@uppy/aws-s3-multipart: fix the chunk size calculation

[aduh95]

We were using Math.ceil instead of Math.floor which ended up creating always one part too many.

[Murderlon]

If I'm reading this correctly, a 200GB file with explicitly passing 5MB as chunk size results in 40K chunks, but then you Math.min it to 10K, only uploading 1/4 of the file?

In tus-node-server I solve it like this:

  private calcOptimalPartSize(size: number): number {
    let optimalPartSize: number

    // When upload is smaller or equal to PreferredPartSize, we upload in just one part.
    if (size <= this.preferredPartSize) {
      optimalPartSize = size
    }
    // Does the upload fit in MaxMultipartParts parts or less with PreferredPartSize.
    else if (size <= this.preferredPartSize * this.maxMultipartParts) {
      optimalPartSize = this.preferredPartSize
      // The upload is too big for the preferred size.
      // We devide the size with the max amount of parts and round it up.
    } else {
      optimalPartSize = Math.ceil(size / this.maxMultipartParts)
    }

    return optimalPartSize
  }

[Murderlon]

If we have a 3MB file, we still set the part size to 5MB (or more). In tus servers we always set it to the file size if it's under the minimum part size.

Furthermore, arraySize would be 0.6 which with Math.floor is 0.

[aduh95]

If the file size is 3MB, it will use a single part because of this condition.

[Murderlon]

Okay makes sense. Can we make 10_000 and 5 * MB global variables (or class properties). Something like maxMultipartParts and minPartSize?

Can we also add some docs above #initChunks that explains why we need to do these things?

[mifi]

shall we pull this login out into a function and make a unit test for the different file sizes and expected chunksizes?