preprocess mods through Mono.Cecil to allow rewriting later (#166)

1 files changed, 65 insertions, 0 deletions

diff --git a/src/StardewModdingAPI/Framework/ModAssemblyLoader.cs b/src/StardewModdingAPI/Framework/ModAssemblyLoader.cs
new file mode 100644
index 00000000..2615e1f7
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/ModAssemblyLoader.cs
@@ -0,0 +1,65 @@
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Security.Cryptography;
+using Mono.Cecil;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>Loads mod assemblies.</summary>
+    internal class ModAssemblyLoader
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The directory in which to cache data.</summary>
+        private readonly string CacheDirPath;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="cacheDirPath">The cache directory.</param>
+        public ModAssemblyLoader(string cacheDirPath)
+        {
+            this.CacheDirPath = cacheDirPath;
+        }
+
+        /// <summary>Read an assembly from the given path.</summary>
+        /// <param name="assemblyPath">The assembly file path.</param>
+        public Assembly ProcessAssembly(string assemblyPath)
+        {
+            // read assembly data
+            byte[] assemblyBytes = File.ReadAllBytes(assemblyPath);
+            byte[] hash = MD5.Create().ComputeHash(assemblyBytes);
+
+            // get cache data
+            string key = Path.GetFileNameWithoutExtension(assemblyPath);
+            string cachePath = Path.Combine(this.CacheDirPath, $"{key}.dll");
+            string cacheHashPath = Path.Combine(this.CacheDirPath, $"{key}-hash.txt");
+            bool canUseCache = File.Exists(cachePath) && File.Exists(cacheHashPath) && hash.SequenceEqual(File.ReadAllBytes(cacheHashPath));
+
+            // process assembly if not cached
+            if (!canUseCache)
+            {
+                // read assembly definition
+                AssemblyDefinition definition;
+                using (Stream readStream = new MemoryStream(assemblyBytes))
+                    definition = AssemblyDefinition.ReadAssembly(readStream);
+
+                // write cache
+                using (MemoryStream outStream = new MemoryStream())
+                {
+                    definition.Write(outStream);
+                    byte[] outBytes = outStream.ToArray();
+                    File.WriteAllBytes(cachePath, outBytes);
+                    File.WriteAllBytes(cacheHashPath, hash);
+                }
+            }
+
+            // load assembly
+            return Assembly.UnsafeLoadFrom(cachePath);
+        }
+    }
+}