Serpent

Lua serializer and pretty printer.

Features

• Human readable:
  • Provides single-line and multi-line output.
  • Nested tables are properly indented in the multi-line output.
  • Numerical keys are listed first.
  • Array part skips keys ({'a', 'b'} instead of {[1] = 'a', [2] = 'b'}).
  • nil values are included when expected ({1, nil, 3} instead of {1, [3]=3}).
  • Keys use short notation ({foo = 'foo'} instead of {['foo'] = 'foo'}).
  • Shared and self-references are marked in the output.
• Machine readable: provides reliable deserialization using loadstring().
• Supports deeply nested tables.
• Supports tables with self-references.
• Shared tables and functions stay shared after de/serialization.
• Supports function serialization using string.dump().
• Supports serialization of global functions.
• Escapes new-line \010 and end-of-file control \026 characters in strings.

Usage

local serpent = require("serpent")
local a = {1, nil, 3, x=1, ['true'] = 2, [not true]=3}
a[a] = a -- self-reference with a table as key and value

print(serpent.serialize(a)) -- full serialization
print(serpent.printsing(a)) -- single line, no self-ref section
print(serpent.printmult(a)) -- multi-line indented, no self-ref section

local fun, err = loadstring(serpent.serialize(a))
if err then error(err) end
local copy = fun()

Limitations

• Doesn't handle userdata (except filehandles in io.* table).
• Threads, function upvalues/environments, and metatables are not serialized.

Performance

A simple performance test against serialize.lua from metalua, pretty.write from Penlight, and tserialize.lua from lua-nucleo is included in t/bench.lua.

These are the results from one of the runs:

• nucleo (1000): 0.256s
• metalua (1000): 0.177s
• serpent (1000): 0.22s
• serpent (1000): 0.161s -- no comments, no string escapes, no math.huge check
• penlight (1000): 0.132s

Serpent does additional processing to escape \010 and \026 characters in strings (to address http://lua-users.org/lists/lua-l/2007-07/msg00362.html, which is already fixed in Lua 5.2) and to check all numbers for math.huge. The seconds number excludes this processing to put it on an equal footing with other modules that skip these checks (nucleo still checks for math.huge). There is no switch to disable this processing though as without it there is no guarantee that the generated string is deserializable.

Author

Paul Kulchenko (paul@kulchenko.com)

License

See LICENSE file.