gotosocial/internal/media/ffmpeg/wasm.go

// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package ffmpeg

import (
	"context"
	"io"
	"os"

	ffmpeglib "codeberg.org/gruf/go-ffmpreg/embed/ffmpeg"
	ffprobelib "codeberg.org/gruf/go-ffmpreg/embed/ffprobe"
	"github.com/tetratelabs/wazero"
	"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
	"github.com/tetratelabs/wazero/sys"
)

// Use all core features required by ffmpeg / ffprobe
// (these should be the same but we OR just in case).
const corefeatures = ffprobelib.CoreFeatures |
	ffmpeglib.CoreFeatures

var (
	// shared WASM runtime instance.
	runtime wazero.Runtime

	// ffmpeg / ffprobe compiled WASM.
	ffmpeg  wazero.CompiledModule
	ffprobe wazero.CompiledModule
)

// Args encapsulates the passing of common
// configuration options to run an instance
// of a compiled WebAssembly module that is
// run in a typical CLI manner.
type Args struct {

	// Optional further module configuration function.
	// (e.g. to mount filesystem dir, set env vars, etc).
	Config func(wazero.ModuleConfig) wazero.ModuleConfig

	// Standard FDs.
	Stdin  io.Reader
	Stdout io.Writer
	Stderr io.Writer

	// CLI args.
	Args []string
}

// run will run the given compiled
// WebAssembly module using given args,
// using the global wazero runtime.
func run(
	ctx context.Context,
	cmod wazero.CompiledModule,
	args Args,
) (
	uint32, // exit code
	error,
) {
	// Prefix module name as argv0 to args.
	cargs := make([]string, len(args.Args)+1)
	copy(cargs[1:], args.Args)
	cargs[0] = cmod.Name()

	// Create base module config.
	modcfg := wazero.NewModuleConfig()
	modcfg = modcfg.WithArgs(cargs...)
	modcfg = modcfg.WithStdin(args.Stdin)
	modcfg = modcfg.WithStdout(args.Stdout)
	modcfg = modcfg.WithStderr(args.Stderr)

	if args.Config != nil {
		// Pass through config fn.
		modcfg = args.Config(modcfg)
	}

	// Instantiate the module from precompiled wasm module data.
	mod, err := runtime.InstantiateModule(ctx, cmod, modcfg)

	if mod != nil {
		// Ensure closed.
		_ = mod.Close(ctx)
	}

	// Try extract exit code.
	switch err := err.(type) {
	case *sys.ExitError:
		return err.ExitCode(), nil
	default:
		return 0, err
	}
}

// compileFfmpeg ensures the ffmpeg WebAssembly has been
// pre-compiled into memory. If already compiled is a no-op.
func compileFfmpeg(ctx context.Context) error {
	if ffmpeg != nil {
		return nil
	}

	// Ensure runtime already initialized.
	if err := initRuntime(ctx); err != nil {
		return err
	}

	// Compile the ffmpeg WebAssembly module into memory.
	cmod, err := runtime.CompileModule(ctx, ffmpeglib.B)
	if err != nil {
		return err
	}

	// Set module.
	ffmpeg = cmod
	return nil
}

// compileFfprobe ensures the ffprobe WebAssembly has been
// pre-compiled into memory. If already compiled is a no-op.
func compileFfprobe(ctx context.Context) error {
	if ffprobe != nil {
		return nil
	}

	// Ensure runtime already initialized.
	if err := initRuntime(ctx); err != nil {
		return err
	}

	// Compile the ffprobe WebAssembly module into memory.
	cmod, err := runtime.CompileModule(ctx, ffprobelib.B)
	if err != nil {
		return err
	}

	// Set module.
	ffprobe = cmod
	return nil
}

// initRuntime initializes the global wazero.Runtime,
// if already initialized this function is a no-op.
func initRuntime(ctx context.Context) error {
	if runtime != nil {
		return nil
	}

	var cache wazero.CompilationCache

	if dir := os.Getenv("GTS_WAZERO_COMPILATION_CACHE"); dir != "" {
		var err error

		// Use on-filesystem compilation cache given by env.
		cache, err = wazero.NewCompilationCacheWithDir(dir)
		if err != nil {
			return err
		}
	}

	// Prepare config with cache.
	cfg := wazero.NewRuntimeConfig()
	cfg = cfg.WithCoreFeatures(corefeatures)
	cfg = cfg.WithCompilationCache(cache)

	// Instantiate runtime with prepared config.
	rt := wazero.NewRuntimeWithConfig(ctx, cfg)

	// Prepare default "env" host module.
	env := rt.NewHostModuleBuilder("env")

	// Instantiate host "env" module.
	_, err := env.Instantiate(ctx)
	if err != nil {
		return err
	}

	// Instantiate wasi snapshot preview features in runtime.
	_, err = wasi_snapshot_preview1.Instantiate(ctx, rt)
	if err != nil {
		return err
	}

	// Set runtime.
	runtime = rt
	return nil
}