added support for 7zip SFX archives by handling ReaderOptions.LookForHeader

src/SharpCompress/Archives/ArchiveFactory.cs

@@ -239,4 +239,6 @@ public static class ArchiveFactory
             }
         }
     }
+
+    public static IArchiveFactory AutoFactory { get; } = new AutoArchiveFactory();
 }

src/SharpCompress/Archives/AutoArchiveFactory.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using SharpCompress.Common;
+using SharpCompress.Readers;
+
+namespace SharpCompress.Archives;
+
+class AutoArchiveFactory : IArchiveFactory
+{
+    public string Name => nameof(AutoArchiveFactory);
+
+    public ArchiveType? KnownArchiveType => null;
+
+    public IEnumerable<string> GetSupportedExtensions() => throw new NotSupportedException();
+
+    public bool IsArchive(Stream stream, string? password = null) =>
+        throw new NotSupportedException();
+
+    public FileInfo? GetFilePart(int index, FileInfo part1) => throw new NotSupportedException();
+
+    public IArchive Open(Stream stream, ReaderOptions? readerOptions = null) =>
+        ArchiveFactory.Open(stream, readerOptions);
+
+    public IArchive Open(FileInfo fileInfo, ReaderOptions? readerOptions = null) =>
+        ArchiveFactory.Open(fileInfo, readerOptions);
+}

src/SharpCompress/Archives/SevenZip/SevenZipArchive.cs

@@ -163,7 +163,7 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
         {
             stream.Position = 0;
             var reader = new ArchiveReader();
-            reader.Open(stream);
+            reader.Open(stream, lookForHeader: ReaderOptions.LookForHeader);
             _database = reader.ReadDatabase(new PasswordProvider(ReaderOptions.Password));
         }
     }

src/SharpCompress/Common/SevenZip/ArchiveReader.cs

@@ -1220,23 +1220,46 @@ internal class ArchiveReader
 
     #region Public Methods
 
-    public void Open(Stream stream)
+    public void Open(Stream stream, bool lookForHeader)
     {
         Close();
 
         _streamOrigin = stream.Position;
         _streamEnding = stream.Length;
 
-        // TODO: Check Signature!
-        _header = new byte[0x20];
-        for (var offset = 0; offset < 0x20; )
+        var canScan = lookForHeader ? 0x80000 - 20 : 0;
+        while (true)
         {
-            var delta = stream.Read(_header, offset, 0x20 - offset);
-            if (delta == 0)
+            // TODO: Check Signature!
+            _header = new byte[0x20];
+            for (var offset = 0; offset < 0x20; )
             {
-                throw new EndOfStreamException();
+                var delta = stream.Read(_header, offset, 0x20 - offset);
+                if (delta == 0)
+                {
+                    throw new EndOfStreamException();
+                }
+
+                offset += delta;
             }
-            offset += delta;
+
+            if (
+                !lookForHeader
+                || _header
+                    .AsSpan(0, length: 6)
+                    .SequenceEqual<byte>([0x37, 0x7A, 0xBC, 0xAF, 0x27, 0x1C])
+            )
+            {
+                break;
+            }
+
+            if (canScan == 0)
+            {
+                throw new InvalidFormatException("Unable to find 7z signature");
+            }
+
+            canScan--;
+            stream.Position = ++_streamOrigin;
         }
 
