Introduce the possibility to exclude variable value retrieval for certain storage drivers

src/modules/Elsa.Workflows.Api/Endpoints/WorkflowInstances/Variables/List/Endpoint.cs

@@ -27,7 +27,7 @@ internal class List(IWorkflowInstanceVariableManager workflowInstanceVariableMan
             return;
         }
         
-        var variables = await workflowInstanceVariableManager.GetVariablesAsync(workflowInstanceId, cancellationToken).ToList();
+        var variables = await workflowInstanceVariableManager.GetVariablesAsync(workflowInstanceId, true,cancellationToken).ToList();
         var variableModels = variables.Select(x => new ResolvedVariableModel(x.Variable.Id, x.Variable.Name, x.Value)).ToList();
         var response = new ListResponse<ResolvedVariableModel>(variableModels);
         await SendOkAsync(response, cancellationToken);

src/modules/Elsa.Workflows.Core/Contracts/IStorageDriver.cs

@@ -10,6 +10,11 @@ public interface IStorageDriver
     /// </summary>
     double Priority { get; }
     
+    /// <summary>
+    /// A list of tags assigned to the driver used to describe the data contents.
+    /// </summary>
+    StorageDriverTag[] Tags { get; }
+    
     /// <summary>
     /// Writes a value to the storage driver.
     /// </summary>

src/modules/Elsa.Workflows.Core/Contracts/IVariablePersistenceManager.cs

@@ -6,9 +6,12 @@ namespace Elsa.Workflows;
 public interface IVariablePersistenceManager
 {
     /// <summary>
-    /// Loads the variables into the specified <see cref="WorkflowExecutionContext"/>. 
+    /// Loads the variables into the specified <see cref="WorkflowExecutionContext"/>.
     /// </summary>
-    Task LoadVariablesAsync(WorkflowExecutionContext context);
+    /// <param name="context"></param>
+    /// <param name="excludeValueRetrievalForLargeDataDrivers"></param>
+    /// <returns></returns>
+    Task LoadVariablesAsync(WorkflowExecutionContext context, bool excludeValueRetrievalForLargeDataDrivers = false);
 
     /// <summary>
     /// Persists all persistable variables from the specified <see cref="WorkflowExecutionContext"/>. 

src/modules/Elsa.Workflows.Core/Contracts/IWorkflowInstanceVariableReader.cs

@@ -9,7 +9,8 @@ public interface IWorkflowInstanceVariableReader
     /// Retrieves all variables from the specified <see cref="WorkflowExecutionContext"/>.
     /// </summary>
     /// <param name="workflowExecutionContext">The context of the workflow execution.</param>
+    /// <param name="excludeValueRetrievalForLargeDataDrivers"></param>
     /// <param name="cancellationToken">The cancellation token to cancel the operation.</param>
     /// <returns>A task that represents the asynchronous operation. The task result contains a collection of <see cref="ResolvedVariable"/> instances.</returns>
-    Task<IEnumerable<ResolvedVariable>> GetVariables(WorkflowExecutionContext workflowExecutionContext, CancellationToken cancellationToken = default);
+    Task<IEnumerable<ResolvedVariable>> GetVariables(WorkflowExecutionContext workflowExecutionContext, bool excludeValueRetrievalForLargeDataDrivers = false, CancellationToken cancellationToken = default);
 }

src/modules/Elsa.Workflows.Core/Enums/StorageDriverTag.cs

@@ -0,0 +1,6 @@
+namespace Elsa.Workflows;
+
+public enum StorageDriverTag
+{
+    LargeData
+}

src/modules/Elsa.Workflows.Core/Services/DefaultWorkflowInstanceVariableReader.cs

@@ -2,7 +2,7 @@ namespace Elsa.Workflows;
 
 public class DefaultWorkflowInstanceVariableReader(IVariablePersistenceManager variablePersistenceManager) : IWorkflowInstanceVariableReader
 {
-    public async Task<IEnumerable<ResolvedVariable>> GetVariables(WorkflowExecutionContext workflowExecutionContext, CancellationToken cancellationToken = default)
+    public async Task<IEnumerable<ResolvedVariable>> GetVariables(WorkflowExecutionContext workflowExecutionContext, bool excludeValueRetrievalForLargeDataDrivers = false, CancellationToken cancellationToken = default)
     {
         var workflow = workflowExecutionContext.Workflow;
         var workflowVariables = workflow.Variables;
@@ -11,7 +11,7 @@ public class DefaultWorkflowInstanceVariableReader(IVariablePersistenceManager v
         if (rootWorkflowActivityExecutionContext == null) 
             return [];
         
-        await variablePersistenceManager.LoadVariablesAsync(workflowExecutionContext);
+        await variablePersistenceManager.LoadVariablesAsync(workflowExecutionContext, excludeValueRetrievalForLargeDataDrivers);
         var resolvedVariables = new List<ResolvedVariable>();
 
         foreach (var workflowVariable in workflowVariables)

src/modules/Elsa.Workflows.Core/Services/MemoryStorageDriver.cs

@@ -9,8 +9,10 @@ namespace Elsa.Workflows;
 public class MemoryStorageDriver : IStorageDriver
 {
     private readonly IDictionary<string, object> _dictionary = new Dictionary<string, object>();
-
+    /// <inheritdoc />
     public double Priority => 0;
+    /// <inheritdoc />
+    public StorageDriverTag[] Tags => [];
 
