Zip FileSystem support (#1617)

* #include an absolute path didn't work - because paths were taken to always be relative.

* Add miniz

* Fix for separator in CacheFileSystem.
Add compression unit test for zip.

* Put zip compression into core.

* Remove delimiter stripping if simplifying a path - as stripping will fix delimiters.

* ZipFileSystem WIP.

* More ZipFileSystem working.

* Added isEmpty.
Fixed small bug is contains.

* First pass support for mutability on zip.

* Improvements to File::read/writeAllBytes

* Can access and save archive - but has memory leaks.

* Fix memory leak.

* Some ZIP compression tests.

* Fix memory leak on ScopedAllocation.
Fix off by one bug on UIntSet

* Bug fix in UIntSet

* Fix remaining ZipFileSystem issues.
Adde stand alone unit-test.

* Turn tabs to spaces in slang-io.h

* Renamed mode ReadWrite (instead of just Write)

* Make miniz it's own project.

* Fix windows warning on win32.

* Remove warnings needed when miniz was included as a header library.

* Set the C++ standard via 'flags' in premake.

* Add support for 'implicit' paths.

* Add testing for implicit directories.
Better handling of implicit directories.

* Improve comments in ZipFileSystem.

* Update comment around reader/writer transformation.

7 files changed, 1008 insertions, 22 deletions

diff --git a/source/core/core.vcxproj b/source/core/core.vcxproj
index 063d1aa0b..528c7c590 100644
--- a/source/core/core.vcxproj
+++ b/source/core/core.vcxproj
@@ -216,6 +216,7 @@
     <ClInclude Include="slang-uint-set.h" />
     <ClInclude Include="slang-visual-studio-compiler-util.h" />
     <ClInclude Include="slang-writer.h" />
+    <ClInclude Include="slang-zip-file-system.h" />
     <ClInclude Include="windows\slang-win-visual-studio-util.h" />
   </ItemGroup>
   <ItemGroup>
@@ -249,6 +250,7 @@
     <ClCompile Include="slang-uint-set.cpp" />
     <ClCompile Include="slang-visual-studio-compiler-util.cpp" />
     <ClCompile Include="slang-writer.cpp" />
+    <ClCompile Include="slang-zip-file-system.cpp" />
     <ClCompile Include="windows\slang-win-process-util.cpp" />
     <ClCompile Include="windows\slang-win-visual-studio-util.cpp" />
   </ItemGroup>
diff --git a/source/core/core.vcxproj.filters b/source/core/core.vcxproj.filters
index afae1d124..fc5cede9e 100644
--- a/source/core/core.vcxproj.filters
+++ b/source/core/core.vcxproj.filters
@@ -147,6 +147,9 @@
     <ClInclude Include="slang-writer.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="slang-zip-file-system.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="windows\slang-win-visual-studio-util.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -242,6 +245,9 @@
     <ClCompile Include="slang-writer.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="slang-zip-file-system.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="windows\slang-win-process-util.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
diff --git a/source/core/slang-io.cpp b/source/core/slang-io.cpp
index 8e7266dc5..2e2ec3d8b 100644
--- a/source/core/slang-io.cpp
+++ b/source/core/slang-io.cpp
@@ -832,6 +832,68 @@ namespace Slang
         return _Move(buffer);
     }
 
+    SlangResult File::readAllBytes(const String& path, ScopedAllocation& out)
+    {
+        try
+        {
+            FileStream stream(path, FileMode::Open, FileAccess::Read, FileShare::ReadWrite);
+
+            const Int64 start = stream.getPosition();
+            stream.seek(SeekOrigin::End, 0);
+            const Int64 end = stream.getPosition();
+            stream.seek(SeekOrigin::Start, start);
+
+            const Int64 positionSizeInBytes = end - start;
+
+            if (UInt64(positionSizeInBytes) > UInt64(~size_t(0)))
+            {
+                // It's too large to fit in memory.
+                return SLANG_FAIL;
+            }
+
+            const size_t sizeInBytes = size_t(positionSizeInBytes);
+            void* data = out.allocate(sizeInBytes);
+            if (!data)
+            {
+                return SLANG_E_OUT_OF_MEMORY;
+            }
+
+            const size_t readSizeInBytes = stream.read(data, sizeInBytes);
+
+            // If not all read just return an error
+            if (sizeInBytes != readSizeInBytes)
+            {
+                return SLANG_FAIL;
+            }
+        }
+        catch (const IOException&)
+        {
+            return SLANG_FAIL;
+        }
+        return SLANG_OK;
+    }
+
+    SlangResult File::writeAllBytes(const String& path, const void* data, size_t size)
+    {
+        try
+        {
+            FileStream stream(path, FileMode::Create, FileAccess::Write, FileShare::ReadWrite);
+
+            const size_t writeSizeInBytes = stream.write(data, size);
+
+            // If not all written just return an error
+            if (size != writeSizeInBytes)
+            {
+                return SLANG_FAIL;
+            }
+        }
+        catch (const IOException&)
+        {
+            return SLANG_FAIL;
+        }
+        return SLANG_OK;
+    }
+    
     void File::writeAllText(const Slang::String& fileName, const Slang::String& text)
     {
         StreamWriter writer(new FileStream(fileName, FileMode::Create));
diff --git a/source/core/slang-io.h b/source/core/slang-io.h
index 3a5510566..5a611c445 100644
--- a/source/core/slang-io.h
+++ b/source/core/slang-io.h
@@ -5,26 +5,34 @@
 #include "slang-stream.h"
 #include "slang-text-io.h"
 #include "slang-secure-crt.h"
+#include "slang-blob.h"
 
