Add support for MSFZ/PDZ files (#4868)

This adds support for reading MSFZ/PDZ files. MSFZ files are a new
container format for PDB files, which allows for efficient compression
and decompression of small fragments of a file, without decompressing
the entire file.

Co-authored-by: Arlie Davis <[email protected]>

src/Microsoft.FileFormats/PDB/IMSFFile.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.FileFormats.PDB
+{
+    /// <summary>
+    /// An abstraction for reading both MSF (normal PDB files) and MSFZ files (compressed PDB files).
+    /// </summary>
+    internal interface IMSFFile
+    {
+        /// <summary>
+        /// The number of streams stored in the file. This will always be at least 1.
+        /// </summary>
+        uint NumStreams { get; }
+
+        /// <summary>
+        /// Gets an object which can read the given stream.
+        /// </summary>
+        /// <param name="stream">The index of the stream. This must be less than NumStreams.</param>
+        /// <returns>A Reader which can read the stream.</returns>
+        Reader GetStream(uint stream);
+    }
+}

src/Microsoft.FileFormats/PDB/MSFFile.cs

@@ -0,0 +1,71 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.FileFormats.PDB
+{
+    /// <summary>
+    /// This class can read from PDB files that use the MSF container format.
+    /// </summary>
+    internal sealed class MSFFile : IMSFFile
+    {
+        private Reader[] _streams;
+
+        private MSFFile(Reader[] streams)
+        {
+            _streams = streams;
+        }
+
+        internal static MSFFile OpenInternal(Reader fileReader, PDBFileHeader msfFileHeader)
+        {
+            // Read the Stream Directory and build the list of streams.
+
+            uint pageSize = msfFileHeader.PageSize;
+
+            uint secondLevelPageCount = ToPageCount(pageSize, msfFileHeader.DirectorySize);
+            ulong pageIndicesOffset = fileReader.SizeOf<PDBFileHeader>();
+            PDBPagedAddressSpace secondLevelPageList = CreatePagedAddressSpace(fileReader.DataSource, fileReader.DataSource, msfFileHeader.PageSize, pageIndicesOffset, secondLevelPageCount * sizeof(uint));
+            PDBPagedAddressSpace directoryContent = CreatePagedAddressSpace(fileReader.DataSource, secondLevelPageList, msfFileHeader.PageSize, 0, msfFileHeader.DirectorySize);
+
+            Reader directoryReader = new(directoryContent);
+            ulong position = 0;
+            uint countStreams = directoryReader.Read<uint>(ref position);
+            uint[] streamSizes = directoryReader.ReadArray<uint>(ref position, countStreams);
+            Reader[] streams = new Reader[countStreams];
+            for (uint i = 0; i < streamSizes.Length; i++)
+            {
+                uint streamSize = streamSizes[i];
+                streams[i] = new Reader(CreatePagedAddressSpace(fileReader.DataSource, directoryContent, pageSize, position, streamSize));
+                position += ToPageCount(pageSize, streamSizes[i]) * sizeof(uint);
+            }
+
+            return new MSFFile(streams);
+        }
+
+        private static PDBPagedAddressSpace CreatePagedAddressSpace(IAddressSpace fileData, IAddressSpace indicesData, uint pageSize, ulong offset, uint length)
+        {
+            uint[] indices = new Reader(indicesData).ReadArray<uint>(offset, ToPageCount(pageSize, length));
+            return new PDBPagedAddressSpace(fileData, indices, pageSize, length);
+        }
+
+        private static uint ToPageCount(uint pageSize, uint size)
+        {
+            return unchecked((pageSize + size - 1) / pageSize);
+        }
+
+        public uint NumStreams
+        {
+            get
+            {
+                return (uint)_streams.Length;
+            }
+        }
+
+        public Reader GetStream(uint index)
+        {
+            return _streams[index];
+        }
+    }
+}