     /// <inheritdoc />
     public ValueTask WriteAsync(string id, object value, StorageDriverContext context)

src/modules/Elsa.Workflows.Core/Services/VariablePersistenceManager.cs

@@ -8,7 +8,7 @@ namespace Elsa.Workflows;
 public class VariablePersistenceManager(IStorageDriverManager storageDriverManager) : IVariablePersistenceManager
 {
     /// <inheritdoc />
-    public async Task LoadVariablesAsync(WorkflowExecutionContext workflowExecutionContext)
+    public async Task LoadVariablesAsync(WorkflowExecutionContext workflowExecutionContext, bool excludeValueRetrievalForLargeDataDrivers = false)
     {
         var cancellationToken = workflowExecutionContext.CancellationToken;
         var contexts = workflowExecutionContext.ActivityExecutionContexts.ToList();
@@ -34,6 +34,9 @@ public class VariablePersistenceManager(IStorageDriverManager storageDriverManag
                 if (driver == null)
                     continue;
 
+                if (excludeValueRetrievalForLargeDataDrivers && driver.Tags.Contains(StorageDriverTag.LargeData))
+                    continue;
+
                 var id = GetStateId(variable);
                 var value = await driver.ReadAsync(id, storageDriverContext);
                 if (value == null) continue;

src/modules/Elsa.Workflows.Core/VariableStorageDrivers/WorkflowInstanceStorageDriver.cs

@@ -17,8 +17,11 @@ public class WorkflowInstanceStorageDriver : IStorageDriver
     /// The key used to store the variables in the workflow state.
     /// </summary>
     public const string VariablesDictionaryStateKey = "Variables";
-
+    
+    /// <inheritdoc />
     public double Priority => 5;
+    /// <inheritdoc />
+    public StorageDriverTag[] Tags => [];
 
     /// <inheritdoc />
     public ValueTask WriteAsync(string id, object value, StorageDriverContext context)

src/modules/Elsa.Workflows.Core/VariableStorageDrivers/WorkflowStorageDriver.cs

@@ -20,6 +20,8 @@ public class WorkflowStorageDriver : IStorageDriver
 
     /// <inheritdoc />
     public double Priority => -1;
+    /// <inheritdoc />
+    public StorageDriverTag[] Tags => [];
 
     /// <inheritdoc />
     public ValueTask WriteAsync(string id, object value, StorageDriverContext context)

src/modules/Elsa.Workflows.Management/Contracts/IWorkflowInstanceVariableManager.cs

@@ -6,17 +6,19 @@ public interface IWorkflowInstanceVariableManager
     /// Retrieves all variables for the specified workflow instance.
     /// </summary>
     /// <param name="workflowInstanceId">The ID of the workflow instance.</param>
+    /// <param name="excludeValueRetrievalForLargeDataDrivers"></param>
     /// <param name="cancellationToken">The cancellation token to cancel the operation.</param>
     /// <returns>A task that represents the asynchronous operation. The task result contains a collection of <see cref="ResolvedVariable"/> instances.</returns>
-    Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(string workflowInstanceId, CancellationToken cancellationToken = default);
+    Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(string workflowInstanceId, bool excludeValueRetrievalForLargeDataDrivers = false, CancellationToken cancellationToken = default);
 
     /// <summary>
     /// Retrieves all variables from the specified <see cref="WorkflowExecutionContext"/>.
     /// </summary>
     /// <param name="workflowExecutionContext">The context of the workflow execution.</param>
+    /// <param name="excludeValueRetrievalForLargeDataDrivers"></param>
     /// <param name="cancellationToken">The cancellation token to cancel the operation.</param>
     /// <returns>A task that represents the asynchronous operation. The task result contains a collection of <see cref="ResolvedVariable"/> instances.</returns>
-    Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(WorkflowExecutionContext workflowExecutionContext, CancellationToken cancellationToken = default);
+    Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(WorkflowExecutionContext workflowExecutionContext, bool excludeValueRetrievalForLargeDataDrivers = false, CancellationToken cancellationToken = default);
     
     /// <summary>
     /// Sets the specified variables in the specified workflow instance.

src/modules/Elsa.Workflows.Management/Services/WorkflowInstanceVariableManager.cs

@@ -7,16 +7,16 @@ public class WorkflowInstanceVariableManager(
     IWorkflowInstanceVariableReader variableReader,
     IWorkflowInstanceVariableWriter variableWriter) : IWorkflowInstanceVariableManager
 {
-    public async Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(string workflowInstanceId, CancellationToken cancellationToken = default)
+    public async Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(string workflowInstanceId, bool excludeValueRetrievalForLargeDataDrivers = false, CancellationToken cancellationToken = default)
     {
         var workflowExecutionContext = await GetWorkflowExecutionContextAsync(workflowInstanceId, cancellationToken);
         if (workflowExecutionContext == null) return [];
-        return await variableReader.GetVariables(workflowExecutionContext, cancellationToken);
+        return await variableReader.GetVariables(workflowExecutionContext, excludeValueRetrievalForLargeDataDrivers, cancellationToken);
     }
 
-    public Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(WorkflowExecutionContext workflowExecutionContext, CancellationToken cancellationToken = default)
+    public Task<IEnumerable<ResolvedVariable>> GetVariablesAsync(WorkflowExecutionContext workflowExecutionContext, bool excludeValueRetrievalForLargeDataDrivers = false, CancellationToken cancellationToken = default)
     {
-        return variableReader.GetVariables(workflowExecutionContext, cancellationToken);
+        return variableReader.GetVariables(workflowExecutionContext, excludeValueRetrievalForLargeDataDrivers, cancellationToken);
     }
 
     public async Task<IEnumerable<ResolvedVariable>> SetVariablesAsync(string workflowInstanceId, IEnumerable<VariableUpdateValue> variables, CancellationToken cancellationToken = default)