Build query string for System Net HttpClient get

Question

If I wish to submit a http get request using System Net HttpClient there seems to be no api to add parameters  is this correct    Is there any simple api available to build the query string that doesn t involve building a name value collection and url encoding those and then finally concatenating them  I was hoping to use something like RestSharp s api  i e AddParameter

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Or simply using my Uri extension  Code  public static Uri AttachParameters this Uri uri  NameValueCollection parameters        var stringBuilder   new StringBuilder        string str            for  int index   0  index  lt  parameters Count    index                stringBuilder Append str   parameters AllKeys index          parameters index            str     amp              return new Uri uri   stringBuilder ToString         Usage  Uri uri   new Uri  http   www example com index php   AttachParameters new NameValueCollection                                                                                                                                                               Bill    Gates                                                                                     Steve    Jobs                                                                                    Result     http   www example com index php Bill Gates amp Steve Jobs

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Darin offered an interesting and clever solution  and here is something that may be another option   public class ParameterCollection       private Dictionary lt string  string gt   parms   new Dictionary lt string  string gt          public void Add string key  string val                if   parms ContainsKey key                         throw new InvalidOperationException string Format  The key  0  already exists    key                       parms Add key  val              public override string ToString                 var server   HttpContext Current Server          var sb   new StringBuilder            foreach  var kvp in  parms                        if  sb Length  gt  0    sb Append   amp                   sb AppendFormat   0   1                    server UrlEncode kvp Key                   server UrlEncode kvp Value                      return sb ToString              and so when using it  you might do this   var parms   new ParameterCollection    parms Add  key    value     var url       url          parms

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Since I have to reuse this few time  I came up with this class that simply help to abstract how the query string is composed   public class UriBuilderExt       private NameValueCollection collection      private UriBuilder builder       public UriBuilderExt string uri                builder   new UriBuilder uri           collection   System Web HttpUtility ParseQueryString string Empty              public void AddParameter string key  string value            collection Add key  value              public Uri Uri          get                       builder Query   collection ToString                return builder Uri                       The use will be simplify to something like this   var builder   new UriBuilderExt  http   example com     builder AddParameter  foo    bar lt  gt  amp -baz    builder AddParameter  bar    second    var uri   builder Uri    that will return the uri  http   example com  foo bar 3c 3e 26-baz amp bar second

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Thanks to  Darin Dimitrov   This is the extension methods    public static partial class Ext       public static Uri GetUriWithparameters this Uri uri Dictionary lt string string gt  queryParams   null int port   -1                var builder   new UriBuilder uri           builder Port   port          if null    queryParams  amp  amp  0  lt  queryParams Count                        var query   HttpUtility ParseQueryString builder Query               foreach var item in queryParams                                query item Key    item Value                            builder Query   query ToString                      return builder Uri             public static string GetUriWithparameters string uri Dictionary lt string string gt  queryParams   null int port   -1                var builder   new UriBuilder uri           builder Port   port          if null    queryParams  amp  amp  0  lt  queryParams Count                        var query   HttpUtility ParseQueryString builder Query               foreach var item in queryParams                                query item Key    item Value                            builder Query   query ToString                      return builder Uri ToString

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In a ASP NET Core project you can use the QueryHelpers class  available in the Microsoft AspNetCore WebUtilities namespace for ASP NET Core  or the  NET Standard 2 0 NuGet package for other consumers     using Microsoft AspNetCore WebUtilities  var query   new Dictionary lt string  string gt          quot foo quot      quot bar quot         quot foo2 quot      quot bar2 quot                  var response   await client GetAsync QueryHelpers AddQueryString  quot  api  quot   query

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To avoid double encoding issue described in taras roshko s answer and to keep possibility to easily work with query parameters  you can use uriBuilder Uri ParseQueryString   instead of HttpUtility ParseQueryString

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TL DR  do not use accepted version as It s completely broken in relation to handling unicode characters  and never use internal API  I ve actually found weird double encoding issue with the accepted solution   So  If you re dealing with characters which need to be encoded  accepted solution leads to double encoding    query parameters are auto encoded by using NameValueCollection indexer  and this uses UrlEncodeUnicode  not regular expected UrlEncode     Then  when you call uriBuilder Uri it creates new Uri using constructor which does encoding one more time  normal url encoding  That cannot be avoided by doing uriBuilder ToString    even though this returns correct Uri which IMO is at least inconsistency  maybe a bug  but that s another question  and then using HttpClient method accepting string - client still creates Uri out of your passed string like this  new Uri uri  UriKind RelativeOrAbsolute    Small  but full repro   var builder   new UriBuilder       Scheme   Uri UriSchemeHttps      Port   -1      Host    127 0 0 1       Path    app      NameValueCollection query   HttpUtility ParseQueryString builder Query    query  cyrillic                  builder Query   query ToString    Console WriteLine builder Query     query with cyrillic stuff UrlEncodedUnicode  and that s not what you want  var uri   builder Uri     creates new Uri using constructor which does encode and messes cyrillic parameter even more Console WriteLine uri       this is still wrong  var stringUri   builder ToString       returns more  correct   still  UrlEncodedUnicode   but at least once  not twice  new HttpClient   GetStringAsync stringUri      this creates Uri object out of  stringUri  so we still end up sending double encoded cyrillic text to server  Ouch    Output    cyrillic  u043a u0438 u0440 u0438 u043b u0438 u0446 u044f  https   127 0 0 1 app cyrillic  25u043a 25u0438 25u0440 25u0438 25u043b 25u0438 25u0446 25u044f   As you may see  no matter if you do uribuilder ToString     httpClient GetStringAsync string  or uriBuilder Uri   httpClient GetStringAsync Uri  you end up sending double encoded parameter  Fixed example could be   var uri   new Uri builder ToString    dontEscape  true   new HttpClient   GetStringAsync uri     But this uses obsolete Uri constructor  P S on my latest  NET on Windows Server  Uri constructor with bool doc comment says  obsolete  dontEscape is always false   but actually works as expected  skips escaping   So It looks like another bug     And even this is plain wrong - it send UrlEncodedUnicode to server  not just UrlEncoded what server expects  Update  one more thing is  NameValueCollection actually does UrlEncodeUnicode  which is not supposed to be used anymore and is incompatible with regular url encode decode  see NameValueCollection to URL Query     So the bottom line is  never use this hack with NameValueCollection query   HttpUtility ParseQueryString builder Query   as it will mess your unicode query parameters  Just build query manually and assign it to UriBuilder Query which will do necessary encoding and then get Uri using UriBuilder Uri   Prime example of hurting yourself by using code which is not supposed to be used like this

