8 files changed, 386 insertions, 6 deletions

diff --git a/src/db/plugins/simple/Directory.cxx b/src/db/plugins/simple/Directory.cxx
index b4255b0ac..3ac2f96a2 100644
--- a/src/db/plugins/simple/Directory.cxx
+++ b/src/db/plugins/simple/Directory.cxx
@@ -21,10 +21,12 @@
 #include "Directory.hxx"
 #include "SongSort.hxx"
 #include "Song.hxx"
+#include "Mount.hxx"
 #include "db/LightDirectory.hxx"
 #include "db/LightSong.hxx"
 #include "db/Uri.hxx"
 #include "db/DatabaseLock.hxx"
+#include "db/Interface.hxx"
 #include "SongFilter.hxx"
 #include "lib/icu/Collate.hxx"
 #include "fs/Traits.hxx"
@@ -42,7 +44,8 @@ extern "C" {
 Directory::Directory(std::string &&_path_utf8, Directory *_parent)
 	:parent(_parent),
 	 mtime(0), have_stat(false),
-	 path(std::move(_path_utf8))
+	 path(std::move(_path_utf8)),
+	 mounted_database(nullptr)
 {
 	INIT_LIST_HEAD(&children);
 	INIT_LIST_HEAD(&songs);
@@ -50,6 +53,8 @@ Directory::Directory(std::string &&_path_utf8, Directory *_parent)
 
 Directory::~Directory()
 {
+	delete mounted_database;
+
 	Song *song, *ns;
 	directory_for_each_song_safe(song, ns, *this)
 		song->Free();
@@ -113,6 +118,11 @@ Directory::PruneEmpty()
 
 	Directory *child, *n;
 	directory_for_each_child_safe(child, n, *this) {
+		if (child->IsMount())
+			/* never prune mount points; they're always
+			   empty by definition, but that's ok */
+			continue;
+
 		child->PruneEmpty();
 
 		if (child->IsEmpty())
@@ -233,6 +243,22 @@ Directory::Walk(bool recursive, const SongFilter *filter,
 {
 	assert(!error.IsDefined());
 
+	if (IsMount()) {
+		assert(IsEmpty());
+
+		/* TODO: eliminate this unlock/lock; it is necessary
+		   because the child's SimpleDatabasePlugin::Visit()
+		   call will lock it again */
+		db_unlock();
+		bool result = WalkMount(GetPath(), *mounted_database,
+					recursive, filter,
+					visit_directory, visit_song,
+					visit_playlist,
+					error);
+		db_lock();
+		return result;
+	}
+
 	if (visit_song) {
 		Song *song;
 		directory_for_each_song(song, *this) {
diff --git a/src/db/plugins/simple/Directory.hxx b/src/db/plugins/simple/Directory.hxx
index 5b39231e3..029815d95 100644
--- a/src/db/plugins/simple/Directory.hxx
+++ b/src/db/plugins/simple/Directory.hxx
@@ -57,6 +57,7 @@ struct Song;
 struct db_visitor;
 class SongFilter;
 class Error;
+class Database;
 
 struct Directory {
 	/**
@@ -94,6 +95,12 @@ struct Directory {
 
 	std::string path;
 
+	/**
+	 * If this is not nullptr, then this directory does not really
+	 * exist, but is a mount point for another #Database.
+	 */
+	Database *mounted_database;
+
 public:
 	Directory(std::string &&_path_utf8, Directory *_parent);
 	~Directory();
@@ -106,6 +113,10 @@ public:
 		return new Directory(std::string(), nullptr);
 	}
 
+	bool IsMount() const {
+		return mounted_database != nullptr;
+	}
+
 	/**
 	 * Remove this #Directory object from its parent and free it.  This
 	 * must not be called with the root Directory.
diff --git a/src/db/plugins/simple/DirectorySave.cxx b/src/db/plugins/simple/DirectorySave.cxx
index 6cc5df6cb..b5989dd06 100644
--- a/src/db/plugins/simple/DirectorySave.cxx
+++ b/src/db/plugins/simple/DirectorySave.cxx
@@ -88,7 +88,8 @@ directory_save(FILE *fp, const Directory &directory)
 	directory_for_each_child(cur, directory) {
 		fprintf(fp, DIRECTORY_DIR "%s\n", cur->GetName());
 
