cache-blob-store

cache-blob-store is designed for caching online resources (mainly images) for offline web apps. It uses an abstract-blob-store compatible store for storing blobs (images) and implements and abstract-blob-store compatible interface itself. On top of the abstract-blob-store API it adds additional helper methods for downloading a resource to the store and creating an ObjectUrl for an image in the cache

var cache = new Cache(opts)

Creates a new instance of a cache-blob-store.

Parameters

• opts Object
  • opts.urlTransform function Transforms the url before storing as a key. Default transform removes protocol and numbered sub-domains (for map tiles which are duplicated across numbered subdomains)
  • opts.store Object Instance of an abstract-blob-store. Defaults to idb-content-addressable-blob-store in the browser and content-addressable-blob-store in node / electron (data stored under ./cache-store). Content-addressable stores are preferable, but it should work with any abstract-blob-store
  • opts.metaDb Object Levelup db - defaults to level-js in the browser, in node / electron saves db to ./cache-metadb

Caching helper methods

cache.download(opts, cb)

Download a resource and store it in the cache

Parameters

• url string
• cb Function called with err, metadata

cache.getObjectURL(url, cb)

Returns an ObjectUrl for an image in the cache

Parameters

• url string Url to the image resource
• cb Function called with err, url where url is an URL representing the image object in the cache. Should be revoked with URL.revokeObjectUrl(url) when no longer needed (i.e. when the Image has loaded)

cache.get(url, cb)

Get a resource (e.g. image) from the cache

Parameters

• url string Url to the resource
• cb Function called with err, blob where blob will have type content-type defined from the URL file extension if an image, or metadata content-type stored when the resource was added to the cache

cache.put(opts, blob, cb)

Store a resource (e.g. image) in the cache

Parameters

• opts string or Object String url key, or options object with required key and optional metadata. content-type metadata will be parsed from the blob
  • opts.key string url key of the resource to cache
• blob Blob Image / blob data
• cb Function called with err, metadata when finished

abstract-blob-store compatible methods

cache.createReadStream(opts)

Open a read stream to a blob in the store for url key

Parameters

• opts string or Object String url key, or options object with key property

cache.createWriteStream(opts, cb)

Create a writable stream to add a new blob to the store. Expects a string url key for the resource, or an object with required property key and optional metadata from resource headers, such as content-type (jpg, png and webp content types are guessed from their extension)

Parameters

• opts string or Object String url key, or options object with required key and optional metadata
  • opts.key string url key of the resource to cache
• cb Function Called when stream has finished writing with err, metadata

cache.exists(opts, cb)

Check if opts.key exists with cb(err, exists)

Parameters

• opts string or Object String key or object with property key
• cb Function cb(err, exists) where exists is boolean

cache.remove(opts, cb)

Remove an image from the cache for url

Parameters

• opts string or Object String url key, or options object with required key and optional metadata. content-type metadata will be parsed from the blob
  • opts.key string url key of the resource to cache
• cb Function called with err

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See it on GitHub