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Deadlock while logging http requests into main UI C#

In my WinForms app I want to see raw request/response data when it interacts with webApi. I need to show request/response in UI RichTextBoxes. To do this I set up my HttpClient as follows:

private HttpClient client;
private void CreateService()

client = new HttpClient(new LoggingHandler(new HttpClientHandler(), this))

BaseAddress = new Uri(this._URI)
;
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(
new MediaTypeWithQualityHeaderValue("application/json"));



My Logging Handler:

public class LoggingHandler : DelegatingHandler

private SimplySignRestClientAsync _client;

public LoggingHandler(HttpMessageHandler innerHandler, SimplySignRestClientAsync client) : base(innerHandler)

this._client = client;


protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)

string p_Request = "";
if (_client._updateRequest != null)

p_Request = request.ToString();
if (request.Content != null)

p_Request += "nnContent:n" + FormatJsonString(await request.Content.ReadAsStringAsync());


//_client._request.Text = p_Request; << this works but causes a cross-thread exception in debug only
SetText(p_Request); << This deadlocks the UI


return response;


delegate void SetTextCallback(string text);

private void SetText(string text)

if (_client._request.InvokeRequired)

SetTextCallback d = new SetTextCallback(SetText);
_client._response.Invoke(d, new object text );

else

_client._request.Text = text;





If i try to access richtextbox directly it works only when i execute app without debugging. But during debug it comes up with cross-thread exception.

This is how I call httpClient:

//This is how the original call gets initiated from UI
private void uiLogin_Click(object sender, EventArgs e)

Agent resp = Client.Login(new Credentials(uiUsername.Text, uiPassword.Text));
uiAuthToken.Text = Client.getAuthToken();


//this method has to stay synchronous, but it in turn calls an async method below
public Agent Login(Credentials loginInfo)

var task = Task.Run(async () => await LoginAsync(loginInfo));
return task.Result.Content; <<< this is where the application stops if i hit pause during debug when deadlock happens


//
async public Task<RestResponse<Agent>> LoginAsync(Credentials loginInfo)

HttpResponseMessage response = await client.PostAsJsonAsync(this._URI + "api/users/login", loginInfo);

var content = await response.Content.ReadAsStringAsync();
RestResponse<Agent> respAgent respAgent = JsonConvert.DeserializeObject<RestResponse<Agent>>(content);

return respAgent;



as I understand my "return task.Result.Content" blocks the UI thread and "_client._response.Invoke(d, new object text );" is waiting for that to unblock causing deadlock. But I'm not sure how to make invoke wait too.

1 Answer
1

If you want to do it using proper asynchronous constructs, you need to make the entry point (your Click event handler) asynchronous, and never block on asynchronous code as it causes the deadlock you are facing.

Click

//This is how the original call gets initiated from UI
private async void uiLogin_Click(object sender, EventArgs e)

Agent resp = await Client.Login(new Credentials(uiUsername.Text, uiPassword.Text));
uiAuthToken.Text = Client.getAuthToken();


public async Task<Agent> Login(Credentials loginInfo)

var result = await LoginAsync(loginInfo);
return result.Content;



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