' })
     @MaxLength(2000, { message: 'Message body too long. Sinch allows max 2000 characters with recommended 6-part concatenation limit.' })
     messageBody: string;
   }
   
   • @IsArray, @ArrayNotEmpty, @ArrayMinSize(1): Ensure recipients is a non-empty array.
   • @IsPhoneNumber(undefined, { each: true, ... }): Validates each element in the recipients array. Checks for a format generally resembling E.164 (starts with "+," followed by digits). Note: This is a basic check; true phone number validity requires more complex lookups.
   • @IsString, @MinLength(1), @MaxLength(2000): Ensure messageBody is a non-empty string within Sinch's limits. Sinch supports:
     • GSM-7 encoding: 160 characters (single message), 153 characters per segment when concatenated (7-byte header overhead)
     • Unicode (UCS-2) encoding: 70 characters (single message), 67 characters per segment when concatenated
     • Maximum: 2000 characters total with recommended maximum of 6 concatenated parts
     • Reference: https://developers.sinch.com/docs/sms/resources/message-info/character-support/

3. Implement MessagingController: Define the API endpoint (POST /messages/bulk) that accepts the DTO and uses SinchService to send the messages.

   src/messaging/messaging.controller.ts:

   typescript

   import { Controller, Post, Body, HttpCode, HttpStatus, Logger, InternalServerErrorException, BadRequestException } from '@nestjs/common';
   import { SinchService } from '../sinch/sinch.service';
   import { BulkSmsDto } from './dto/bulk-sms.dto';
   
   @Controller('messages') // Route prefix: /messages
   export class MessagingController {
     private readonly logger = new Logger(MessagingController.name);
   
     constructor(private readonly sinchService: SinchService) {}
   
     @Post('bulk') // Route: POST /messages/bulk
     @HttpCode(HttpStatus.ACCEPTED) // Return 202 Accepted on successful submission
     async sendBulkSms(@Body() bulkSmsDto: BulkSmsDto) {
       this.logger.log(`Received request to send bulk SMS to ${bulkSmsDto.recipients.length} recipients.`);
   
       try {
         const result = await this.sinchService.sendBulkSms(
           bulkSmsDto.recipients,
           bulkSmsDto.messageBody,
         );
   
         this.logger.log(`Successfully submitted bulk SMS batch. Batch ID: ${result.id}`);
         return {
           message: 'Bulk SMS batch submitted successfully.',
           batchId: result.id,
           submittedAt: result.created_at,
         };
       } catch (error) {
         this.logger.error(`Failed to process bulk SMS request: ${error.message}`, error.stack);
   
         // Handle specific errors thrown by the service or re-throw appropriate HTTP exceptions
         if (error.message.includes('Recipient list cannot be empty') || error.message.includes('Message body cannot be empty')) {
             // These are service-level validation errors caught before API call
             throw new BadRequestException(error.message);
         }
         // If it's already a NestJS exception from SinchService (like InternalServerErrorException), re-throw it.
         if (error instanceof InternalServerErrorException || error instanceof BadRequestException) {
              throw error;
         }
   
         // For other generic errors, throw InternalServerErrorException
         throw new InternalServerErrorException('Failed to send bulk SMS. Please check logs for details.');
       }
     }
   }
   
   • @Controller('messages'): Sets the base route for this controller.
   • @Post('bulk'): Defines a POST endpoint at /messages/bulk.
   • @HttpCode(HttpStatus.ACCEPTED): Sets the default success status code to 202.
   • @Body() bulkSmsDto: BulkSmsDto: Injects and validates the request body.
   • Injects SinchService.
   • Calls sinchService.sendBulkSms.
   • Includes try/catch for robust error handling, mapping service errors to appropriate HTTP exceptions (BadRequestException for input issues detected in the service, re-throwing InternalServerErrorException from the service, or throwing a new one for unexpected errors).
   • Returns a meaningful success response including the Sinch batchId.

4. Import SinchModule into MessagingModule: The MessagingController depends on SinchService.

   src/messaging/messaging.module.ts:

   typescript

   import { Module } from '@nestjs/common';
   import { MessagingController } from './messaging.controller';
   import { SinchModule } from '../sinch/sinch.module'; // Import SinchModule
   
   @Module({
     imports: [SinchModule], // Make SinchService available here
     controllers: [MessagingController],
     providers: [], // No specific providers needed in this module
   })
   export class MessagingModule {}
   

5. Import MessagingModule into AppModule: Make the MessagingModule known to the main application module. Add rate limiting. Remove default controller/service if desired.

