Upgrade play.d2lang.org URLs generated before Dec 06

upd2url.go

/* Upgrade old D2 playground URLs (<= Dec 06 2023) to new URLS (>= Dec 06 2023).
 *
 * usage: go run upd2url.go < file_of_old_urls > new_urls
 *
 * Timeline:
 * 1. Nov 7 2023:
 *    d2 changed their URL encode and decode to avoid the use of a custom DEFLATE dictionary.
 *    https://github.com/terrastruct/d2/commit/5eead31c91fcc1f6c0ecaf28e3006758055efd8b
 * 2. Dec 6 2023:
 *    play.d2lang.org upgraded its WASM compiled version of d2 that is run client-side.
 *    https://github.com/terrastruct/d2-playground/commit/ae1e9c3bcd9896a978f80a0d1d370fea302e85a0
 *
 * If you saved any URLs to play.d2lang.com that included D2 diagrams (compressed, base64
 * encoded, and passed in the script= query parameter) these would no longer decode properly
 * in the newly deployed play.d2lang.org site. If you didn't save a backup the old diagram source
 * was lost.
 *
 * This program reads old URLs and prints out new URLs a line at a time. The old URLs are decoded
 * using the old deflate dictionary and encoded to new URLs which have no custom dictionary.
 *
 * Justin Davis <justin_davis@baxter.com>
 */

package main

import (
	"bufio"
	"bytes"
	"compress/flate"
	"encoding/base64"
	"fmt"
	"io"
	"net/url"
	"os"
	"strings"
)

// these must be pre-sorted
const keywords = `
	3d animated bold border-radius class classes constraint desc direction
	double-border fill fill-pattern filled font font-color font-size
	grid-columns grid-gap grid-rows height horizontal-gap icon italic
	label layers left link multiple near opacity scenarios shadow shape
	source-arrowhead steps stroke stroke-dash stroke-width style
	target-arrowhead text-transform tooltip top underline vars
	vertical-gap width
`

var oldRawDict []byte

func init() {
	common := strings.Fields(keywords)
	oldRawDict = []byte("->" + "<-" + "--" + "<->" + strings.Join(common, ""))
}

func UpgradeURL(old *url.URL) error {
	vals := old.Query()
	oldscript64 := vals.Get("script")
	if oldscript64 == "" {
		return fmt.Errorf("URL missing script query param", old)
	}
	oldscript, err := base64.URLEncoding.DecodeString(oldscript64)
	if err != nil {
		return err
	}
	bin, bout := bytes.NewBuffer(oldscript), &bytes.Buffer{}
	zrdr := flate.NewReaderDict(bin, oldRawDict)
	zwtr, err := flate.NewWriter(bout, flate.BestCompression)
	if err != nil {
		return err
	}
	_, err = io.Copy(zwtr, zrdr)
	if err != nil {
		return err
	}
	zwtr.Close()
	newscript64 := base64.URLEncoding.EncodeToString(bout.Bytes())
	vals.Set("script", newscript64)
	old.RawQuery = vals.Encode()
	return nil
}

func main() {
	scan := bufio.NewScanner(os.Stdin)
	scan.Split(bufio.ScanLines)
	for scan.Scan() {
		var input *url.URL
		var err error
		if input, err = url.ParseRequestURI(scan.Text()); err != nil {
			fmt.Fprintln(os.Stderr, "error: invalid URL")
			continue
		}
		if err := UpgradeURL(input); err != nil {
			fmt.Fprintln(os.Stderr, "error:", err)
			continue
		}
		fmt.Println(input)
	}
}