-		directory_save(fp, *cur);
+		if (!cur->IsMount())
+			directory_save(fp, *cur);
 
 		if (ferror(fp))
 			return;
diff --git a/src/db/plugins/simple/Mount.cxx b/src/db/plugins/simple/Mount.cxx
new file mode 100644
index 000000000..96c7bbb5c
--- /dev/null
+++ b/src/db/plugins/simple/Mount.cxx
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "Mount.hxx"
+#include "PrefixedLightSong.hxx"
+#include "db/Selection.hxx"
+#include "db/LightDirectory.hxx"
+#include "db/LightSong.hxx"
+#include "db/Interface.hxx"
+#include "fs/Traits.hxx"
+#include "util/Error.hxx"
+
+#include <string>
+
+struct PrefixedLightDirectory : LightDirectory {
+	std::string buffer;
+
+	PrefixedLightDirectory(const LightDirectory &directory,
+			       const char *base)
+		:LightDirectory(directory),
+		 buffer(IsRoot()
+			? std::string(base)
+			: PathTraitsUTF8::Build(base, uri)) {
+		uri = buffer.c_str();
+	}
+};
+
+static bool
+PrefixVisitDirectory(const char *base, const VisitDirectory &visit_directory,
+		     const LightDirectory &directory, Error &error)
+{
+	return visit_directory(PrefixedLightDirectory(directory, base), error);
+}
+
+static bool
+PrefixVisitSong(const char *base, const VisitSong &visit_song,
+		const LightSong &song, Error &error)
+{
+	return visit_song(PrefixedLightSong(song, base), error);
+}
+
+static bool
+PrefixVisitPlaylist(const char *base, const VisitPlaylist &visit_playlist,
+		    const PlaylistInfo &playlist,
+		    const LightDirectory &directory,
+		    Error &error)
+{
+	return visit_playlist(playlist,
+			      PrefixedLightDirectory(directory, base),
+			      error);
+}
+
+bool
+WalkMount(const char *base, const Database &db,
+	  bool recursive, const SongFilter *filter,
+	  const VisitDirectory &visit_directory, const VisitSong &visit_song,
+	  const VisitPlaylist &visit_playlist,
+	  Error &error)
+{
+	using namespace std::placeholders;
+
+	VisitDirectory vd;
+	if (visit_directory)
+		vd = std::bind(PrefixVisitDirectory,
+			       base, std::ref(visit_directory), _1, _2);
+
+	VisitSong vs;
+	if (visit_song)
+		vs = std::bind(PrefixVisitSong,
+			       base, std::ref(visit_song), _1, _2);
+
+	VisitPlaylist vp;
+	if (visit_playlist)
+		vp = std::bind(PrefixVisitPlaylist,
+			       base, std::ref(visit_playlist), _1, _2, _3);
+
+	return db.Visit(DatabaseSelection("", recursive, filter),
+			vd, vs, vp, error);
+}
diff --git a/src/db/plugins/simple/Mount.hxx b/src/db/plugins/simple/Mount.hxx
new file mode 100644
index 000000000..a4690114c
--- /dev/null
+++ b/src/db/plugins/simple/Mount.hxx
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2003-2014 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_DB_SIMPLE_MOUNT_HXX
+#define MPD_DB_SIMPLE_MOUNT_HXX
+
+#include "db/Visitor.hxx"
+
+class Database;
+class SongFilter;
+class Error;
+
+bool
+WalkMount(const char *base, const Database &db,
+	  bool recursive, const SongFilter *filter,
+	  const VisitDirectory &visit_directory, const VisitSong &visit_song,
+	  const VisitPlaylist &visit_playlist,
+	  Error &error);
+
+#endif
diff --git a/src/db/plugins/simple/PrefixedLightSong.hxx b/src/db/plugins/simple/PrefixedLightSong.hxx
new file mode 100644
index 000000000..3664de001
--- /dev/null
+++ b/src/db/plugins/simple/PrefixedLightSong.hxx
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2003-2014 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_DB_SIMPLE_PREFIXED_LIGHT_SONG_HXX
+#define MPD_DB_SIMPLE_PREFIXED_LIGHT_SONG_HXX
+
+#include "check.h"
+#include "db/LightSong.hxx"
+#include "fs/Traits.hxx"
+
+#include <string>
+
+class PrefixedLightSong : public LightSong {
+	std::string buffer;
+
+public:
+	PrefixedLightSong(const LightSong &song, const char *base)
+		:LightSong(song),
+		 buffer(PathTraitsUTF8::Build(base, GetURI().c_str())) {
+		uri = buffer.c_str();
+		directory = nullptr;
+	}
+};
+
+#endif
diff --git a/src/db/plugins/simple/SimpleDatabasePlugin.cxx b/src/db/plugins/simple/SimpleDatabasePlugin.cxx
index e83ef575b..68101f564 100644
--- a/src/db/plugins/simple/SimpleDatabasePlugin.cxx
+++ b/src/db/plugins/simple/SimpleDatabasePlugin.cxx
@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "SimpleDatabasePlugin.hxx"
+#include "PrefixedLightSong.hxx"
 #include "db/DatabasePlugin.hxx"
 #include "db/Selection.hxx"
 #include "db/Helpers.hxx"
@@ -32,6 +33,7 @@
 #include "fs/TextFile.hxx"
 #include "config/ConfigData.hxx"
 #include "fs/FileSystem.hxx"
+#include "util/CharUtil.hxx"
 #include "util/Error.hxx"
 #include "util/Domain.hxx"
 #include "Log.hxx"
@@ -42,7 +44,17 @@ static constexpr Domain simple_db_domain("simple_db");
 
