Added a version to host cache.

In #1021 we require the repository parent (in the case of forked repositories) - this data is returned from the API but wasn't getting stored in our cache, meaning that we have invalid data when data is returned from the cache as opposed to from the API.

This adds a `cacheVersion` to host caches. This version is checked when the host cache is first loaded, and if it doesn't match the expected version, the cache is invalidated. In this way each time we make a change as required by #1021 we can bump `HostCacheFactory.CacheVersion` to ensure the cache won't be returning invalid data.

Author: grokys

src/GitHub.App/Factories/HostCacheFactory.cs

@@ -1,17 +1,22 @@
 using System;
 using System.ComponentModel.Composition;
 using System.IO;
+using System.Reactive.Linq;
 using Akavache;
 using GitHub.Primitives;
 using Rothko;
 using GitHub.Extensions;
+using System.Threading.Tasks;
 
 namespace GitHub.Factories
 {
     [Export(typeof(IHostCacheFactory))]
     [PartCreationPolicy(CreationPolicy.Shared)]
     public class HostCacheFactory : IHostCacheFactory
     {
+        const int CacheVersion = 1;
+        const string CacheVersionKey = "cacheVersion";
+
         readonly Lazy<IBlobCacheFactory> blobCacheFactory;
         readonly Lazy<IOperatingSystem> operatingSystem;
 
@@ -22,7 +27,7 @@ public HostCacheFactory(Lazy<IBlobCacheFactory> blobCacheFactory, Lazy<IOperatin
             this.operatingSystem = operatingSystem;
         }
 
-        public IBlobCache Create(HostAddress hostAddress)
+        public async Task<IBlobCache> Create(HostAddress hostAddress)
         {
             var environment = OperatingSystem.Environment;
             // For GitHub.com, the cache file name should be "api.github.com.cache.db"
@@ -34,7 +39,17 @@ public IBlobCache Create(HostAddress hostAddress)
 
             // CreateDirectory is a noop if the directory already exists.
             OperatingSystem.Directory.CreateDirectory(Path.GetDirectoryName(userAccountPath));
-            return BlobCacheFactory.CreateBlobCache(userAccountPath);
+
+            var cache = BlobCacheFactory.CreateBlobCache(userAccountPath);
+            var version = await cache.GetOrCreateObject<int>(CacheVersionKey, () => 0);
+
+            if (version != CacheVersion)
+            {
+                await cache.InvalidateAll();
+                await cache.InsertObject(CacheVersionKey, CacheVersion);
+            }
+
+            return cache;
         }
 
         IOperatingSystem OperatingSystem { get { return operatingSystem.Value; } }

src/GitHub.App/Factories/IHostCacheFactory.cs

@@ -1,11 +1,12 @@
 using Akavache;
 using GitHub.Primitives;
 using System;
+using System.Threading.Tasks;
 
 namespace GitHub.Factories
 {
     public interface IHostCacheFactory : IDisposable
     {
-        IBlobCache Create(HostAddress hostAddress);
+        Task<IBlobCache> Create(HostAddress hostAddress);
     }
 }

src/GitHub.App/Factories/RepositoryHostFactory.cs

@@ -44,7 +44,7 @@ public RepositoryHostFactory(
         public async Task<IRepositoryHost> Create(HostAddress hostAddress)
         {
             var apiClient = await apiClientFactory.Create(hostAddress);
-            var hostCache = hostCacheFactory.Create(hostAddress);
+            var hostCache = await hostCacheFactory.Create(hostAddress);
             var modelService = new ModelService(apiClient, hostCache, avatarProvider);
             var host = new RepositoryHost(apiClient, modelService, loginManager, loginCache, usage);
             hosts.Add(host);