mirror of
https://github.com/matrix-construct/construct
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208 lines
7.3 KiB
C
208 lines
7.3 KiB
C
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// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_JSON_STACK_H
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namespace ircd::json
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{
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struct stack;
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}
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/// Output stack machine for stringifying JSON as-you-go. This device allows
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/// the user to create JSON without knowing the contents when it is first
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/// constructed. An object or array is opened and the user can append to the
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/// stack creating the members or values or recursing further. The JSON is
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/// then closed automatically with exception safety. Partial JSON is written
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/// to the buffer as soon as possible.
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///
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/// The target buffer is not required to maintain earlier output from the same
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/// stack or even earlier members and values of the same object or array. The
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/// buffer may be smaller than the final JSON output and reused when the user
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/// chooses to flush it to some storage or socket. If the buffer becomes full
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/// a flush callback is attempted to make space and continue. This can occur
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/// while the output is still incomplete JSON.
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///
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/// The user first creates a master json::stack instance with some reasonable
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/// backing buffer. A suite of classes is provided to aid with building the
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/// JSON which attach to each other stackfully, and eventually lead to the
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/// root. There should only be one "active path" of instances at any given
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/// time, ideally following the scope of your code itself. You must force
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/// instances to go out of scope to continue at the same recursion depth.
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/// This way the json::stack can "follow" your code and "record" the final
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/// JSON output while allowing you to free the original resources required
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/// for each value.
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///
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struct ircd::json::stack
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{
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struct array;
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struct object;
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struct member;
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using flush_callback = std::function<const_buffer (const const_buffer &)>;
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window_buffer buf;
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flush_callback flusher;
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object *co {nullptr}; ///< The root object instance.
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array *ca {nullptr}; ///< Could be union with top_object but
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template<class gen, class... attr> bool printer(gen&&, attr&&...);
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template<class gen> bool printer(gen&&);
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bool append(const window_buffer::closure &);
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bool append(const string_view &);
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public:
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bool opened() const; ///< Current stacking in progress.
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bool closed() const; ///< No stacking in progress.
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bool clean() const; ///< Never opened.
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bool done() const; ///< Opened and closed.
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size_t remaining() const;
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const_buffer completed() const;
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void clear();
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stack(const mutable_buffer &, flush_callback = {});
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~stack() noexcept;
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};
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/// stack::object is constructed under the scope of either a stack::member,
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/// or a stack::array, or a stack itself. Only stack::member can be
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/// constructed directly under its scope.
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///
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/// For a stack::member parent, the named member is waiting for this value
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/// after leaving the stack at ':' after the name, this object will then
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/// print '{' and dtor with '}' and then return to the stack::member which
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/// will then return to its parent object.
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///
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/// For a stack::array parent, the stack may have been left at '[' or ','
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/// but either way this object will then print '{' and dtor with '}' and
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/// then return to the stack::array.
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///
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/// For a stack itself, this object is considered the "top object" and will
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/// open the stack with '{' and accept member instances under its scope
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/// until closing the stack with '}' after which the stack is done()
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///
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struct ircd::json::stack::object
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{
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stack *s {nullptr}; ///< root stack ref
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member *pm {nullptr}; ///< parent member (if value of one)
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array *pa {nullptr}; ///< parent array (if value in one)
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member *cm {nullptr}; ///< current child member
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size_t mc {0}; ///< members witnessed (monotonic)
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public:
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object() = default;
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object(stack &s); ///< Object is top
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object(array &pa); ///< Object is value in the array
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object(member &pm); ///< Object is value of named member
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~object() noexcept;
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};
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/// stack::array is constructed under the scope of either a stack::member,
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/// or a stack::array, or a stack itself. stack::object and stack::array
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/// can be constructed directly under its scope, but not stack::member.
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///
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/// The same behavior as described by stack::object documentation applies
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/// here translated to arrays.
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///
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struct ircd::json::stack::array
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{
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stack *s {nullptr}; ///< root stack ref
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member *pm {nullptr}; ///< parent member (if value of one)
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array *pa {nullptr}; ///< parent array (if value in one)
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object *co {nullptr}; ///< current child object
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array *ca {nullptr}; ///< current child array
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size_t vc {0}; ///< values witnessed (monotonic)
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void _pre_append();
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void _post_append();
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public:
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template<class... T> void append(const json::tuple<T...> &);
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void append(const json::value &);
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array() = default;
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array(stack &s); ///< Array is top
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array(array &pa); ///< Array is value in the array
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array(member &pm); ///< Array is value of the named member
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~array() noexcept;
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};
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/// stack::member is an intermediary that is constructed under the scope of
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/// a parent stack::object. It takes a name argument. It then requires one
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/// object or array be constructed under its scope as its value, or a
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/// json::value / already strung JSON must be appended as its value.
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///
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/// If the value is supplied in the constructor argument an instance of
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/// this class does not have to be held (use constructor as function).
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///
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struct ircd::json::stack::member
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{
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stack *s {nullptr}; ///< root stack ref
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object *po {nullptr}; ///< parent object
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string_view name; ///< member name state
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object *co {nullptr}; ///< current child object
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array *ca {nullptr}; ///< current child array
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void _pre_append();
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void _post_append();
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public:
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template<class... T> void append(const json::tuple<T...> &);
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void append(const json::value &);
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member() = default;
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member(object &po, const string_view &name);
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member(object &po, const string_view &name, const json::value &v);
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template<class... T> member(object &po, const string_view &name, const json::tuple<T...> &t);
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~member() noexcept;
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};
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template<class... T>
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ircd::json::stack::member::member(object &po,
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const string_view &name,
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const json::tuple<T...> &t)
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:member{po, name}
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{
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append(t);
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}
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template<class... T>
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void
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ircd::json::stack::member::append(const json::tuple<T...> &t)
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{
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_pre_append();
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const unwind post{[this]
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{
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_post_append();
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}};
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s->append([this, &t](mutable_buffer buf)
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{
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return size(stringify(buf, t));
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});
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}
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template<class... T>
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void
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ircd::json::stack::array::append(const json::tuple<T...> &t)
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{
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_pre_append();
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const unwind post{[this]
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{
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_post_append();
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}};
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s->append([&t](mutable_buffer buf)
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{
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return size(stringify(buf, t));
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});
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}
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