 namespace Slang
 {
-	class File
-	{
-	public:
-		static bool exists(const String& fileName);
-		static String readAllText(const String& fileName);
-		static List<unsigned char> readAllBytes(const String& fileName);
-		static void writeAllText(const String& fileName, const String& text);
+    class File
+    {
+    public:
+        static bool exists(const String& fileName);
+
+        static String readAllText(const String& fileName);
+
+        static List<unsigned char> readAllBytes(const String& fileName);
+        static SlangResult readAllBytes(const String& fileName, ScopedAllocation& out);
+
+        static void writeAllText(const String& fileName, const String& text);
+
+        static SlangResult writeAllBytes(const String& fileName, const void* data, size_t size);
+        
         static SlangResult remove(const String& fileName);
 
         static SlangResult makeExecutable(const String& fileName);
 
         static SlangResult generateTemporary(const UnownedStringSlice& prefix, String& outFileName);
-	};
+    };
 
-	class Path
-	{
-	public:
+    class Path
+    {
+    public:
 
         enum class Type
         {
@@ -50,7 +58,7 @@ namespace Slang
             virtual void accept(Type type, const UnownedStringSlice& filename) = 0;
         };
 
-		static const char kPathDelimiter = '/';
+        static const char kPathDelimiter = '/';
 
             /// Finds all all the items in the specified directory, that matches the pattern.
             ///
@@ -64,16 +72,16 @@ namespace Slang
             /// Finds the index of the last dot in a path, else returns -1
         static Index findExtIndex(String const& path);
 
-		static String replaceExt(const String& path, const char* newExt);
-		static String getFileName(const String& path);
-		static String getPathWithoutExt(const String& path);
-		static String getPathExt(const String& path);
-		static String getParentDirectory(const String& path);
+        static String replaceExt(const String& path, const char* newExt);
+        static String getFileName(const String& path);
+        static String getPathWithoutExt(const String& path);
+        static String getPathExt(const String& path);
+        static String getParentDirectory(const String& path);
 
         static String getFileNameWithoutExt(const String& path);
 
-		static String combine(const String& path1, const String& path2);
-		static String combine(const String& path1, const String& path2, const String& path3);
+        static String combine(const String& path1, const String& path2);
+        static String combine(const String& path1, const String& path2, const String& path3);
 
             /// Combine path sections and store the result in outBuilder
         static void combineIntoBuilder(const UnownedStringSlice& path1, const UnownedStringSlice& path2, StringBuilder& outBuilder);
@@ -81,7 +89,7 @@ namespace Slang
             /// Append a path, taking into account path separators onto the end of ioBuilder 
         static void append(StringBuilder& ioBuilder, const UnownedStringSlice& path);
 
-		static bool createDirectory(const String& path);
+        static bool createDirectory(const String& path);
 
             /// Accept either style of delimiter
         SLANG_FORCE_INLINE static bool isDelimiter(char c) { return c == '/' || c == '\\'; }
@@ -131,7 +139,7 @@ namespace Slang
             /// @param path
             /// @return SLANG_OK if file or directory is removed
         static SlangResult remove(const String& path);
-	};
+    };
 
