Check SHA256 hashes, Significantly improve error handling

- Fixed bug with Trace not writing exceptions due to the file being
  closed.
- Handles invalid hash, network connectivity, and general exceptions
  now.

Closes #7 and #35.

Scarab.Tests/DatabaseTest.cs

@@ -102,6 +102,7 @@ public void Serialization()
                     new Version(3, 0, 0, 0),
                     new[] { "Vasi" },
                     "https://github.com/fifty-six/HollowKnight.QoL/releases/download/v3/QoL.zip",
+                    string.Empty,
                     "QoL",
                     "A collection of various quality of life improvements."
                 ),

Scarab.Tests/ModSourceTest.cs

@@ -30,6 +30,7 @@ public async Task Record()
                 new Version("1.3.2.2"),
                 Array.Empty<string>(),
                 string.Empty,
+                string.Empty,
                 "test",
                 "test"
             );

Scarab/Interfaces/IModDatabase.cs

@@ -7,6 +7,6 @@ public interface IModDatabase
     {
         IEnumerable<ModItem> Items { get; }
 
-        (string Url, int Version) Api { get; }
+        (string Url, int Version, string SHA256) Api { get; }
     }
 }

Scarab/Models/ModItem.cs

@@ -16,12 +16,14 @@ public ModItem
             Version version,
             string[] dependencies,
             string link,
+            string shasum,
             string name,
             string description
         )
         {
             _state = state;
 
+            Sha256 = shasum;
             Version = version;
             Dependencies = dependencies;
             Link = link;
@@ -34,6 +36,7 @@ string description
         public Version  Version          { get; }
         public string[] Dependencies     { get; }
         public string   Link             { get; }
+        public string   Sha256           { get; }
         public string   Name             { get; }
         public string   Description      { get; }
         public string   DependenciesDesc { get; }
@@ -95,30 +98,44 @@ string description
 
         public async Task OnInstall(IInstaller inst, Action<ModProgressArgs> setProgress)
         {
-            if (State is InstalledState(var enabled, var updated))
+            ModState origState = State;
+
+            try
             {
-                // If we're not updated, update
-                if (!updated)
+                if (State is InstalledState(var enabled, var updated))
                 {
-                    await inst.Install(this, setProgress, enabled);
+                    // If we're not updated, update
+                    if (!updated)
+                    {
+                        await inst.Install(this, setProgress, enabled);
+                    }
+                    // Otherwise the user wanted to uninstall.
+                    else
+                    {
+                        await inst.Uninstall(this);
+                    }
                 }
-                // Otherwise the user wanted to uninstall.
                 else
                 {
-                    await inst.Uninstall(this);
-                }
-            }
-            else
-            {
-                State = (NotInstalledState) State with { Installing = true };
+                    State = (NotInstalledState) State with { Installing = true };
 
-                setProgress(new ModProgressArgs());
+                    setProgress(new ModProgressArgs());
 
-                await inst.Install(this, setProgress, true);
+                    await inst.Install(this, setProgress, true);
 
-                setProgress(new ModProgressArgs {
-                    Completed = true
-                });
+                    setProgress
+                    (
+                        new ModProgressArgs
+                        {
+                            Completed = true
+                        }
+                    );
+                }
+            }
+            catch
+            {
+                State = origState;
+                throw;
             }
         }
 

Scarab/Models/ModLinks.cs

@@ -92,17 +92,23 @@ public override string ToString()
                 + "}";
         }
 
-        public string GetOSUrl()
+        public string SHA256 => Environment.OSVersion.Platform switch
         {
-            return Environment.OSVersion.Platform switch
-            {
-                PlatformID.Win32NT => Windows.URL,
-                PlatformID.MacOSX => Mac.URL,
-                PlatformID.Unix => Linux.URL,
-
-                var val => throw new NotSupportedException(val.ToString())
-            };
-        }
+            PlatformID.Win32NT => Windows.SHA256,
+            PlatformID.MacOSX => Mac.SHA256,
+            PlatformID.Unix => Linux.SHA256,
+
+            var val => throw new NotSupportedException(val.ToString())
+        };
+
+        public string OSUrl => Environment.OSVersion.Platform switch
+        {
+            PlatformID.Win32NT => Windows.URL,
+            PlatformID.MacOSX => Mac.URL,
+            PlatformID.Unix => Linux.URL,
+
+            var val => throw new NotSupportedException(val.ToString())
+        };
     }
 
     public class Link
@@ -119,7 +125,7 @@ public override string ToString()
         }
     }
 
-    [Serializable]
+    // [Serializable]
     public class ApiManifest
     {
         public int Version { get; set; }

Scarab/Program.cs

@@ -30,7 +30,7 @@ public static void Main(string[] args)
 
         private static void SetupLogging()
         {
-            using var fileListener = new TextWriterTraceListener
+            var fileListener = new TextWriterTraceListener
             (
                 Path.Combine
                 (
@@ -39,6 +39,8 @@ private static void SetupLogging()
                 )
             );
 
+            fileListener.TraceOutputOptions = TraceOptions.DateTime;
+
             Trace.AutoFlush = true;
 
             Trace.Listeners.Add(fileListener);
@@ -70,7 +72,7 @@ private static void WriteExceptionToLog(Exception e)
             if (Debugger.IsAttached)
                 Debugger.Break();
 
-            Trace.WriteLine($"Caught exception, writing to log: {e.StackTrace}");
+            Trace.TraceError(e.ToString());
 
