HTTP POST Returns Error 417 Expectation Failed

Question

When I try to POST to a URL it results in the following exception      The remote server returned an error     417  Expectation Failed    Here s a sample code   var client   new WebClient     var postData   new NameValueCollection    postData Add  postParamName    postParamValue     byte   responseBytes   client UploadValues  http         postData   string response   Encoding UTF8 GetString responseBytes       417  Expectation Failed    Using an HttpWebRequest HttpWebResponse pair or an HttpClient doesn t make a difference   What s causing this exception

User · Answer

Check that your network connection isn t redirecting  I had this issue when on the wrong wifi and any web request was redirecting to a corporate login page

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Solution from proxy side  I faced some problems in the SSL handshake process and I had to force my proxy server to send requests using HTTP 1 0 to solve the problem by setting this argument in the httpd conf SetEnv force-proxy-request-1 0 1 SetEnv proxy-nokeepalive 1 after that I faced the 417 error as my clients application was using HTTP 1 1 and the proxy was forced to use HTTP 1 0  the problem was solved by setting this parameter in the httpd conf on the proxy side RequestHeader unset Expect early without the need to change anything in the client side  hope this helps

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Another way -  Add these lines to your application config file configuration section      lt system net gt       lt settings gt           lt servicePointManager expect100Continue  false    gt       lt  settings gt   lt  system net gt

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If you are using  HttpClient   and you don t want to use global configuration to affect all you program you can use    HttpClientHandler httpClientHandler   new HttpClientHandler     httpClient DefaultRequestHeaders ExpectContinue   false    I you are using  WebClient  I think you can try to remove this header by calling    var client   new WebClient     client Headers Remove HttpRequestHeader Expect

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This same situation and error can also arise with a default wizard generated SOAP Web Service proxy  not 100  if this is also the case on the WCF System ServiceModel stack  when at runtime    the end user machine is configured  in the Internet Settings  to use a proxy that does not understand HTTP 1 1 the client ends up sending something that a HTTP 1 0 proxy doesnt understand  commonly an Expect header as part of a HTTP POST or PUT request due to a standard protocol convention of sending the request in two parts as covered in the Remarks here        yielding a 417   As covered in the other answers  if the specific issue you run into is that the Expect header is causing the problem  then that specific problem can be routed around by doing a relatively global switching off of the two-part PUT POST transmission via System Net ServicePointManager Expect100Continue   However this does not fix the complete underlying problem - the stack may still be using HTTP 1 1 specific things such as KeepAlives etc   though in many cases the other answers do cover the main cases    The actual problem is however that the autogenerated code assumes that it s OK to go blindly using HTTP 1 1 facilities as everyone understands this  To stop this assumption for a specific Web Service proxy  one can change override the default underlying HttpWebRequest ProtocolVersion from the default of 1 1 by creating a derived Proxy class which overrides protected override WebRequest GetWebRequest Uri uri  as shown in this post -  public class MyNotAssumingHttp11ProxiesAndServersProxy   MyWS       protected override WebRequest GetWebRequest Uri uri              HttpWebRequest request    HttpWebRequest base GetWebRequest uri         request ProtocolVersion   HttpVersion Version10        return request             where MyWS is the proxy the Add Web Reference wizard spat out at you      UPDATE  Here s an impl I m using in production   class ProxyFriendlyXXXWs   BasicHttpBinding IXXX       public ProxyFriendlyXXXWs  Uri destination                 Url   destination ToString            this IfProxiedUrlAddProxyOverriddenWithDefaultCredentials                  Make it squirm through proxies that don t understand  or are misconfigured  to only understand HTTP 1 0 without yielding HTTP 417s     protected override WebRequest GetWebRequest  Uri uri                 var request    HttpWebRequest base GetWebRequest  uri            request ProtocolVersion   HttpVersion Version10          return request           static class SoapHttpClientProtocolRealWorldProxyTraversalExtensions          OOTB   NET 1-4 do not submit credentials to proxies         This avoids having to document how to  just override a setting on your default proxy in your app config   or machine config       public static void IfProxiedUrlAddProxyOverriddenWithDefaultCredentials  this SoapHttpClientProtocol that                 Uri destination   new Uri  that Url            Uri proxiedAddress   WebRequest DefaultWebProxy GetProxy  destination            if    destination Equals  proxiedAddress                 that Proxy   new WebProxy  proxiedAddress     UseDefaultCredentials   true

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For Powershell it is   System Net ServicePointManager   Expect100Continue    false

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System Net HttpWebRequest adds the header  HTTP header  Expect  100-Continue   to every request unless you explicitly ask it not to by setting this static property to false   System Net ServicePointManager Expect100Continue   false    Some servers choke on that header and send back the 417 error you re seeing    Give that a shot

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The web config approach works for InfoPath form services calls to IntApp web service enabled rules      lt system net gt       lt defaultProxy   gt       lt settings gt   lt  -- 20130323 bchauvin -- gt           lt servicePointManager expect100Continue  false    gt       lt  settings gt     lt  system net gt

User · Answer

In my situation  this error seems to occur only if my client s computer has a strict firewall policy  which prevents my program from communicating with the web service    So only solution I could find is to catch the error and inform user about changing the firewall settings manually

User · Answer

Does the form you are trying to emulate have two fields  username and password   If so   this line    postData Add  username    password      is not correct   you would need two lines like    postData Add  username    Moose    postData Add  password    NotMoosespasswordreally      Edit   Okay  since that is not the problem  one way to tackle this is to use something like Fiddler or Wireshark to watch what is being sent to the web server from the browser successfully  then compare that to what is being sent from your code   If you are going to a normal port 80 from  Net  Fiddler will still capture this traffic   There is probably some other hidden field on the form that the web server is expecting that you are not sending

[c#] HTTP POST Returns Error: 417 "Expectation Failed."

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