     // Helper class to clean up temporary files on dtor
     class TemporaryFileSet: public RefObject
diff --git a/source/core/slang-uint-set.h b/source/core/slang-uint-set.h
index f89f37df2..334e7ebe8 100644
--- a/source/core/slang-uint-set.h
+++ b/source/core/slang-uint-set.h
@@ -112,7 +112,7 @@ inline void UIntSet::add(UInt val)
     const Index idx = Index(val >> kElementShift);
     if (idx >= m_buffer.getCount())
     {
-        resize(val);
+        resize(val + 1);
     }
     m_buffer[idx] |= Element(1) << (val & kElementMask);
 }
diff --git a/source/core/slang-zip-file-system.cpp b/source/core/slang-zip-file-system.cpp
new file mode 100644
index 000000000..ea9a39445
--- /dev/null
+++ b/source/core/slang-zip-file-system.cpp
@@ -0,0 +1,873 @@
+#include "slang-zip-file-system.h"
+
+#include "../../slang-com-helper.h"
+#include "../../slang-com-ptr.h"
+
+#include "slang-io.h"
+#include "slang-string-util.h"
+#include "slang-blob.h"
+#include "slang-string-slice-pool.h"
+#include "slang-uint-set.h"
+
+#include "../../external/miniz/miniz.h"
+#include "../../external/miniz/miniz_common.h"
+#include "../../external/miniz/miniz_tdef.h"
+#include "../../external/miniz/miniz_tinfl.h"
+#include "../../external/miniz/miniz_zip.h"
+
+namespace Slang
+{
+
+// Allocate static const storage for the various interface IDs that the Slang API needs to expose
+static const Guid IID_ISlangUnknown = SLANG_UUID_ISlangUnknown;
+static const Guid IID_ISlangFileSystem = SLANG_UUID_ISlangFileSystem;
+static const Guid IID_ISlangFileSystemExt = SLANG_UUID_ISlangFileSystemExt;
+static const Guid IID_ISlangMutableFileSystem = SLANG_UUID_ISlangMutableFileSystem;
+
+class ZipFileSystem : public CompressedFileSystem 
+{
+public:
+    // ISlangUnknown 
+   // override ref counting, as DefaultFileSystem is singleton
+    SLANG_REF_OBJECT_IUNKNOWN_ALL
+
+    // ISlangFileSystem
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL loadFile(char const* path, ISlangBlob** outBlob) SLANG_OVERRIDE;
+
+    // ISlangFileSystemExt
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL getFileUniqueIdentity(const char* path, ISlangBlob** uniqueIdentityOut) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL calcCombinedPath(SlangPathType fromPathType, const char* fromPath, const char* path, ISlangBlob** pathOut) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL getPathType(const char* path, SlangPathType* pathTypeOut) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL getSimplifiedPath(const char* path, ISlangBlob** outSimplifiedPath) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL getCanonicalPath(const char* path, ISlangBlob** outCanonicalPath) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW void SLANG_MCALL clearCache() SLANG_OVERRIDE {}
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL enumeratePathContents(const char* path, FileSystemContentsCallBack callback, void* userData) SLANG_OVERRIDE;
+
+    // ISlangModifyableFileSystem
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL saveFile(const char* path, const void* data, size_t size) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL remove(const char* path) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW SlangResult SLANG_MCALL createDirectory(const char* path) SLANG_OVERRIDE;
+
+    // CompressedFileSystem
+    virtual ArrayView<uint8_t> getArchive() SLANG_OVERRIDE;
+    virtual void setCompressionType(CompressionType type) SLANG_OVERRIDE;
+
+    ZipFileSystem();
+    ~ZipFileSystem();
+
+    SlangResult init(const uint8_t* archive, size_t size);
+
+protected:
+
+    /// Maps a SubString (owned) to an index
+    struct SubStringIndexMap
+    {
+        void set(const UnownedStringSlice& slice, Index index)
+        {
+            StringSlicePool::Handle handle;
+            m_pool.findOrAdd(slice, handle);
+            const Index poolIndex = StringSlicePool::asIndex(handle);
+
+            if (poolIndex >= m_indexMap.getCount())
+            {
+                SLANG_ASSERT(poolIndex == m_indexMap.getCount());
+                m_indexMap.add(index);
+            }
+            else
+            {
+                m_indexMap[poolIndex] = index;
+            }
+        }
+        Index get(const UnownedStringSlice& slice)
+        {
+            const Index poolIndex = m_pool.findIndex(slice);
+            return (poolIndex >= 0) ? m_indexMap[poolIndex] : -1;
+        }
+
+        Index getCount() const { return m_indexMap.getCount(); }
+
+        KeyValuePair<UnownedStringSlice, Index> getAt(Index index) const
+        {
+            KeyValuePair<UnownedStringSlice, Index> pair;
+            pair.Key = m_pool.getSlice(StringSlicePool::Handle(index));
+            pair.Value = m_indexMap[index];
+            return pair;
+        }
+
+        void clear()
+        {
+            m_pool.clear();
+            m_indexMap.clear();
+        }
+
+        SubStringIndexMap():
+            m_pool(StringSlicePool::Style::Empty)
