Add UnmanagedCallersOnly attribute to SafeDeleteSslContext.ReadFromConnection/WriteToConnection methods

[MaximLipnin]

Fixes #55736

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Issue Details

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#55736

It doesn't work yet and needs any feedback about the correctness of approach.

Author:	MaximLipnin
Assignees:	-
Labels:	area-System.Net.Security
Milestone:	-

[mdh1418]

I'm not very familiar, but based on what @lambdageek mentioned #55736 (comment), UnmanagedCallersOnlyAttribute the changes seem like the right path. Are void* and void** blittable?

Perhaps once Argument 2: cannot convert from '&method group' to 'delegate* unmanaged<void*, byte*, void**>' and An object reference is required for the non-static field, method, or property 'SafeDeleteSslContext._outputBuffer' are resolved we'll know more?

[jkotas]

An object reference is required for the non-static field, method, or property 'SafeDeleteSslContext._outputBuffer

You will need to have some way to go from the call arguments back to the object. Do these APIs have a way to pass pointer to user data around? If not, you will need to pass the extra data around using some sort of global state, e.g. Dictionary that uses connection pointer as the key.

[lambdageek]

In theory that void* connection is the user data. You have to call https://developer.apple.com/documentation/security/1398843-sslsetconnection to assign a connection value to an SSLContext (somewhere before

runtime/src/libraries/System.Net.Security/src/System/Net/Security/Pal.OSX/SafeDeleteSslContext.cs

Lines 44 to 47 in 4a4f6c0

	osStatus = Interop.AppleCrypto.SslSetIoCallbacks(
	_sslContext,
	&ReadFromConnection,
	&WriteToConnection);

) and then the Apple API will pass it back to the read and write callbacks.

We could probably just put a GCHandle to this SafeDeleteSslContext into the connection value. No need for a dictionary.

[steveisok]

@MaximLipnin I put up a commit that should help. Please validate.

Thanks for the tips everyone.

[lambdageek]

Nice!

[steveisok]

@MaximLipnin You might want to merge w/ main b/c it'll resolve a bunch of test failures on iOS.