 inline SimpleDatabase::SimpleDatabase()
 	:Database(simple_db_plugin),
-	 path(AllocatedPath::Null()) {}
+	 path(AllocatedPath::Null()),
+	 cache_path(AllocatedPath::Null()),
+	 prefixed_light_song(nullptr) {}
+
+inline SimpleDatabase::SimpleDatabase(AllocatedPath &&_path)
+	:Database(simple_db_plugin),
+	 path(std::move(_path)),
+	 path_utf8(path.ToUTF8()),
+	 cache_path(AllocatedPath::Null()),
+	 prefixed_light_song(nullptr) {
+}
 
 Database *
 SimpleDatabase::Create(gcc_unused EventLoop &loop,
@@ -71,6 +83,10 @@ SimpleDatabase::Configure(const config_param &param, Error &error)
 
 	path_utf8 = path.ToUTF8();
 
+	cache_path = param.GetBlockPath("cache_directory", error);
+	if (path.IsNull() && error.IsDefined())
+		return false;
+
 	return true;
 }
 
@@ -169,6 +185,8 @@ SimpleDatabase::Load(Error &error)
 bool
 SimpleDatabase::Open(Error &error)
 {
+	assert(prefixed_light_song == nullptr);
+
 	root = Directory::NewRoot();
 	mtime = 0;
 
@@ -195,6 +213,7 @@ void
 SimpleDatabase::Close()
 {
 	assert(root != nullptr);
+	assert(prefixed_light_song == nullptr);
 	assert(borrowed_song_count == 0);
 
 	delete root;
@@ -204,11 +223,27 @@ const LightSong *
 SimpleDatabase::GetSong(const char *uri, Error &error) const
 {
 	assert(root != nullptr);
+	assert(prefixed_light_song == nullptr);
 	assert(borrowed_song_count == 0);
 
 	db_lock();
 
 	auto r = root->LookupDirectory(uri);
+
+	if (r.directory->IsMount()) {
+		/* pass the request to the mounted database */
+		db_unlock();
+
+		const LightSong *song =
+			r.directory->mounted_database->GetSong(r.uri, error);
+		if (song == nullptr)
+			return nullptr;
+
+		prefixed_light_song =
+			new PrefixedLightSong(*song, r.directory->GetPath());
+		return prefixed_light_song;
+	}
+
 	if (r.uri == nullptr) {
 		/* it's a directory */
 		db_unlock();
@@ -245,11 +280,17 @@ SimpleDatabase::GetSong(const char *uri, Error &error) const
 void
 SimpleDatabase::ReturnSong(gcc_unused const LightSong *song) const
 {
-	assert(song == &light_song);
+	assert(song != nullptr);
+	assert(song == &light_song || song == prefixed_light_song);
+
+	delete prefixed_light_song;
+	prefixed_light_song = nullptr;
 
 #ifndef NDEBUG
-	assert(borrowed_song_count > 0);
-	--borrowed_song_count;
+	if (song == &light_song) {
+		assert(borrowed_song_count > 0);
+		--borrowed_song_count;
+	}
 #endif
 }
 
