Körperbewegung

mods/modlib/doc/bluon.md

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+# Bluon
+
+Binary Lua object notation.
+
+## `new(def)`
+
+```lua
+def = {
+	aux_is_valid = function(object)
+		return is_valid
+	end,
+	aux_len = function(object)
+		return length_in_bytes
+	end,
+	-- read type byte, stream providing :read(count), map of references -> id
+	aux_read = function(type, stream, references)
+		... = stream:read(...)
+		return object
+	end,
+	-- object to be written, stream providing :write(text), list of references
+	aux_write = function(object, stream, references)
+		stream:write(...)
+	end
+}
+```
+
+## `:is_valid(object)`
+
+Returns whether the given object can be represented by the instance as boolean.
+
+## `:len(object)`
+
+Returns the expected length of the object if serialized by the current instance in bytes.
+
+## `:write(object, stream)`
+
+Writes the object to a stream supporting `:write(text)`. Throws an error if invalid.
+
+## `:read(stream)`
+
+Reads a single bluon object from a stream supporting `:read(count)`. Throws an error if invalid bluon.
+
+Checking whether the stream has been fully consumed by doing `assert(not stream:read(1))` is left up to the user.
+
+## Format
+
+Bluon uses a "tagged union" binary format:
+Values are stored as a one-byte tag followed by the contents of the union.
+For frequently used "constants", only a tag is used.
+
+`nil` is an exception; since it can't appear in tables, it gets no tag.
+If the value to be written by Bluon is `nil`, Bluon simply writes *nothing*.
+
+The following is an enumeration of tag numbers, which are assigned *in this order*.
+
+* `false`: 0
+* `true`: 1
+* Numbers:
+  * Constants: 0, nan, +inf, -inf
+  * Integers: Little endian:
+  	* Unsigned: `U8`, `U16`, `U32`, `U64`
+  	* Negative: `-U8`, `-U16`, `-U32`, `-U64`
+  * Floats: Little endian `F32`, `F64`
+* Strings:
+  * Constant: `""`
+  * Length is written as unsigned integer according to the tag: `S8`, `S16`, `S32`, `S64`
+	* followed by the raw bytes
+* Tables:
+  * Tags: `M0`, `M8`, `M16`, `M32`, `M64` times `L0`, `L8`, `L16`, `L32`, `L64`
+  * `M` is more significant than `L`: The order of the cartesian product is `M0L0`, `M0L1`, ...
+  * List and map part count encoded as unsigned integers according to the tag,
+    list part count comes first
+  * followed by all values in the list part written as Bluon
+  * followed by all key-value pairs in the map part written as Bluon
+    (first the key is written as Bluon, then the value)
+* Reference:
+  * Reference ID as unsigned integer: `R8`, `R16`, `R32`, `R64`
+  * References a previously encountered table or string by an index:
+    All tables and strings are numbered in the order they occur in the Bluon
+* Reserved tags:
+  * All tags <= 55 are reserved. This gives 200 free tags.
+
+## Features
+
+* Embeddable: Written in pure Lua
+* Storage efficient: No duplication of strings or reference-equal tables
+* Flexible: Can serialize circular references and strings containing null
+
+## Simple example
+
+```lua
+local object = ...
+-- Write to file
+local file = io.open(..., "wb")
+modlib.bluon:write(object, file)
+file:close()
+-- Write to text
+local rope = modlib.table.rope{}
+modlib.bluon:write(object, rope)
+text = rope:to_text()
+-- Read from text
+local inputstream = modlib.text.inputstream"\1"
+assert(modlib.bluon:read(object, rope) == true)
+```
+
+## Advanced example
+
+```lua
+-- Serializes all userdata to a constant string:
+local custom_bluon = bluon.new{
+	aux_is_valid = function(object)
+		return type(object) == "userdata"
+	end,
+	aux_len = function(object)
+		return 1 + ("userdata"):len())
+	end,
+	aux_read = function(type, stream, references)
+		assert(type == 100, "unsupported type")
+		assert(stream:read(("userdata"):len()) == "userdata")
+		return userdata()
+	end,
+	-- object to be written, stream providing :write(text), list of references
+	aux_write = function(object, stream, references)
+		assert(type(object) == "userdata")
+		stream:write"\100userdata"
+	end
+}
+-- Write to text
+local rope = modlib.table.rope{}
+custom_bluon:write(userdata(), rope)
+assert(rope:to_text() == "\100userdata")
+```