Pascal (Lazarus/Delphi)

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. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.HttpCurl,
  Chilkat.StringBuilder;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  sbCurl: TStringBuilder;
  curl: THttpCurl;
  sbRawRequest: TStringBuilder;

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

  curl := THttpCurl.Create;

  //  Provide values for variables
  curl.SetVar('name','José O''Connor');
  curl.SetVar('city','München');
  curl.SetVar('note','He said "Hello, world!" — and left…');
  curl.SetVar('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 := TStringBuilder.Create;
  success := curl.ToRawRequest(sbCurl.GetAsString(),sbRawRequest);
  if (success = False) then
    begin
      WriteLn(curl.LastErrorText);
      Exit;
    end;

  WriteLn(sbRawRequest.GetAsString());

  //  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
  //    }
  //  }


  sbCurl.Free;
  curl.Free;
  sbRawRequest.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.