poc: Try to extract an embedded .msi file

src/LessMsi.Core/Msi/MsiDatabase.cs

@@ -23,6 +23,9 @@
 //	Scott Willeke (scott@willeke.com)
 //
 using Microsoft.Tools.WindowsInstallerXml.Msi;
+using System;
+using System.IO;
+using System.IO.MemoryMappedFiles;
 
 namespace LessMsi.Msi
 {
@@ -53,5 +56,81 @@ public static Database Create(LessIO.Path msiDatabaseFilePath)
 				return new Database(msiDatabaseFilePath.PathString, OpenDatabase.ReadOnly | (OpenDatabase)MSIDBOPEN_PATCHFILE);
 			}
 		}
+
+
+		// 'Magic bytes' that identify the beginning of an 'StgStorage' file, which is the format used by MSI files.
+		static readonly Byte[] STG_STORAGE_magic_bytes = new byte[]{ 0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1 };
+
+		public static bool TryDetectMsiHeader(LessIO.Path filePath, out long offset)
+		{
+			using (var mapped = MemoryMappedFile.CreateFromFile(filePath.PathString, System.IO.FileMode.Open, null, 0L, MemoryMappedFileAccess.Read))
+			{
+				using (var accessor = mapped.CreateViewAccessor(0, 0, MemoryMappedFileAccess.Read))
+				{
+					byte[] buffer = new byte[4096];
+					long readOffset = 0;
+					while (true)
+					{
+						var totalRemaining = accessor.Capacity - readOffset;
+						if (totalRemaining <= 0)
+							break;
+						int remaining = accessor.ReadArray(readOffset, buffer, 0, (int)Math.Min(totalRemaining, buffer.Length));
+
+						bool moveLess = false;
+						for (int n = 0; n < remaining; n++)
+						{
+							if (buffer[n] == STG_STORAGE_magic_bytes[0])
+							{
+								if (buffer.Length - n >= STG_STORAGE_magic_bytes.Length)
+								{
+									bool match = true;
+									for (int m = 1; m < STG_STORAGE_magic_bytes.Length; m++)
+									{
+										if (buffer[n + m] != STG_STORAGE_magic_bytes[m])
+										{
+											match = false;
+											break;
+										}
+									}
+									if (match)
+									{
+										offset = readOffset + n;
+										return true;
+									}
+								}
+								else
+								{
+									moveLess = true;
+									break;
+								}
+							}
+						}
+
+						if (moveLess && remaining > STG_STORAGE_magic_bytes.Length && readOffset > STG_STORAGE_magic_bytes.Length)
+						{
+							readOffset -= STG_STORAGE_magic_bytes.Length;
+						}
+						readOffset += remaining;
+					}
+
+					offset = -1;
+					return false;
+				}
+			}
+		}
+
+		public static void ExtractMsiFromExe(LessIO.Path filePath, LessIO.Path outputFile, long offset)
+		{
+			using (var mapped = MemoryMappedFile.CreateFromFile(filePath.PathString, FileMode.Open, null, 0L, MemoryMappedFileAccess.Read))
+			{
+				using (var reader = mapped.CreateViewStream(offset, 0, MemoryMappedFileAccess.Read))
+				{
+					using (var output = File.Create(outputFile.PathString))
+					{
+						reader.CopyTo(output);
+					}
+				}
+			}
+		}
 	}
 }

src/LessMsi.Gui/IMainFormView.cs

@@ -78,6 +78,11 @@ internal interface IMainFormView
 		/// </summary>
 		void ShowUserError(string formatStr, params object[] args);
         /// <summary>
+        /// Displays a message to the user with a Yes/No question and returns the user's response.
+        /// </summary>
+        /// <param name="message">The message to display to the user.</param>
+        bool ShowUserMessageQuestionYesNo(string message);
+        /// <summary>
         /// Adds a column to the MSI table grid.
         /// </summary>
         void AddTableViewGridColumn(string headerText);

