# S3 Reference

## Presigned URLs (GET / PUT)

```js
import { S3Client, GetObjectCommand, PutObjectCommand } from "@aws-sdk/client-s3";
import { getSignedUrl } from "@aws-sdk/s3-request-presigner";

const client = new S3Client({ region: "us-east-1" });

// GET — default expiry 900s
const getUrl = await getSignedUrl(client, new GetObjectCommand({ Bucket: "b", Key: "k" }), { expiresIn: 3600 });

// PUT
const putUrl = await getSignedUrl(client, new PutObjectCommand({ Bucket: "b", Key: "k" }), { expiresIn: 3600 });
```

Signing non-x-amz headers (e.g. Content-Type):

```js
const url = await getSignedUrl(client, new PutObjectCommand({ Bucket: "b", Key: "k", ContentType: "image/png" }), {
  signableHeaders: new Set(["content-type"]),
  expiresIn: 3600,
});
```

Signing x-amz-* headers (must use `unhoistableHeaders`):

```js
const url = await getSignedUrl(client, new PutObjectCommand({ Bucket: "b", Key: "k", ChecksumSHA256: sha }), {
  unhoistableHeaders: new Set(["x-amz-checksum-sha256"]),
  expiresIn: 3600,
});
```

## Presigned POST (browser file upload)

```js
import { createPresignedPost } from "@aws-sdk/s3-presigned-post";

const { url, fields } = await createPresignedPost(client, {
  Bucket: "b",
  Key: "uploads/${filename}",  // ${filename} replaced by browser
  Expires: 600,
  Conditions: [["content-length-range", 0, 10485760]],
  Fields: { acl: "bucket-owner-full-control" },
});
// Use url + fields in an HTML <form> or FormData POST
```

## Multipart Upload (lib-storage)

Use `@aws-sdk/lib-storage` for large files, streams, or unknown-size bodies:

```js
import { Upload } from "@aws-sdk/lib-storage";
import { S3Client } from "@aws-sdk/client-s3";

const upload = new Upload({
  client: new S3Client({}),
  params: { Bucket: "b", Key: "k", Body: readableStream },
  queueSize: 4,          // parallel part uploads (default 4)
  partSize: 5 * 1024 * 1024, // min 5MB per part
  leavePartsOnError: false,
});

upload.on("httpUploadProgress", (progress) => console.log(progress));
await upload.done();
```

## Waiters

```js
import { S3Client } from "@aws-sdk/client-s3";
import { waitUntilBucketExists, waitUntilObjectExists } from "@aws-sdk/client-s3";

const client = new S3Client({});

await waitUntilBucketExists({ client, maxWaitTime: 60 }, { Bucket: "my-bucket" });
await waitUntilObjectExists({ client, maxWaitTime: 120 }, { Bucket: "my-bucket", Key: "my-key" });
```

Available S3 waiters: `waitUntilBucketExists`, `waitUntilBucketNotExists`, `waitUntilObjectExists`, `waitUntilObjectNotExists`.

Waiter config: `maxWaitTime` (seconds, required), `minDelay` (default 5s), `maxDelay` (default 120s).

Other services export their own `waitUntil*` functions from the same client package.