Hidden gems in ASP.Core and .NET Core 3.0

You've likely heard about the headline features in .NET Core 3.0 including Blazor, gRPC, and Windows desktop app support, but what else is there?

This is a big release so come and see David Fowler and Damian Edwards from the .NET Core team showcase their favorite new features you probably haven't heard about in this demo-packed session.

Transcript

1. Hidden gems in ASP.NET
   Core & .NET Core 3.0
   David Fowler @davidfowl
   Damian Edwards @damianedwards
   

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2. First, the usual suspects
   SingleFileExe!
   

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3. Core CLR
   Let’s start at the bottom
   

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4. GC limits & new defaults
   • Can now set limits for how much memory the GC has available to it
   • Limits can be % or size based
   • Set via environment variables
   • Runtime API to get limits: GC.GetGCMemoryInfo
   • New defaults use much less memory by default
   

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5. AssemblyLoadContext
   • New plugin model: AssemblyDependencyResolver
   • Determines assembly paths given an application path and assembly name
   • Unloadable contexts, meaning you can now unload assemblies (yay!)
   • Support for resolving native and managed assemblies
   • Not an isolation boundary for security purposes
   • Logical successor to AppDomains
   • DEMO
   

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6. Startup hooks
   • Register code to execute before Program.Main
   • Set an env var with assembly name or full path
   • Assembly must contain an internal type named StartupHook with a
   public static Initialize method
   • DEMO
   

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7. Diagnostics improvements
   • New dotnet global diag tools: counters, trace, dump
   • Default diagnostics pipe open on every .NET Core process
   • Runtime APIs for accessing runtime counters for GC, ThreadPool, etc.
   • New “dumpasync” sos command
   • Dump on crash: export COMPlus_DbgEnableMiniDump=1
   • DEMO
   

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8. Publish options: ReadyToRun (pre-JIT)
   • During publish, generate “ReadyToRun” native images for your app
   • A form of AOT or pre-JIT similar to ngen
   • Slightly larger file sizes but faster startup
   • Tiered Compilation will re-JIT after startup to improve throughput
   dotnet publish /p:PublishReadyToRun=true -r win-x86
   

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9. Publish options: SingleFile
   • Publish your app to a single executable file for selected platform
   • Produces a bootstrapper executable with your app files embedded
   • Self-extracts on first launch to the user profile and runs from there
   dotnet publish /p:PublishSingleFile=true –r win-x86
   DEMO
   

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10. Publish options: Assembly linking
    • Linker tech from Mono incorporated into the SDK
    • Trims unused code from your code and your dependencies
    • Configurable to keep assemblies the tool can’t detect you’re using
    dotnet publish /p:PublishTrimmed=true –r win-x86
    DEMO
    

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11. Native interop improvements
    • Managed C++ CLI
    • COM interop
    • WinRT
    • NativeLibrary
    • New API that’s the imperative equivalent of DllImport
    • Uses the CLR host logic to find native libraries from known locations
    • Platform agnostic LoadLibrary and GetProcAddress
    • SAMPLES
    

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12. Misc. for CoreCLR
    • ARM64 support (Linux only)
    • Hardware intrinsics (UTF8 encoding is optimized using these now)
    

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13. BCL
    APIs for all
    

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14. IAsyncDisposable
    • Ability to call async methods in objects’ dispose methods in a non-
    blocking way
    • Implemented on Stream, StreamReader, and other types that do I/O
    • Use with C# 8 await using
    

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15. Distributed tracing
    • Updates to Activity type to support W3C Trace-Context
    • On by default
    • Provides correlated logs for requests that span multiple processes
    • Integrates with Open Telemetry (prev. Open Census)
    • DEMO
    

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16. Runtime feature detection
    • IsDynamicCodeCompiled
    • Is the generated code optimized or interpreted (JIT vs interpreter)
    • IsDynamicCodeSupported
    • Can I generate code at runtime (RefEmit)
    • Used by serializers, DI containers, ORMs, and other dynamic code
    generators
    

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17. ThreadPool enhancements
    • UnsafeQueueUserWorkItem
    • Advanced API that runs the enqueued work item without the current
    ExecutionContext
    • IThreadPoolWorkItem
    • Allows you to implement your own type that gets queued to the ThreadPool,
    which allows for advanced optimizations in appropriate cases
    • Used by Kestrel & ANCM and various parts of the BCL to reduce allocations
    for enqueued work
    

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18. Misc.
    • Process.Kill(bool entireProcessTree)
    • BitOperations for advanced bit twiddling
    • Microsoft.VisualBasic is back
    • DbCommand
    • Async transactions
    

