How to wait for HttpClient GetAsync call until it returns the request in C#

Question

I am trying to get data by the HttpClient. Data vary in size, it could be from few bytes to megabyte. I noticed many times my application exist even before it returns from the GetAsync. How can I wait until GetAsync complete it call? From the main app:-

        backup.DoSaveAsync();
        Console.ForegroundColor = ConsoleColor.Yellow;
        Console.BackgroundColor = ConsoleColor.Red;
        // My app exist by printing this msg, wihout getting any data. 
        // someitmes it gets data and other times it gets notinng.
        // I used sleep to wait to get the call completed. 
        Console.WriteLine("\nBackup has done successfully in SQL database")

        public async void DoSaveAsync()
        {
            using (var client = GetHttpClient(BaseAddress, path, ApiKey))
            {
                Stream snapshot = await  GetData(client, path);

                if (snapshot != Stream.Null)
                {
                    snapshot.Position = 0;
                    SaveSnapshot(snapshot);
                }
            }
        }

   private async Task<Stream> GetData(HttpClient client, string path)
    {
        HttpResponseMessage response = null;
        try
        {
            response = await client.GetAsync(path);
            System.Threading.Thread.Sleep(5000);
            if (response.IsSuccessStatusCode == false)
            {
                Console.WriteLine($"Failed to get snapshot");
                return Stream.Null;
            }
            return await response.Content.ReadAsStreamAsync();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            return Stream.Null;
        }
    }

Code update after the comments and answer:

     // in my main app, I have this code. 
     // How can I get the completed task or any error return by the task here.
    backup.DoBackupAsync().Wait();

    public async Task<Stream> DoSaveAsync()
    {
        using (var client = GetHttpClient(BaseAddress, SnapshotPath, ApiKey))
        {
            try
            {
                Stream snapshot = await GetSnapshot(client, SnapshotPath);

                if (snapshot != Stream.Null)
                {
                    snapshot.Position = 0;
                    SaveSnapshot(snapshot);
                }
                return snapshot;
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return null;
            }

        }
    }

Where is the code calling GetData? Why did you use Thread.Sleep(5000)? — Jeroen Heier, Jan 07 '18 at 18:56
Properly await'ed the code will not have behavior you described. Please post real [mcve]. — Alexei Levenkov, Jan 07 '18 at 18:57
Code's are in 3 different class. I must not give all the code. I gave only the problematic part. — masiboo, Jan 07 '18 at 20:49
When I added Console.ReadLine(); I could get the return all the time successfully. So I don't know how can I wait to successfully complete the call. — masiboo, Jan 07 '18 at 21:02

Treziac · Accepted Answer · 2018-01-07T22:04:52.913

2

As the method is async, the backup.DoSaveAsync() line only start a Task but doesn't wait for the result, so you may call Console.ReadLine (and possibly exit your program) before the task is completed. You should return Task instead of void - it's generally bad design to have a void async method, and younhave to await backup.DoSaveAsync() either via await (if you call from an async method), either via .Wait().

Also, in case of error in GetData, you don't return any error for DoSaveAsync - you may want to deal with this, in the current code, you would print "Failed to get snapshot" and then "Backup has done successfully in SQL database". Consider to not use Console.ReadLine in GetData and return a Task in DoSaveAsync indicating success

No need to put a thread.sleep here - you already await the result.

edited Jan 07 '18 at 22:04

answered Jan 07 '18 at 21:17

Treziac

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Can you please check my updated question? And answer me? – masiboo Jan 08 '18 at 20:10
Use `Task myTask = backup.DoBackupAsync()` you can then use `myTask.Wait()`, `myTask.Result` (calling this will also wait for the task - you have to call one of these to be sure the task completed - or failed) and `myTask.Status` – Treziac Jan 09 '18 at 21:13

How to wait for HttpClient GetAsync call until it returns the request in C#

1 Answers1