+        {
+        }
+
+        StringSlicePool m_pool;     ///< Pool holds the substrings
+        List<Index> m_indexMap;     ///< Maps a pool index to the output index
+    };
+
+    enum class Mode
+    {
+        None,               // m_archive is not initialized
+        Read,               // m_archive is a reader
+        ReadWrite,          // m_archive is a writer (that can be read from)
+    };
+
+    SlangResult _requireMode(Mode mode);
+        /// Do the mode change.
+    SlangResult _requireModeImpl(Mode newMode);
+
+    bool _hasArchive() { return m_mode != Mode::None; }
+    SlangResult _getFixedPath(const char* path, String& outPath);
+    SlangResult _findEntryIndex(const char* path, mz_uint& outIndex);
+    SlangResult _findEntryIndexFromFixedPath(const String& fixedPath, mz_uint& outIndex);
+
+    SlangResult _copyToAndInitWriter(mz_zip_archive& outWriter);
+
+        /// Returns SLANG_E_NOT_FOUND if no directory or contents found
+        /// If outContents not set, will just determine if the directory exists
+    SlangResult _getPathContents(const String& fixedPath, SubStringIndexMap* outContents);
+
+    void _rebuildMap();
+
+        /// Returns true if the named item is at the index
+    UnownedStringSlice _getPathAtIndex(Index index);
+
+    ISlangMutableFileSystem* getInterface(const Guid& guid);
+
+    void _initReadWrite(mz_zip_archive& outWriter);
+
+    // Maps from a path to an index in the m_archive
+    SubStringIndexMap m_pathMap;
+    // If bit is set (at the archive index) this index has been deleted.
+    UIntSet m_removedSet;
+
+    ScopedAllocation m_data;
+
+    mz_uint m_compressionLevel = MZ_BEST_COMPRESSION;
+    Mode m_mode = Mode::None;
+
+    mz_file_read_func m_readFunc;
+
+    mz_zip_archive m_archive;           
+};
+
+ISlangMutableFileSystem* ZipFileSystem::getInterface(const Guid& guid)
+{
+    return (guid == IID_ISlangUnknown || guid == IID_ISlangFileSystem || guid == IID_ISlangFileSystemExt || guid == IID_ISlangMutableFileSystem) ? static_cast<ISlangMutableFileSystem*>(this) : nullptr;
+}
+
+// This is a very awkward hack to make it so we can get a read func, without having to implement all of the tracking etc.
+// All this does is create an empty zip, convert into a reader, and then grab the read function
+static mz_file_read_func _calcReadFunc()
+{
+    mz_zip_archive archive;
+    mz_zip_zero_struct(&archive);
+    mz_zip_writer_init_heap(&archive, 0, 0);
+    // Convert to reader
+
+    void* buf;
+    size_t size;
+    mz_zip_writer_finalize_heap_archive(&archive, &buf, &size);
+    ScopedAllocation alloc;
+    alloc.attach(buf, size);
+    mz_zip_writer_end(&archive);
+
+    // Read
+    mz_zip_zero_struct(&archive);
+    mz_zip_reader_init_mem(&archive, alloc.getData(), alloc.getSizeInBytes(), 0);
+
+    auto readFunc = archive.m_pRead;
+
+    mz_zip_end(&archive);
+    return readFunc;
+}
+
+static mz_file_read_func _getReadFunc()
+{
+    static const auto readFunc = _calcReadFunc();
+    return readFunc;
+}
+
+ZipFileSystem::ZipFileSystem():
+    m_mode(Mode::None)
+{
+   m_readFunc = _getReadFunc();
+}
+
+ ZipFileSystem::~ZipFileSystem()
+ {
+     _requireMode(Mode::None);
+ }
+
+SlangResult ZipFileSystem::init(const uint8_t* archive, size_t size)
+{
+     SLANG_RETURN_ON_FAIL(_requireMode(Mode::None));
+
+     // Store a copy
+     if (!m_data.set(archive, size))
+     {
+         return SLANG_E_OUT_OF_MEMORY;
+     }
+
+    // Initialize archive
+    mz_zip_zero_struct(&m_archive);
+
+    // Read the contents of the archive, and make m_archive own it
+    if (!mz_zip_reader_init_mem(&m_archive, m_data.getData(), size, 0))
+    {
+        return SLANG_FAIL;
+    }
+
+     m_mode = Mode::Read;
+
+     // Set up the mapping from paths to indices
+     _rebuildMap();
+
+     return SLANG_OK;
+}
+
+void ZipFileSystem::_rebuildMap()
+{
+    m_pathMap.clear();
+
+    const mz_uint entryCount = mz_zip_reader_get_num_files(&m_archive);
+
+    m_removedSet.resizeAndClear(0);
+
+    for (mz_uint i = 0; i < entryCount; ++i)
+    {
+        mz_zip_archive_file_stat fileStat;
+        if (!mz_zip_reader_file_stat(&m_archive, mz_uint(i), &fileStat))
+        {
+            continue;
+        }
+
+        UnownedStringSlice currentName(fileStat.m_filename);
+
+        // Get rid of '/'
+        currentName = currentName.trim('/');
+
+        m_pathMap.set(currentName, Index(i));
+    }
+}
+
+UnownedStringSlice ZipFileSystem::_getPathAtIndex(Index index)
+{
+    SLANG_ASSERT(m_mode != Mode::None);
+
+    mz_zip_archive_file_stat fileStat;
+    // Check it's added at the end
+    if (!mz_zip_reader_file_stat(&m_archive, mz_uint(index), &fileStat))
+    {
+        return UnownedStringSlice();
+    }
+
+    return UnownedStringSlice(fileStat.m_filename).trim('/');
+}
+
+void ZipFileSystem::_initReadWrite(mz_zip_archive& outWriter)
+{
+    mz_zip_zero_struct(&outWriter);
+    mz_zip_writer_init_heap(&outWriter, 0, 0);
