c# HttpClient PostAsync with async and await not working

Question

I am running into a deadlock situation when trying to post to WebApi 2 from WebApi 1 using HttpClient PostAsync and using async and await.

Below is WebAPI 1:

public HttpResponseMessage Get([FromUri]int oid) 
{
    var orderdetails = _orderServices.GetOrderDetails(oid);

    var xml = new XmlMediaTypeFormatter();
    xml.UseXmlSerializer = true;
    string orderdetailsser = Serialize(xml, orderdetails);

    var result = PostXml(orderdetailsser);

    return Request.CreateResponse(HttpStatusCode.OK);
}

public static async Task<HttpResponseMessage> PostXml(string str)
{
    using (var client = new HttpClient())
    {

        client.BaseAddress = new Uri("http://localhost:58285/");

        var content = new StringContent(str);
        var response = await client.PostAsync("api/default/ReceiveXml", content).ConfigureAwait(false);
        return response;
    }

}

And WebApi2:

[System.Web.Http.HttpPost]
public HttpResponseMessage ReceiveXml(HttpRequestMessage request)
{

    var xmlDoc = new XmlDocument();
    xmlDoc.Load(request.Content.ReadAsStreamAsync().Result);

    xmlDoc.Save(@"C:\xmlfiles\xml2.xml");

    XmlSerializer deserializer = new XmlSerializer(typeof(OrderInfoModel));
    TextReader reader = new StreamReader(@"C:\xmlfiles\xml2.xml");
    object obj = deserializer.Deserialize(reader);
    OrderInfoModel orderdetails = (OrderInfoModel)obj;
    reader.Close();

    var patient_id = _patientServices.ProcessPatient(orderdetails.Patient, orderdetails.OrderInfo);
    var orderid = _orderServices.ProcessOrder(orderdetails.Patient, orderdetails.OrderInfo, patient_id);

    if (orderdetails.OrderNotes != null && orderdetails.OrderNotes.Count() > 0)
    {
        var success = _orderServices.ProcessOrderNotes(orderid, orderdetails.OrderNotes);
    }

    var prvid = _orderServices.ProcessOrderProvider(orderid, orderdetails.ReferringProvider);

    var shpngid = _orderServices.ProcessOrderShipping(orderid, orderdetails.ShippingInfo);

    var payerid = _orderServices.ProcessOrderPayer(orderid, orderdetails.Insurances);

    return Request.CreateResponse(HttpStatusCode.OK, orderid);
}

I am not getting any response back to WebAPI 1 from WebAPI 2. I have gone through several articles online about deadlock situation. However, I am unable to resolve the deadlock in my case. What am I doing wrong here? Am I using async and await properly?

Looks like Classic deadlock situation, answer at https://stackoverflow.com/questions/17248680/await-works-but-calling-task-result-hangs-deadlocks — Orel Eraki, Dec 24 '17 at 21:39
Hello Orel Eraki - I have gone through the article you suggested. I am still unable to fix the deadlock. — Harish Solige, Dec 24 '17 at 22:17
Possible duplicate of [await works but calling task.Result hangs/deadlocks](https://stackoverflow.com/questions/17248680/await-works-but-calling-task-result-hangs-deadlocks) — MechMK1, Dec 24 '17 at 22:17
Hello Orel Eraki/David, Can any one of you just modify my code ? I have been trying to modify it according to articles but its still not working? Any help from you in modifying my code is greatly appreciated — Harish Solige, Dec 24 '17 at 22:20
@Harish Change `request.Content.ReadAsStreamAsync().Result` to `await request.Content.ReadAsStreamAsync()`. You'll also need to change both your api1 and api2 methods to have `async` signatures and then you'll `await` the chain all the way up the call stack. [Don't Block on Async Code](https://blog.stephencleary.com/2012/07/dont-block-on-async-code.html) — JSteward, Dec 24 '17 at 22:36
Thank you Orel and David for your help. Your links were very informative. — Harish Solige, Dec 25 '17 at 00:37

score 1 · Answer 1 · answered Dec 24 '17 at 22:51

To build off my comment above, modify your code so that you are not blocking on an async operation. Additionally _orderServices.GetOrderDetails(oid); sounds like a method that hits a database and as such should be await _orderServices.GetOrderDetailsAsync(oid); wherein you use the whatever async api is available for your database access.

[HttpGet()]
public async Task<HttpResponseMessage> Get([FromUri]int oid) {
    var orderdetails = _orderServices.GetOrderDetails(oid);

    var xml = new XmlMediaTypeFormatter();
    xml.UseXmlSerializer = true;
    string orderdetailsser = Serialize(xml, orderdetails);

    var result = await PostXml(orderdetailsser);

    return Request.CreateResponse(HttpStatusCode.OK);
}

public static async Task<HttpResponseMessage> PostXml(string str) {
    using(var client = new HttpClient()) {

        client.BaseAddress = new Uri("http://localhost:58285/");

        var content = new StringContent(str);
        var response = await client.PostAsync("api/default/ReceiveXml", content).ConfigureAwait(false);
        return response;
    }

}

[HttpPost()]
public async Task<HttpResponseMessage> ReceiveXml(HttpRequestMessage request) {

    var xmlDoc = new XmlDocument();
    xmlDoc.Load(await request.Content.ReadAsStreamAsync());

    xmlDoc.Save(@"C:\xmlfiles\xml2.xml");

    XmlSerializer deserializer = new XmlSerializer(typeof(OrderInfoModel));
    TextReader reader = new StreamReader(@"C:\xmlfiles\xml2.xml");
    object obj = deserializer.Deserialize(reader);
    OrderInfoModel orderdetails = (OrderInfoModel)obj;
    reader.Close();

    var patient_id = _patientServices.ProcessPatient(orderdetails.Patient, orderdetails.OrderInfo);
    var orderid = _orderServices.ProcessOrder(orderdetails.Patient, orderdetails.OrderInfo, patient_id);

    if(orderdetails.OrderNotes != null && orderdetails.OrderNotes.Count() > 0) {
        var success = _orderServices.ProcessOrderNotes(orderid, orderdetails.OrderNotes);
    }

    var prvid = _orderServices.ProcessOrderProvider(orderid, orderdetails.ReferringProvider);

    var shpngid = _orderServices.ProcessOrderShipping(orderid, orderdetails.ShippingInfo);

    var payerid = _orderServices.ProcessOrderPayer(orderid, orderdetails.Insurances);

    return Request.CreateResponse(HttpStatusCode.OK, orderid);
}

Resources

Don't Block on Async Code

Avoid Async Void

Hello J Steward - Thanks a lot for all your help. I was finally able to figure it out. It turns out it was the await in API 2 as well as incorrectly placed breakpoints. However you made my day by correctly pointing out where I need to place the async. Merry Xmas! — Harish Solige, Dec 25 '17 at 00:35

c# HttpClient PostAsync with async and await not working

1 Answers1