ints as byte representation

[Wes Chow]

I'm writing some networking code and would like to send an int as a sequence of binary bytes (not as a string). A socket:write(25) call appears to send the string '25'. In regular Lua I would use the struct module to convert 25 into bytes and then send that, however it seems as if many of the standard libraries don't exist with luvit. What's a poor engineer to do?

Thanks,

Wes

[Tim Caswell]

The libuv bindings assume all input is a lua string since lua strings are binary safe (they are just arrays of 8-bit data, nothing more).

If you want to send the single int8_t 25, you can do it with "\25" or "\x19" or string.char(25).  If you want larger integers you can either encode them by hand using the bit library or use luajit's ffi structs.

For example, here is encoding a 32-bit integer as 4 bytes https://github.com/creationix/msgpack-lua/blob/master/msgpack.lua#L27-L33

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[Wes Chow]

write32 is perfect for my needs, thanks, and I was about to look for a msgpack implementation for luvit too!

Wes

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[Tim Caswell]

By the way, there is a built-in Buffer class in luvit that ports most the node.js Buffer methods including read/write of integers of various sizes.  It works on mutable buffers instead of strings, but the buffers should convert to strings properly when passing them to libuv APIs.

[Wes Chow]

Hm interesting, that might be what I want to use. I’m building a custom network messaging system at the moment and basically want to be sending datagrams over tcp. I was shooting for the most basic strategy of sending a uint32 of data size, and then a sequence of bytes of that amount of data. Buffer looks like it will work for that.

Wes

[Ryan Phillips]

Tim wrote a fast msgpack implementation in luajit as well:

 

https://github.com/creationix/msgpack-lua