@ chunkd/ 中间软件

为所有获取逻辑提供高级特性的源的中间软件层

缓存

缓存 请求的缓存响应, 并带有 LRU 缓存

import { SourceCache } from '@chunkd/middleware';
import { Source } from '@chunkd/source';
import { SourceHttp } from '@chunk/http';

/** Create a cache with 1MB of storage */
const cache = new SourceCache({ size: 1024 * 1024 * 1024 });
sources.use(cache);

const sourceHttp = sources.wrap(new SourceHttp('https://example.com/cog.tiff'));

// Cache Miss
sourceHttp.fetch(0, 1024);
// Cache hit
sourceHttp.fetch(0, 1024);

// Clear the cache
cache.clear();
// Cache Miss
sourceHttp.fetch(0, 1024);

绝对

绝对 将相接字节请求转换为绝对字节请求,以加强缓存

import { SourceCache } from '@chunkd/middleware';
import { Source } from '@chunkd/source';
import { SourceHttp } from '@chunk/http';

const abs = new SourceAbsolute();
sources.use(abs);

const sourceHttp = sources.wrap(new SourceHttp('https://example.com/cog.tiff'));

await sourceHttp.head(); // Ensure the file size is know

sourceHttp.fetch(-10); // Instead of a request for -10 bytes it will now request Bytes=[fileSize-10]-[fileSize]

块对齐取取取 (Chunking)

块 块对齐读取并大大提高缓存效率

// read files in 32KB chunks
const chunk = new SourceChunk({ size: 32 * 1024 });
const cache = new SourceCache({ size: 1024 * 1024 * 1024 });

source.use(chunk);
source.use(cache);

const sourceHttp = sources.wrap(new SourceHttp('https://example.com/cog.tiff'));

// Cache Miss, will fetch the first 32KB of the file
sourceHttp.fetch(0, 1024);
// Cache hit
sourceHttp.fetch(0, 1024);

// Cache hit
sourceHttp.fetch(1024, 1024);
// Cache hit
sourceHttp.fetch(2048, 1024);