abstract-stream-cache v0.9.1

Abstract-Stream-Cache

Provides utilities for creating Stream-Caches for javascript and typescript projects.

WritablePatch

Used to modify nodejs' writable.

InterceptWritable

Takes any WritableStream and redirects received data into an Rx-Observable. No data is received by the original target.

            Rx-Observable
                  ^
                  |
WritableStream ---+     Target

let observable: Observable<Buffer> = interceptWritable(writable);

MapWritable

Takes any WritableStream and forks received data into an Rx-Observable. The data is still received by the original target.

            Rx-Observable
                  ^
                  |
WritableStream ---+---> Target

The modules can be used in chunked and unchunked mode. In chunked mode, every time data is written to the stream, the observable and original target receive this data part. In unchunked mode the written data is collected in memory (using BufferBuilder) until the stream is ended. The observable and original target receive all the data as one buffer at this point.

// Chunked mode
let observable: Observable<Buffer> = mapWritable(writable, true);

// Unchunked mode
let observable: Observable<Buffer> = mapWritable(writable, false);

Cache

Provides an abstract base for general purpose caches. The cache has two generic Type-Arguments, (K)ey and (R)equest. Request is the object type the cache receives and needs to create data for. An example could be a Express-Request. Key is the primitive id that identifies the data. And example could be a request's url.

The cache needs 4 arguments to be created:

cache({
    keyExtractor,
    streamExtractor,
    producer,
    cacheBackend,
});

KeyExtractor

Takes a Request and generates a Key for it. It method must be deterministic.

StreamExtractor

Takes a Request and returns a Writable that represents the target for the data to create.

Producer

Producer for the data if it is not found in the cache.

CacheBackend

Backend where data is cached to. A file backend is provided with this package.