Seekable stream for cloud blobs (#6719)

* Added OpenReadStreamAsync to ISimpleCloudBlob to enable seekable reading from the blob storage.

* null check

Author: agr

src/NuGetGallery.Core/Services/CloudBlobWrapper.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Net;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.WindowsAzure.Storage;
 using Microsoft.WindowsAzure.Storage.Blob;
@@ -29,6 +30,22 @@ public CloudBlobWrapper(CloudBlockBlob blob)
             _blob = blob;
         }
 
+        public static CloudBlobWrapper FromUri(Uri uri)
+        {
+            if (uri == null)
+            {
+                throw new ArgumentNullException(nameof(uri));
+            }
+
+            if (!IsBlobStorageUri(uri))
+            {
+                throw new ArgumentException($"{nameof(uri)} must point to blob storage", nameof(uri));
+            }
+
+            var blob = new CloudBlockBlob(uri);
+            return new CloudBlobWrapper(blob);
+        }
+
         public async Task<Stream> OpenReadAsync(AccessCondition accessCondition)
         {
             return await _blob.OpenReadAsync(
@@ -141,6 +158,28 @@ await _blob.StartCopyAsync(
                 operationContext: null);
         }
 
+        public async Task<Stream> OpenReadStreamAsync(
+            TimeSpan serverTimeout,
+            TimeSpan maxExecutionTime,
+            CancellationToken cancellationToken)
+        {
+            var accessCondition = AccessCondition.GenerateEmptyCondition();
+            var blobRequestOptions = new BlobRequestOptions
+            {
+                ServerTimeout = serverTimeout,
+                MaximumExecutionTime = maxExecutionTime,
+                RetryPolicy = new ExponentialRetry(),
+            };
+            var operationContext = new OperationContext();
+
+            return await _blob.OpenReadAsync(accessCondition, blobRequestOptions, operationContext, cancellationToken);
+        }
+
+        private static bool IsBlobStorageUri(Uri uri)
+        {
+            return uri.Authority.EndsWith(".blob.core.windows.net");
+        }
+
         // The default retry policy treats a 304 as an error that requires a retry. We don't want that!
         private class DontRetryOnNotModifiedPolicy : IRetryPolicy
         {

src/NuGetGallery.Core/Services/ISimpleCloudBlob.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.WindowsAzure.Storage;
 using Microsoft.WindowsAzure.Storage.Blob;
@@ -50,5 +51,17 @@ public interface ISimpleCloudBlob
         /// </param>
         /// <returns>Shared access signature in form of URI query portion.</returns>
         string GetSharedAccessSignature(SharedAccessBlobPermissions permissions, DateTimeOffset? endOfAccess);
+
+        /// <summary>
+        /// Opens the seekable read stream to the file in blob storage.
+        /// </summary>
+        /// <param name="serverTimeout">Timeout for a single HTTP request issued by implementation. See <see cref="BlobRequestOptions.ServerTimeout"/>.</param>
+        /// <param name="maxExecutionTime">Total timeout accross all potential retries. See <see cref="BlobRequestOptions.MaximumExecutionTime"/>.</param>
+        /// <param name="cancellationToken">Cancellation token.</param>
+        /// <returns>Read stream for a blob in blob storage.</returns>
+        Task<Stream> OpenReadStreamAsync(
+            TimeSpan serverTimeout,
+            TimeSpan maxExecutionTime,
+            CancellationToken cancellationToken);
     }
 }