(Delphi DLL) Impossible Execution Plan

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This example demonstrates what happens when it is not possible to construct an execution plan due to missing dependencies.

The target curl command requires a {{drive_id}} value. However, no variable named drive_id has been defined, and no helper function is registered that can produce it. Although a helper function (getSite) is defined, it only produces site_id, which does not satisfy the requirement.

When ExaminePlan is called, it reports that the execution plan cannot be created because a required input is missing and no function exists to provide it.

When DoYourThing is called, it fails for the same reason. The failure is not due to a network or HTTP error, but because the dependency graph cannot be resolved. The FailReason property indicates this condition with a specific error code.

This example highlights that for an execution plan to be valid, every required input must either:

• Already have a defined value, or
• Be producible by a defined curl function with resolvable inputs

If neither condition is met, the system correctly detects the unresolved dependency and prevents execution.

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

For more information, see https://www.chilkatsoft.com/curl_dependency_engine.asp

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, JsonObject, HttpCurl;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
httpCurl: HCkHttpCurl;
targetCurl: PWideChar;
fnName: PWideChar;
planJson: HCkJsonObject;

begin
success := False;

success := False;

httpCurl := CkHttpCurl_Create();

// This target curl command requires {{drive_id}}.
targetCurl := 'curl -X GET https://graph.microsoft.com/v1.0/drives/{{drive_id}}/root/children';

// Define a helper function that can produce site_id.
// However, it does NOT produce drive_id.
fnName := 'getSite';
CkHttpCurl_AddFunction(httpCurl,fnName,'curl -X GET https://graph.microsoft.com/v1.0/sites/root:/sites/{{site_name}}');
CkHttpCurl_AddOutput(httpCurl,fnName,'id','site_id');

// Provide site_name, so getSite can run.
CkHttpCurl_SetVar(httpCurl,'site_name','test');

// Try to examine the execution plan.
// This fails because {{drive_id}} is required by the target curl command,
// but drive_id is not already known and no defined function produces it.
planJson := CkJsonObject_Create();
CkJsonObject_putEmitCompact(planJson,False);

success := CkHttpCurl_ExaminePlan(httpCurl,targetCurl,planJson);
if (success = False) then
  begin
    // Should equal 5.
    Memo1.Lines.Add('ExaminePlan fail reason = ' + IntToStr(CkHttpCurl_getFailReason(httpCurl)));

    // Examine the error(s) returned in planJson
    Memo1.Lines.Add(CkJsonObject__emit(planJson));

    // Expected output:
    // {
    //   "errors": [{
    //     "variable": "drive_id",
    //     "msg": "No candidate functions"
    //   }]
    // }
  end;

// DoYourThing will fail for the same reason.
success := CkHttpCurl_DoYourThing(httpCurl,targetCurl);

// We expect DoYourThing to fail because it is not possible to construct
// a valid execution plan (drive_id cannot be resolved).
if (success = False) then
  begin
    // FailReason provides a numeric code indicating why the operation failed.
    // A value of 5 specifically means that an execution plan could not be created
    // due to unresolved dependencies (i.e., a required variable has no source).
    Memo1.Lines.Add('DoYourThing fail reason = ' + IntToStr(CkHttpCurl_getFailReason(httpCurl)));
  end
else
  begin
    // If execution succeeds, it means the plan was somehow resolved,
    // which would be unexpected in this scenario.
    Memo1.Lines.Add('Unexpected success.');
  end;

CkHttpCurl_Dispose(httpCurl);
CkJsonObject_Dispose(planJson);

end;