mrubyをブラウザで実行するまで (WebAssembly)

git clone https://github.com/juj/emsdk.git
cd emsdk

# 20-30分くらい時間がかかります。アニメ１話でも消化しましょう。
./emsdk install --build=Release sdk-incoming-64bit binaryen-master-64bit

# emccのパスが通るので展開場所を意識したほうがいいかもしれません。
./emsdk activate --global --build=Release sdk-incoming-64bit binaryen-master-64bit
source ./emsdk_env.sh

git clone https://github.com/mruby/mruby.git
cd mruby

# build_config.rb
...
# Define wasm build settings
MRuby::CrossBuild.new('wasm') do |conf|
  toolchain :clang

  # C compiler settings
  conf.cc do |cc|
    cc.command = 'emcc' # 通常のコンパイルは emcc を使います。
    cc.flags = [ENV['CFLAGS'] || %w()]
    cc.include_paths = ["#{root}/include"]
    cc.defines = %w(_WASM) # 後述
    cc.option_include_path = '-I%s'
    cc.option_define = '-D%s'
    cc.compile_options = "%{flags} -c %{infile} -s WASM=1 -o %{outfile}"
  end

  # Archiver settings
  # ※本来はオブジェクトファイルを固めるものですが、ここではemccでllvmを固めます。
  conf.archiver do |archiver| 
    archiver.command = 'emcc'
    archiver.archive_options = '%{objs} -s WASM=1 -o %{outfile}'
  end

  # file extensions
  # 成果物、中間ファイルの拡張子を設定します。
  conf.exts do |exts|
    exts.object = '.bc'
    exts.executable = '' # '.exe' if Windows
    exts.library = '.bc'
  end

  conf.gembox 'wasm'  # 後述
end

cp mrbgems/default.gembox mrbgems/wasm.gembox

 11   # Use standard Time class
 12   # conf.gem :core => "mruby-time"  <- コメントアウト (実装上の理由)
...
 65   # Generate mirb command
 66   #conf.gem :core => "mruby-bin-mirb"  <- コメントアウト
 67
 68   # Generate mruby command
 69   #conf.gem :core => "mruby-bin-mruby"  <- コメントアウト
 70
 71   # Generate mruby-strip command
 72   #conf.gem :core => "mruby-bin-strip"  <- コメントアウト

# mrbgems/mruby-print/src/print.c
...
 35    fwrite(RSTRING_PTR(obj), RSTRING_LEN(obj), 1, stdout);
 36    fflush(stdout);

...
static void
printstr(mrb_state *mrb, mrb_value obj)
{
  if (mrb_string_p(obj)) {
#if defined(_WIN32)
    if (isatty(fileno(stdout))) {
      DWORD written;
      int mlen = (int)RSTRING_LEN(obj);
      char* utf8 = RSTRING_PTR(obj);
      int wlen = MultiByteToWideChar(CP_UTF8, 0, utf8, mlen, NULL, 0);
      wchar_t* utf16 = (wchar_t*)mrb_malloc(mrb, (wlen+1) * sizeof(wchar_t));
      if (utf16 == NULL) return;
      if (MultiByteToWideChar(CP_UTF8, 0, utf8, mlen, utf16, wlen) > 0) {
        utf16[wlen] = 0;
        WriteConsoleW(GetStdHandle(STD_OUTPUT_HANDLE),
          utf16, wlen, &written, NULL);
      }
      mrb_free(mrb, utf16);
    } else
#endif
#if defined(_WASM)
    if((*(RSTRING_PTR(obj)+RSTRING_LEN(obj)) == '\0')){
      printf("%s",RSTRING_PTR(obj)); // WASMビルド時は printfを使う
    }
#else
      fwrite(RSTRING_PTR(obj), RSTRING_LEN(obj), 1, stdout);
    fflush(stdout);
#endif
  }
}
...

make

================================================
      Config Name: wasm
 Output Directory: build/wasm
    Included Gems:
             mruby-sprintf - standard Kernel#sprintf method
             ... #中略
             mruby-class-ext - class/module extension
             mruby-compiler - mruby compiler library
================================================

cd ..
mkdir hello
cd hello

#include <stdio.h>
#include <mruby.h>
#include <mruby/compile.h>

int
main(void)
{
  mrb_state *mrb = mrb_open();
  if (!mrb) { /* handle error */ }
  puts("Executing Ruby code from C!");
  mrb_load_string(mrb, "p 'hello world! This message is executed Ruby!'"); // <- ここのRubyコードが実行される!
  mrb_close(mrb);
  return 0;
}

emcc hello.c -I ../mruby/include ../mruby/build/wasm/lib/libmruby.bc -O2 -s WASM=1 -o hello.html

ls
# hello.c    hello.html hello.js   hello.wasm

docker run -dit --name my-apache-app -p 8080:80 -v "$PWD":/usr/local/apache2/htdocs/ httpd:alpine