How do you set the Content-Type header for an HttpClient request

Question

I m trying to set the Content-Type header of an HttpClient object as required by an API I am calling   I tried setting the Content-Type like below   using  var httpClient   new HttpClient          httpClient BaseAddress   new Uri  http   example com         httpClient DefaultRequestHeaders Add  Accept    application json        httpClient DefaultRequestHeaders Add  Content-Type    application json                   It allows me to add the Accept header but when I try to add Content-Type it throws the following exception      Misused header name  Make sure request headers are used with   HttpRequestMessage  response headers with HttpResponseMessage  and   content headers with HttpContent objects    How can I set the Content-Type header in a HttpClient request

User · Answer

For those who didn t see Johns comment to carlos solution      req Content Headers ContentType   new MediaTypeHeaderValue  application octet-stream

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The content type is a header of the content  not of the request  which is why this is failing  AddWithoutValidation as suggested by Robert Levy may work  but you can also set the content type when creating the request content itself  note that the code snippet adds application json in two places-for Accept and Content-Type headers   HttpClient client   new HttpClient    client BaseAddress   new Uri  quot http   example com  quot    client DefaultRequestHeaders        Accept        Add new MediaTypeWithQualityHeaderValue  quot application json quot      ACCEPT header  HttpRequestMessage request   new HttpRequestMessage HttpMethod Post   quot relativeAddress quot    request Content   new StringContent  quot    quot name  quot    quot John Doe  quot    quot age  quot  33  quot                                       Encoding UTF8                                        quot application json quot     CONTENT-TYPE header  client SendAsync request         ContinueWith responseTask   gt                    Console WriteLine  quot Response   0  quot   responseTask Result

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For those who troubled with charset I had very special case that the service provider didn t accept charset  and they refuse to change the substructure to allow it    Unfortunately HttpClient was setting the header automatically through StringContent  and  no matter if you pass null or Encoding UTF8  it will always set the charset    Today i was on the edge to change the sub-system  moving from HttpClient to anything else  that something came to my mind     why not use reflection to empty out the  quot charset quot       And before i even try it  i thought of a way   quot maybe I can change it after initialization quot   and that worked  Here s how you can set the exact  quot application json quot  header without  quot   charset utf-8 quot   var jsonRequest   JsonSerializeObject req  options      Custom function that parse object to string var stringContent   new StringContent jsonRequest  Encoding UTF8   quot application json quot    stringContent Headers ContentType CharSet   null  return stringContent   Note  The null value in following won t work  and append  quot   charset utf-8 quot  return new StringContent jsonRequest  null   quot application json quot     EDIT  DesertFoxAZ suggests that also the following code can be used and works fine   didn t test it myself  if it work s rate and credit him in comments  stringContent Headers ContentType   new MediaTypeHeaderValue  quot application json quot

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You need to do it like this       HttpContent httpContent   new StringContent     the json string          httpContent Headers ContentType   new MediaTypeHeaderValue  application json        client DefaultRequestHeaders Accept Add new MediaTypeWithQualityHeaderValue  application json                         HttpResponseMessage message   client PostAsync    url    httpContent  Result

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Some extra information about  NET Core  after reading erdomke s post about setting a private field to supply the content-type on a request that doesn t have content      After debugging my code  I can t see the private field to set via reflection - so I thought I d try to recreate the problem   I have tried the following code using  Net 4 6     HttpRequestMessage httpRequest   new HttpRequestMessage HttpMethod Get    myUrl    httpRequest Content   new StringContent string Empty  Encoding UTF8   application json     HttpClient client   new HttpClient    Task lt HttpResponseMessage gt  response    client SendAsync httpRequest      I know I should have used async await here  var result   response Result    And  as expected  I get an aggregate exception with the content  Cannot send a content-body with this verb-type      However  if i do the same thing with  NET Core  1 1  - I don t get an exception  My request was quite happily answered by my server application  and the content-type was picked up   I was pleasantly surprised about that  and I hope it helps someone

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stringContent Headers ContentType   new MediaTypeHeaderValue contentType   capture And  YES       that cleared up the problem with ATS REST API  SharedKey works now     https   github com dotnet runtime issues 17036 issuecomment-212046628

