download(to:, completionHandler:) doesn't work.

[ghost]

Hi all,
I'm faced with the issue, that download method just creates an empty file, but actually no content downloads.

Tested on my mac, with XCode 11, SwiftyRequest v3.0.0.
The problem is that DownloadDelegate methods doesn't fire as expected. Currently, it only creates an empty file by this method:

func didSendRequestHead(task: HTTPClient.Task<Response>, _ head: HTTPRequestHead)

and this method never fires:

func didReceivePart(task: HTTPClient.Task<Response>, _ buffer: ByteBuffer) -> EventLoopFuture<Void>

Also, seems that testFileDownload test is false-positive.

Completion handler check only response status code, but not written data length or something else:

case .success(let result):
                XCTAssertEqual(result.status.code, 200)

So, what happens here on my local machine:

1. it is trying to download file with JSON
2. during the download it creates an empty file
3. checks status code (200) and pass the test
4. removes an empty file

Modified test code to reproduce the issue:

func testFileDownload() {
        let expectation = self.expectation(description: "download file SwiftyRequest test")

        let url = "https://raw.githubusercontent.com/IBM-Swift/SwiftyRequest/c7cfc669a5872831e816d9f9c6fec06bc638222b/Tests/SwiftyRequestTests/test_file.json"

        let request = RestRequest(url: url)

        // 1. change destination URL. (file should be created at root of the project dir)
        let bundleURL = URL(fileURLWithPath: "./")
        let destinationURL = bundleURL.appendingPathComponent("test_file.json")

        request.download(to: destinationURL) { response in
            switch response {
            case .success(let result):
                XCTAssertEqual(result.status.code, 200)
            case .failure(let error):
                XCTFail("Failed download with error: \(error)")
            }
            // 2. print destination URL
            print(destinationURL)
            // 3. Don't remove the file in order to check it content
            expectation.fulfill()
        }

        waitForExpectations(timeout: 10)
    }

[djones6]

@harish1992 Could you take a look at this?

[codemeister64]

Any updates?