Fix opening decrypted NCAs

Fixes an issue where the decrypted NCA could be incorrect if the first section didn't start at offset 0x4000

src/LibHac/IO/ConcatenationStorageBuilder.cs

@@ -0,0 +1,63 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace LibHac.IO
+{
+    public class ConcatenationStorageBuilder
+    {
+        private List<ConcatenationStorageSegment> Segments { get; }
+
+        public ConcatenationStorageBuilder()
+        {
+            Segments = new List<ConcatenationStorageSegment>();
+        }
+
+        public ConcatenationStorageBuilder(IEnumerable<ConcatenationStorageSegment> segments)
+        {
+            Segments = segments.ToList();
+        }
+
+        public void Add(IStorage storage, long offset)
+        {
+            Segments.Add(new ConcatenationStorageSegment(storage, offset));
+        }
+
+        public ConcatenationStorage Build()
+        {
+            List<ConcatenationStorageSegment> segments = Segments.OrderBy(x => x.Offset).ToList();
+            var sources = new List<IStorage>();
+
+            long offset = 0;
+
+            foreach (ConcatenationStorageSegment segment in segments)
+            {
+                long paddingNeeded = segment.Offset - offset;
+
+                if (paddingNeeded < 0) throw new InvalidDataException("Builder has segments that overlap.");
+
+                if (paddingNeeded > 0)
+                {
+                    sources.Add(new NullStorage(paddingNeeded));
+                }
+
+                sources.Add(segment.Storage);
+                offset = segment.Offset + segment.Storage.Length;
+            }
+
+            return new ConcatenationStorage(sources, true);
+        }
+    }
+
+    public class ConcatenationStorageSegment
+    {
+        public IStorage Storage { get; }
+        public long Offset { get; }
+
+        public ConcatenationStorageSegment(IStorage storage, long offset)
+        {
+            Storage = storage;
+            Offset = offset;
+        }
+    }
+}

src/LibHac/IO/NcaUtils/Nca.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using LibHac.IO.RomFs;
@@ -314,14 +313,15 @@ namespace LibHac.IO.NcaUtils
 
         public IStorage OpenDecryptedNca()
         {
-            var list = new List<IStorage> { OpenHeaderStorage() };
+            var builder = new ConcatenationStorageBuilder();
+            builder.Add(OpenHeaderStorage(), 0);
 
-            foreach (NcaSection section in Sections.Where(x => x != null).OrderBy(x => x.Offset))
+            foreach (NcaSection section in Sections.Where(x => x != null))
             {
-                list.Add(OpenRawStorage(section.SectionNum));
+                builder.Add(OpenRawStorage(section.SectionNum), section.Offset);
             }
 
-            return new ConcatenationStorage(list, true);
+            return builder.Build();
         }
 
         private NcaHeader DecryptHeader()
@@ -336,11 +336,13 @@ namespace LibHac.IO.NcaUtils
 
         private CachedStorage OpenHeaderStorage()
         {
-            int size = 0x4000;
+            long size = 0xc00;
 
-            // Support reading headers that are only 0xC00 bytes long, but still return
+            // Encrypted portion continues until the first section
-            // the entire header if available.
+            if (Sections.Any(x => x != null))
-            if (BaseStorage.Length >= 0xC00 && BaseStorage.Length < 0x4000) size = 0xC00;
+            {
+                size = Sections.Where(x => x != null).Min(x => x.Offset);
+            }
 
             return new CachedStorage(new Aes128XtsStorage(BaseStorage.Slice(0, size), Keyset.HeaderKey, 0x200, true), 1, true);
         }

src/LibHac/IO/NcaUtils/NcaExtensions.cs

@@ -4,13 +4,15 @@ namespace LibHac.IO.NcaUtils
 {
     public static class NcaExtensions
     {
-        public static IStorage OpenStorage(this Nca nca, int index, IntegrityCheckLevel integrityCheckLevel, bool openRaw)
+        public static IStorage OpenStorage(this Nca nca, int index, IntegrityCheckLevel integrityCheckLevel,
+            bool openRaw)
         {
             if (openRaw) return nca.OpenRawStorage(index);
             return nca.OpenStorage(index, integrityCheckLevel);
         }
 
-        public static IStorage OpenStorage(this Nca nca, NcaSectionType type, IntegrityCheckLevel integrityCheckLevel, bool openRaw)
+        public static IStorage OpenStorage(this Nca nca, NcaSectionType type, IntegrityCheckLevel integrityCheckLevel,
+            bool openRaw)
         {
             if (openRaw) return nca.OpenRawStorage(type);
             return nca.OpenStorage(type, integrityCheckLevel);
@@ -23,7 +25,8 @@ namespace LibHac.IO.NcaUtils
                 .WriteAllBytes(filename, logger);
         }
 
-        public static void ExtractSection(this Nca nca, int index, string outputDir, IntegrityCheckLevel integrityCheckLevel = IntegrityCheckLevel.None, IProgressReport logger = null)
+        public static void ExtractSection(this Nca nca, int index, string outputDir,
+            IntegrityCheckLevel integrityCheckLevel = IntegrityCheckLevel.None, IProgressReport logger = null)
         {
             if (index < 0 || index > 3) throw new IndexOutOfRangeException();
             if (!nca.SectionIsDecryptable(index)) return;
@@ -55,7 +58,8 @@ namespace LibHac.IO.NcaUtils
             NcaHashType hashType = sect.Header.HashType;
             if (hashType != NcaHashType.Sha256 && hashType != NcaHashType.Ivfc) return Validity.Unchecked;
 
-            var stream = nca.OpenStorage(index, IntegrityCheckLevel.IgnoreOnInvalid, false) as HierarchicalIntegrityVerificationStorage;
+            var stream = nca.OpenStorage(index, IntegrityCheckLevel.IgnoreOnInvalid, false)
+                as HierarchicalIntegrityVerificationStorage;
             if (stream == null) return Validity.Unchecked;
 
             if (!quiet) logger?.LogMessage($"Verifying section {index}...");