Upload checksums for installation artifacts (#4191)

The checksums are SHA-512 hashes, which users can use to verify file
integrity and authenticity.

build_projects/dotnet-cli-build/CopyBlobsToLatest.cs

@@ -0,0 +1,108 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class CopyBlobsToLatest : Task
+    {
+        private AzurePublisher _azurePublisher;
+
+        [Required]
+        public string AccountName { get; set; }
+
+        [Required]
+        public string AccountKey { get; set; }
+
+        [Required]
+        public string Channel { get; set; }
+
+        [Required]
+        public string CommitHash { get; set; }
+
+        [Required]
+        public string ContainerName { get; set; }
+
+        [Required]
+        public string NugetVersion { get; set; }
+
+        private AzurePublisher AzurePublisherTool
+        {
+            get
+            {
+                if (_azurePublisher == null)
+                {
+                    _azurePublisher = new AzurePublisher(AccountName, AccountKey, ContainerName);
+                }
+
+                return _azurePublisher;
+            }
+        }
+
+        public override bool Execute()
+        {
+            string targetFolder = $"{AzurePublisher.Product.Sdk}/{Channel}";
+
+            string targetVersionFile = $"{targetFolder}/{CommitHash}";
+            string semaphoreBlob = $"{targetFolder}/publishSemaphore";
+            AzurePublisherTool.CreateBlobIfNotExists(semaphoreBlob);
+            string leaseId = AzurePublisherTool.AcquireLeaseOnBlob(semaphoreBlob);
+
+            // Prevent race conditions by dropping a version hint of what version this is. If we see this file
+            // and it is the same as our version then we know that a race happened where two+ builds finished 
+            // at the same time and someone already took care of publishing and we have no work to do.
+            if (AzurePublisherTool.IsLatestSpecifiedVersion(targetVersionFile))
+            {
+                AzurePublisherTool.ReleaseLeaseOnBlob(semaphoreBlob, leaseId);
+                return true;
+            }
+            else
+            {
+                Regex versionFileRegex = new Regex(@"(?<CommitHash>[\w\d]{40})");
+
+                // Delete old version files
+                AzurePublisherTool.ListBlobs(targetFolder)
+                    .Where(s => versionFileRegex.IsMatch(s))
+                    .ToList()
+                    .ForEach(f => AzurePublisherTool.TryDeleteBlob(f));
+
+                // Drop the version file signaling such for any race-condition builds (see above comment).
+                AzurePublisherTool.DropLatestSpecifiedVersion(targetVersionFile);
+            }
+
+            try
+            {
+                CopyBlobs(targetFolder);
+
+                string cliVersion = Utils.GetVersionFileContent(CommitHash, NugetVersion);
+                AzurePublisherTool.PublishStringToBlob($"{targetFolder}/latest.version", cliVersion);
+            }
+            finally
+            {
+                AzurePublisherTool.ReleaseLeaseOnBlob(semaphoreBlob, leaseId);
+            }
+
+            return true;
+        }
+
+        private void CopyBlobs(string destinationFolder)
+        {
+            Log.LogMessage("Copying blobs to {0}/{1}", ContainerName, destinationFolder);
+
+            foreach (string blob in AzurePublisherTool.ListBlobs(AzurePublisher.Product.Sdk, NugetVersion))
+            {
+                string targetName = Path.GetFileName(blob)
+                                        .Replace(NugetVersion, "latest");
+
+                string target = $"{destinationFolder}/{targetName}";
+
+                AzurePublisherTool.CopyBlob(blob, target);
+            }
+        }
+    }
+}