(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.

Note: This example requires Chilkat v11.5.0 or greater.

Chilkat for Delphi Downloads

Chilkat non-ActiveX DLL for Delphi

Chilkat ActiveX DLL for Delphi

* The examples here use the non-ActiveX 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;