+    outWriter.m_pRead = m_readFunc;
+}
+
+SlangResult ZipFileSystem::_copyToAndInitWriter(mz_zip_archive& outWriter)
+{
+    mz_zip_zero_struct(&outWriter);
+    switch (m_mode)
+    {
+        case Mode::None:
+        {
+            _initReadWrite(outWriter);
+            return SLANG_OK;
+        }
+        case Mode::Read:
+        case Mode::ReadWrite:
+        {
+            _initReadWrite(outWriter);
+
+            const mz_uint entryCount = mz_zip_reader_get_num_files(&m_archive);
+
+            for (mz_uint i = 0; i < entryCount; ++i)
+            {
+                if (m_removedSet.contains(i))
+                {
+                    continue;
+                }
+
+                // It's worth noting - it's not clear if this will work, because m_archive might not be a reader, in the miniz docs.
+                // If it's a writer, it's not clear how to convert a writer to a reader *selectively* which
+                // we require if we are going to lazily handle removals.
+                //
+                // The fix to make this work is the hack that sets the m_reader, such that in effect the writer is both read and write.
+                // That works because the default writer behavior is a single block of memory for the archive, and that is compatible
+                // with the reader.
+                if (! mz_zip_writer_add_from_zip_reader(&outWriter, &m_archive, i))
+                {
+                    mz_zip_end(&outWriter);
+                    return SLANG_FAIL;
+                }
+            }
+
+            return SLANG_OK;
+        }
+
+        default: break;
+    }
+    return SLANG_FAIL;   
+}
+
+SlangResult ZipFileSystem::_requireModeImpl(Mode newMode)
+{
+    SLANG_ASSERT(newMode != m_mode);
+
+    switch (m_mode)
+    {
+        case Mode::None:
+        {
+            switch (newMode)
+            {
+                case Mode::Read:
+                {
+                    mz_uint flags = 0;
+                    mz_zip_zero_struct(&m_archive);
+                    mz_zip_reader_init(&m_archive, 0, flags);
+                    break;
+                }
+                case Mode::ReadWrite:
+                {
+                    _initReadWrite(m_archive);
+                    break;
+                }
+                default: break;
+            }
+            break;
+        }
+        case Mode::Read:
+        {
+            switch (newMode)
+            {
+                case Mode::None:
+                {
+                    m_data.deallocate();
+                    mz_zip_end(&m_archive);
+                    break;
+                }
+                case Mode::ReadWrite:
+                {
+                    // If nothing is removed, we can just convert
+                    if (m_removedSet.isEmpty())
+                    {
+                        // Convert the reader into the writer
+                        if (!mz_zip_writer_init_from_reader(&m_archive, nullptr))
+                        {
+                            return SLANG_FAIL;
+                        }
+                        // If it's now a writer the memory is owned by the m_archive
+                        m_data.detach();
+                    }
+                    else
+                    {
+                        // Copy into a new writer
+                        mz_zip_archive writer;
+                        SLANG_RETURN_ON_FAIL(_copyToAndInitWriter(writer));
+
+                        // In the process we have removed anything that was deleted
+                        m_removedSet.clear();
+                        // Don't need the read data anymore
+                        m_data.deallocate();
+
+                        // Free the current archive
+                        mz_zip_end(&m_archive);
+                        // Make the writer current
+                        m_archive = writer;
+                        break;
+                    }
+                    break;
+                }
+            }
+            break;
+        }
+        case Mode::ReadWrite:
+        {
+            switch (newMode)
+            {
+                case Mode::None:
+                {
+                    mz_zip_writer_end(&m_archive);
+                    break;
+                }
+                case Mode::Read:
+                {
+                    // If anything has been removed we copy selectively into a new writer, and then convert that
+                    if (!m_removedSet.isEmpty())
+                    {
+                        // There are entries that are deleted... so we need to copy selectively
+                        mz_zip_archive writer;
+                        SLANG_RETURN_ON_FAIL(_copyToAndInitWriter(writer));
+
+                        // In the process we have removed anything that was deleted
+                        m_removedSet.clear();
+
+                        // Get rid of the old writer
+                        mz_zip_writer_end(&m_archive);
