S3FileStorage.ts

import type { S3Client } from "@aws-sdk/client-s3";
import {
  DeleteObjectCommand,
  GetObjectCommand,
  HeadObjectCommand,
} from "@aws-sdk/client-s3";
import { Upload } from "@aws-sdk/lib-storage";
import { LazyFile, LazyContent } from "@mjackson/lazy-file";
import { FileStorage } from "./file-storage.js";

/**
 * An S3 implementation of the `FileStorage` interface.
 */
export class S3FileStorage implements FileStorage {
  #s3: S3Client;
  #bucketName: string;

  constructor(s3: S3Client, bucketName: string) {
    this.#s3 = s3;
    this.#bucketName = bucketName;
  }

  async has(key: string): Promise<boolean> {
    try {
      await this.#s3.send(
        new HeadObjectCommand({
          Bucket: this.#bucketName,
          Key: key,
        }),
      );
      return true;
    } catch (error) {
      if (error instanceof Error ? error.name === "NotFound" : "") {
        return false;
      }
      throw error;
    }
  }

  async set(key: string, file: File): Promise<void> {
    const upload = new Upload({
      client: this.#s3,
      params: {
        Bucket: this.#bucketName,
        Key: key,
        Body: file.stream(),
      },
    });
    await upload.done();
  }
  
  async put(key: string, file: File): Promise<File> {
    await set(key, file)
    const file = await this.get(key)
    if (!file) {
      throw new Error('Failed to fetch file are put')
    }
    return file
  }

  async get(key: string): Promise<File | null> {
    try {
      const head = await this.#s3.send(
        new HeadObjectCommand({
          Bucket: this.#bucketName,
          Key: key,
        }),
      );

      const contentLength = Number(head.ContentLength);
      const contentType = head.ContentType || "application/octet-stream";

      const s3 = this.#s3;
      const bucketName = this.#bucketName;

      const lazyContent: LazyContent = {
        byteLength: contentLength,
        stream: (start: number = 0, end: number = contentLength) => {
          const range = `bytes=${start}-${end - 1}`;
          return new ReadableStream({
            async start(controller) {
              try {
                const command = new GetObjectCommand({
                  Bucket: bucketName,
                  Key: key,
                  Range: range,
                });
                const { Body } = await s3.send(command);

                if (!Body) {
                  throw new Error("Failed to retrieve a valid stream from S3");
                }

                const reader = Body.transformToWebStream().getReader();

                const read = async () => {
                  const { done, value } = await reader.read();
                  if (done) {
                    controller.close();
                  } else {
                    controller.enqueue(value);
                    await read();
                  }
                };

                await read();
              } catch (error) {
                controller.error(error);
              }
            },
          });
        },
      };

      return new LazyFile(lazyContent, key, { type: contentType });
    } catch (error) {
      if (error instanceof Error && error.name === "NoSuchKey") {
        return null;
      }
      throw error;
    }
  }

  async remove(key: string): Promise<void> {
    await this.#s3.send(
      new DeleteObjectCommand({
        Bucket: this.#bucketName,
        Key: key,
      }),
    );
  }
}

Does this work for you for files that are larger than the default partSize of the s3 Upload class? (1024 * 1024 * 5)

It works fine for me when files are smaller than 5MB, but if they exceed that and need to use multipart uploads then the s3 class throws:

InvalidPart: One or more of the specified parts could not be found.  The part may not have been uploaded, or the specified entity tag may not match the part's entity tag.