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// SPDX-FileCopyrightText: 2025 Stefan Majewsky <majewsky@gmx.net>
// SPDX-License-Identifier: GPL-3.0-only
package mdedit
import (
"bytes"
"context"
"crypto/sha256"
_ "embed"
"encoding/hex"
"fmt"
"io"
"io/ioutil"
"log"
"net/http"
"os"
"os/signal"
"regexp"
"sync"
"sync/atomic"
"syscall"
"time"
"github.com/yuin/goldmark"
"github.com/yuin/goldmark/extension"
"github.com/yuin/goldmark/renderer/html"
)
var (
withMermaid bool
)
// Exec executes the mdedit applet and returns an exit code (0 for success, >0 for error).
func Exec(fullArgs []string) int {
// consume optional arguments
var args []string
for _, arg := range fullArgs {
switch arg {
case "--with-mermaid":
withMermaid = true
default:
args = append(args, arg)
}
}
// consume positional arguments
if len(args) != 2 {
os.Stderr.Write([]byte(" Usage: mdedit [--with-mermaid] <file.md> <listenaddr>\nExample: mdedit todolist.md localhost:8080\n Note: If --with-mermaid is given, the UI may connect to https://cdn.jsdelivr.net to fetch mermaid.js\n"))
return 1
}
markdownPath, listenAddress := args[0], args[1]
// prepare HTTP server
l := logic{markdownPath}
m := http.NewServeMux()
m.HandleFunc("GET /{$}", l.handleGetFile("index.html", embeddedHTML))
m.HandleFunc("GET /res.css", l.handleGetFile("res.css", embeddedCSS))
m.HandleFunc("GET /res.js", l.handleGetFile("res.js", embeddedJS))
if withMermaid {
buf, err := loadMermaidJS()
if err != nil {
log.Println(err.Error())
return 1
}
m.HandleFunc("GET /mermaid.js", l.handleGetFile("mermaid.js", buf))
}
m.HandleFunc("GET /data.html", l.handleGetDataHTML)
m.HandleFunc("GET /data.md", l.handleGetDataMarkdown)
m.HandleFunc("PUT /data.md", l.handlePutDataMarkdown)
s := &http.Server{Addr: listenAddress, Handler: m}
exitCode := &atomic.Int32{}
exitCode.Store(0)
// setup termination of HTTP server on SIGINT/SIGTERM
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()
var wg sync.WaitGroup
wg.Go(func() {
for range ctx.Done() {
}
ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
err := s.Shutdown(ctx)
if err != nil {
log.Println("shutdown error: " + err.Error())
exitCode.Store(1)
}
cancel()
})
// run HTTP server
log.Printf("listening on %s...\n", listenAddress)
err := s.ListenAndServe()
if err != http.ErrServerClosed {
log.Println("listen error: " + err.Error())
exitCode.Store(1)
}
stop()
wg.Wait()
return int(exitCode.Load())
}
func loadMermaidJS() ([]byte, error) {
// load dependencies
const (
mermaidURL = "https://cdn.jsdelivr.net/npm/mermaid@11.17.2/dist/mermaid.min.js"
mermaidSHA256 = "581ed7d74bd9048d0e3a91363927d72ef22942d7722546b27f7cc29e35390eb8"
)
resp, err := http.Get(mermaidURL)
if err != nil {
return nil, fmt.Errorf("could not fetch %s: %w", mermaidURL, err)
}
defer resp.Body.Close()
buf, err := ioutil.ReadAll(resp.Body)
if err != nil {
return nil, fmt.Errorf("could not read response from %s: %w", mermaidURL, err)
}
hash := sha256.Sum256(buf)
digest := hex.EncodeToString(hash[:])
if digest != mermaidSHA256 {
return nil, fmt.Errorf("expected %s to match %s, but got %s", mermaidURL, mermaidSHA256, digest)
}
return buf, nil
}
type logic struct {
MarkdownPath string
}
var (
//go:embed res/index.html
embeddedHTML []byte
//go:embed res/style.css
embeddedCSS []byte
//go:embed res/app.js
embeddedJS []byte
withMermaidBlockRx = regexp.MustCompile(`<with-mermaid>(.*)</with-mermaid>`)
)
// Handles `GET /` and `GET /res/...`.
func (l logic) handleGetFile(name string, contents []byte) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
if name == "index.html" {
if withMermaid {
contents = withMermaidBlockRx.ReplaceAll(contents, []byte("$1"))
} else {
contents = withMermaidBlockRx.ReplaceAll(contents, nil)
}
}
http.ServeContent(w, r, name, time.Time{}, bytes.NewReader(contents))
}
}
// Handles `GET /data.html`.
func (l logic) handleGetDataHTML(w http.ResponseWriter, r *http.Request) {
buf, err := os.ReadFile(l.MarkdownPath)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
l.respondByRenderingMarkdown(w, buf)
}
// Handles `GET /data.md`.
func (l logic) handleGetDataMarkdown(w http.ResponseWriter, r *http.Request) {
buf, err := os.ReadFile(l.MarkdownPath)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
w.Header().Set("X-Mdedit-Path", l.MarkdownPath)
http.ServeContent(w, r, "data.md", time.Time{}, bytes.NewReader(buf))
}
// Handles `PUT /data.md`.
func (l logic) handlePutDataMarkdown(w http.ResponseWriter, r *http.Request) {
const maxSizeBytes = 8 * 1024 * 1024 // 8 MiB ought to be enough for a single Markdown file
buf, err := io.ReadAll(io.LimitReader(r.Body, maxSizeBytes))
if err != nil {
http.Error(w, "while reading request body: "+err.Error(), http.StatusInternalServerError)
return
}
err = os.WriteFile(l.MarkdownPath, buf, 0666)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
l.respondByRenderingMarkdown(w, buf)
}
var md = goldmark.New(
goldmark.WithExtensions(extension.GFM),
goldmark.WithRendererOptions(html.WithUnsafe()),
)
func (l logic) respondByRenderingMarkdown(w http.ResponseWriter, source []byte) {
var buf bytes.Buffer
err := md.Convert(source, &buf)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
w.Header().Set("Content-Type", "text/html; charset=utf-8")
w.Write(buf.Bytes())
}
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