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For those who do not want to include System Web in projects that don t already use it  you can use FormUrlEncodedContent from System Net Http and do something like the following   keyvaluepair version  string query  using var content   new FormUrlEncodedContent new KeyValuePair lt string  string gt         new KeyValuePair lt string  string gt   ham    Glazed         new KeyValuePair lt string  string gt   x-men    Wolverine   Logan        new KeyValuePair lt string  string gt   Time   DateTime UtcNow ToString               query   content ReadAsStringAsync   Result      dictionary version  string query  using var content   new FormUrlEncodedContent new Dictionary lt string  string gt             ham    Glaced            x-men    Wolverine   Logan           Time   DateTime UtcNow ToString                query   content ReadAsStringAsync   Result

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You might want to check out Flurl  disclosure  I m the author   a fluent URL builder with optional companion lib that extends it into a full-blown REST client   var result   await  https   api com         basic URL building       AppendPathSegment  endpoint        SetQueryParams new           api key   ConfigurationManager AppSettings  SomeApiKey            max results   20          q    Don t worry  I ll get encoded               SetQueryParams myDictionary       SetQueryParam  q    overwrite q            extensions provided by Flurl Http       WithOAuthBearerToken  token        GetJsonAsync lt TResult gt       Check out the docs for more details  The full package is available on NuGet   PM gt  Install-Package Flurl Http  or just the stand-alone URL builder   PM gt  Install-Package Flurl

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I couldn t find a better solution than creating a extension method to convert a Dictionary to QueryStringFormat  The solution proposed by Waleed A K  is good as well   Follow my solution   Create the extension method   public static class DictionaryExt       public static string ToQueryString lt TKey  TValue gt  this Dictionary lt TKey  TValue gt  dictionary                return ToQueryString lt TKey  TValue gt  dictionary                   public static string ToQueryString lt TKey  TValue gt  this Dictionary lt TKey  TValue gt  dictionary  string startupDelimiter                string result   string Empty          foreach  var item in dictionary                        if  string IsNullOrEmpty result                   result    startupDelimiter                      else                 result      amp                 result    string Format   0   1    item Key  item Value                     return result            And them   var param   new Dictionary lt string  string gt                             param1    value1                    param2    value2                  param ToQueryString      By default will add     question mark at begining     param1 value1 amp param2 value2  param ToQueryString   amp       Will add   amp       amp param1 value1 amp param2 value2  param ToQueryString        Won t add anything    param1 value1 amp param2 value2

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Along the same lines as Rostov s post  if you do not want to include a reference to System Web in your project  you can use FormDataCollection from System Net Http Formatting and do something like the following   Using System Net Http Formatting FormDataCollection  var parameters   new Dictionary lt string  string gt             ham    Glaced             x-men    Wolverine   Logan            Time   DateTime UtcNow ToString          var query   new FormDataCollection parameters  ReadAsNameValueCollection   ToString

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Good part of accepted answer  modified to use UriBuilder Uri ParseQueryString   instead of HttpUtility ParseQueryString     var builder   new UriBuilder  http   example com    var query   builder Uri ParseQueryString    query  foo      bar lt  gt  amp -baz   query  bar      bazinga   builder Query   query ToString    string url   builder ToString

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If I wish to submit a http get request using System Net HttpClient   there seems to be no api to add parameters  is this correct    Yes      Is there any simple api available to build the query string that   doesn t involve building a name value collection and url encoding   those and then finally concatenating them    Sure   var query   HttpUtility ParseQueryString string Empty   query  foo      bar lt  gt  amp -baz   query  bar      bazinga   string queryString   query ToString      will give you the expected result   foo bar 3c 3e 26-baz amp bar bazinga   You might also find the UriBuilder class useful   var builder   new UriBuilder  http   example com    builder Port   -1  var query   HttpUtility ParseQueryString builder Query   query  foo      bar lt  gt  amp -baz   query  bar      bazinga   builder Query   query ToString    string url   builder ToString      will give you the expected result   http   example com  foo bar 3c 3e 26-baz amp bar bazinga   that you could more than safely feed to your HttpClient GetAsync method

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The RFC 6570 URI Template library I m developing is capable of performing this operation  All encoding is handled for you in accordance with that RFC  At the time of this writing  a beta release is available and the only reason it s not considered a stable 1 0 release is the documentation doesn t fully meet my expectations  see issues  17   18   32   43    You could either build a query string alone   UriTemplate template   new UriTemplate    params      var parameters   new Dictionary lt string  string gt             param1    value1            param2    value2          Uri relativeUri   template BindByName parameters     Or you could build a complete URI   UriTemplate template   new UriTemplate  path to item  params      var parameters   new Dictionary lt string  string gt             param1    value1            param2    value2          Uri baseAddress   new Uri  http   www example com    Uri relativeUri   template BindByName baseAddress  parameters

[c#] Build query string for System.Net.HttpClient get

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