Fix SevenZipReader to iterate entries as contiguous streams

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>

src/SharpCompress/Archives/SevenZip/SevenZipArchive.cs

@@ -216,6 +216,9 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
     {
         private readonly SevenZipArchive _archive;
         private SevenZipEntry? _currentEntry;
+        private Stream? _currentFolderStream;
+        private CFolder? _currentFolder;
+        private int _currentFolderIndex = -1;
 
         internal SevenZipReader(ReaderOptions readerOptions, SevenZipArchive archive)
             : base(readerOptions, ArchiveType.SevenZip) => this._archive = archive;
@@ -231,9 +234,10 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
                 _currentEntry = dir;
                 yield return dir;
             }
-            // For non-directory entries, yield them without creating shared streams
-            // Each call to GetEntryStream() will create a fresh decompression stream
-            // to avoid state corruption issues with async operations
+            // For solid archives (entries in the same folder share a compressed stream),
+            // we must iterate entries sequentially and maintain the folder stream state
+            // across entries in the same folder to avoid recreating the decompression
+            // stream for each file, which breaks contiguous streaming.
             foreach (var entry in entries.Where(x => !x.IsDirectory))
             {
                 _currentEntry = entry;
@@ -243,19 +247,47 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
 
         protected override EntryStream GetEntryStream()
         {
-            // Create a fresh decompression stream for each file (no state sharing).
-            // However, the LZMA decoder has bugs in its async implementation that cause
-            // state corruption even on fresh streams. The SyncOnlyStream wrapper
-            // works around these bugs by forcing async operations to use sync equivalents.
-            //
-            // TODO: Fix the LZMA decoder async bugs (in LzmaStream, Decoder, OutWindow)
-            // so this wrapper is no longer necessary.
             var entry = _currentEntry.NotNull("currentEntry is not null");
             if (entry.IsDirectory)
             {
                 return CreateEntryStream(Stream.Null);
             }
-            return CreateEntryStream(new SyncOnlyStream(entry.FilePart.GetCompressedStream()));
+
+            var folder = entry.FilePart.Folder;
+
+            // Check if we're starting a new folder - dispose old folder stream if needed
+            if (folder != _currentFolder)
+            {
+                _currentFolderStream?.Dispose();
+                _currentFolderStream = null;
+                _currentFolder = folder;
+                _currentFolderIndex = _archive._database!._folders.IndexOf(folder!);
+            }
+
+            // Create the folder stream once per folder
+            if (_currentFolderStream is null)
+            {
+                _currentFolderStream = _archive._database!.GetFolderStream(
+                    _archive.Volumes.Single().Stream,
+                    folder!,
+                    _archive._database.PasswordProvider
+                );
+            }
+
+            // Wrap with SyncOnlyStream to work around LZMA async bugs
+            // Return a ReadOnlySubStream that reads from the shared folder stream
+            return CreateEntryStream(
+                new SyncOnlyStream(
+                    new ReadOnlySubStream(_currentFolderStream, entry.Size, leaveOpen: true)
+                )
+            );
+        }
+
+        public override void Dispose()
+        {
+            _currentFolderStream?.Dispose();
+            _currentFolderStream = null;
+            base.Dispose();
         }
     }
 

tests/SharpCompress.Test/SevenZip/SevenZipArchiveTests.cs

@@ -251,4 +251,28 @@ public class SevenZipArchiveTests : ArchiveTests
         );
         Assert.False(nonSolidArchive.IsSolid);
     }
+
+    [Fact]
+    public void SevenZipArchive_Solid_ExtractAllEntries_Contiguous()
+    {
+        // This test verifies that solid archives iterate entries as contiguous streams
+        // rather than recreating the decompression stream for each entry
+        var testArchive = Path.Combine(TEST_ARCHIVES_PATH, "7Zip.solid.7z");
+        using var archive = SevenZipArchive.Open(testArchive);
+        Assert.True(archive.IsSolid);
+
+        using var reader = archive.ExtractAllEntries();
+        while (reader.MoveToNextEntry())
+        {
+            if (!reader.Entry.IsDirectory)
+            {
+                reader.WriteEntryToDirectory(
+                    SCRATCH_FILES_PATH,
+                    new ExtractionOptions { ExtractFullPath = true, Overwrite = true }
+                );
+            }
+        }
+
+        VerifyFiles();
+    }
 }

tests/SharpCompress.Test/packages.lock.json

@@ -29,6 +29,12 @@
           "Microsoft.NETFramework.ReferenceAssemblies.net48": "1.0.3"
         }
       },
+      "Mono.Posix.NETStandard": {
+        "type": "Direct",
+        "requested": "[1.0.0, )",
+        "resolved": "1.0.0",
+        "contentHash": "vSN/L1uaVwKsiLa95bYu2SGkF0iY3xMblTfxc8alSziPuVfJpj3geVqHGAA75J7cZkMuKpFVikz82Lo6y6LLdA=="
+      },
       "xunit": {
         "type": "Direct",
         "requested": "[2.9.3, )",
@@ -216,6 +222,12 @@
           "Microsoft.NETFramework.ReferenceAssemblies.net461": "1.0.3"
         }
       },
+      "Mono.Posix.NETStandard": {
+        "type": "Direct",
+        "requested": "[1.0.0, )",
+        "resolved": "1.0.0",
+        "contentHash": "vSN/L1uaVwKsiLa95bYu2SGkF0iY3xMblTfxc8alSziPuVfJpj3geVqHGAA75J7cZkMuKpFVikz82Lo6y6LLdA=="
+      },
       "xunit": {
         "type": "Direct",
         "requested": "[2.9.3, )",