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structModule

Binary codec for fixed C struct layouts.

Calling the module on a layout descriptor (as generated by autogen, e.g. require("linux.netlink").layout.nlmsghdr) derives a string.pack format once and returns a codec exposing pack/unpack/size, so callers never hand-write the byte layout.

Usage

local struct = require("struct")
local nlmsghdr = struct(require("linux.netlink").layout.nlmsghdr)
local bytes = nlmsghdr:pack(len, mtype, flags, seq, pid)
local len, mtype = nlmsghdr:unpack(bytes)

Class codec

codec:fieldsize (name) Returns the size in bytes of a named field.
codec:pack (...) Serializes the field values (in offset order) into the struct’s bytes.
codec:unpack (buf[, pos]) Deserializes the struct’s fields from a buffer.

struct

struct (layout) Builds a codec from a layout descriptor.

Class codec in detail

Codec a layout builds, packing its fields in native byte order. Its size field holds the struct’s size in bytes.
codec:fieldsize (name)
Returns the size in bytes of a named field.

Parameters

Returns

    integer or nil the field size, or nil if the layout has no such field.
codec:pack (...)
Serializes the field values (in offset order) into the struct’s bytes.

Parameters

  • ... the field values

Returns

    string
codec:unpack (buf[, pos])
Deserializes the struct’s fields from a buffer.

Parameters

  • buf string
  • pos integer starting offset (1-based) (optional)

Returns

    the field values in offset order, then the position past the struct

struct in detail

struct (layout)
Builds a codec from a layout descriptor.

Parameters

  • layout table { size = bytes, fields = { {name, offset, size, signed}, ... } }

Returns

    codec a codec exposing :pack, :unpack, :fieldsize and a size field.

Raises

“struct: derived format does not match the layout size (overlapping fields?)”