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NestJS Enterprise Backend APIs · Pelajaran

Unggahan Langsung ke S3 dengan URL Bertanda Tangan

Alihkan unggahan berat ke penyimpanan objek dengan menerbitkan URL bertanda tangan berumur pendek dari API.

Unggahan Langsung ke S3 dengan URL Bertanda Tangan adalah pelajaran NestJS Enterprise Backend APIs gratis di CoddyKit. Ini adalah pelajaran 3 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar NestJS Enterprise Backend APIs, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus NestJS Enterprise Backend APIs mencakup 4 pelajaran total.

Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.

Why Not Proxy Uploads Through the API?

When a client uploads a large file, the naive design sends the bytes to your NestJS API, which then forwards them to object storage. This makes your server a bottleneck.

  • Memory & CPU pressure — every upload occupies a request thread and buffers/streams through your process.
  • Doubled bandwidth — bytes travel client → API → S3, so you pay for the same data twice.
  • Request timeouts — load balancers (e.g. ALB, Nginx) cap request duration; multi-GB uploads stall.

The fix: let the browser upload directly to S3. Your API only issues a short-lived, signed URL that grants permission for one specific operation.

What Is a Presigned URL?

A presigned URL is a normal S3 object URL with extra query parameters that encode a temporary, cryptographically-signed grant. Anyone holding the URL can perform exactly one operation (e.g. PutObject) on exactly one key, until it expires.

  • Signed with your AWS credentials, but the credentials are never exposed — only the signature is.
  • Scoped to a single HTTP method, bucket, and object key.
  • Has a hard expiry (seconds), after which S3 rejects it with 403.

Because S3 validates the signature itself, your API does not touch the file bytes at all.

The Upload Flow

The end-to-end flow has three actors: the browser, your NestJS API, and S3.

  • 1. Request: Browser asks the API, "I want to upload avatar.png, 240 KB, image/png."
  • 2. Sign: API validates the request, generates a unique key, and returns a presigned PUT URL.
  • 3. Upload: Browser PUTs the raw bytes straight to that URL on S3.
  • 4. Confirm: Browser tells the API the upload succeeded; API persists the key in the database.

Your API stays fast and stateless — it never proxies the payload.

Configuring the S3 Client

Use the AWS SDK v3 modular packages. Create a single S3Client instance and share it via a NestJS provider so credentials and region are configured in one place.

Credentials come from environment variables (or, in production, an IAM role). Never hardcode them.

import { Injectable } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { S3Client } from '@aws-sdk/client-s3';

@Injectable()
export class S3Provider {
  readonly client: S3Client;
  readonly bucket: string;

  constructor(private readonly config: ConfigService) {
    this.bucket = config.getOrThrow<string>('S3_BUCKET');
    this.client = new S3Client({
      region: config.getOrThrow<string>('AWS_REGION'),
      credentials: {
        accessKeyId: config.getOrThrow<string>('AWS_ACCESS_KEY_ID'),
        secretAccessKey: config.getOrThrow<string>('AWS_SECRET_ACCESS_KEY'),
      },
    });
  }
}

Generating a Presigned PUT URL

The @aws-sdk/s3-request-presigner package signs a command without executing it. You build a PutObjectCommand describing the target key and content type, then call getSignedUrl with an expiresIn.

  • ContentType in the command is enforced: the browser must send a matching Content-Type header.
  • expiresIn is in seconds — keep it short (60–300s) so leaked URLs die quickly.
import { Injectable } from '@nestjs/common';
import { PutObjectCommand } from '@aws-sdk/client-s3';
import { getSignedUrl } from '@aws-sdk/s3-request-presigner';
import { S3Provider } from './s3.provider';

@Injectable()
export class UploadsService {
  constructor(private readonly s3: S3Provider) {}

  async createUploadUrl(key: string, contentType: string): Promise<string> {
    const command = new PutObjectCommand({
      Bucket: this.s3.bucket,
      Key: key,
      ContentType: contentType,
    });
    return getSignedUrl(this.s3.client, command, { expiresIn: 120 });
  }
}

Generating Safe, Unique Object Keys

Never trust the client's filename as the S3 key. A user could send ../../etc/passwd or collide with another user's file. Generate the key server-side.

