Class ZipAssetProvider

Namespace

VpnHood.Net.Toolkit.Assets

Assembly

VpnHood.Net.Toolkit.dll

Provides the entries of a zip as assets: extracted once into a folder named after the zip's stamp (ZipStamp), and read from there as files.

public class ZipAssetProvider : IAssetProvider

Inheritance

object

ZipAssetProvider

Implements

IAssetProvider

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Remarks

A start reads only the stamp in front of the zip, and the whole zip only to extract it; a zip without a stamp is hashed whole instead, a pass over it before the first read. A name from outside the bytes would not do: a phone's update unpacks the app again, changed or not, and a file's time and size are not reliable.

The folder is the provider's: it tries to delete the other folders in it, so no other zip may be given it. Two instances, or two processes, each write their copy to a folder of their own and move it into place, and a version already there is taken as it stands; a race between them is not fully guarded.

Constructors

ZipAssetProvider(IAsset, string)

Provides the entries of a zip as assets: extracted once into a folder named after the zip's stamp (ZipStamp), and read from there as files.

public ZipAssetProvider(IAsset zip, string extractFolderPath)

Parameters

zip IAsset

The zip.

extractFolderPath string

The folder the zip is extracted into, the provider's alone.

Remarks

A start reads only the stamp in front of the zip, and the whole zip only to extract it; a zip without a stamp is hashed whole instead, a pass over it before the first read. A name from outside the bytes would not do: a phone's update unpacks the app again, changed or not, and a file's time and size are not reliable.

The folder is the provider's: it tries to delete the other folders in it, so no other zip may be given it. Two instances, or two processes, each write their copy to a folder of their own and move it into place, and a version already there is taken as it stands; a race between them is not fully guarded.

Methods

OpenReadAsync(string, CancellationToken)

Opens the asset at a path, such as fonts/text.ttf.

public Task<Stream> OpenReadAsync(string assetPath, CancellationToken cancellationToken)

Parameters

assetPath string

The asset's path.

cancellationToken CancellationToken

The token to monitor for cancellation requests.

Returns

Task<Stream>

A task whose result is a new stream, which the caller owns and disposes.

Remarks

It is asynchronous because a page in a browser fetches over the network and cannot wait. Read the stream forward: whether it can seek is the platform's answer, not a promise; a file can, an HTTP body and an Android asset cannot. A caller that needs more than one pass opens the asset again where it can, and copies it into memory only where it cannot, so the cost is paid where it is decided. A caller that only asks, such as a language falling back to another, takes TryOpenReadAsync, which gives null for an absent asset.

Exceptions

AssetNotFoundException

The provider classes the asset as absent; exactly this type, as a file it finds and cannot open is another failure.