Alamofire Progress status showing 0.0 in some URL cases using swift ios

Question

CODE:

Alamofire.request(URL(string: imageUrl)!).downloadProgress(closure: { (progress) in

            DispatchQueue.main.async {
                print(progress.fractionCompleted)
                successCallback(progress.fractionCompleted as Double)

            }

        }).responseData { (response) in
            print(response.result)
            completionCallback(response as DataResponse)

            switch response.result {
            case .success(let responseJSON):
                print(responseJSON)
            case .failure(let error):
                failureCallback(error.localizedDescription)
            }
        }

Answer 1

The HTTP Header Content-Length is required to determine the progress. Alamofire knows the size of data received, but to show the progress it need the total Content-Length

Here i've prepared a sample test. I will compare two site

1. https://www.cocoacontrols.com
2. https://www.stackoverflow.com

First one have no Content-Length in their responses, but second one have.

Use CURL to check the HTTP Headers.

curl -I https://www.cocoacontrols.com

...

... // there is no content length header in this output.

...

curl -I https://www.stackoverflow.com

...

content-length: 149

...

Sample test.

func sampleTest(link: String) {
    let url = URL.init(string: link)!
    Alamofire.request(url,
                      method: .get,
                      parameters: nil,
                      encoding: JSONEncoding.default,
                      headers: nil)
        .downloadProgress(queue: DispatchQueue.global(qos: .utility)) { progress in
            print("TEST Progress: \(progress.fractionCompleted)")
        }
        .validate { _, _, _ in
            return .success
        }
        .responseData { response in
            print("repsonse received")
    }
} 

Now calling this method as followings

Test #1

sampleTest(link: "https://www.cocoacontrols.com")

Output #1

TEST Progress: 0.0   
TEST Progress: 0.0   
TEST Progress: 0.0   
TEST Progress: 0.0

Test #2

sampleTest(link: "https://www.stackoverflow.com")

Output #2

TEST Progress: 0.0   
TEST Progress: 0.0   
TEST Progress: 0.8040637101235478 
TEST Progress: 1.0

Hope it helps understands your problem of missing the Content-Length HEADER in your HTTP response. For further reference, even there is a github issue in Alamofire repository, facing the same problem, solved by adding the Content-Lenght header adding in the response HEADER field.