         _stream = stream;

tests/SharpCompress.Test/ArchiveTests.cs

@@ -73,27 +73,45 @@ public class ArchiveTests : ReaderTests
         }
     }
 
-    protected void ArchiveStreamRead(string testArchive, ReaderOptions? readerOptions = null)
+    protected void ArchiveStreamRead(string testArchive, ReaderOptions? readerOptions = null) =>
+        ArchiveStreamRead(ArchiveFactory.AutoFactory, testArchive, readerOptions);
+
+    protected void ArchiveStreamRead(
+        IArchiveFactory archiveFactory,
+        string testArchive,
+        ReaderOptions? readerOptions = null
+    )
     {
         testArchive = Path.Combine(TEST_ARCHIVES_PATH, testArchive);
-        ArchiveStreamRead(readerOptions, testArchive);
+        ArchiveStreamRead(archiveFactory, readerOptions, testArchive);
     }
 
     protected void ArchiveStreamRead(
         ReaderOptions? readerOptions = null,
         params string[] testArchives
+    ) => ArchiveStreamRead(ArchiveFactory.AutoFactory, readerOptions, testArchives);
+
+    protected void ArchiveStreamRead(
+        IArchiveFactory archiveFactory,
+        ReaderOptions? readerOptions = null,
+        params string[] testArchives
     ) =>
         ArchiveStreamRead(
+            archiveFactory,
             readerOptions,
             testArchives.Select(x => Path.Combine(TEST_ARCHIVES_PATH, x))
         );
 
-    protected void ArchiveStreamRead(ReaderOptions? readerOptions, IEnumerable<string> testArchives)
+    protected void ArchiveStreamRead(
+        IArchiveFactory archiveFactory,
+        ReaderOptions? readerOptions,
+        IEnumerable<string> testArchives
+    )
     {
         foreach (var path in testArchives)
         {
             using (var stream = NonDisposingStream.Create(File.OpenRead(path), true))
-            using (var archive = ArchiveFactory.Open(stream, readerOptions))
+            using (var archive = archiveFactory.Open(stream, readerOptions))
             {
                 try
                 {
@@ -218,10 +236,14 @@ public class ArchiveTests : ReaderTests
         }
     }
 
-    protected void ArchiveFileRead(string testArchive, ReaderOptions? readerOptions = null)
+    protected void ArchiveFileRead(
+        IArchiveFactory archiveFactory,
+        string testArchive,
+        ReaderOptions? readerOptions = null
+    )
     {
         testArchive = Path.Combine(TEST_ARCHIVES_PATH, testArchive);
-        using (var archive = ArchiveFactory.Open(testArchive, readerOptions))
+        using (var archive = archiveFactory.Open(new FileInfo(testArchive), readerOptions))
         {
             foreach (var entry in archive.Entries.Where(entry => !entry.IsDirectory))
             {
@@ -234,6 +256,9 @@ public class ArchiveTests : ReaderTests
         VerifyFiles();
     }
 
+    protected void ArchiveFileRead(string testArchive, ReaderOptions? readerOptions = null) =>
+        ArchiveFileRead(ArchiveFactory.AutoFactory, testArchive, readerOptions);
+
     protected void ArchiveFileSkip(
         string testArchive,
         string fileOrder,

tests/SharpCompress.Test/SevenZip/SevenZipArchiveTests.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using SharpCompress.Archives;
 using SharpCompress.Archives.SevenZip;
 using SharpCompress.Common;
+using SharpCompress.Factories;
 using SharpCompress.Readers;
 using Xunit;
 
@@ -54,6 +55,14 @@ public class SevenZipArchiveTests : ArchiveTests
     [Fact]
     public void SevenZipArchive_LZMA2_PathRead() => ArchiveFileRead("7Zip.LZMA2.7z");
 
+    [Fact]
+    public void SevenZipArchive_LZMA2_EXE_StreamRead() =>
+        ArchiveStreamRead(new SevenZipFactory(), "7Zip.LZMA2.exe", new() { LookForHeader = true });
+
+    [Fact]
+    public void SevenZipArchive_LZMA2_EXE_PathRead() =>
+        ArchiveFileRead(new SevenZipFactory(), "7Zip.LZMA2.exe", new() { LookForHeader = true });
+
     [Fact]
     public void SevenZipArchive_LZMA2AES_StreamRead() =>
         ArchiveStreamRead("7Zip.LZMA2.Aes.7z", new ReaderOptions { Password = "testpassword" });