+                        m_archive = writer;
+                    }
+
+                    void* buf;
+                    size_t size;
+                    mz_zip_writer_finalize_heap_archive(&m_archive, &buf, &size);
+                    m_data.attach(buf, size);
+
+                    mz_zip_writer_end(&m_archive);
+
+                    // Read
+                    mz_zip_zero_struct(&m_archive);
+                    if (!mz_zip_reader_init_mem(&m_archive, m_data.getData(), m_data.getSizeInBytes(), 0))
+                    {
+                        m_data.deallocate();
+                        return SLANG_FAIL;
+                    }
+                    break;
+                }
+                default: break;
+            }
+        }
+    }
+
+    // Set the new mode
+    m_mode = newMode;
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::_requireMode(Mode newMode)
+{
+    if (newMode == m_mode)
+    {
+        return SLANG_OK;
+    }
+
+    SlangResult res = _requireModeImpl(newMode);
+    if (SLANG_SUCCEEDED(res))
+    {
+        m_mode = newMode;
+    }
+
+    _rebuildMap();
+    return res;
+}
+
+SlangResult ZipFileSystem::_getFixedPath(const char* path, String& outPath)
+{
+    String simplifiedPath = Path::simplify(UnownedStringSlice(path));
+    // Can simplify to just ., thats okay, if it otherwise has something relative it means it couldn't be simplified into the
+    // contents of the archive
+    if (simplifiedPath != "." && Path::hasRelativeElement(simplifiedPath))
+    {
+        // If it still has a relative element, then it must be 'outside' of the archive
+        return SLANG_E_NOT_FOUND;
+    }
+
+    outPath = simplifiedPath;
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::_findEntryIndexFromFixedPath(const String& fixedPath, mz_uint& outIndex)
+{
+    const Index index = m_pathMap.get(fixedPath.getUnownedSlice());
+
+    // If not in list or deleted - it is removed
+    if (index < 0 || m_removedSet.contains(index))
+    {
+        return SLANG_E_NOT_FOUND;
+    }
+
+    outIndex = mz_uint(index);
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::_findEntryIndex(const char* path, mz_uint& outIndex)
+{
+    String fixedPath;
+    SLANG_RETURN_ON_FAIL(_getFixedPath(path, fixedPath));
+    SLANG_RETURN_ON_FAIL(_findEntryIndexFromFixedPath(fixedPath, outIndex));
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::loadFile(char const* path, ISlangBlob** outBlob)
+{
+    mz_uint index;
+    SLANG_RETURN_ON_FAIL(_findEntryIndex(path, index));
+
+    // Check it's a file
+    mz_zip_archive_file_stat fileStat;
+    if (!mz_zip_reader_file_stat(&m_archive, index, &fileStat) || fileStat.m_is_directory)
+    {
+        return SLANG_E_NOT_FOUND;
+    }
+
+    ScopedAllocation alloc;
+    if (!alloc.allocate(size_t(fileStat.m_uncomp_size)))
+    {
+        return SLANG_E_OUT_OF_MEMORY;
+    }
+
+    const mz_uint flags = 0;
+
+    // Extract to memory
+    if (!mz_zip_reader_extract_to_mem(&m_archive, index, alloc.getData(), alloc.getSizeInBytes(), flags))
+    {
+        return SLANG_FAIL;
+    }
+
+    *outBlob = RawBlob::moveCreate(alloc).detach();
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::getPathType(const char* path, SlangPathType* outPathType)
+{
+    if (!_hasArchive())
+    {
+        return SLANG_E_NOT_FOUND;
+    }
+
+    String fixedPath;
+    SLANG_RETURN_ON_FAIL(_getFixedPath(path, fixedPath));
+
+    // First look if there is an *explicit* entry - either file or directory
+    mz_uint index;
+    if (SLANG_SUCCEEDED(_findEntryIndexFromFixedPath(fixedPath, index)))
+    {
+        mz_zip_archive_file_stat fileStat;
+        if (!mz_zip_reader_file_stat(&m_archive, index, &fileStat))
+        {
+            return SLANG_FAIL;
+        }
+
+        *outPathType = fileStat.m_is_directory ? SLANG_PATH_TYPE_DIRECTORY : SLANG_PATH_TYPE_FILE;
+        return SLANG_OK;
+    }
+    else
+    {
+        // It could be an *implicit* directory (ie as part of a path). So lets look for that...
+        if (SLANG_SUCCEEDED(_getPathContents(fixedPath, nullptr)))
+        {
+            *outPathType = SLANG_PATH_TYPE_DIRECTORY;
+            return SLANG_OK;
+        }
+    }
+
+    return SLANG_E_NOT_FOUND;
+}
+
+SlangResult ZipFileSystem::getCanonicalPath(const char* path, ISlangBlob** outCanonicalPath)
+{
+    mz_uint index;
+    SLANG_RETURN_ON_FAIL(_findEntryIndex(path, index));
+
+    mz_zip_archive_file_stat fileStat;
+    if (!mz_zip_reader_file_stat(&m_archive, index, &fileStat))
+    {
+        return SLANG_FAIL;
+    }
+
+    // Use the path in the archive itself
+    *outCanonicalPath = StringUtil::createStringBlob(fileStat.m_filename).detach();
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::getFileUniqueIdentity(const char* path, ISlangBlob** outUniqueIdentity)
+{
+    return getCanonicalPath(path, outUniqueIdentity);
+}
+
