Disable buffering for stream responses (#1060)

src/AutoRest.CSharp/Generation/Writers/RestClientWriter.cs

@@ -126,6 +126,10 @@ private void WriteRequestCreation(CodeWriter writer, RestClientMethod clientMeth
                 writer.Line($"var {message:D} = {PipelineField}.CreateMessage();");
                 writer.Line($"var {request:D} = {message}.Request;");
                 var method = clientMethod.Request.HttpMethod;
+                if (!clientMethod.BufferResponse)
+                {
+                    writer.Line($"{message}.BufferResponse = false;");
+                }
                 writer.Line($"{request}.Method = {typeof(RequestMethod)}.{method.ToRequestMethodName()};");
 
                 writer.Line($"var {uri:D} = new RawRequestUriBuilder();");

src/AutoRest.CSharp/Input/CodeModelPartials.cs

@@ -84,6 +84,8 @@ public string[] Formats
         }
 
         public string? HeaderCollectionPrefix => TryGetValue("x-ms-header-collection-prefix", out object? value) ? value?.ToString() : null;
+
+        public bool? BufferResponse => TryGetValue("x-csharp-buffer-response", out object? value) && value != null ? (bool?)Convert.ToBoolean(value) : null;
     }
 
     internal partial class ServiceResponse

src/AutoRest.CSharp/Output/Models/Requests/RestClientMethod.cs

@@ -9,7 +9,7 @@ namespace AutoRest.CSharp.Output.Models.Requests
 {
     internal class RestClientMethod
     {
-        public RestClientMethod(string name, string? description, CSharpType? returnType, Request request, Parameter[] parameters, Response[] responses, ResponseHeaderGroupType? headerModel)
+        public RestClientMethod(string name, string? description, CSharpType? returnType, Request request, Parameter[] parameters, Response[] responses, ResponseHeaderGroupType? headerModel, bool bufferResponse)
         {
             Name = name;
             Request = request;
@@ -18,6 +18,7 @@ public RestClientMethod(string name, string? description, CSharpType? returnType
             Description = description;
             ReturnType = returnType;
             HeaderModel = headerModel;
+            BufferResponse = bufferResponse;
         }
 
         public string Name { get; }
@@ -26,6 +27,7 @@ public RestClientMethod(string name, string? description, CSharpType? returnType
         public Parameter[] Parameters { get; }
         public Response[] Responses { get; }
         public ResponseHeaderGroupType? HeaderModel { get; }
+        public bool BufferResponse { get; }
         public CSharpType? ReturnType { get; }
     }
 }

src/AutoRest.CSharp/Output/Models/RestClient.cs

@@ -380,14 +380,22 @@ private RestClientMethod BuildMethod(Operation operation, HttpRequest httpReques
                 };
             }
 
+            bool isStreamOnlyResponse = clientResponse.Count == 1 &&
+                                        clientResponse[0].ResponseBody is StreamResponseBody;
+
+            // Don't buffer stream-only responses
+            bool bufferResponse =
+                operation.Extensions?.BufferResponse ?? !isStreamOnlyResponse;
+
             return new RestClientMethod(
                 operationName,
                 BuilderHelpers.EscapeXmlDescription(operation.Language.Default.Description),
                 responseType,
                 request,
                 OrderParameters(methodParameters.Values),
                 clientResponse.ToArray(),
-                responseHeaderModel
+                responseHeaderModel,
+                bufferResponse
             );
         }
 
@@ -521,7 +529,8 @@ private static RestClientMethod BuildNextPageMethod(RestClientMethod method, Ope
                 request,
                 parameters,
                 responses,
-                method.HeaderModel);
+                method.HeaderModel,
+                bufferResponse: true);
         }
 
         public RestClientMethod? GetNextOperationMethod(ServiceRequest request)

test/AutoRest.TestServer.Tests/body-file.cs

@@ -48,6 +48,7 @@ public Task FileStreamVeryLarge() => Test(async (host, pipeline) =>
             }
 
             Assert.AreEqual(3000 * 1024 * 1024L, total);
+            Assert.False(stream.CanSeek);
             await result.Value.DisposeAsync().ConfigureAwait(false);
         }, ignoreScenario: false, useSimplePipeline: true);
 
@@ -58,6 +59,7 @@ public Task FileStreamVeryLarge_Sync() => Test((host, pipeline) =>
             var result = new FilesClient(ClientDiagnostics, pipeline, host).GetFileLarge();
             var buffer = new byte[2 * 1024 * 1024L];
             var stream = result.Value;
+
             long total = 0;
             var count = stream.Read(buffer, 0, buffer.Length);
             while (count > 0)
@@ -67,6 +69,7 @@ public Task FileStreamVeryLarge_Sync() => Test((host, pipeline) =>
             }
 
             Assert.AreEqual(3000 * 1024 * 1024L, total);
+            Assert.False(stream.CanSeek);
             result.Value.Dispose();
         }, ignoreScenario: false, useSimplePipeline: true);
     }