  • Namespace by owner: uploads/{userId}/... so authorization is easy to reason about.
  • Use a random UUID to guarantee uniqueness.
  • Preserve only a sanitized extension for content-type hints and tooling.
import { randomUUID } from 'node:crypto';
import { extname } from 'node:path';

function buildObjectKey(userId: string, originalName: string): string {
  const ext = extname(originalName).toLowerCase().replace(/[^.a-z0-9]/g, '');
  const safeExt = /^\.[a-z0-9]{1,8}$/.test(ext) ? ext : '';
  return `uploads/${userId}/${randomUUID()}${safeExt}`;
}

console.log(buildObjectKey('user-42', 'My Vacation Photo.PNG'));
console.log(buildObjectKey('user-42', 'sneaky/../../etc/passwd'));

The Controller Endpoint

Expose a guarded endpoint that takes the file metadata, validates it with a DTO, and returns the presigned URL plus the final key. The client needs the key later to confirm or to build the public/read URL.

Authentication matters here: the signing endpoint is your access-control gate. S3 itself trusts any valid signature, so all checks (who, what size, what type) must happen before you sign.

import { Body, Controller, Post, UseGuards, Req } from '@nestjs/common';
import { JwtAuthGuard } from '../auth/jwt-auth.guard';
import { UploadsService } from './uploads.service';
import { CreateUploadDto } from './dto/create-upload.dto';

@UseGuards(JwtAuthGuard)
@Controller('uploads')
export class UploadsController {
  constructor(private readonly uploads: UploadsService) {}

  @Post('presign')
  async presign(@Req() req, @Body() dto: CreateUploadDto) {
    return this.uploads.presignForUser(req.user.id, dto);
  }
}

Validating the Upload Request DTO

Validate metadata before signing. Reject disallowed MIME types and oversized files at the API layer — but remember the client could lie, so this is a first line of defense, not the last.

  • Whitelist contentType against an allow-list.
  • Cap the declared size to fail fast on obviously huge uploads.
import { IsIn, IsInt, IsString, Max, Min } from 'class-validator';

const ALLOWED = ['image/png', 'image/jpeg', 'image/webp', 'application/pdf'] as const;

export class CreateUploadDto {
  @IsString()
  filename: string;

  @IsIn(ALLOWED)
  contentType: (typeof ALLOWED)[number];

  @IsInt()
  @Min(1)
  @Max(10 * 1024 * 1024) // 10 MB
  size: number;
}

Enforcing Size with a Signed Content-Length

The DTO size check is advisory — the browser still controls how many bytes it actually PUTs. To make S3 itself reject oversized uploads, bind a content-length range into the signature.

For a single PUT, sign ContentLength so S3 enforces an exact byte count. For more flexible limits (a min/max range), use a presigned POST policy instead, which supports content-length-range conditions.

import { createPresignedPost } from '@aws-sdk/s3-presigned-post';

async function presignPost(client, bucket: string, key: string) {
  return createPresignedPost(client, {
    Bucket: bucket,
    Key: key,
    Conditions: [
      ['content-length-range', 1, 10 * 1024 * 1024], // 1 byte – 10 MB
      ['starts-with', '$Content-Type', 'image/'],
    ],
    Fields: { 'Content-Type': 'image/png' },
    Expires: 120,
  });
}

The Browser-Side Upload

With the presigned PUT URL in hand, the browser uploads with a plain fetch. There is no SDK and no AWS credentials on the client — just the bytes and a matching Content-Type.

  • The header must equal the ContentType you signed, or S3 returns 403 SignatureDoesNotMatch.
  • Do not send Authorization — the signature lives in the query string.
async function uploadFile(presignedUrl: string, file: File): Promise<void> {
  const res = await fetch(presignedUrl, {
    method: 'PUT',
    headers: { 'Content-Type': file.type },
    body: file,
  });
  if (!res.ok) {
    throw new Error(`Upload failed: ${res.status} ${res.statusText}`);
  }
}

Confirming the Upload & Reading Back

Because S3 doesn't notify your API, the client calls back after a successful PUT so you can persist the key. For extra safety, the API can HeadObject to verify the object truly exists and check its real size/type before trusting it.