@@ -347,6 +388,104 @@ SimpleDatabase::Save(Error &error)
 	return true;
 }
 
+bool
+SimpleDatabase::Mount(const char *uri, Database *db, Error &error)
+{
+	assert(uri != nullptr);
+	assert(*uri != 0);
+	assert(db != nullptr);
+
+	ScopeDatabaseLock protect;
+
+	auto r = root->LookupDirectory(uri);
+	if (r.uri == nullptr) {
+		error.Format(db_domain, DB_CONFLICT,
+			     "Already exists: %s", uri);
+		return nullptr;
+	}
+
+	if (strchr(r.uri, '/') != nullptr) {
+		error.Format(db_domain, DB_NOT_FOUND,
+			     "Parent not found: %s", uri);
+		return nullptr;
+	}
+
+	Directory *mnt = r.directory->CreateChild(r.uri);
+	mnt->mounted_database = db;
+	return true;
+}
+
+static constexpr bool
+IsSafeChar(char ch)
+{
+	return IsAlphaNumericASCII(ch) || ch == '-' || ch == '_' || ch == '%';
+}
+
+static constexpr bool
+IsUnsafeChar(char ch)
+{
+	return !IsSafeChar(ch);
+}
+
+bool
+SimpleDatabase::Mount(const char *local_uri, const char *storage_uri,
+		      Error &error)
+{
+	if (cache_path.IsNull()) {
+		error.Format(db_domain, DB_NOT_FOUND,
+			     "No 'cache_directory' configured");
+		return nullptr;
+	}
+
+	std::string name(storage_uri);
+	std::replace_if(name.begin(), name.end(), IsUnsafeChar, '_');
+
+	auto db = new SimpleDatabase(AllocatedPath::Build(cache_path,
+							  name.c_str()));
+	if (!db->Open(error)) {
+		delete db;
+		return false;
+	}
+
+	// TODO: update the new database instance?
+
+	if (!Mount(local_uri, db, error)) {
+		db->Close();
+		delete db;
+		return false;
+	}
+
+	return true;
+}
+
+Database *
+SimpleDatabase::LockUmountSteal(const char *uri)
+{
+	ScopeDatabaseLock protect;
+
+	auto r = root->LookupDirectory(uri);
+	if (r.uri != nullptr || !r.directory->IsMount())
+		return nullptr;
+
+	Database *db = r.directory->mounted_database;
+	r.directory->mounted_database = nullptr;
+	r.directory->Delete();
+
+	return db;
+}
+
+bool
+SimpleDatabase::Unmount(const char *uri)
+{
+	Database *db = LockUmountSteal(uri);
+	if (db == nullptr)
+		return false;
+
+	db->Close();
+	delete db;
+	return true;
+}
+
 const DatabasePlugin simple_db_plugin = {
 	"simple",
 	DatabasePlugin::FLAG_REQUIRE_STORAGE,
diff --git a/src/db/plugins/simple/SimpleDatabasePlugin.hxx b/src/db/plugins/simple/SimpleDatabasePlugin.hxx
index 9836a6bcf..a03969f92 100644
--- a/src/db/plugins/simple/SimpleDatabasePlugin.hxx
+++ b/src/db/plugins/simple/SimpleDatabasePlugin.hxx
@@ -32,16 +32,28 @@ struct Directory;
 struct DatabasePlugin;
 class EventLoop;
 class DatabaseListener;
+class PrefixedLightSong;
 
 class SimpleDatabase : public Database {
 	AllocatedPath path;
 	std::string path_utf8;
 
+	/**
+	 * The path where cache files for Mount() are located.
+	 */
+	AllocatedPath cache_path;
+
 	Directory *root;
 
 	time_t mtime;
 
 	/**
+	 * A buffer for GetSong() when prefixing the #LightSong
+	 * instance from a mounted #Database.
+	 */
+	mutable PrefixedLightSong *prefixed_light_song;
+
+	/**
 	 * A buffer for GetSong().
 	 */
 	mutable LightSong light_song;
@@ -52,6 +64,8 @@ class SimpleDatabase : public Database {
 
 	SimpleDatabase();
 
+	SimpleDatabase(AllocatedPath &&_path);
+
 public:
 	static Database *Create(EventLoop &loop, DatabaseListener &listener,
 				const config_param &param,
@@ -73,6 +87,20 @@ public:
 		return mtime > 0;
 	}
 
+	/**
+	 * @param db the #Database to be mounted; must be "open"; on
+	 * success, this object gains ownership of the given #Database
+	 */
+	gcc_nonnull_all
+	bool Mount(const char *uri, Database *db, Error &error);
+
+	gcc_nonnull_all
+	bool Mount(const char *local_uri, const char *storage_uri,
+		   Error &error);
+
+	gcc_nonnull_all
+	bool Unmount(const char *uri);
+
 	/* virtual methods from class Database */
 	virtual bool Open(Error &error) override;
 	virtual void Close() override;
@@ -107,6 +135,8 @@ private:
 	bool Check(Error &error) const;
 
 	bool Load(Error &error);
+
+	Database *LockUmountSteal(const char *uri);
 };
 
 extern const DatabasePlugin simple_db_plugin;