construct/include/ircd/m/state.h

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_M_STATE_H

namespace ircd::m::state
{
	struct node;

	using id_closure = std::function<void (const string_view &)>;
	using node_closure = std::function<void (const json::object &)>;
	using key_closure = std::function<void (const json::array &)>;

	constexpr size_t ID_MAX_SZ { 64 };
	constexpr size_t KEY_MAX_SZ { 256 + 256 + 16 };
	constexpr size_t VAL_MAX_SZ { 256 + 16 };
	constexpr size_t NODE_MAX_SZ { 4_KiB };
	constexpr size_t NODE_MAX_KEY { 2 }; // tmp for now
	constexpr size_t NODE_MAX_VAL { NODE_MAX_KEY };
	constexpr size_t NODE_MAX_DEG { NODE_MAX_KEY + 1 }; // tmp for now
	constexpr int8_t MAX_HEIGHT { 16 }; // good for few mil at any degree :)

	int keycmp(const json::array &a, const json::array &b);

	json::array make_key(const mutable_buffer &out, const string_view &type, const string_view &state_key);
	string_view set_node(db::txn &txn, const mutable_buffer &id, const json::object &node);

	void get_node(db::column &, const string_view &id, const node_closure &);
	void get_node(const string_view &id, const node_closure &);

	string_view get_head(db::column &, const mutable_buffer &out, const id::room &);
	string_view get_head(const mutable_buffer &out, const id::room &);
	void set_head(db::txn &txn, const id::room &, const string_view &head);

	void get_value(db::column &, const string_view &head, const json::array &key, const id_closure &);
	void get_value(const string_view &head, const json::array &key, const id_closure &);
	void get_value(const string_view &head, const string_view &type, const string_view &state_key, const id_closure &);
	void get_value__room(const id::room &, const string_view &type, const string_view &state_key, const id_closure &);

	void insert(db::txn &txn, const id::room &, const json::array &key, const id::event &);
	void insert(db::txn &txn, const id::room &, const string_view &type, const string_view &state_key, const id::event &);

	void append_nodes(db::txn &, const event &);
}

namespace ircd::m::state::name
{
	constexpr const char *const k {"k"};
	constexpr const char *const v {"v"};
	constexpr const char *const c {"c"};
}

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsubobject-linkage"

/// Format for node: Node is plaintext and not binary at this time. In fact,
/// *evil chuckle*, node might as well be JSON and can easily become content
/// of another event sent to other rooms over network *snorts*. (important:
/// database is well compressed).
///
/// {                                                ;
///     "k":                                         ; Key array
///     [                                            ;
///         ["m.room.member", "@ar4an:matrix.org"],  ; Left key
///         ["m.room.member", "@jzk:matrix.org"]     ; Right key
///     ],                                           ;
///     "v":                                         ; Value array
///     [                                            ;
///         "$14961836116kXQRA:matrix.org",          ; Left accept
///         "$15018692261xPQDB:matrix.org",          ; Right accept
///     ]                                            ;
///     "c":                                         ; Child array
///     [                                            ;
///         "nPKN9twTF9a8k5dD7AApFcaraHTX",          ; Left child
///         "PcxAAACvkvyUMz19AZcCfrC3S84s",          ; Center child
///         "2jVYKIMKErJ6w6BLMhfVjsXearhB",          ; Right child
///     ]                                            ;
/// }                                                ;
///
/// Elements are ordered based on type+state_key lexical sort. The type
/// and the state_key strings are literally concatenated to this effect.
/// They're not hashed. We can have some more control over data locality
/// this way. Any number of values may be in a key array, not just type+
/// state_key. The concatenation involves the string with its surrounding
/// quotes as to not allow the user to mess about conflicting values.
/// ```
/// "m.room.member""@jzk" > "m.room.create"""
/// ```
/// Unlike traditional trees of such variety, the number of elements is not
/// really well defined and not even fixed. There just has to be one more
/// value in the "child" list than there are keys in the "key" list. To make
/// this structure efficient we have to figure out a good number of
/// children per node, and that might even be a contextual decision. The
/// more children, the less depth to the query, but at the cost of a larger
/// node size. A larger node in this system isn't just relevant to
/// retrieval, but consider nodes are also immutable. Changes to the tree
/// create new nodes for each changed path so the old nodes can still
/// represent the old state.
struct ircd::m::state::node
:json::tuple
<
	json::property<name::k, json::array>,
	json::property<name::v, json::array>,
	json::property<name::c, json::array>
>
{
	struct rep;

	size_t keys() const;
	size_t vals() const;
	size_t childs() const;

	json::array key(const size_t &) const;
	string_view val(const size_t &) const;
	string_view child(const size_t &) const;

	size_t keys(json::array *const &out, const size_t &max) const;
	size_t vals(string_view *const &out, const size_t &max) const;
	size_t childs(string_view *const &out, const size_t &max) const;

	size_t find(const json::array &key) const;
	bool has_key(const json::array &key) const;
	bool has_child(const size_t &) const;

	using super_type::tuple;
	using super_type::operator=;
};
#pragma GCC diagnostic pop

struct ircd::m::state::node::rep
{
	std::array<json::array, NODE_MAX_KEY + 1> keys;
	std::array<string_view, NODE_MAX_VAL + 1> vals;
	std::array<string_view, NODE_MAX_DEG + 1> chld;
	size_t kn {0};
	size_t vn {0};
	size_t cn {0};

	bool full() const;
	bool overfull() const;
	size_t find(const json::array &key) const;

	void shr(const size_t &pos);

	json::object write(const mutable_buffer &out);
	string_view write(db::txn &, const mutable_buffer &id);

	rep(const node &node);
	rep() = default;
};

static_assert
(
	ircd::m::state::NODE_MAX_KEY == ircd::m::state::NODE_MAX_VAL
);