Altair-sh
59 lines
2.2 KiB
TypeScript
59 lines
2.2 KiB
TypeScript
// Zstandard compression and decompression as stream transforms.
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//
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// Saves are re-compressed in the browser because the parser backend runs on a
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// cheap two core server with little disk space. zstd was picked over lzma2 and
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// brotli because its decompression speed does not depend on the level the data
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// was compressed with, so the level can be raised without costing the server
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// anything, and because its wasm build is by far the smallest of the three.
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//
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// @tootallnate/zstd-wasm does the work: it is upstream zstd 1.5.7 built with
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// wasi-sdk and driven through ZSTD_compressStream2, so it compresses a stream
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// as it arrives rather than a buffer at a time. A save of any size comes out
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// as one zstd frame, and memory stays at the library's own input and output
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// buffers.
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import {
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ZstdCompressStream,
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ZstdDecompressStream,
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} from '@tootallnate/zstd-wasm'
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// The wasm file ships inside the package. Turbopack rewrites this into the URL
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// it emits the asset at, so the 534 kB binary is fetched once at runtime and
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// cached by the browser instead of being inlined into the worker bundle.
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const wasmUrl = new URL(
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'../../../node_modules/@tootallnate/zstd-wasm/dist/zstd.wasm',
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import.meta.url
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)
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// Compiling takes a moment, so it happens once and both directions share it.
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let wasmModule: Promise<WebAssembly.Module> | null = null
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function getWasm(): Promise<WebAssembly.Module> {
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// compileStreaming would need the server to send Content-Type:
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// application/wasm, which is not worth depending on.
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wasmModule ??= fetch(wasmUrl)
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.then((res) => res.arrayBuffer())
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.then((bytes) => WebAssembly.compile(bytes))
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return wasmModule
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}
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/**
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* Compresses a stream into a single zstd frame. The level goes from 1 to 22.
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*/
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export function createZstdCompressStream(
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compressionLevel: number
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): TransformStream<Uint8Array, Uint8Array> {
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return new ZstdCompressStream(getWasm(), compressionLevel)
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}
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/**
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* Decompresses a zstd stream. Frames that follow one another are read straight
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* through, so an archive packed as several frames still opens.
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*/
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export function createZstdDecompressStream(): TransformStream<
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Uint8Array,
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Uint8Array
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> {
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return new ZstdDecompressStream(getWasm())
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}
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