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var content   new JsonContent    content Headers ContentType   new MediaTypeHeaderValue  application json    content Headers ContentType Parameters Add new NameValueHeaderValue  charset    utf-8     content Headers ContentType Parameters Add new NameValueHeaderValue  IEEE754Compatible    true       It s all what you need    With using Newtonsoft Json  if you need a content as json string   public class JsonContent   HttpContent          private readonly MemoryStream  stream   new MemoryStream         JsonContent                  stream Dispose               public JsonContent object value                Headers ContentType   new MediaTypeHeaderValue  application json            using  var contexStream   new MemoryStream            using  var jw   new JsonTextWriter new StreamWriter contexStream     Formatting   Formatting Indented                          var serializer   new JsonSerializer                serializer Serialize jw  value               jw Flush                contexStream Position   0              contexStream WriteTo  stream                      stream Position   0              private JsonContent string content                Headers ContentType   new MediaTypeHeaderValue  application json            using  var contexStream   new MemoryStream            using  var sw   new StreamWriter contexStream                         sw Write content               sw Flush                contexStream Position   0              contexStream WriteTo  stream                      stream Position   0             protected override Task SerializeToStreamAsync Stream stream  TransportContext context                return  stream CopyToAsync stream              protected override bool TryComputeLength out long length                length    stream Length          return true             public static HttpContent FromFile string filepath                var content   File ReadAllText filepath           return new JsonContent content             public string ToJsonString                 return Encoding ASCII GetString  stream GetBuffer    0   stream GetBuffer   Length  Trim

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Call AddWithoutValidation instead of Add  see this MSDN link    Alternatively  I m guessing the API you are using really only requires this for POST or PUT requests  not ordinary GET requests    In that case  when you call HttpClient PostAsync and pass in an HttpContent  set this on the Headers property of that HttpContent object

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Ok  it s not HTTPClient but if u can use it  WebClient is quite easy   using  var client   new System Net WebClient           client Headers Add  Accept    application json        client Headers Add  Content-Type    application json  charset utf-8        client DownloadString

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I find it most simple and easy to understand in the following way   async Task SendPostRequest         HttpClient client   new HttpClient        var requestContent   new StringContent  lt content gt        requestContent Headers ContentType   new MediaTypeHeaderValue  application json        var response   await client PostAsync  lt url gt   requestContent       var responseString   await response Content ReadAsStringAsync           SendPostRequest   Wait

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Net tries to force you to obey certain standards  namely that the Content-Type header can only be specified on requests that have content  e g  POST  PUT  etc     Therefore  as others have indicated  the preferred way to set the Content-Type header is through the HttpContent Headers ContentType property   With that said  certain APIs  such as the LiquidFiles Api  as of 2016-12-19  requires setting the Content-Type header for a GET request    Net will not allow setting this header on the request itself -- even using TryAddWithoutValidation   Furthermore  you cannot specify a Content for the request -- even if it is of zero-length   The only way I could seem to get around this was to resort to reflection   The code  in case some else needs it  is   var field   typeof System Net Http Headers HttpRequestHeaders       GetField  invalidHeaders   System Reflection BindingFlags NonPublic   System Reflection BindingFlags Static        typeof System Net Http Headers HttpRequestHeaders        GetField  s invalidHeaders   System Reflection BindingFlags NonPublic   System Reflection BindingFlags Static   if  field    null      var invalidFields    HashSet lt string gt  field GetValue null     invalidFields Remove  Content-Type       client DefaultRequestHeaders TryAddWithoutValidation  Content-Type    text xml      Edit   As noted in the comments  this field has different names in different versions of the dll   In the source code on GitHub  the field is currently named s invalidHeaders   The example has been modified to account for this per the suggestion of  David Thompson

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I end up having similar issue  So I discovered that the Software PostMan can generate code when clicking the  quot Code quot  button at upper left corner  From that we can see what going on  quot under the hood quot  and the HTTP call is generated in many code language  curl command  C  RestShart  java  nodeJs      That helped me a lot and instead of using  Net base HttpClient I ended up using RestSharp nuget package  Hope that can help someone else

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try to use TryAddWithoutValidation          var client   new HttpClient      client DefaultRequestHeaders TryAddWithoutValidation  Content-Type    application json  charset utf-8

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You can use this it will be work   HttpRequestMessage msg   new HttpRequestMessage HttpMethod Get  URL    msg Content   new StringContent string Empty  Encoding UTF8   application json     HttpResponseMessage response   await  httpClient SendAsync msg   response EnsureSuccessStatusCode     string json   await response Content ReadAsStringAsync

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If you don t mind a small library dependency  Flurl Http  disclosure  I m the author  makes this uber-simple  Its PostJsonAsync method takes care of both serializing the content and setting the content-type header  and ReceiveJson deserializes the response  If the accept header is required you ll need to set that yourself  but Flurl provides a pretty clean way to do that too  using Flurl Http   var result   await  quot http   example com  quot       WithHeader  quot Accept quot    quot application json quot        PostJsonAsync new               ReceiveJson lt TResult gt      Flurl uses HttpClient and Json NET under the hood  and it s a PCL so it ll work on a variety of platforms  PM gt  Install-Package Flurl Http

[c#] How do you set the Content-Type header for an HttpClient request?

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