src/LessMsi.Gui/MainForm.cs

@@ -54,7 +54,7 @@ internal class MainForm : Form, IMainFormView
         private Panel pnlStreamsBottom;
         private Button btnExtractStreamFiles;
         private ToolStripMenuItem searchFileToolStripMenuItem;
-        readonly static string[] AllowedDragDropExtensions = new[] { ".msi", ".msp" };
+        readonly static string[] AllowedDragDropExtensions = new[] { ".msi", ".msp", ".exe" };
 
         public MainForm(string defaultInputFile)
         {
@@ -169,6 +169,12 @@ public void ShowUserError(string formatStr, params object[] args)
             ShowUserMessageBox(string.Format(CultureInfo.CurrentUICulture, formatStr, args));
         }
 
+        public bool ShowUserMessageQuestionYesNo(string message)
+        {
+            return MessageBox.Show(this, message, "LessMSI", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes;
+        }
+
+
         #region MSI Table Grid Stuff
 
         public void AddTableViewGridColumn(string headerText)

src/LessMsi.Gui/MainFormPresenter.cs

@@ -22,19 +22,20 @@
 // Authors:
 //	Scott Willeke (scott@willeke.com)
 //
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Diagnostics;
-using System.IO;
-using System.Linq;
 using LessIO;
 using LessMsi.Gui.Model;
 using LessMsi.Gui.Resources.Languages;
 using LessMsi.Gui.Windows.Forms;
 using LessMsi.Msi;
 using LessMsi.OleStorage;
 using Microsoft.Tools.WindowsInstallerXml.Msi;
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Diagnostics;
+using System.IO;
+using System.IO.MemoryMappedFiles;
+using System.Linq;
 
 namespace LessMsi.Gui
 {
@@ -545,6 +546,16 @@ public void LoadCurrentFile()
 			}
 			catch (Exception eCatchAll)
 			{
+				if (eCatchAll is IOException && this.SelectedMsiFile.Extension.ToLower() == ".exe" && MsiDatabase.TryDetectMsiHeader(new LessIO.Path(this.SelectedMsiFile.FullName), out long offset))
+				{
+					if (View.ShowUserMessageQuestionYesNo("It looks like this file contains a .msi file, do you want to extract it?"))
+					{
+						var tempFile = System.IO.Path.GetTempFileName();
+						MsiDatabase.ExtractMsiFromExe(new LessIO.Path(this.SelectedMsiFile.FullName), new LessIO.Path(tempFile), offset);
+						LoadFile(tempFile);
+						return;
+					}
+				}
 				isBadFile = true;
 				Error(Strings.OpenFileError, eCatchAll);
 			}

src/Lessmsi.Tests/MiscTests.cs

@@ -140,5 +140,27 @@ public void MissingParentDirectoryEntry()
         {
             ExtractAndCompareToMaster("IviNetSharedComponents32_Fx20_1.3.0.msi");
         }
+
+        /// <summary>
+        /// From https://github.com/activescott/lessmsi/pull/237
+        /// </summary>
+        [Fact]
+        public void TryDetectEmbeddedMsi()
+        {
+            const long stg_storage_offset_in_vmware_tools_setup = 0x315E3C;
+            bool containsMsi = Msi.MsiDatabase.TryDetectMsiHeader(GetMsiTestFile("vmware_tools_setup.exe"), out long offset);
+            Assert.True(containsMsi);
+            Assert.Equal(stg_storage_offset_in_vmware_tools_setup, offset);
+
+            const long stg_storage_offset_in_ivinetsharedcomponents_msi = 0;
+            containsMsi = Msi.MsiDatabase.TryDetectMsiHeader(GetMsiTestFile("IviNetSharedComponents32_Fx20_1.3.0.msi"), out offset);
+            Assert.True(containsMsi);
+            Assert.Equal(stg_storage_offset_in_ivinetsharedcomponents_msi, offset);
+
+            const long no_stg_storage_magic_found = -1;
+            containsMsi = Msi.MsiDatabase.TryDetectMsiHeader(GetMsiTestFile("msi_with_external_cab.cab"), out offset);
+            Assert.False(containsMsi);
+            Assert.Equal(no_stg_storage_magic_found, offset);
+        }
     }
 }