[Group 4] Enable nullable annotations for Microsoft.Extensions.Http

[maxkoshevoi]

Related to #43605

Questions:

• InnerHandler can be null
  

  runtime/src/libraries/Microsoft.Extensions.Http/src/DefaultHttpClientFactory.cs

  Line 267 in 3e2a45c

  entry.InnerHandler.Dispose();

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Issue Details

---

Related to #43605

Questions:

• InnerHandler can be null
  

  runtime/src/libraries/Microsoft.Extensions.Http/src/DefaultHttpClientFactory.cs

  Line 267 in 3e2a45c

  entry.InnerHandler.Dispose();

Author:	maxkoshevoi
Assignees:	-
Labels:	new-api-needs-documentation, area-Extensions-HttpClientFactory
Milestone:	-

[CarnaViire]

Questions:
InnerHandler can be null

InnerHandler cannot be null if DefaultHttpClientFactory is used.

Code links below.

ExpiredHandlerTrackingEntry.InnerHandler is assigned only in .ctor from ActiveHandlerTrackingEntry.Handler.InnerHandler.

ActiveHandlerTrackingEntry.Handler is assigned only in .ctor, and ActiveHandlerTrackingEntry is created only in one place where LifetimeTrackingHttpMessageHandler is also explicitly created.

LifetimeTrackingHttpMessageHandler.InnerHandler is always assigned in .ctor (it cannot be unassigned).

LifetimeTrackingHttpMessageHandler is derived from DelegatingHandler. DelegatingHandler.InnerHandler disallows null on assignment. So even if null is somehow passed to LifetimeTrackingHttpMessageHandler's .ctor -- it might be achievable by substituting HttpMessageHandlerBuilder in DI and making Build() return null -- DelegatingHandler's .ctor will throw.

runtime/src/libraries/Microsoft.Extensions.Http/src/ExpiredHandlerTrackingEntry.cs

Lines 17 to 23 in 57bfe47

	public ExpiredHandlerTrackingEntry(ActiveHandlerTrackingEntry other)
	{
	Name = other.Name;
	Scope = other.Scope;
	_livenessTracker = new WeakReference(other.Handler);
	InnerHandler = other.Handler.InnerHandler;

runtime/src/libraries/Microsoft.Extensions.Http/src/DefaultHttpClientFactory.cs

Lines 179 to 188 in 57bfe47

	var handler = new LifetimeTrackingHttpMessageHandler(builder.Build());
	// Note that we can't start the timer here. That would introduce a very very subtle race condition
	// with very short expiry times. We need to wait until we've actually handed out the handler once
	// to start the timer.
	//
	// Otherwise it would be possible that we start the timer here, immediately expire it (very short
	// timer) and then dispose it without ever creating a client. That would be bad. It's unlikely
	// this would happen, but we want to be sure.
	return new ActiveHandlerTrackingEntry(name, handler, scope, options.HandlerLifetime);

runtime/src/libraries/Microsoft.Extensions.Http/src/LifetimeTrackingHttpMessageHandler.cs

Lines 13 to 14 in 57bfe47

	public LifetimeTrackingHttpMessageHandler(HttpMessageHandler innerHandler)
	: base(innerHandler)

runtime/src/libraries/System.Net.Http/src/System/Net/Http/DelegatingHandler.cs

Lines 19 to 31 in 57bfe47

	[DisallowNull]
	public HttpMessageHandler? InnerHandler
	{
	get
	{
	return _innerHandler;
	}
	set
	{
	if (value == null)
	{
	throw new ArgumentNullException(nameof(value));
	}

[CarnaViire]

Thanks a lot! LGTM, with one nit.

[CarnaViire]

Thanks!