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// Package mastosan takes Mastodon flavored HTML and emits Slack-flavored
// markdown.
//
// It works by using an embedded Rust program compiled to WebAssembly. At
// the time of writing this adds an extra 0.2 seconds to compile and run the
// WebAssembly module, but this can probably be fixed with aggressive sync.Once
// caching should this prove a problem in the real world.
//
// Building this Rust program outside of Nix flakes is UNSUPPORTED.
//
// To build the Rust module from inside the Nix flake:
//
// cargo install wasm-snip
// cargo build --release
// wasm-opt -Oz -o ./testdata/mastosan-pre-snip.wasm
// wasm-snip --skip-producers-section --snip-rust-panicking-code --snip-rust-fmt-code -i ./testdata/mastosan-pre-snip.wasm ./testdata/mastosan.wasm
// rm ./testdata/mastosan-pre-snip.wasm
//
// This adds about two megabytes to the resulting binary, including the AOT
// WebAssembly runtime wazero: https://wazero.io/
package mastosan
import (
"bytes"
"context"
_ "embed"
"log"
"math/rand"
"strconv"
"strings"
"github.com/tetratelabs/wazero"
"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
)
var (
//go:embed testdata/mastosan.wasm
mastosanWasm []byte
r wazero.Runtime
code wazero.CompiledModule
)
func init() {
ctx := context.Background()
r = wazero.NewRuntime(ctx)
wasi_snapshot_preview1.MustInstantiate(ctx, r)
var err error
code, err = r.CompileModule(ctx, mastosanWasm)
if err != nil {
log.Panicln(err)
}
}
func runWASM(ctx context.Context, text, mode string) (string, error) {
fout := &bytes.Buffer{}
fin := bytes.NewBufferString(text)
name := strconv.Itoa(rand.Int())
config := wazero.NewModuleConfig().WithStdout(fout).WithStdin(fin).WithArgs("mastosan", mode).WithName(name)
mod, err := r.InstantiateModule(ctx, code, config)
if err != nil {
return "", err
}
defer mod.Close(ctx)
return strings.TrimSpace(fout.String()), nil
}
// Slackdown converts a string full of HTML text to slack-flavored markdown.
//
// Internally this works by taking that HTML and piping it to a small Rust program
// using lol_html to parse the HTML and rejigger it into slack-flavored markdown.
func Slackdown(ctx context.Context, text string) (string, error) {
return runWASM(ctx, text, "slackdown")
}
// Text converts a string with HTML content into an approximation of plain text.
//
// Internally this works by taking that HTML and piping it to a small Rust program
// using lol_html to parse the HTML and rejigger it into plain text.
func Text(ctx context.Context, text string) (string, error) {
return runWASM(ctx, text, "text")
}
// Markdown converts a string with HTML content into an approximation of plain text.
//
// Internally this works by taking that HTML and piping it to a small Rust program
// using lol_html to parse the HTML and rejigger it into generic markdown.
func Markdown(ctx context.Context, text string) (string, error) {
return runWASM(ctx, text, "markdown")
}
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