+SlangResult ZipFileSystem::calcCombinedPath(SlangPathType fromPathType, const char* fromPath, const char* path, ISlangBlob** pathOut)
+{
+    String relPath;
+    switch (fromPathType)
+    {
+        case SLANG_PATH_TYPE_FILE:
+        {
+            relPath = Path::combine(Path::getParentDirectory(fromPath), path);
+            break;
+        }
+        case SLANG_PATH_TYPE_DIRECTORY:
+        {
+            relPath = Path::combine(fromPath, path);
+            break;
+        }
+    }
+
+    *pathOut = StringUtil::createStringBlob(relPath).detach();
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::getSimplifiedPath(const char* path, ISlangBlob** outSimplifiedPath)
+{
+    *outSimplifiedPath = StringUtil::createStringBlob(Path::simplify(path)).detach();
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::_getPathContents(const String& inFixedPath, SubStringIndexMap* outContents)
+{
+    if (!_hasArchive())
+    {
+        return SLANG_E_NOT_FOUND;
+    }
+
+    String fixedPath(inFixedPath);
+    if (fixedPath == ".")
+    {
+        fixedPath = "";
+    }
+    else
+    {
+        fixedPath.append('/');
+    }
+
+    bool foundDirectory = false;
+
+    // Okay - I want to iterate through all of the entries and look for the ones with this prefix
+    const Index entryCount = Index(mz_zip_reader_get_num_files(&m_archive));
+    for (Index i = 0; i < entryCount; ++i)
+    {
+        // Skip if it's been deleted.
+        if (m_removedSet.contains(i))
+        {
+            continue;
+        }
+
+        mz_zip_archive_file_stat fileStat;
+        if (!mz_zip_reader_file_stat(&m_archive, mz_uint(i), &fileStat))
+        {
+            continue;
+        }
+
+        UnownedStringSlice currentPath(fileStat.m_filename);
+        if (!currentPath.startsWith(fixedPath.getUnownedSlice()))
+        {
+            continue;
+        }
+
+        UnownedStringSlice remaining(currentPath.begin() + fixedPath.getLength(), currentPath.end());
+
+        if (!outContents)
+        {
+            // We found the directory, as we found contents. And since we aren't adding to map, we are done
+            return SLANG_OK;
+        }
+
+        // We found the directory (either implicitly or explicitly)
+        foundDirectory = true;
+
+        if (remaining.getLength() == 0)
+        {
+            // It's the explicit directory to this path, we don't need to add
+            continue;
+        }
+
+        // Work out if it's a file that implicitly implies the directory, by looking for it it contains a /
+        const Index delimiterIndex = remaining.indexOf('/');
+
+        SlangPathType pathType;
+        if (delimiterIndex >= 0)
+        {
+            // If we have the delimiter index, then it's an implicit *contained* directory, and we need to strip to just get the name.
+            remaining = UnownedStringSlice(remaining.begin(), delimiterIndex);
+            pathType = SLANG_PATH_TYPE_DIRECTORY;
+        }
+        else
+        {
+            // Just use what the zip archive says the type is
+            pathType = fileStat.m_is_directory ? SLANG_PATH_TYPE_DIRECTORY : SLANG_PATH_TYPE_FILE;
+        }
+
+        // Set what type this path is
+        outContents->set(remaining, pathType);
+    }
+
+    // Check we found the directory at all...
+    return foundDirectory ? SLANG_OK : SLANG_E_NOT_FOUND;
+}
+
+SlangResult ZipFileSystem::enumeratePathContents(const char* path, FileSystemContentsCallBack callback, void* userData)
+{
+    if (!_hasArchive())
+    {
+        return SLANG_E_NOT_FOUND;
+    }
+
+    String fixedPath;
+    SLANG_RETURN_ON_FAIL(_getFixedPath(path, fixedPath));
+
+    // Maps the name to the SLANG_PATH_TYPE
+    SubStringIndexMap map;
+    SLANG_RETURN_ON_FAIL(_getPathContents(fixedPath, &map));
+
+    const Index entryCount = map.getCount();
+    for (Index i = 0; i < entryCount; ++i)
+    {
+        auto pair = map.getAt(i);
+        SlangPathType pathType = SlangPathType(pair.Value);
+        UnownedStringSlice name = pair.Key;
+
+        // Name is zero terminated (as in StringPool). Lets check that though..
+        SLANG_ASSERT(name.begin()[name.getLength()] == 0);
+     
+        callback(pathType, name.begin(), userData);
+    }
+
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::saveFile(const char* path, const void* data, size_t size)
+{
+    String fixedPath;
+    SLANG_RETURN_ON_FAIL(_getFixedPath(path, fixedPath));
+
+    mz_uint32 index;
+    if (SLANG_SUCCEEDED(_findEntryIndexFromFixedPath(fixedPath, index)))
+    {
+        // Mark as removed
+        m_removedSet.add(index);
+    }
+
+    // We need to be able to write to the archive
+    _requireMode(Mode::ReadWrite);
+
+    // TODO(JS):
+    // We may want to check the directory exists that holds the path exists
+    // Which is easy to do. Without this check it allows directories to come into exisitance
+    // when the path to the file is used.
+    // This behaviour *isn't* strictly the same as the file system, which requires the path
