Table of Contents

Protocol

tools

http://yura415.github.io/js-protobuf-encode-decode/

Libraries

sean-lin based

https://github.com/sean-lin/protoc-gen-lua

https://github.com/djungelorm/protobuf-lua

https://github.com/urbanairship/protobuf-lua

others

https://github.com/indygreg/lua-protobuf

https://github.com/haberman/upb

https://github.com/starwing/lua-protobuf 

This project offers a simple C library for basic protobuf wire format
encode/decode, it splits to several modules:
  - pb.decoder: a wire format decode module.
  - pb.buffer:  a buffer implement that use to encode basic types into
                protobuf's wire format. It also can be used to support
		streaming decode protobuf data.
  - pb.conv:    a module to convert between integers in protobuf.
  - pb.io:      a module to support binary mode read/write to stdin/stdout.

Neopalium

https://github.com/Neopallium/lua-pb

Library API

-- -------------------------------------------
-- @return string with message dump
local function dumpRawProtoc (binMsg)
  local p = io.popen ("protoc --decode_raw", "w")
  local stdout
  if p then
    p:write(binMsg)
    local stdout = p:read("*a")
    p:close()
  end  
  return stdout
end

Neopalium

local pb = require 'pb' 
-- loading 'pb' module will replace 'require' function
-- now .proto files are automatically loaded by require.
local proto = require 'protos.messages' -- load 'protos/messages.proto'
 
-- Two methods of message creation
-- 1) direct assign
local protoMsg = proto.Message()
protoMsg.deviceId = 0x1234   -- simple type value
protoMsg.deviceType = 'MODEM' -- enum value
protoMsg.repeatedSubMessage = { { id = 'TEMPERATURE',
                                  value = 34 
                                },
                                { id = 'WIND',
                                  value = 2 
                                }
                              }
protoMsg.subMessage.serialNumber = '123456-1234'
protoMsg.subMessage.version      = '2'
 
-- 2) Initialize from structure
local luaData = {
  deviceId = 0x1234,
  deviceType = 'MODEM',
  repeatedSubMessage = { { id = 'TEMPERATURE',
                           value = 34 
                         },
                         { id = 'WIND',
                           value = 2 
                         }
                       },
   subMessage = { serialNumber = '123456-1234',
                  version      = '2' 
                }
}
 
local protoMsg = proto.Message(luaData) -- initialize from luaData
 
-- 3) Still possible to directly modify, add values into message
protoMsg.deviceId = 0xdeadbeef
 
 
local binProtoMsg = protoMsg:Serialize() -- binProtoMsg is string
print (binProtoMsh:len())
local dumpProtoMsg = protoMsg:SerializePartial('text')
 
 
local receivedProtoMsg = proto.Message()
if receivedProtoMsh == nil then
  error ("Malformed message")
end
 
receivedProtoMsg:Parse(binProtoMsg)
print (receivedProtoMsg:SerializePartial('text'))

Raw dump of protobuf message (.proto files not needed) 

local function dump_fields(unknown)
    local o = ""
    for i, v in ipairs(unknown) do
      o = o..string.format("#%02d Tag=[%2d] Wire=[%2d] %q\n", i, v.tag, v.wire, tostring(v.value))
      if type (v.value) == 'table' then
        o = o..dump_fields(v.value)
      end
    end    
    return o
end
 
-- -------------------------------------------
-- @return string with message dump
function PD:pbDumpRawPB(binMsg)
  local msg, off = pb.decode_raw(binMsg)
  return dump_fields(msg.unknown_fields)
end

Issue with 64bit number

18446744073709551615 is exactly 2^64-1

in LuaJIT 64bit numbers are stored as double, so some precision is lost: 

print (0xFFFFFFFFFFFFFFFF == 0xFFFFFFFFFFFFFF00)
true

If library detects LuaJIT with FFI support, it is using FFI cdata to store 64 bit numbers int64_t or uint64_t depends on signed argument passed to make_int64_func. If no LuaJIT is used, big values are represented as 8 bytes strings. 

local pb = require"pb"
local make_int64 = pb.get_make_int64_func()
-- make_int64(b8,b7,b6,b5,b4,b3,b2,b1, signed)
fakeNodeId = make_int64(0,0,0,0,  0,0,0,1 )
-- or initialize from string
local v = \255\255\255\255\255\255\255\255"
fakeNodeId = make_int65(v:byte(1,8))
print (fakeNodeId) 
-- prints: '1ULL'
fakeNodeIs = fakeNodeId * 22
print (fakeNodeId) 
-- prints: '22ULL'

But library encoder doesn't work: 

luaData = {
   ["deviceId"] = 1.844674407371e+19;
};

binProtoMsg=
  0000 08 00                                            ..

binProtoMsg decoded=deviceId: 0

djungelorm

No documentation. Poor examples. Need to dig in sources to familiarize.

First, proto files needs to be compile with protoc compile with lua output plugin. For messages.proto corresponding lua file messages_pb.lua will be created.

API:

Other internal methods: 

p = require 'messages_pb'
local message = p.Message()
message.deviceId = 0xdeadbeef -- assign int value
message.code = p.Code.OK -- assign enum value (defined in Code enum)
message.repeatedSubMessage:add()
message.repeatedSubMessage[1].ts = 12345 -- assign int value
message.repeatedSubMessage:add()
message.repeatedSubMessage[2].ts = 6789 -- assign int value
 
print (message:SerializeToString())