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19. ASP.NET Core
    Up to the server now
    

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20. UnixDomainSocket in Kestrel w/o libuv
    • Kestrel can now listen via a unix domain sockets without libuv
    • Provides higher speed transport for reverse-proxying scenarios, e.g.
    ngnix
    • Supported thanks to updates to System.Net.Sockets
    • Works on Linux and Windows 10
    

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21. Static web assets in class libraries
    • Razor class libraries now support embedding static web assets
    • Allows you to include images, scripts, CSS, etc. along with views,
    pages, and components
    • Projects referencing the class library will be automatically configured
    to include the static assets from the class library
    • Reference the static assets from libraries via “_content/libname/…”
    
    

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22. Access IIS server variables
    • IIS server variables are now available to ASP.NET Core applications
    when hosted in IIS
    • Allows you to read values about the server, the connection, and the
    current request
    

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23. System.IO.Pipelines
    • Can now get access to the underlying pipeline instance backing each
    request/response
    • Pipeline is created and managed by the web server including
    allocation of memory buffers for reading and writing to the
    connection
    • Allows directly reading and writing to the request using Span and
    avoids going through the Stream adapter
    • HttpRequest.BodyReader
    • HttpRequest.BodyWriter
    

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24. New networking abstractions (Bedrock)
    • Kestrel's transport layer is now isolated as a public API
    • You can implement your own servers and clients based on Kestrel's
    high-performance networking stack
    • Handles the networking essentials, e.g. exposing endpoints, managing
    memory, etc.
    • Used in SignalR .NET client
    • WebSocket pipe abstraction
    • DEMO
    

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25. Routing HostMatcherPolicy and HostAttribute
    • Ability to have route matching consider the host and port
    • Can be used anywhere Endpoint Routing is used for dispatching
    • e.g. could isolate a specific Controller to only match when served via a
    specific host name
    • Can be useful in multi-tenancy scenarios, or when exposing extra
    endpoints on internal-only ports
    • DEMO
    

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26. Support for trailing headers
    • Support for HTTP response trailers
    • Required to support gRPC
    • Literally response headers that are sent *after* the response body
    • Useful for sending information to client that is dependent on body,
    e.g. server timing
    

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27. Developer exception page improvements
    • Support for non-HTML aware clients, error will be returned in
    plaintext
    • Extensibility via IDeveloperPageExceptionFilter to allow for custom
    views per exception type, e.g. Entity Framework Core's specific
    exception page will move to use this instead
    • DEMO
    

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28. Compression improvements
    • Previously, compression was disabled over HTTPS connections due
    to security concerns, e.g. CRIME, BREACH
    • Requests can now declare they're safe for compression
    • Static files middleware utilizes this to enable compression over HTTPS
    • Compression middleware now supports Brotli by default
    • DEMO
    

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29. Microsoft.Extensions.*
    That other layer
    

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30. Systemd integration
    • Linux equivalent to support for Windows Services hosting
    • Supports ASP.NET Core and Worker Service apps
    • Handles lifetime management of the application including start,
    ready, shutdown
    • Interacts with sd_notify
    • Community contributed and coming in preview7
    

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31. IConfigurationRoot.GetDebugView
    • Provides a way to dump all configuration values and their sources
    • Useful for debugging configuration issues
    • DEMO
    

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32. ServiceProviderOptions.ValidateOnBuild
    • Validates when the container is built, that dependencies or all
    registered types are fully satisfied
    • Enabled by default in Development environment
    • Causes the app to fail on startup rather than when an invalid service
    is first requested
    • DEMO
    

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33. Options validation
    • Support for validation of Options types in DI during app startup
    • Validate using custom logic or existing validation attributes
    • Use to ensure all require configuration is present during app startup
    • Usually better to fail fast on boot rather than fail later during a
    request
    

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34. LoggerFactory.Create
    • New API to easily enable creating a logger factory in non-hosted
    scenarios, i.e. when a DI container is not in use
    • Makes using ILogger in other app types much easier, e.g. console
    apps, WinForms, etc.
    • DEMO
    

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35. StreamConfigurationSource
    • Enables reading configuration from stream-based sources
    • Existing file-based providers have been refactored to extract stream-
    based implementations as well, e.g. JSON
    • Means you can now ready JSON configuration from other sources
    such as embedded resources, KeyVault, blobs, etc.
    

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36. Thank you!
    • Follow us on twitter:
    • @davidfowl
    • @damianedwards
    • Code samples and this deck will be available at
    • https://github.com/davidfowl/Core3HiddenGems
    

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