   src/app.module.ts:

   typescript

   import { Module } from '@nestjs/common';
   import { ConfigModule } from '@nestjs/config';
   import { SinchModule } from './sinch/sinch.module';
   import { MessagingModule } from './messaging/messaging.module'; // Import MessagingModule
   import { ThrottlerModule, ThrottlerGuard } from 'nestjs-throttler'; // Import Throttler
   import { APP_GUARD } from '@nestjs/core'; // Import APP_GUARD
   
   @Module({
     imports: [
       ConfigModule.forRoot({
         isGlobal: true,
         envFilePath: '.env',
       }),
       // Configure Rate Limiting Globally
       ThrottlerModule.forRoot([{
         ttl: 60000, // Time-to-live in milliseconds (e.g., 60 seconds)
         limit: 10,  // Max requests per TTL per IP
       }]),
       SinchModule,
       MessagingModule, // Add MessagingModule here
     ],
     controllers: [], // Remove AppController if not needed
     providers: [
       // Apply ThrottlerGuard globally to all endpoints
       {
         provide: APP_GUARD,
         useClass: ThrottlerGuard,
       },
       // Remove AppService if not needed
     ],
   })
   export class AppModule {}
   
   • We added ThrottlerModule configuration and registered ThrottlerGuard globally.

5. Error Handling and Logging

We've incorporated logging and error handling. Let's review the strategy.

• Logging:

  • Uses NestJS's built-in Logger (v11+ includes improved ConsoleLogger with better formatting for nested objects, maps, sets, and JSON logging support).
  • Logs occur in SinchService (API calls, request/response details, errors) and MessagingController (request lifecycle).
  • Best Practice: Enhance production logging (JSON format, centralized logging service). Use correlation IDs. Pay attention to log levels.
  • Example Log Analysis: Check logs for Sinch API Error, Sinch Response Status, and Sinch Response Data from SinchService when troubleshooting failed batches.

• Error Handling Strategy:

  • Validation Errors (DTO): Handled automatically by the ValidationPipe (Section 6), returning 400 Bad Request.
  • Service Input Errors (SinchService): Basic checks (e.g., empty recipients) throw Error.
  • Sinch API Errors (SinchService): catchError intercepts Axios errors, logs details, and throws InternalServerErrorException containing Sinch status and response data.
  • Controller Errors (MessagingController): Catches errors from SinchService. Maps service input errors to BadRequestException. Re-throws NestJS exceptions from the service (like InternalServerErrorException). Catches other unexpected errors and throws InternalServerErrorException.
  • Consistency: Uses standard NestJS HTTP exceptions for clear API responses.
  • Rate Limiting: Note that Sinch batches queue in FIFO (First-In-First-Out) order and send at your plan's rate limit. A batch with 10 recipients counts as 10 messages for rate limit calculation. Rate limits are plan-specific; consult your account manager for your sending rate and ensure batches don't exceed thresholds. Reference: https://developers.sinch.com/docs/sms/resources/message-info/rate-limits/

• Retry Mechanisms (Optional but Recommended):

  • Consider retrying transient network issues or Sinch 5xx errors.
  • Use libraries like async-retry. Install with types: npm i async-retry @types/async-retry or yarn add async-retry @types/async-retry.
  • Caution: Only retry on retriable errors (network issues, 5xx). Don't retry 4xx errors. Implement exponential backoff.

  Example Sketch (using async-retry in SinchService):

  typescript

  // Inside src/sinch/sinch.service.ts
  // NOTE: Ensure you install async-retry and its types:
  // npm install async-retry @types/async-retry
  // or
  // yarn add async-retry @types/async-retry
  import * as retry from 'async-retry';
  import { Injectable, Logger, InternalServerErrorException } from '@nestjs/common';
  import { ConfigService } from '@nestjs/config';
  import { HttpService } from '@nestjs/axios';
  import { firstValueFrom, map, catchError } from 'rxjs';
  import { AxiosError } from 'axios';
  
  // ... (Keep SinchBatchResponse interface and other parts of the class)
  
  @Injectable()
  export class SinchService {
    // ... (Keep logger, properties, constructor, and original sendBulkSms)
  
    async sendBulkSmsWithRetry(recipients: string[], messageBody: string): Promise<SinchBatchResponse&gt; {
       // ... input validation (same as sendBulkSms) ...
       if (!recipients || recipients.length === 0) throw new Error('Recipient list cannot be empty.');
       if (!messageBody) throw new Error('Message body cannot be empty.');
  
       const payload = {
         from: this.sinchFromNumber,
         to: recipients,
         body: messageBody,
       };
       const endpointPath = `/xms/v1/${this.servicePlanId}/batches`;
  