             File.WriteAllText(dir + $"ModInstaller_Error_{date}.log", e.ToString());
             File.WriteAllText(Path.Combine(Settings.GetOrCreateDirPath(), $"ModInstaller_Error_{date}.log"), e.ToString());

Scarab/Services/Installer.cs

@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Net.Http;
 using System.Net.Http.Headers;
+using System.Security.Cryptography;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Toolkit.HighPerformance;
@@ -15,6 +16,32 @@
 
 namespace Scarab.Services
 {
+    public class HashMismatchException : Exception
+    {
+        /// <summary>
+        /// The SHA256 value that was received
+        /// </summary>
+        public string Actual { get; }
+
+        /// <summary>
+        /// Expected SHA256 value
+        /// </summary>
+        public string Expected { get; }
+
+        /// <summary>
+        ///  The name of the object being checked
+        /// </summary>
+        public string Name { get; }
+
+        public HashMismatchException(string name, string actual, string expected)
+        {
+            Name = name;
+            Actual = actual;
+            Expected = expected;
+        }
+
+    }
+
     public class Installer : IInstaller
     {
         private enum Update
@@ -113,7 +140,7 @@ public async Task InstallApi()
             }
         }
 
-        private async Task _InstallApi((string Url, int Version) manifest)
+        private async Task _InstallApi((string Url, int Version, string SHA256) manifest)
         {
             bool was_vanilla = true;
 
@@ -124,12 +151,14 @@ private async Task _InstallApi((string Url, int Version) manifest)
 
                 was_vanilla = false;
             }
-
-            (string api_url, int ver) = manifest;
+            
+            (string api_url, int ver, string hash) = manifest;
 
             string managed = _config.ManagedFolder;
 
             (ArraySegment<byte> data, string _) = await DownloadFile(api_url, _ => { });
+
+            ThrowIfInvalidHash("the API", data, hash);
 
             // Backup the vanilla assembly
             if (was_vanilla)
@@ -181,6 +210,13 @@ private async Task _ToggleApi(Update update = Update.ForceUpdate)
                 await _InstallApi(_db.Api);
         }
 
+        /// <summary>
+        /// Installs the given mod.
+        /// </summary>
+        /// <param name="mod">Mod to install</param>
+        /// <param name="setProgress">Action called to indicate progress asynchronously</param>
+        /// <param name="enable">Whether the mod is enabled after installation</param>
+        /// <exception cref="HashMismatchException">Thrown if the download doesn't match the given hash</exception>
         public async Task Install(ModItem mod, Action<ModProgressArgs> setProgress, bool enable)
         {
             await InstallApi();
@@ -244,6 +280,8 @@ private async Task _Install(ModItem mod, Action<DownloadProgressArgs> setProgres
 
             var (data, filename) = await DownloadFile(mod.Link, setProgress);
 
+            ThrowIfInvalidHash(mod.Name, data, mod.Sha256);
+
             // Sometimes our filename is quoted, remove those.
             filename = filename.Trim('"');
 
@@ -295,6 +333,18 @@ private async Task _Install(ModItem mod, Action<DownloadProgressArgs> setProgres
             await _installed.RecordInstalledState(mod);
         }
 
+        private static void ThrowIfInvalidHash(string name, ArraySegment<byte> data, string modSha256)
+        {
+            var sha = SHA256.Create();
+
+            byte[] hash = sha.ComputeHash(data.AsMemory().AsStream());
+
+            string strHash = BitConverter.ToString(hash).Replace("-", string.Empty);
+
+            if (!string.Equals(strHash, modSha256, StringComparison.OrdinalIgnoreCase))
+                throw new HashMismatchException(name, actual: strHash, expected: modSha256);
+        }
+
         private async Task<(ArraySegment<byte> data, string filename)> DownloadFile(string uri, Action<DownloadProgressArgs> setProgress)
         {
             (ArraySegment<byte> bytes, HttpResponseMessage response) = await _hc.DownloadBytesWithProgressAsync(

Scarab/Services/ModDatabase.cs

@@ -19,7 +19,7 @@ public class ModDatabase : IModDatabase
         private const string FALLBACK_MODLINKS_URI = "https://cdn.jsdelivr.net/gh/hk-modding/modlinks@latest/ModLinks.xml";
         private const string FALLBACK_APILINKS_URI = "https://cdn.jsdelivr.net/gh/hk-modding/modlinks@latest/ApiLinks.xml";
 
-        public (string Url, int Version) Api { get; }
+        public (string Url, int Version, string SHA256) Api { get; }
 
         public IEnumerable<ModItem> Items => _items;
 
@@ -31,9 +31,10 @@ private ModDatabase(IModSource mods, ModLinks ml, ApiLinks al)
             {
                 var item = new ModItem
                 (
-                    link: mod.Links.GetOSUrl(),
+                    link: mod.Links.OSUrl,
                     version: mod.Version.Value,
                     name: mod.Name,
+                    shasum: mod.Links.SHA256,
                     description: mod.Description,
                     dependencies: mod.Dependencies,
 
@@ -45,7 +46,7 @@ private ModDatabase(IModSource mods, ModLinks ml, ApiLinks al)
 
             _items.Sort((a, b) => string.Compare(a.Name, b.Name));
 
-            Api = (al.Manifest.Links.GetOSUrl(), al.Manifest.Version);
+            Api = (al.Manifest.Links.OSUrl, al.Manifest.Version, al.Manifest.Links.SHA256);
         }
 
         public ModDatabase(IModSource mods, (ModLinks ml, ApiLinks al) links) : this(mods, links.ml, links.al) { }