png画像にバイナリデータを埋め込んだり、pngに埋め込まれたバイナリデータを抽出するヤツ

bng.d

import imageformats;
import std.algorithm;
import std.conv;
import std.exception;
import std.file;
import std.math;
import std.stdio;
import std.string;


void main()
{
    ubyte[] dst = cast(ubyte[])`×ご検証
○ご健勝
`;
    encodeBng(dst, "output.png", 100);
    decodeBng("output.png", dst);
    std.file.write("output2.dat", dst);
}


void decodeBng(string pngFile, ref ubyte[] dst)
{
    auto img = read_png(pngFile, 4);
    enforce(img.c == ColFmt.RGBA);

    auto ps = img.pixels;
    immutable uint numBytes = (cast(uint[])(ps[0 .. 4].reverse(), ps))[0];

    dst.length = numBytes;
    dst[] = ps[4 .. 4 + numBytes];
}


void encodeBng(in ubyte[] data, string pngFile, size_t minWH = 0)
{
    immutable numPixels = (data.length + 4) / 4;
    size_t w = cast(size_t)sqrt(cast(real)numPixels);
    size_t h = numPixels / w;

    if(numPixels > w * h) ++w;

    if(w < minWH) w = minWH;
    if(h < minWH) h = minWH;

    auto buf = new ubyte[w * h * 4];

    buf[0 .. 4] = (a => (a.reverse(), a))(cast(ubyte[])([data.length].dup))[];
    buf[4 .. 4 + data.length] = data[];

    write_png(pngFile, w, h, buf, 4);
}