       return retry(async (bail, attempt) =&gt; {
           this.logger.log(`Attempt ${attempt} to send bulk SMS via Sinch`);
           try {
               const response = await firstValueFrom(
                   this.httpService.post<SinchBatchResponse&gt;(endpointPath, payload).pipe(
                       map(res =&gt; res.data),
                       catchError((error: AxiosError) =&gt; {
                           const status = error.response?.status;
                           // Decide if we should retry or bail
                           // Bail on 4xx client errors (except maybe 429 if you want to retry rate limits carefully)
                           if (status && status &gt;= 400 && status &lt; 500 && status !== 429) {
                               this.logger.warn(`Non-retriable Sinch API Error (Status ${status}). Bailing.`);
                               // Construct the error to be thrown by bail
                               const bailError = new InternalServerErrorException(`Sinch API request failed with status ${status}: ${JSON.stringify(error.response?.data || error.message)}`);
                               bail(bailError); // bail throws a special error to stop retrying
                               // bail() throws_ so we technically don't reach here_ but return undefined for type safety if needed.
                               // Depending on strict TS settings_ you might need a `throw bailError` after `bail(bailError)`.
                               return undefined as never; // Or throw bailError
                           }
                           this.logger.warn(`Retriable Sinch API Error (Status ${status || 'N/A'}) or Network Error. Retrying...`);
                           // Throw the original AxiosError or a wrapped NestJS exception to trigger retry
                           throw new InternalServerErrorException(`Sinch API request failed on attempt ${attempt}: ${error.message}`_ error.stack);
                       })_
                   )_
               );
               this.logger.log(`Sinch API call successful on attempt ${attempt}. Batch ID: ${response.id}`);
               return response;
           } catch (error) {
                // Log error for the failed attempt before retry or final failure
                this.logger.error(`Attempt ${attempt} failed: ${error.message}`_ error.stack);
                // Re-throw error if bail wasn't called_ to potentially retry or fail finally
                throw error;
           }
       }_ {
           retries: 3_ // Number of retries
           factor: 2_ // Exponential backoff factor
           minTimeout: 1000_ // Initial timeout in ms
           onRetry: (error_ attempt) =&gt; {
               this.logger.warn(`Retrying Sinch API call (Attempt ${attempt}) due to error: ${error.message}`);
           },
       });
    }
  }
  

  Remember to update the MessagingController to call sendBulkSmsWithRetry instead of sendBulkSms if you implement this retry logic.

6. Validate Requests with DTOs and ValidationPipe

You created the BulkSmsDto with class-validator decorators. Now, enable the ValidationPipe globally.

1. Enable ValidationPipe Globally: Modify src/main.ts.

   src/main.ts:

   typescript

   import { NestFactory } from '@nestjs/core';
   import { AppModule } from './app.module';
   import { ValidationPipe, Logger } from '@nestjs/common'; // Import ValidationPipe and Logger
   import { ConfigService } from '@nestjs/config'; // Import ConfigService
   
   async function bootstrap() {
     const app = await NestFactory.create(AppModule);
     const configService = app.get(ConfigService); // Get ConfigService instance
   
     // Enable CORS (Cross-Origin Resource Sharing) if needed (adjust origins for production)
     app.enableCors();
   
     // Apply ValidationPipe globally
     app.useGlobalPipes(new ValidationPipe({
       whitelist: true, // Strip properties not in DTO
       forbidNonWhitelisted: true, // Throw error if non-whitelisted properties are present
       transform: true, // Automatically transform payloads to DTO instances
       transformOptions: {
         enableImplicitConversion: true, // Allow basic type conversions
       },
     }));
   
     const port = configService.get<number&gt;('PORT') || 3000; // Get port from env
     await app.listen(port);
     Logger.log(`Application is running on: http://localhost:${port}`, 'Bootstrap'); // Use Logger
   }
   bootstrap();
   
   • Import ValidationPipe and Logger.
   • Use app.useGlobalPipes() to apply the ValidationPipe.
   • whitelist: true: Automatically removes properties from the request body not defined in the DTO (Data Transfer Object).
   • forbidNonWhitelisted: true: Throws an error if properties not defined in the DTO are present.
   • transform: true: Attempts to transform the incoming payload to match the DTO types (e.g., string to number if expected).
   • transformOptions: { enableImplicitConversion: true }: Helps with basic type conversions during transformation.
   • Import ConfigService and Logger to get the port from environment variables and log the startup message.
   • Enable CORS (Cross-Origin Resource Sharing) if your frontend runs on a different domain. Adjust origins for production security.

Frequently Asked Questions

What is the maximum batch size for Sinch SMS messages?

Sinch supports sending SMS messages to multiple recipients in a single batch request. While there's no hard limit on the number of recipients per batch, practical limits depend on your service plan's rate limits. A batch with 10 recipients counts as 10 messages toward your rate limit calculation. Sinch batches queue in FIFO (First-In-First-Out) order and send at your plan-specific rate limit. Consult your Sinch account manager for your specific sending rate and structure batches accordingly.

