@upflowi/provider-s3

A StorageProvider for upflowi that drives AWS S3 multipart uploads entirely through presigned URLs your own backend generates. This package never receives or stores AWS credentials — it only calls the getPresignedUrl callback you provide.

pnpm add @upflowi/core @upflowi/transport-fetch @upflowi/provider-s3

import { createUploader } from "@upflowi/core";
import { createFetchTransport } from "@upflowi/transport-fetch";
import { createS3Provider } from "@upflowi/provider-s3";

const provider = createS3Provider({
  getPresignedUrl: (operation) => backendClient.getS3PresignedUrl(operation),
});

const uploader = createUploader({
  concurrency: 3,
  chunkSize: 8 * 1024 * 1024, // 8 MiB parts
  transport: createFetchTransport(),
  provider,
});

How it works

createS3Provider calls your getPresignedUrl callback once per S3 operation the multipart lifecycle needs (create, uploadPart, complete, abort, listParts) and does the rest — signing, XML parsing, and mapping the result onto StorageProvider. Your backend's only job is to sign a CreateMultipartUploadCommand/UploadPartCommand/CompleteMultipartUploadCommand/AbortMultipartUploadCommand/ListPartsCommand and return the URL — it never needs the AWS SDK client itself to touch the request body.

listParts support (via StorageProvider.resume) lets a paired UploadStore (@upflowi/store-indexeddb or @upflowi/store-memory) resume a multipart upload after a reload or crash without re-transferring parts S3 already has.

Checksums

Supports "SHA-256", "CRC32", and "MD5" via @upflowi/core's optional checksum config — compute() must return base64. SHA-256/CRC32 use S3's additional-checksums feature (x-amz-checksum-*); MD5 uses the older Content-MD5 header. See the monorepo README's checksum table for the exact wiring, including the ChecksumAlgorithm your backend must pass to CreateMultipartUploadCommand.

Peer dependency

Requires @upflowi/core as a peer dependency — install both.

Documentation

See the monorepo README for the full multipart S3 example (client + backend) and AGENTS.md for the architecture.

License

ISC