Building VoIP Backends with NestJS: SIP Signalling and FreeSWITCH ESL

import { Injectable, OnModuleInit, OnModuleDestroy } from '@nestjs/common';
import { Connection } from 'node-esl';

@Injectable()
export class FreeSwitchService implements OnModuleInit, OnModuleDestroy {
  private conn: Connection;

  async onModuleInit() {
    this.conn = new Connection(
      process.env.FS_HOST || '127.0.0.1',
      8021,
      process.env.FS_PASSWORD || 'ClueCon',
    );
    await new Promise<void>((resolve) => this.conn.on('esl::ready', resolve));
    this.conn.subscribe('CHANNEL_CREATE CHANNEL_ANSWER CHANNEL_HANGUP DTMF');
    this.conn.on('esl::event::CHANNEL_ANSWER::*', this.onCallAnswered.bind(this));
  }

  async onModuleDestroy() { this.conn.disconnect(); }

  async originateCall(from: string, to: string): Promise<string> {
    const response = await this.conn.api(
      `originate {origination_caller_id_number=${from}}sofia/external/${to}@your-gateway &echo()`
    );
    return response.getBody();
  }

  private onCallAnswered(event: any) {
    const callUuid = event.getHeader('Unique-ID');
    // Emit to your call state management service
  }
}