How to verify that a website is reachable with Swift?-CodePudding

My app shall access a php file on a hosted website in order to get data from a backend SQL database. This works fine but I want to be prepared or all kind of possible errors. In case there is no internet connection or the host cannot be reached, an error is thrown - fine. But if the url address is modified to an address which does not exist on the host, no error is thrown. But I want to cover this condition as well. What is the best way in Swift to do this?

Here is my code:

    @available(iOS 15.0, *)
   func checkCustomerExistsInBackend(emailAddress: String) async throws -> String 
   {
    
    let url = URL(string: "https://myHost.de/mySite/checkCustomerexists.php")!
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    
    let dataString = "EmailAddress=\(emailAddress)"
    var returnValue = ""
    do {
        let dataD = dataString.data(using: .utf8)
        let (data, _) = try await URLSession.shared.upload(for: request, from: dataD!, delegate: nil)
        let answer = try JSONDecoder().decode(BackendMessage.self, from: data)
        returnValue = answer.Message
    }
    catch {
        let myError: NSError = error as NSError
        switch myError.localizedDescription {
        case "The Internet connection appears to be offline.":
            throw BackendError.noInternet
        case "A server with the specified hostname could not be found.":
            throw BackendError.serverNotFound
        default:
            throw error
        }
    }
    return returnValue
}

The url above with "https://myHost.de/mySite/checkCustomerexists.php" is not the true address of course. But when I replace "myHost.de" with the true host address, no error is thrown even though a site "mySite" does not exist.

I spent several hours searching for the answer in SO but could not find anything that works for my constellation.

Any hint would be appreciated!

CodePudding user response：

Larme's comment answered this question. In case it is helpful for anybody stepping over the same subject, here the modified code of my example with the solution based on Larme's advice:

   @available(iOS 15.0, *)
func checkCustomerExistsInBackend(emailAddress: String) async throws -> String {
    
    let url = URL(string: "https://myHost.de/mySite/checkCustomerexists.php")!
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    
    let dataString = "EmailAddress=\(emailAddress)"
    var returnValue = ""
    do {
        let dataD = dataString.data(using: .utf8)
        let (data, response) = try await URLSession.shared.upload(for: request, from: dataD!, delegate: nil)
       
        let httpURLResponse = response as? HTTPURLResponse
        let statusCode = httpURLResponse?.statusCode
        if statusCode != 404 {
            let answer = try JSONDecoder().decode(BackendMessage.self, from: data)
            returnValue = answer.Message
        }
        else {
            throw BackendError.invalidURL
        }
    }
    catch {
        let myError: NSError = error as NSError
        print(myError.localizedDescription)
        switch myError.localizedDescription {
        case "The Internet connection appears to be offline.":
            throw BackendError.noInternet
        case "A server with the specified hostname could not be found.":
            throw BackendError.serverNotFound
        default:
            throw error
        }
    }
    return returnValue
}