test(DtmSample): add tests for workflow return values and fix null handling

- Add new test endpoints for different workflow return
- Fix null value handling for the twice execute
- Update workflow execution to handle null and empty byte arrays consistently

Author: wooln

samples/DtmSample/Controllers/WfTestController.cs

@@ -6,12 +6,14 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using System;
+using System.Diagnostics;
 using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Text;
 using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
+using Exception = System.Exception;
 
 namespace DtmSample.Controllers
 {
@@ -65,6 +67,52 @@ public async Task<IActionResult> Simple(CancellationToken cancellationToken)
             }
         }
 
+        [HttpPost("wf-twice")]
+        public async Task<IActionResult> SimpleTwice(CancellationToken cancellationToken)
+        {
+            try
+            {
+                string wfNameReturnNormal = $"wfNameReturnNormal-{Guid.NewGuid().ToString("N")[..8]}";
+                _globalTransaction.Register(wfNameReturnNormal, async (wf, data) => await Task.FromResult(Encoding.UTF8.GetBytes("my result")));
+                string wfNameReturnEmpty = $"wfNameReturnEmpty-{Guid.NewGuid().ToString("N")[..8]}";
+                _globalTransaction.Register(wfNameReturnEmpty, async (wf, data) => await Task.FromResult(Encoding.UTF8.GetBytes("")));
+                string wfNameReturnNull = $"wfNameReturnNull-{Guid.NewGuid().ToString("N")[..8]}";
+                _globalTransaction.Register(wfNameReturnNull, (wf, data) => Task.FromResult<byte[]>(null));
+
+                string req = JsonSerializer.Serialize(new TransRequest("1", -30));
+
+                string gid;
+                byte[] result1, result2;
+                string resultStr1, resultStr2;
+                gid = wfNameReturnNormal + " " + Guid.NewGuid().ToString("N");
+                result1 = await _globalTransaction.Execute(wfNameReturnNormal, gid, Encoding.UTF8.GetBytes(req), true);
+                result2 = await _globalTransaction.Execute(wfNameReturnNormal, gid, Encoding.UTF8.GetBytes(req), true);
+                resultStr1 = Encoding.UTF8.GetString(result1);
+                resultStr2 = Encoding.UTF8.GetString(result2);
+                if ("my result" != resultStr1) throw new Exception("\"my result\" != resultStr1");
+                if (resultStr1 != resultStr2) throw new Exception("resultStr1 != resultStr2");
+
+                gid = wfNameReturnEmpty + " " + Guid.NewGuid().ToString("N");
+                result1 = await _globalTransaction.Execute(wfNameReturnEmpty, gid, Encoding.UTF8.GetBytes(req), true);
+                result2 = await _globalTransaction.Execute(wfNameReturnEmpty, gid, Encoding.UTF8.GetBytes(req), true);
+                if (null != result1) throw new Exception("String.Empty != resultStr1");
+                if (result1 != result2) throw new Exception("resultStr1 != resultStr2");
+
+                gid = wfNameReturnNull + " " + Guid.NewGuid().ToString("N");
+                result1 = await _globalTransaction.Execute(wfNameReturnNull, gid, Encoding.UTF8.GetBytes(req), true);
+                result2 = await _globalTransaction.Execute(wfNameReturnNull, gid, Encoding.UTF8.GetBytes(req), true);
+                if (null != result1) throw new Exception("String.Empty != resultStr1");
+                if (result1 != result2) throw new Exception("resultStr1 != resultStr2");
+
+                return Ok(TransResponse.BuildSucceedResponse());
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "Workflow Error");
+                return Ok(TransResponse.BuildFailureResponse());
+            }
+        }
+
         [HttpPost("wf-saga")]
         public async Task<IActionResult> Saga(CancellationToken cancellationToken)
         {

src/Dtmworkflow/Workflow.Imp.cs

@@ -39,7 +39,9 @@ internal async Task<byte[]> Process(WfFunc2 handler, byte[] data)
             var status = reply.Transaction.Status;
             if (status == DtmCommon.Constant.StatusSucceed)
             {
-                var sRes = Convert.FromBase64String(reply.Transaction.Result);
+                var sRes = reply.Transaction.Result != null
+                    ? Convert.FromBase64String(reply.Transaction.Result)
+                    : null;
                 return sRes;
             }
             else if (status == DtmCommon.Constant.StatusFailed)
@@ -75,11 +77,15 @@ internal async Task<byte[]> Process(WfFunc2 handler, byte[] data)
             }
 
             if (err == null || err is DtmCommon.DtmFailureException)
-            {
+            {                
+                // The DTM server does not distinguish between byte[0] and null,
+                // when execute the second time (eg. executeByQs), the previous query result returned is null.
                 await this.Submit(res, err, default);
             }
-
-            return res;
+            
+            // Before the DTM server side (v1.18.0) distinguish between byte[0] and null,
+            // in order to be compatible with the same return values for twice call, byte[] has been uniformly changed to return null.
+            return (res != null && res.Length == 0) ? null : res;
         }
 
         private async Task SaveResult(string branchId, string op, StepResult sr)