server/app/ws/routes/fs.flush.js

const { Errors } = require('../../shared')
const { NodeDescriptorType } = require('../../enum')
const fs = require('fs')
const tmp = require('tmp-promise')
const CombinedStream = require('combined-stream')

module.exports = exports = async (message, di) => {
    const Node = di.models.get('fs:Node')
    const { descriptor } = message.data()

    const node_uuid = message.socket.session.file_descriptors?.[descriptor]
    if ( !node_uuid ) {
        return message.send_response(
            message.fresh().error(Errors.NodeDoesNotExist)
        )
    }

    // Check if we have a temporary files which have been written to.
    // If so, we should "flush" the temporary files to the proper storage.
    const placeholders = message.socket.session.temp_write_files?.[descriptor]
    if ( !placeholders ) {
        return message.send_response(
            message.fresh()
        )
    }

    const node = await Node.findOne({
        uuid: node_uuid,
        deleted: false,
        descriptor_type: NodeDescriptorType.File,
    })

    if ( !node ) {
        return message.send_response(
            message.fresh().error(Errors.NodeDoesNotExist)
        )
    }

    const existing_file = await node.uploaded_file()
    if ( existing_file ) {
        // This is a new write, so delete the old file
        await existing_file.delete()
        delete node.uploaded_file_id
    }

    // Sort the placeholders by the byte starting position
    placeholders.sort((a, b) => {
        if ( a.position < b.position ) return -1
        if ( a.position > b.position ) return 1
        return 0
    })

    // Combine them into a single stream
    const stream = CombinedStream.create()
    const combined_file = await tmp.file()

    for ( const placeholder of placeholders ) {
        stream.append(fs.createReadStream(placeholder.path))
    }

    const pipe = stream.pipe(fs.createWriteStream(combined_file.path))

    await new Promise(res => pipe.on('finish', res))

    // Store the temporary file
    const new_file = await di.upload.provider().store({
        temp_path: combined_file.path,
        original_name: node.pied_name,
        mime_type: 'application/octet-stream',  // TODO determine from file extension?
    })

    const stat = await fs.promises.stat(combined_file.path)
    await fs.promises.unlink(combined_file.path)

    node.uploaded_file_id = new_file.id
    node.size = stat.size
    await node.save()

    message.send_response(
        message.fresh()
    )
}