Delphi DLL

curl with Variable Substitution in a GraphQL Request Body

See more CURL Examples

This example shows how to use variables inside a graphql request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates graphql, Chilkat automatically applies proper escaping to each substituted value, ensuring the resulting graphql remains valid. Delphi DLL

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, HttpCurl, StringBuilder;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
sbCurl: HCkStringBuilder;
curl: HCkHttpCurl;
sbRawRequest: HCkStringBuilder;

begin
success := False;

success := False;

// Variable names are enclosed between {{ and }}
// Important: Variables should be placed inside the quotes.

// curl -X POST https://api.example.com/graphql \
//   -H "Content-Type: application/graphql; charset=utf-8" \
//   -H "Accept: application/json" \
//   --data-binary "mutation {
//   createUser(
//     input: {
//       name: \"{{name}}\"
//       city: \"{{city}}\"
//       note: \"{{note}}\"
//       bio: \"{{bio}}\"
//     }
//   ) {
//     id
//     name
//   }
// }"

// Build the above curl command.
sbCurl := CkStringBuilder_Create();
CkStringBuilder_AppendLn(sbCurl,'curl -X POST https://api.example.com/graphql \");
CkStringBuilder_AppendLn(sbCurl,'  -H "Content-Type: application/graphql; charset=utf-8" \");
CkStringBuilder_AppendLn(sbCurl,'  -H "Accept: application/json" \");
CkStringBuilder_AppendLn(sbCurl,'  -d "mutation {');
CkStringBuilder_AppendLn(sbCurl,'  createUser(');
CkStringBuilder_AppendLn(sbCurl,'    input: {');
CkStringBuilder_AppendLn(sbCurl,'      name: \\"{{name}}\\"');
CkStringBuilder_AppendLn(sbCurl,'      city: \\"{{city}}\\"');
CkStringBuilder_AppendLn(sbCurl,'      note: \\"{{note}}\\"');
CkStringBuilder_AppendLn(sbCurl,'      bio: \\"{{bio}}\\"');
CkStringBuilder_AppendLn(sbCurl,'    }');
CkStringBuilder_AppendLn(sbCurl,'  ) {');
CkStringBuilder_AppendLn(sbCurl,'    id');
CkStringBuilder_AppendLn(sbCurl,'    name');
CkStringBuilder_AppendLn(sbCurl,'  }');
CkStringBuilder_AppendLn(sbCurl,'}"');

curl := CkHttpCurl_Create();

// Provide values for variables
CkHttpCurl_SetVar(curl,'name','José O''Connor');
CkHttpCurl_SetVar(curl,'city','München');
CkHttpCurl_SetVar(curl,'note','He said "Hello, world!" — and left…');
CkHttpCurl_SetVar(curl,'bio','Loves sushi, café visits, and π ≈ 3.14159');

// To demonstrate how the variables are replaced, this example does not execute the curl command. 
// Instead, it generates the raw HTTP request that would be sent if the curl command were run.
sbRawRequest := CkStringBuilder_Create();
success := CkHttpCurl_ToRawRequest(curl,CkStringBuilder__getAsString(sbCurl),sbRawRequest);
if (success = False) then
  begin
    Memo1.Lines.Add(CkHttpCurl__lastErrorText(curl));
    Exit;
  end;

Memo1.Lines.Add(CkStringBuilder__getAsString(sbRawRequest));

// The output is shown below.
// Notice the quote chars around "Hello, world!" are properly escaped.

// POST /graphql HTTP/1.1
// Accept: application/json
// Host: api.example.com
// Content-Type: application/graphql; charset=utf-8
// Content-Length: 250
// 
// mutation {
//   createUser(
//     input: {
//       name: "José O'Connor"
//       city: "München"
//       note: "He said \"Hello, world!\" — and left…"
//       bio: "Loves sushi, café visits, and π ≈ 3.14159"
//     }
//   ) {
//     id
//     name
//   }
// }

CkStringBuilder_Dispose(sbCurl);
CkHttpCurl_Dispose(curl);
CkStringBuilder_Dispose(sbRawRequest);

end;