(Unicode C++) 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

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#include <CkHttpCurlW.h>
#include <CkJsonObjectW.h>

void ChilkatSample(void)
    {
    bool success = false;

    success = false;

    CkHttpCurlW httpCurl;

    // This target curl command requires {{drive_id}}.
    const wchar_t *targetCurl = L"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.
    const wchar_t *fnName = L"getSite";
    httpCurl.AddFunction(fnName,L"curl -X GET https://graph.microsoft.com/v1.0/sites/root:/sites/{{site_name}}");
    httpCurl.AddOutput(fnName,L"id",L"site_id");

    // Provide site_name, so getSite can run.
    httpCurl.SetVar(L"site_name",L"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.
    CkJsonObjectW planJson;
    planJson.put_EmitCompact(false);

    success = httpCurl.ExaminePlan(targetCurl,planJson);
    if (success == false) {
        // Should equal 5.
        wprintf(L"ExaminePlan fail reason = %d\n",httpCurl.get_FailReason());

        // Examine the error(s) returned in planJson
        wprintf(L"%s\n",planJson.emit());

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

    // DoYourThing will fail for the same reason.
    success = httpCurl.DoYourThing(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) {
        // 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).
        wprintf(L"DoYourThing fail reason = %d\n",httpCurl.get_FailReason());
    }
    else {
        // If execution succeeds, it means the plan was somehow resolved,
        // which would be unexpected in this scenario.
        wprintf(L"Unexpected success.\n");
    }
    }