+    // to a file to exist before it is written.
+    //
+    // Not enforcing this allows zips that don't explicitly specify paths - which saves space
+    // and is simpler.
+    //
+    // NOTE! This also means that if a file that produces an implicit path is *removed* that
+    // the implicit directories are also in effect removed.
+
+    // Need to add to the end of the file
+    const mz_uint32 entryCount = mz_zip_reader_get_num_files(&m_archive);
+    if (!mz_zip_writer_add_mem(&m_archive, fixedPath.getBuffer(), data, size, m_compressionLevel))
+    {
+        return SLANG_FAIL;
+    }
+
+    // Make sure it is added at expended index
+    SLANG_ASSERT(_getPathAtIndex(entryCount) == fixedPath.getUnownedSlice());
+
+    // Set in the map
+    m_pathMap.set(fixedPath.getUnownedSlice(), entryCount);
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::remove(const char* path)
+{
+    String fixedPath;
+    SLANG_RETURN_ON_FAIL(_getFixedPath(path, fixedPath));
+
+    mz_uint32 index;
+    SLANG_RETURN_ON_FAIL(_findEntryIndexFromFixedPath(fixedPath, index));
+
+    mz_zip_archive_file_stat fileStat;
+    if (!mz_zip_reader_file_stat(&m_archive, index, &fileStat))
+    {
+        return SLANG_FAIL;
+    }
+
+    if (fileStat.m_is_directory)
+    {
+        // Find the directory contents
+        SubStringIndexMap map;
+        SLANG_RETURN_ON_FAIL(_getPathContents(fixedPath, &map));
+
+        if (map.getCount() > 0)
+        {
+            // If it contains children we can't remove it
+            return SLANG_FAIL;
+        }
+    }
+
+    // Mark as removed
+    m_removedSet.add(index);
+    return SLANG_OK;
+}
+
+SlangResult ZipFileSystem::createDirectory(const char* path)
+{
+    String fixedPath;
+    SLANG_RETURN_ON_FAIL(_getFixedPath(path, fixedPath));
+
+    // If we find something with this name, we can't create it
+    mz_uint32 index;
+    if (SLANG_SUCCEEDED(_findEntryIndexFromFixedPath(fixedPath, index)))
+    {
+        return SLANG_FAIL;
+    }
+
+    // Make writable
+    SLANG_RETURN_ON_FAIL(_requireMode(Mode::ReadWrite));
+
+    const mz_uint entryCount = mz_zip_reader_get_num_files(&m_archive);
+
+    // The terminating / in the path indicates it's a directory
+    {
+        String dirPath(fixedPath);
+        dirPath.appendChar('/');
+        if (!mz_zip_writer_add_mem(&m_archive, dirPath.getBuffer(), nullptr, 0, m_compressionLevel))
+        {
+            return SLANG_FAIL;
+        }
+    }
+
+    SLANG_ASSERT(_getPathAtIndex(entryCount) == fixedPath.getUnownedSlice());
+
+    // Set the index, that we added at end
+    m_pathMap.set(fixedPath.getUnownedSlice(), entryCount); 
+    return SLANG_OK;
+}
+
+ArrayView<uint8_t> ZipFileSystem::getArchive()
+{
+    // If we have anything deleted in 'Read', we need to convert to 'Write' and then back to read
+    if (m_mode == Mode::Read && !m_removedSet.isEmpty())
+    {
+        _requireMode(Mode::ReadWrite);
+    }
+        
+    _requireMode(Mode::Read);
+    return ArrayView<uint8_t>((uint8_t*)m_data.getData(), Index(m_data.getSizeInBytes()));
+}
+
+ void ZipFileSystem::setCompressionType(CompressionType type)
+ {
+     switch (type)
+     {
+         case CompressionType::BestSpeed:       m_compressionLevel = MZ_BEST_SPEED; break;
+         case CompressionType::BestCompression: m_compressionLevel = MZ_BEST_COMPRESSION; break;
+     }
+ }
+
+/* static */SlangResult CompressedFileSystem::createZip(const void* data, size_t size, RefPtr<CompressedFileSystem>& out)
+{
+    RefPtr<ZipFileSystem> fileSystem(new ZipFileSystem);
+    SLANG_RETURN_ON_FAIL(fileSystem->init((const uint8_t*)data, size));
+
+    out = fileSystem;
+    return SLANG_OK;
+}
+
+/* static */SlangResult CompressedFileSystem::createZip(RefPtr<CompressedFileSystem>& out)
+{
+    out = new ZipFileSystem;
+    return SLANG_OK;
+}
+
+} // namespace Slang
diff --git a/source/core/slang-zip-file-system.h b/source/core/slang-zip-file-system.h
new file mode 100644
index 000000000..47c7b8db3
--- /dev/null
+++ b/source/core/slang-zip-file-system.h
@@ -0,0 +1,35 @@
+#ifndef SLANG_ZIP_FILE_SYSTEM_H
+#define SLANG_ZIP_FILE_SYSTEM_H
+
+#include "slang-basic.h"
+
+#include "../../slang-com-ptr.h"
+
+namespace Slang
+{
+
+class CompressedFileSystem : public RefObject, public ISlangMutableFileSystem
+{
+public:
+
+    enum class CompressionType
+    {
+        BestSpeed,
+        BestCompression,
+    };
+
+        /// Get as an archive (that can be saved to disk)
+    virtual ArrayView<uint8_t> getArchive() = 0;
+        /// Set the compression - used for any subsequent items added
+    virtual void setCompressionType(CompressionType type) = 0;
+
+        /// Create a zip with the contents of data/size (the contents of a zip file)
+    static SlangResult createZip(const void* data, size_t size, RefPtr<CompressedFileSystem>& out);
+
+        /// Create an empty zip
+    static SlangResult createZip(RefPtr<CompressedFileSystem>& out);
+};
+
+}
+
+#endif