HttpResponseMessage to string

Question

I am calling a method of which returns Task, in the calling method I need to read the response in form of string.

Here's the code that I have put:

static public async Task<HttpResponseMessage> Validate(string baseUri,HttpContent content) {
    HttpResponseMessage response = new HttpResponseMessage();   
    response = await client.PostAsync(baseUri,content);    
    return response;
}

public string test(){
    string postJson = "{Login = \"user\", Password =  \"pwd\"}";
    HttpContent stringContent = new StringContent(postJson, 
    UnicodeEncoding.UTF8, "application/json");
    HttpResponseMessage result=Validate(Uri,stringContent);
    var json = result.Content.ReadAsStringAsync().Result;
}

I expect string but this error is thrown:

Cannot implicitly convert type 
'System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage>' to 
'System.Net.Http.HttpResponseMessage'

Try HttpResponseMessage result=Validate(Uri,stringContent).Result; — auburg, Jul 25 '19 at 07:54
@auburg: blocking this way could possibly [cause a deadlock](https://blog.stephencleary.com/2012/07/dont-block-on-async-code.html). — Wiktor Zychla, Jul 25 '19 at 07:55

kovac · Accepted Answer · 2019-07-25T08:07:34.063

5

Your problem is at:

HttpResponseMessage result=Validate(Uri,stringContent);

Validate is returning a task, not a HttpResponseMessage.

Change that to:

var result = Validate(Uri,stringContent).Result;

Just to clean up the code a bit and avoid using Result if you can afford to change it like:

static public async Task<HttpResponseMessage> Validate(string baseUri, HttpContent content)
{  
   return await client.PostAsync(baseUri,content);
}

public async Task<string> test()
{
   var postJson = "{Login = \"user\", Password =  \"pwd\"}";
   var stringContent = new StringContent(postJson, UnicodeEncoding.UTF8, "application/json");
   var result = await Validate(Uri,stringContent);
   return await result.Content.ReadAsStringAsync();
}

Be consistent with your coding style. As to why calling .Result is bad, as people are pointing out in the comments, check this blog.

edited Jul 25 '19 at 08:07

answered Jul 25 '19 at 08:01

kovac

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Calling `.Result` is bad, because of possible locks. – user743414 Jul 25 '19 at 08:04
Yes, but that's a whole different issue. It's not my responsibility to redesign his code :) – kovac Jul 25 '19 at 08:05
2

@swdon: but you could reflect that in the answer. Remember that SO is a source of knowledge not only directly to the OP but also to other people visiting this years later. An answer that suggests a possible bad approach could definitely be improved then. – Wiktor Zychla Jul 25 '19 at 08:07
return await result.Content.ReadAsStringAsync(); - can I convert this to plain string? – Srikanth Yadake Jul 25 '19 at 08:55
What do you mean convert to plain string? – kovac Jul 25 '19 at 08:56
I meant, I need a String instead of Task. – Srikanth Yadake Jul 25 '19 at 08:58
1

`return result.Content.ReadAsStringAsync().Result` – kovac Jul 25 '19 at 09:00

score 0 · Answer 2 · edited Jul 29 '19 at 15:14

Just for readability change the method name from Validate(..) to ValidateAsync(..). Just to make clear that this method returns a task and you have to await it.
You're missing an await when calling your Validate method. If you do not want or can make the caller async then use the method GetAwaiter().GetResult() and you'll get what you want.
Replace ReadAsStringAsync().Result with ReadAsStringAsync().GetAwaiter().GetResult()

Like others wrote in comments calling .Result is bad because it could cause locks. The same applies in general to GetAwaiter().GetResult() but calling them is preferred over calling Result. The best option is to use await/async.

When you want to know whats the difference between GetAwaiter().GetResult() vs calling Result you can read this: Is Task.Result the same as .GetAwaiter.GetResult()?

Jacek · Answer 3 · 2019-07-25T08:15:07.480

Method Validate returns the task and is asynchronous. Basically you can call this method in two different ways:

1) await the result of Validate in another async method, like this...

public async Task<string> test() {
    string postJson = "{Login = \"user\", Password =  \"pwd\"}";
    HttpContent stringContent = new StringContent(postJson, 
        UnicodeEncoding.UTF8, "application/json");
    HttpResponseMessage result = await Validate(Uri,stringContent);
    var json = result.Content.ReadAsStringAsync().Result;
}

2) block current execution while waiting for this resul, like this...

public string test() {
    string postJson = "{Login = \"user\", Password =  \"pwd\"}";
    HttpContent stringContent = new StringContent(postJson, 
        UnicodeEncoding.UTF8, "application/json");
    HttpResponseMessage result = Validate(Uri,stringContent).Result;
    var json = result.Content.ReadAsStringAsync().Result;
}

Choose the 1st way by default unless you really have an urge to block the calling thread.

Note that when using 2nd solution in WinForms, WPF or ASP.NET apps you will probably have a deadlock. modifying Validate method like this should solve the problem:

response = await client.PostAsync(baseUri,content).ConfigureAwait(false);

score 0 · Answer 4 · edited Aug 12 '22 at 00:43

0

You can easily write:

var json = result.Content.ReadAsStringAsync().GetAwaiter().GetResult();

edited Aug 12 '22 at 00:43

Jeremy Caney

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answered Aug 09 '22 at 06:28

Eduard Carreras

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Why do you prefer this over the existing answers? The existing answers also use `Content.ReadAsStringAsync().`; the only difference is that you use `GetAwaiter().GetResult()` instead of e.g. `Result`. What's the value of that here? – Jeremy Caney Aug 12 '22 at 00:44

HttpResponseMessage to string

4 Answers4