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Published 41 hours ago • verified publisherleonidov.dev
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Pure-Dart core of Hydraline: real semantic HTML for Flutter Web. DocumentNode, SafeUrl, SEO, JSON-LD, sitemap, robots, audit CLI. + hydraline_server, hydraline_flutter.

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hydraline #

Part of Hydraline - real crawlable HTML for Flutter Web. Three packages, one toolkit.

hydraline (core, you are here) · hydraline_server (SSR) · hydraline_flutter (widgets)

Pure-Dart core - the foundation everything else builds on. No Flutter, no dart:ui, no dart:html. Works on any Dart VM.

Build, serialize and audit real semantic HTML from Dart: headings, paragraphs, images with alt, links, tables, sections, ordered/unordered lists, and island placeholders - all typed, all safe, all crawlable.

pub tests

Why #

Flutter Web renders into a <canvas> — crawlers see an empty shell. Hydraline fixes this: your pages become real semantic HTML in view-source. This package is the foundation — the DocumentNode tree that both the SSR server and the SSG compiler consume. One model, two delivery paths, same bytes.

  • Safe by construction. SafeUrl rejects javascript:/data: at type level; context-aware escaping (text vs attribute); sanitizeHtml() strips scripts and event handlers. 1e6-input XSS fuzz suite.
  • Full SEO head. Open Graph (with image dimensions), Twitter Card, 9 JSON-LD types (Product, Article, FAQ, Recipe, Event...), sitemap.xml (auto-split at 50k URLs), robots.txt, hreflang alternates, audit CLI.
  • Zero dependencies on Flutter. Works in any Dart VM — servers, CLIs, build pipelines. The hydraline_server and hydraline_flutter packages build on this core, adding SSR/streaming (server) and widgets/SSG/islands (Flutter).

What's inside #

Module Description
DocumentNode Sealed immutable tree: HeadingNode, ParagraphNode, ImageNode, AnchorNode, SectionNode (<main>/<nav>/<article>), ListNode (<ol>/<ul> + ListItemNode), TableNode, DetailsNode, BlockquoteNode, PreNode, CodeNode, TimeNode, IslandPlaceholderNode, HtmxIslandNode, VanillaIslandNode, JsonLdNode
HtmlSerializer Single-pass deterministic HTML serializer - buffered, streaming, and fragment modes. O(nodes + text), 10k paragraphs in 29 ms
SafeUrl Type-safe URL - no public constructor, scheme allowlist blocks javascript:/data: at construction. A node can never hold an unchecked URL
sanitizeHtml() Baseline HTML sanitizer: strips <script> and on* event handlers
UnsafeHtmlNode / .trusted() Opt-in raw HTML escape hatch. .trusted() explicitly signals reviewed content
escapeHtmlText / escapeHtmlAttribute Context-aware escaping - text vs attribute, never confused. Backed by a 1e6-input XSS fuzz suite
SeoMeta / buildHead() Deterministic <head>: title, description, canonical, viewpoint, robots, full Open Graph (with image dimensions), Twitter Card, hreflang alternates, extra meta/link
JsonLd Type-safe JSON-LD builders: Article, Product (+Offer/price), BreadcrumbList, WebPage, Organization, FAQPage, Event, Recipe, Review + raw() escape hatch
Sitemap sitemap.xml with auto-split at 50k URLs / 50 MB, hreflang per URL, changefreq, priority, lastmod (UTC)
Robots robots.txt with programmable rules, line-break validation
RouteManifest hydraline.routes.yaml parser + Dart builder - document / hybrid / app modes
IslandSpec / IslandStateCodec data-state props contract - JSON-safe, validated
SsgCollector Widget-to-node registration with nested sectioning (beginSection, beginList)
islandRuntime() One-liner for runtime script injection: engine config + dispatcher + custom element. Optional SRI (integrity/crossorigin)
SeoValidator / Audit SEO validator: title/description length, alt text, duplicate canonicals, hreflang, unsafe HTML. Audit CLI: dart run hydraline:audit
Csp Recommended Content-Security-Policy: script-src 'self' 'wasm-unsafe-eval'
vanillaIslandsJs Level-1 vanilla islands bundle (≤ 8 KB) - accordion, tabs, carousel, theme, copy-button, lazy-image with hardened null guards
htmxGlueJs HTMX bootstrap glue - loads self-hosted HTMX runtime on demand
web/vanilla-islands.js Browser-consumable mirror, byte-identical to the Dart constant (locked by test)

Rules #

No package:flutter, dart:ui, or dart:html - ever. This package is pure Dart. Enforced at build time by melos run boundaries.

Quick start #

import 'package:hydraline/hydraline.dart';

final root = DocumentRootNode(
  lang: 'en',
  head: buildHead(SeoMeta(
    title: 'Espresso Machine',
    description: 'Compact 15-bar espresso machine.',
    canonical: SafeUrl.parse('https://shop.example/'),
    openGraph: OpenGraph(
      type: 'product',
      image: SafeUrl.parse('https://shop.example/og.jpg'),
    ),
  ), structuredData: [JsonLd.product(name: 'Espresso', price: 249, currency: 'EUR')]),
  body: [
    HeadingNode(level: 1, children: [TextNode('Espresso Machine')]),
    ParagraphNode(children: [TextNode('Real HTML. Real rankings.')]),
    SectionNode(role: SectionRole.main, children: [
      ListNode(ordered: false, items: [
        ListItemNode(children: [ParagraphNode(children: [TextNode('Feature one')])]),
      ]),
    ]),
    IslandPlaceholderNode(
      id: 'calculator',
      directive: HydrationDirective.onVisible,
      size: IslandSize(width: 640, height: 320),
      state: {'price': 249},
    ),
    ...islandRuntime(),
  ],
);

const serializer = HtmlSerializer();
print(serializer.serialize(root));
// <!DOCTYPE html><html lang="en"><head>...<main><ol><li>...

dart run hydraline:audit dist/index.html       # what a crawler sees

Proven #

  • 229 unit/widget tests - including a 1e6-input XSS fuzz suite
  • Single-pass serializer: 10k paragraphs 29 ms (16.7 MB/s), no quadratic concat
  • Security: SafeUrl type-level allowlist, context-aware escaping, HTML sanitizer
  • CI-gated: analyze (--fatal-infos), format:check, boundaries (I1), coverage

Runnable example: example/main.dart.

Documentation #

License #

MIT - Yevhen Leonidov

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Pure-Dart core of Hydraline: real semantic HTML for Flutter Web. DocumentNode, SafeUrl, SEO, JSON-LD, sitemap, robots, audit CLI. + hydraline_server, hydraline_flutter.

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Topics

#seo #ssr #flutter-web #html #prerender

License

MIT (license)

Dependencies

html, yaml

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