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/*
* Copyright 2003-2020 The Music Player Daemon Project
* http://www.musicpd.org
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef MPD_COMPOSITE_STORAGE_HXX
#define MPD_COMPOSITE_STORAGE_HXX
#include "StorageInterface.hxx"
#include "thread/Mutex.hxx"
#include "util/Compiler.h"
#include <memory>
#include <string>
#include <map>
/**
* A #Storage implementation that combines multiple other #Storage
* instances in one virtual tree. It is used to "mount" new #Storage
* instances into the storage tree.
*
* This class is thread-safe: mounts may be added and removed at any
* time in any thread.
*/
class CompositeStorage final : public Storage {
/**
* A node in the virtual directory tree.
*/
struct Directory {
/**
* The #Storage mounted in this virtual directory. All
* "leaf" Directory instances must have a #Storage.
* Other Directory instances may have one, and child
* mounts will be "mixed" in.
*/
std::unique_ptr<Storage> storage;
std::map<std::string, Directory, std::less<>> children;
gcc_pure
bool IsEmpty() const noexcept {
return storage == nullptr && children.empty();
}
gcc_pure
const Directory *Find(const char *uri) const noexcept;
Directory &Make(const char *uri);
bool Unmount() noexcept;
bool Unmount(const char *uri) noexcept;
gcc_pure
bool MapToRelativeUTF8(std::string &buffer,
const char *uri) const noexcept;
};
struct FindResult {
const Directory *directory;
const char *uri;
};
/**
* Protects the virtual #Directory tree.
*
* TODO: use readers-writer lock
*/
mutable Mutex mutex;
Directory root;
mutable std::string relative_buffer;
public:
CompositeStorage() noexcept;
~CompositeStorage() override;
/**
* Get the #Storage at the specified mount point. Returns
* nullptr if the given URI is not a mount point.
*
* The returned pointer is unprotected. No other thread is
* allowed to unmount the given mount point while the return
* value is being used.
*/
gcc_pure gcc_nonnull_all
Storage *GetMount(const char *uri) noexcept;
/**
* Call the given function for each mounted storage, including
* the root storage. Passes mount point URI and the a const
* Storage reference to the function.
*/
template<typename T>
void VisitMounts(T t) const {
const std::lock_guard<Mutex> protect(mutex);
std::string uri;
VisitMounts(uri, root, t);
}
void Mount(const char *uri, std::unique_ptr<Storage> storage);
bool Unmount(const char *uri);
/* virtual methods from class Storage */
StorageFileInfo GetInfo(const char *uri, bool follow) override;
std::unique_ptr<StorageDirectoryReader> OpenDirectory(const char *uri) override;
std::string MapUTF8(const char *uri) const noexcept override;
AllocatedPath MapFS(const char *uri) const noexcept override;
const char *MapToRelativeUTF8(const char *uri) const noexcept override;
private:
template<typename T>
void VisitMounts(std::string &uri, const Directory &directory,
T t) const {
if (directory.storage)
t(uri.c_str(), *directory.storage);
if (!uri.empty())
uri.push_back('/');
const size_t uri_length = uri.length();
for (const auto &i : directory.children) {
uri.resize(uri_length);
uri.append(i.first);
VisitMounts(uri, i.second, t);
}
}
/**
* Follow the given URI path, and find the outermost directory
* which is a #Storage mount point. If there are no mounts,
* it returns the root directory (with a nullptr "storage"
* attribute, of course). FindResult::uri contains the
* remaining unused part of the URI (may be empty if all of
* the URI was used).
*/
gcc_pure
FindResult FindStorage(const char *uri) const noexcept;
const char *MapToRelativeUTF8(const Directory &directory,
const char *uri) const;
};
#endif
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