Download from S3 to local file in Swift

s3.swift

import Foundation
import Logging
import S3

let LOGGER = Logger(label: "S3")

enum S3Error: Error {
    case runtimeError(String)
}

public func download(
    directory: String,
    from address: String,
    accessKeyId: String,
    secretAccessKey: String,
    endpoint: String
) throws -> String {
    precondition(address.hasPrefix("s3://"), "Invalid S3 address \(address).")
    precondition(endpoint.hasPrefix("https://"), "Invalid endpoint address \(endpoint).")

    LOGGER.debug("S3 address \(address).")
    LOGGER.debug("S3 endpoint \(endpoint).")

    let s3 = S3(
        accessKeyId: accessKeyId,
        secretAccessKey: secretAccessKey,
        endpoint: endpoint
    )

    let splitted = address.components(separatedBy: "/")
    let bucket = splitted[2]
    let key = splitted[3...].joined(separator: "/")
    let name = splitted.last!

    LOGGER.debug("S3 bucket \(bucket), key \(key), name \(name).")

    let object = try s3.getObject(S3.GetObjectRequest(
        bucket: bucket,
        key: key
    )).wait()

    guard let body = object.body else {
        throw S3Error.runtimeError("Something went wrong with S3 getObject.")
    }

    let path = "\(directory)/\(name)"
    LOGGER.debug("S3 output path \(path).")

    let url = URL(string: "file://\(path)")!
    LOGGER.debug("S3 output url \(url).")

    try body.write(to: url)

    return path
}