Validate required environment variables at startup

Author: yosemite01

src/app.module.ts

@@ -3,6 +3,7 @@ import { APP_GUARD } from '@nestjs/core';
 import { AppController } from './app.controller';
 import { ConfigModule } from '@nestjs/config';
 import { PrismaModule } from './prisma/prisma.module';
+import { validateEnvironment } from './common/config/env.validation';
 import { AppService } from './app.service';
 import { UsersModule } from './users/users.module';
 import { IdempotentUserModule } from './users/idempotent-user.module';
@@ -29,6 +30,7 @@ import { HealthModule } from './health/health.module';
     ConfigModule.forRoot({
       isGlobal: true,
       envFilePath: '.env',
+      validate: validateEnvironment,
     }),
     PrismaModule,
     AuthModule,

src/common/config/env.validation.ts

@@ -0,0 +1,57 @@
+import { plainToInstance } from 'class-transformer';
+import {
+  IsInt,
+  IsNotEmpty,
+  IsOptional,
+  IsString,
+  IsUrl,
+  Min,
+  MinLength,
+  validateSync,
+} from 'class-validator';
+
+export class EnvironmentVariables {
+  @IsString()
+  @IsNotEmpty()
+  DATABASE_URL!: string;
+
+  @IsString()
+  @IsNotEmpty()
+  @MinLength(32)
+  WALLET_ENCRYPTION_KEY!: string;
+
+  @IsString()
+  @IsNotEmpty()
+  @IsUrl({ require_protocol: true })
+  STELLAR_HORIZON_URL!: string;
+
+  @IsOptional()
+  @IsInt()
+  @Min(1)
+  PORT?: number;
+}
+
+export function validateEnvironment(config: Record<string, unknown>) {
+  const validatedConfig = plainToInstance(EnvironmentVariables, config, {
+    enableImplicitConversion: true,
+  });
+
+  const errors = validateSync(validatedConfig, {
+    skipMissingProperties: false,
+  });
+
+  if (errors.length > 0) {
+    const message = errors
+      .map((error) => {
+        const constraints = error.constraints
+          ? Object.values(error.constraints).join(', ')
+          : 'invalid value';
+        return `${error.property}: ${constraints}`;
+      })
+      .join('; ');
+
+    throw new Error(`Invalid environment configuration: ${message}`);
+  }
+
+  return validatedConfig;
+}