xpdt: eXPeditious Data Transfer

About

xpdt is (yet another) language for defining data-types and generating code for serializing and deserializing them. It aims to produce code with little or no overhead and is based on fixed-length representations which allows for zero-copy deserialization and (at-most-)one-copy writes (source to buffer).

The generated C code, in particular, is highly optimized and often permits the elimination of data-copying for writes and enables optimizations such as loop-unrolling for fixed-length objects. This can lead to read speeds in excess of 500 million objects per second (~1.8 nsec per object).

Examples

The xpdt source language looks similar to C struct definitions:

struct timestamp {
	u32	tv_sec;
	u32	tv_nsec;
};

struct point {
	i32	x;
	i32	y;
	i32	z;
};

struct line {
	timestamp	time;
	point		line_start;
	point		line_end;
	bytes		comment;
};

Fixed width integer types from 8 to 128 bit are supported, along with the bytes type, which is a variable-length sequence of bytes.

Target Languages

The following target languages are currently supported:

• C
• Python

The C code is very highly optimized.

The Python code is about as well optimized for CPython as I can make it. It uses typed NamedTuple for objects, which has some small overhead over regular tuples, and it uses struct.Struct to do the packing/unpacking. I have also code-golfed the generated bytecodes down to what I think is minimal given the design constraints. As a result, performance of the pure Python code is comparable to a JSON library implemented in C or Rust.

For better performance in Python, it may be desirable to develop a Cython target. In some instances CFFI structs may be more performant since they can avoid the creation/destruction of an object for each record.

Target languages are implemented purely as jinja2 templates.

Serialization format

The serialization format for fixed-length objects is simply a packed C struct.

For any object which contains bytes type fields:

• a 32bit unsigned record length is prepended to the struct
• all bytes type fields are converted to u32 and contain the length of the bytes
• all bytes contents are appended after the struct in the order in which they appear

For example, following the example above, the serialization would be:

u32 tot_len # = 41
u32 time.tv_sec
u32 time.tv_usec
i32 line_start.x
i32 line_start.y
i32 line_start.z
i32 line_end.x
i32 line_end.y
i32 line_end.z
u32 comment # = 5
u8 'H'
u8 'e'
u8 'l'
u8 'l'
u8 'o'

Features

The feature-set is, as of now, pretty slim.

There are no array / sequence / map types, and no keyed unions.

Support for such things may be added in future provided that suitable implementations exist. An implementation is suitable if:

• It admits a zero (or close to zero) overhead implementation
• it causes no overhead when the feature isn't being used

License

The compiler is released under the GPLv3.

The C support code/headers are released under the MIT license.

The generated code is yours.