ext/web

Active contributors: Bartek Iwańczuk, Divy Srivastava, Marvin Hagemeister

Purpose

ext/web is the foundational web platform extension. It implements the DOM-style globals that have nothing to do with networking or the filesystem: events, abort signals, message ports, structured clone, blobs, file readers, base64, text encoding, streams, the URL constructor, the URL pattern matcher, performance API, and the timer functions. Most other web platform extensions (ext/fetch, ext/websocket, ext/webstorage) depend on ext/web for their primitives.

Directory layout

ext/web/
├── Cargo.toml
├── lib.rs                  # extension!() macro, ops registration
├── 00_infra.js             # primordials, basic infra
├── 00_url.js               # URL parsing
├── 01_broadcast_channel.js
├── 01_console.js           # console.* implementation
├── 01_dom_exception.js     # DOMException
├── 01_mimesniff.js         # MIME sniffing
├── 01_urlpattern.js        # URLPattern
├── 02_event.js             # EventTarget, Event, CustomEvent
├── 02_structured_clone.js  # structuredClone()
├── 02_timers.js            # setTimeout / setInterval / queueMicrotask
├── 03_abort_signal.js      # AbortController / AbortSignal
├── 04_global_interfaces.js # WindowOrWorkerGlobalScope shared
├── 05_base64.js            # atob / btoa
├── 06_streams.js           # ReadableStream, WritableStream, TransformStream
├── 06_streams_types.d.ts
├── 08_text_encoding.js     # TextEncoder / TextDecoder
├── 09_file.js              # Blob, File
├── 10_filereader.js        # FileReader
├── 12_location.js          # Worker location
├── 13_message_port.js      # MessageChannel, MessagePort
├── 14_compression.js       # CompressionStream, DecompressionStream
├── 15_performance.js       # performance.now(), PerformanceObserver
├── 16_image_data.js        # ImageData
├── blob.rs, broadcast_channel.rs, compression.rs, console.rs,
│   css_value.rs, f64.rs, geometry.rs, message_port.rs,
│   stream_resource.rs, timers.rs, url.rs, urlpattern.rs   # ops
├── benches/
└── webtransport.js         # WebTransport (in-progress)

The 24 *.js files are loaded in numeric order during snapshot creation, so something at 02_* can rely on 00_* and 01_* having already defined their globals.

Key abstractions

Type	Where	Role
BlobStore	blob.rs	In-memory store backing Blob/File/object URLs; passed into worker construction
InMemoryBroadcastChannel	broadcast_channel.rs	Backs BroadcastChannel when not crossing process boundaries
MessagePort resource	message_port.rs	Half of a port pair backing MessageChannel and Worker.postMessage
stream_resource	stream_resource.rs	Bridge between Rust AsyncRead/AsyncWrite and ReadableStream/WritableStream
urlpattern ops	urlpattern.rs	Parser/matcher for URLPattern
compression ops	compression.rs	gzip/deflate streams (via flate2)
timers ops	timers.rs	setTimeout / setInterval backed by Tokio
console ops	console.rs	Minimal native helpers; bulk of console.* is in 01_console.js

How it works

graph LR
    UserCode["fetch(url) / new Blob(...) / setTimeout(...)"] --> JsFiles["ext/web/*.js<br/>(numbered, snapshotted)"]
    JsFiles -->|core.ops.op_*| Ops["ext/web/*.rs<br/>#[op2]"]
    Ops --> Tokio["Tokio runtime"]
    Ops --> BlobStore[("BlobStore")]
    Ops --> Streams["stream_resource bridge"]
    Streams --> Rust["AsyncRead / AsyncWrite"]

Streams

06_streams.js (the largest file in this extension) implements ReadableStream, WritableStream, and TransformStream per the WHATWG spec — including byob byte streams, queueing strategies, and tee'ing. The Rust side (stream_resource.rs) is a shim that lets ops produce or consume streams without each op re-implementing the buffering protocol.

Timers

02_timers.js exposes setTimeout, setInterval, setImmediate, and queueMicrotask. The actual scheduling lives in timers.rs using Tokio's timer wheel; the JS layer is mostly responsible for the v8-side bookkeeping (handle ids, ref/unref).

MessagePort

message_port.rs + 13_message_port.js implement the MessageChannel/MessagePort primitives. They're the same primitives Worker uses internally for postMessage. The Rust side owns the cross-thread MPSC channel; the JS side wraps it in event-emitter semantics.

URL and URLPattern

url.rs + 00_url.js implement the URL spec on top of the url crate, plus origin/host/pattern helpers. urlpattern.rs + 01_urlpattern.js implement the URLPattern spec used by Deno.serve for routing.

Integration points

• Depended on by: ext/fetch, ext/websocket, ext/webstorage, ext/webgpu, ext/cache, ext/http (for streams + AbortSignal), and parts of ext/node (which re-exposes web globals to Node code).
• Depends on: ext/webidl for type conversion (webidl::convert<...>(...) calls), deno_core primordials.
• Worker integration: BlobStore and InMemoryBroadcastChannel are constructed by the CLI / runtime caller and passed into MainWorker::bootstrap_from_options.

Entry points for modification

• New web API global — pick the appropriate numbered slot, add a *.js file, define ops in a *.rs sibling, register both in lib.rs's extension!() macro.
• Stream behavior — most logic is in 06_streams.js; the Rust shim in stream_resource.rs is mostly stable.
• URL spec update — url.rs (URL crate version) plus 00_url.js. URLPattern is split out into urlpattern.rs / 01_urlpattern.js.
• structuredClone types — 02_structured_clone.js plus the message-port serializer in 13_message_port.js.

Key source files

File	Purpose
ext/web/lib.rs	deno_core::extension!() registration of ops + JS
ext/web/06_streams.js	WHATWG Streams implementation (largest single JS file)
ext/web/stream_resource.rs	Bridge between Rust AsyncRead/Write and JS streams
ext/web/timers.rs + 02_timers.js	setTimeout/setInterval
ext/web/message_port.rs + 13_message_port.js	MessagePort/Channel
ext/web/blob.rs + 09_file.js + 10_filereader.js	Blob/File/FileReader
ext/web/url.rs + 00_url.js + urlpattern.rs + 01_urlpattern.js	URL + URLPattern
ext/web/02_event.js	EventTarget / Event / CustomEvent
ext/web/03_abort_signal.js	AbortController / AbortSignal
ext/web/06_streams_types.d.ts	Type declarations for streams (used by editor tooling)