#include <MergingFileSystem.h>

Inheritance diagram for MergingFileSystem:

Public Member Functions
	MergingFileSystem (std::vector< const FileSystem * > bases)

virtual	~MergingFileSystem ()

Public Member Functions inherited from FileSystem
	FileSystem ()=default

virtual	~FileSystem ()=default

bool	exists (std::string_view path) const

bool	exists (FileSystemPathView path) const

FileStat	stat (std::string_view path) const

FileStat	stat (FileSystemPathView path) const

std::vector< DirectoryEntry >	ls (std::string_view path) const

std::vector< DirectoryEntry >	ls (FileSystemPathView path) const

void	ls (std::string_view path, std::vector< DirectoryEntry > *entries) const

void	ls (FileSystemPathView path, std::vector< DirectoryEntry > *entries) const

Blob	read (std::string_view path) const

Blob	read (FileSystemPathView path) const

void	write (std::string_view path, const Blob &data)

void	write (FileSystemPathView path, const Blob &data)

std::unique_ptr< InputStream >	openForReading (std::string_view path) const

std::unique_ptr< InputStream >	openForReading (FileSystemPathView path) const

std::unique_ptr< OutputStream >	openForWriting (std::string_view path)

std::unique_ptr< OutputStream >	openForWriting (FileSystemPathView path)

void	rename (std::string_view srcPath, std::string_view dstPath)

void	rename (FileSystemPathView srcPath, FileSystemPathView dstPath)

bool	remove (std::string_view path)

bool	remove (FileSystemPathView path)

std::string	displayPath (std::string_view path) const

std::string	displayPath (FileSystemPathView path) const

Private Member Functions
virtual bool	_exists (FileSystemPathView path) const override

virtual FileStat	_stat (FileSystemPathView path) const override

virtual void	_ls (FileSystemPathView path, std::vector< DirectoryEntry > *entries) const override

virtual Blob	_read (FileSystemPathView path) const override

virtual std::unique_ptr< InputStream >	_openForReading (FileSystemPathView path) const override

virtual std::string	_displayPath (FileSystemPathView path) const override

const FileSystem *	locateForReading (FileSystemPathView path) const

const FileSystem *	locateForReadingOrNull (FileSystemPathView path) const

Private Attributes
std::vector< const FileSystem * >	_bases

Additional Inherited Members
Protected Types inherited from FileSystem
template<class T >
using	FileSystemTrieNode = detail::FileSystemTrieNode< T >

template<class T >
using	FileSystemTrie = detail::FileSystemTrie< T >

virtual bool	_exists (FileSystemPathView path) const =0

virtual FileStat	_stat (FileSystemPathView path) const =0

virtual void	_ls (FileSystemPathView path, std::vector< DirectoryEntry > *entries) const =0

virtual Blob	_read (FileSystemPathView path) const =0

virtual void	_write (FileSystemPathView path, const Blob &data)=0

virtual std::unique_ptr< InputStream >	_openForReading (FileSystemPathView path) const =0

virtual std::unique_ptr< OutputStream >	_openForWriting (FileSystemPathView path)=0

virtual void	_rename (FileSystemPathView srcPath, FileSystemPathView dstPath)

virtual bool	_remove (FileSystemPathView path)=0

virtual std::string	_displayPath (FileSystemPathView path) const =0

Detailed Description

Merges several filesystems into a single read-only view:

Read operations go one by one over the underlying filesystems. This effectively means that files on filesystem #0 will hide the files on filesystem #1 that have the same names.
Folder contents are merged.
The resulting view is kind of a Schrodinger's filesystem because it can contain files and folders with the same name.
In case there is a file and a folder with the same name, stat() returns information for a file, so that it's possible to know its size. ls() will return both entries, in unspecified order.

Some notes on why go Schrodingermaxxxing. When there is a conflict between underlying filesystems, and we have a file and a folder with the same names, we have several different options:

Only the file is visible.
Only the folder is visible.
Whichever is first in the filesystem list, is visible.
Conflicting path is not visible through the merged filesystem at all.
Schrodingermaxxx and make both visible.

When picking between the options, we must remember that: a. A tree of MergingFileSystems should behave the same way as a single flattened MergingFileSystem. E.g. if we have a MergingFileSystem containing another MergingFileSystem, it should be no different from just having a single MergingFileSystem with all the leaf filesystems added to it. b. Ideally, each method of the merging filesystem should call into each of the base filesystems at most once. c. The behavior shouldn't be surprising.

Point #1 above fails (b) and (c). We can fix (b) by introducing a walk() method to FileSystem that would return the longest existing prefix of a path, but then we're still left with the fact that behaviour is surprising.

Point #2 fails (c).

Point #3 fails (a), (b) and (c). How exactly it does it fail (a)? Imagine the following sequence of conflicts: folder x, file x, then again folder x and file x, with the first pair in the first MergingFileSystem and the second pair in the second MergingFileSystem, which are then merged into a single common MergingFileSystem. The common MergingFileSystem will merge the contents of the folders in this case, which (supposedly) would not be the case if all the conflicts were to happen inside a single MergingFileSystem. This can be worked around, but the workaround is questionable.

Point #4 fails (b), can be fixed in the same way as point #1. So, a viable option.

Point #5 satisfies all the criteria, even though it's suffering a low-key bipolar disorder. So this is what we do.

Constructor & Destructor Documentation

◆ MergingFileSystem()

MergingFileSystem::MergingFileSystem ( std::vector< const FileSystem * > bases )

explicit

◆ ~MergingFileSystem()

MergingFileSystem::~MergingFileSystem ( )

virtualdefault

Member Function Documentation

◆ _displayPath()

std::string MergingFileSystem::_displayPath ( FileSystemPathView path ) const

overrideprivatevirtual

Implements FileSystem.

◆ _exists()

bool MergingFileSystem::_exists ( FileSystemPathView path ) const

overrideprivatevirtual

Implements FileSystem.

◆ _ls()

void MergingFileSystem::_ls	(	FileSystemPathView	path,
		std::vector< DirectoryEntry > *	entries
	)		const

overrideprivatevirtual

Implements FileSystem.

◆ _openForReading()

std::unique_ptr< InputStream > MergingFileSystem::_openForReading ( FileSystemPathView path ) const

overrideprivatevirtual

Implements FileSystem.

◆ _read()

Blob MergingFileSystem::_read ( FileSystemPathView path ) const

overrideprivatevirtual

Implements FileSystem.

◆ _stat()

FileStat MergingFileSystem::_stat ( FileSystemPathView path ) const

overrideprivatevirtual

Implements FileSystem.

◆ locateForReading()

const FileSystem * MergingFileSystem::locateForReading ( FileSystemPathView path ) const

private

◆ locateForReadingOrNull()

const FileSystem * MergingFileSystem::locateForReadingOrNull ( FileSystemPathView path ) const

private

Member Data Documentation

◆ _bases

std::vector<const FileSystem *> MergingFileSystem::_bases

private

The documentation for this class was generated from the following files:

src/Library/FileSystem/Merging/MergingFileSystem.h
src/Library/FileSystem/Merging/MergingFileSystem.cpp

Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ MergingFileSystem()

◆ ~MergingFileSystem()

Member Function Documentation

◆ _displayPath()

◆ _exists()

◆ _ls()

◆ _openForReading()

◆ _read()

◆ _stat()

◆ locateForReading()

◆ locateForReadingOrNull()

Member Data Documentation

◆ _bases