Which Node.js version should I use with NestJS for Sinch SMS integration?

Use Node.js v22 LTS for optimal compatibility and long-term support. Node.js v22 entered Active LTS in October 2024 and remains in Active LTS until October 2025, then transitions to Maintenance LTS until April 2027. This version provides security updates, performance improvements, and stability for production applications. NestJS v11.1.6 (released January 2025) works seamlessly with Node.js v22, providing improved ConsoleLogger, microservices enhancements, and performance optimizations.

How do I format phone numbers for Sinch SMS API?

Format all phone numbers in E.164 international format: a plus sign (+) followed by the country code and subscriber number with no spaces or special characters. Examples: +12025550101 (US), +447911123456 (UK), +61412345678 (Australia). The @IsPhoneNumber validator in the BulkSmsDto checks for E.164 format compliance on each recipient. Sinch requires E.164 formatting for accurate message routing across international carriers.

What are the SMS character limits for Sinch messages?

Sinch supports up to 2000 characters per message with a recommended maximum of 6 concatenated parts. Character limits depend on encoding: GSM-7 encoding allows 160 characters for single messages and 153 characters per segment for concatenated messages (7-byte header overhead). Unicode (UCS-2) encoding allows 70 characters for single messages and 67 characters per segment for concatenated messages. The BulkSmsDto includes a @MaxLength(2000) validator to enforce Sinch's character limit. Reference: https://developers.sinch.com/docs/sms/resources/message-info/character-support/

How does NestJS dependency injection work with the Sinch service?

NestJS uses constructor-based dependency injection to provide instances of services to controllers and other services. The SinchService is marked with the @Injectable() decorator, registered in SinchModule providers, and exported for use in other modules. The MessagingController declares SinchService in its constructor parameters, and NestJS automatically injects the singleton instance. This pattern promotes loose coupling, testability, and maintainable code architecture.

How should I handle Sinch API errors in production?

Implement multi-layer error handling: catch Axios errors in SinchService using RxJS catchError, log detailed error information (status code, response data), and throw appropriate NestJS exceptions (InternalServerErrorException for 5xx errors, BadRequestException for validation errors). In the controller, catch service exceptions and map them to HTTP status codes. For production, implement retry logic with exponential backoff for transient failures (network issues, 5xx errors) using libraries like async-retry. Never retry 4xx client errors except possibly 429 rate limit errors.

How do I test the Sinch SMS integration locally?

Create a test endpoint in MessagingController with hardcoded test recipients (your own phone numbers) and test messages. Start your NestJS application with npm run start:dev, then send POST requests to http://localhost:3000/messages/bulk using tools like curl, Postman, or Thunder Client. Example curl command: curl -X POST http://localhost:3000/messages/bulk -H "Content-Type: application/json" -d '{"recipients":["+12025550101"],"messageBody":"Test message"}'. Monitor console logs for Sinch API responses and check your phone for message delivery. Sinch charges for all sent messages including test messages.

What's the best way to deploy a NestJS Sinch SMS service to production?

Deploy to platforms like Heroku, AWS Elastic Beanstalk, Google Cloud Run, or DigitalOcean App Platform. Build your application with npm run build, which compiles TypeScript to JavaScript in the dist/ directory. Set environment variables (SINCH_API_URL, SINCH_SERVICE_PLAN_ID, SINCH_API_TOKEN, SINCH_FROM_NUMBER, PORT) in your platform's configuration panel. Use process managers like PM2 for traditional VPS deployments. Implement health check endpoints for load balancers. Enable structured JSON logging and integrate with monitoring services like Datadog, New Relic, or Sentry for production observability.

How do I secure my NestJS Sinch SMS API endpoint?

Implement multiple security layers: apply rate limiting using nestjs-throttler (configured in AppModule with TTL and request limits per IP), add authentication middleware (JWT tokens, API keys, or OAuth), validate all inputs using class-validator decorators in DTOs, enable CORS with specific allowed origins (not wildcard * in production), use HTTPS for all production traffic, store sensitive credentials in environment variables (never commit to Git), implement request signing for internal services, and audit logs for suspicious activity patterns.

How can I optimize costs when sending bulk SMS with Sinch?

Optimize costs by batching messages efficiently to reduce API calls, monitoring delivery reports to identify failed messages and invalid numbers, implementing message deduplication to prevent sending duplicates to the same recipient, caching valid phone numbers to avoid repeated validation, using alphanumeric sender IDs where supported (often cheaper than long codes), scheduling non-urgent messages during off-peak hours if your plan has variable pricing, monitoring character count to avoid unnecessary message segmentation (stay under 160 chars for GSM-7 or 70 for Unicode), and regularly reviewing your Sinch service plan to ensure it matches your usage patterns.