Add a hosting abstraction to provide a location on disk that components can use to read data from

[javiercn]

[javiercn]

IHosting application data

Motivation

• There are components/libraries in our platform that require of a predefined location on disc to read/store data.
  • DataProtection keys.
  • Default kestrel HTTPS certificates.
  • User secrets.
  • ASP.NET Core buffering. BufferingHelper.cs#L25
• Right now every component chooses their own locations for storing state, which increases the footprint of every
  application on the machine.
• Like our own frameworks, other frameworks may have the need to read or store some state on a well-known location
  on disk, in order to avoid the need to avoid configuring an explicit path on disk.

Proposed solution

• We can introduce at the hosting level the concept of IHostingApplicationData.
• This service defines a location where components in the framework can search for files that they need to work.
  • For example, certificates for HTTPS, keys for data protection, etc.
• This location should be considered GLOBAL for the machine, components requiring more isolation for their data
  MUST further namespace the data by using the application name (for example, caching).
• The existence of this folder must not be required by any component to work, nor it is the ability to write to
  that folder.
  • For example, with DataProtection we will just fallback to ephemeral if the location is not available.
• Compoments on the framework must provide the ability to override this folder if they require a location on disk
  to work.
  • For example, with the default kestrel HTTPS certificate users can provide the path to the certificate explicitly.

Options

There are a couple of ways we can go about with this service:

Make it something meant for ASP.NET Core components internal comsumption.

• We follow the same pattern HostingEnvironment has for other locations on disk like ContentRoot.
• We use the same set of folders data protection uses to store the keys plus an additional fallback folder APP_DATA.

public interface IHostingApplicationData
{
    /// <summary>
    /// Gets or sets the absolute path to the directory that applications use to
    /// store data outside of the content root of the application.
    /// </summary>
    string ApplicationDataPath { get; set; }

    /// <summary>
    /// Gets or sets an <see cref="IFileProvider"/> pointing at <see cref="ApplicationDataPath"/>.
    /// </summary>
    IFileProvider ApplicationDataFileProvider { get; set; }
}

Make it something all our components and user applications can use to optimistically read/store state.

• We provide a set of abstractions designed to read and write state to this location, with application scoping by default and optionally global scoping.
• We prioritize local/app scoped folders like APP_DATA over other more global/machine scoped folders like %HOME% or %USERPROFILE%
• We might provide different folders instead of a single one for different kinds of data.
  • Global folders use the same conventions as data protection.
  • Local folders prioritize an APP_DATA folder relative to the app and fall-back to
    a global folder with automatic namespacing.
• We might provide three categories of data:
  • Data that is exclusively local and can live in a folder along side your app. (Caching data, etc.)
  • Data that is exclusively global and should be shared across the machine. (Data protection keys)
  • Data that is exclusively local but can't live in a folder along side your app. (User secrets)

public interface IHostingApplicationData
{
    string LocalApplicationDataPath { get; set; }
    string GlobalApplicationDataPath { get; set; }

    Stream GetApplicationDataStream(
        string path,
         /* options: read, write, create if not exists, */,
          /* local, global, global-namespaced */);
}

public enum StreamCreationOptions
{
    Read,
    Write,
    CreateIfNotExists
}

public enum DataKind{
    Local,
    Global,
    ApplicationScopedGlobal
}

Details

• By default we try to find the folder to use following the same criteria as data protection, plus an additional fallback location:
  • Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData)/ASP.NET (For windows only).
  • %LOCALAPPDATA%/ASP.NET.
  • %USERPROFILE%/AppData/Local/ASP.NET
  • %HOME%/.aspnet
  • Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData)/ASP.NET
  • AppContext.BaseDirectory/APP_DATA
• The location used can be overriden through configuration.

[javiercn]

Replace the kestrel logic to use this:

https://github.com/aspnet/KestrelHttpServer/pull/2246/files/e6bb55101893142f92912c748e66115bc4aacdb4#diff-30cd221b1afd076c151780af8b8d3413R328