enabled VW string format stream download via API

Experimentation/Experimentation.csproj

@@ -130,6 +130,7 @@
     <Compile Include="Metrics.cs" />
     <Compile Include="OfflineTrainer.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="VowpalWabbitStreamWriter.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="app.config" />

Experimentation/VowpalWabbitStreamWriter.cs

@@ -0,0 +1,39 @@
+using System.IO;
+using System.Text;
+using VW;
+using VW.Serializer;
+
+namespace Experimentation
+{
+    public class VowpalWabbitStreamWriter : StreamWriter
+    {
+        private VowpalWabbit vw;
+
+        public VowpalWabbitStreamWriter(Stream stream, Encoding encoding, string arguments) : base(stream, encoding)
+        {
+            vw = new VowpalWabbit(new VowpalWabbitSettings { Arguments = arguments, EnableStringExampleGeneration = true, EnableStringFloatCompact = true });
+        }
+
+        public override void WriteLine(string value)
+        {
+            using (var jsonSerializer = new VowpalWabbitJsonSerializer(vw))
+            using (var example = jsonSerializer.ParseAndCreate(value))
+            {
+                if (example == null)
+                    throw new InvalidDataException($"Invalid example: {value}");
+
+                var str = example.VowpalWabbitString;
+                if (example is VowpalWabbitMultiLineExampleCollection)
+                    str += "\n";
+
+                base.WriteLine(str);
+            }
+        }
+
+        public override void Close()
+        {
+            vw.Dispose();
+            base.Close();
+        }
+    }
+}

mc/Controllers/AutomationController.cs

@@ -82,14 +82,37 @@ namespace DecisionServicePrivateWeb.Controllers
         }
 
         [HttpGet]
-        public async Task<ActionResult> Offline(string startTimeInclusive, string endTimeExclusive)
+        public async Task<ActionResult> Offline(string startTimeInclusive, string endTimeExclusive, string dataFormat = "json")
         {
             var token = Request.Headers["auth"];
             if (token != ConfigurationManager.AppSettings[ApplicationMetadataStore.AKPassword])
                 throw new UnauthorizedAccessException();
 
             var storageAccount = CloudStorageAccount.Parse(ConfigurationManager.AppSettings[ApplicationMetadataStore.AKConnectionString]);
-            using (var responseWriter = new StreamWriter(Response.OutputStream, Encoding.UTF8))
+
+            var blobClient = storageAccount.CreateCloudBlobClient();
+
+            StreamWriter responseWriter = null;
+            switch (dataFormat)
+            {
+                case "json":
+                    responseWriter = new StreamWriter(Response.OutputStream, Encoding.UTF8);
+                    break;
+                case "vw":
+                    var settingsBlobContainer = blobClient.GetContainerReference(ApplicationBlobConstants.SettingsContainerName);
+                    var blob = settingsBlobContainer.GetBlockBlobReference(ApplicationBlobConstants.LatestClientSettingsBlobName);
+                    if (!await blob.ExistsAsync())
+                    {
+                        return new HttpStatusCodeResult(HttpStatusCode.InternalServerError, "Application settings blob not found.");
+                    }
+                    ApplicationClientMetadata clientMeta = JsonConvert.DeserializeObject<ApplicationClientMetadata>(await blob.DownloadTextAsync());
+                    responseWriter = new VowpalWabbitStreamWriter(Response.OutputStream, Encoding.UTF8, clientMeta.TrainArguments);
+                    break;
+                default:
+                    return new HttpStatusCodeResult(HttpStatusCode.BadRequest, "Unrecognized data format.");
+            }
+
+            using (responseWriter)
             {
                 await AzureBlobDownloader.Download(
                     storageAccount,