Don't pointlessly make copies of every file when verifying. (#225)

DepotDownloader/ContentDownloader.cs

@@ -1067,7 +1067,8 @@ namespace DepotDownloader
                 {
                     neededChunks = new List<ProtoManifest.ChunkData>();
 
-                    if (Config.VerifyAll || !oldManifestFile.FileHash.SequenceEqual(file.FileHash))
+                    var hashMatches = oldManifestFile.FileHash.SequenceEqual(file.FileHash);
+                    if (Config.VerifyAll || !hashMatches)
                     {
                         // we have a version of this file, but it doesn't fully match what we want
                         if (Config.VerifyAll)
@@ -1092,8 +1093,35 @@ namespace DepotDownloader
 
                         var orderedChunks = matchingChunks.OrderBy(x => x.OldChunk.Offset);
 
+                        var copyChunks = new List<ChunkMatch>();
+
+                        using (var fsOld = File.Open(fileFinalPath, FileMode.Open))
+                        {
+                            foreach (var match in orderedChunks)
+                            {
+                                fsOld.Seek((long)match.OldChunk.Offset, SeekOrigin.Begin);
+
+                                byte[] tmp = new byte[match.OldChunk.UncompressedLength];
+                                fsOld.Read(tmp, 0, tmp.Length);
+
+                                byte[] adler = Util.AdlerHash(tmp);
+                                if (!adler.SequenceEqual(match.OldChunk.Checksum))
+                                {
+                                    neededChunks.Add(match.NewChunk);
+                                }
+                                else
+                                {
+                                    copyChunks.Add(match);
+                                }
+                            }
+                        }
+
+                        if (!hashMatches || neededChunks.Count > 0)
+                        {
                             File.Move(fileFinalPath, fileStagingPath);
 
+                            using (var fsOld = File.Open(fileStagingPath, FileMode.Open))
+                            {
                                 fs = File.Open(fileFinalPath, FileMode.Create);
                                 try
                                 {
@@ -1104,31 +1132,22 @@ namespace DepotDownloader
                                     throw new ContentDownloaderException(String.Format("Failed to resize file to expected size {0}: {1}", fileFinalPath, ex.Message));
                                 }
 
-                        using (var fsOld = File.Open(fileStagingPath, FileMode.Open))
+                                foreach (var match in copyChunks)
-                        {
-                            foreach (var match in orderedChunks)
                                 {
                                     fsOld.Seek((long)match.OldChunk.Offset, SeekOrigin.Begin);
 
                                     byte[] tmp = new byte[match.OldChunk.UncompressedLength];
                                     fsOld.Read(tmp, 0, tmp.Length);
 
-                                byte[] adler = Util.AdlerHash(tmp);
-                                if (!adler.SequenceEqual(match.OldChunk.Checksum))
-                                {
-                                    neededChunks.Add(match.NewChunk);
-                                }
-                                else
-                                {
                                     fs.Seek((long)match.NewChunk.Offset, SeekOrigin.Begin);
                                     fs.Write(tmp, 0, tmp.Length);
                                 }
                             }
-                        }
 
                             File.Delete(fileStagingPath);
                         }
                     }
+                }
                 else
                 {
                     // No old manifest or file not in old manifest. We must validate.