To serve the file later, either keep the bucket private and issue a presigned GET URL on demand, or (for public assets) store and return the public URL.

import { GetObjectCommand, HeadObjectCommand } from '@aws-sdk/client-s3';
import { getSignedUrl } from '@aws-sdk/s3-request-presigner';

async confirm(userId: string, key: string) {
  const head = await this.s3.client.send(
    new HeadObjectCommand({ Bucket: this.s3.bucket, Key: key }),
  );
  if ((head.ContentLength ?? 0) > 10 * 1024 * 1024) {
    throw new BadRequestException('Object exceeds size limit');
  }
  await this.files.save({ userId, key, size: head.ContentLength });
}

async downloadUrl(key: string) {
  return getSignedUrl(
    this.s3.client,
    new GetObjectCommand({ Bucket: this.s3.bucket, Key: key }),
    { expiresIn: 300 },
  );
}

Quick Check

Test your understanding of where access control lives in this pattern.

Recap

You learned how to offload heavy uploads to S3 using presigned URLs:

  • Why: proxying bytes through the API wastes bandwidth, memory, and hits request timeouts.
  • How: the API signs a short-lived PutObjectCommand with getSignedUrl; the browser PUTs straight to S3.
  • Keys: always generate them server-side (UUID + namespaced by user); never trust client filenames.
  • Security: the presign endpoint is the access-control gate — authenticate, whitelist MIME types, and cap size there. Use presigned POST content-length-range to let S3 enforce size.
  • After upload: confirm with HeadObject, persist the key, and serve later via presigned GetObjectCommand URLs.

Pertanyaan yang Sering Diajukan

Apakah pelajaran “Unggahan Langsung ke S3 dengan URL Bertanda Tangan” gratis?

Ya — teks lengkap “Unggahan Langsung ke S3 dengan URL Bertanda Tangan” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus NestJS Enterprise Backend APIs, upgrade ke CoddyKit PRO. Kursus NestJS Enterprise Backend APIs mencakup 4 pelajaran total.

Apa yang akan aku pelajari di “Unggahan Langsung ke S3 dengan URL Bertanda Tangan”?

Alihkan unggahan berat ke penyimpanan objek dengan menerbitkan URL bertanda tangan berumur pendek dari API. Kamu berlatih NestJS Enterprise Backend APIs dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.

Apakah aku perlu pengalaman untuk memulai NestJS Enterprise Backend APIs?

Tidak diperlukan pengalaman sebelumnya. NestJS Enterprise Backend APIs di CoddyKit dirancang untuk pemula hingga pelajar tingkat lanjut, jadi kamu bisa memulai di sini atau dari awal dan belajar sesuai kecepatan kamu sendiri. Ini adalah pelajaran 3 dari 4.

Berapa lama pelajaran “Unggahan Langsung ke S3 dengan URL Bertanda Tangan” memakan waktu?

Sebagian besar pelajaran CoddyKit memakan waktu sekitar 5–10 menit. Setiap pelajaran ringkas dan interaktif, jadi kamu membuat kemajuan stabil dan melanjutkan dari tempat kamu tinggalkan di web dan aplikasi.

Bisakah aku menulis dan menjalankan kode dalam pelajaran NestJS Enterprise Backend APIs ini?

Ya. Setiap pelajaran NestJS Enterprise Backend APIs menyertakan editor kode bawaan, jadi kamu menulis dan menjalankan kode nyata langsung di browser dan mendapatkan umpan balik AI instan — tidak diperlukan penyiapan lokal.

Semua pelajaran dalam kursus ini

  1. Unggahan Multipart dengan Pencegat Multer
  2. Mengalirkan Respons Besar dengan StreamableFile
  3. Unggahan Langsung ke S3 dengan URL Bertanda Tangan
  4. Alur Pemrosesan Gambar dengan Sharp
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