Possible Socket.SendFileAsync issue with files >2GiB.

[scalablecory]

Within our Unix code, we are casting FileStream.Length to an int here:

runtime/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Unix.cs

Lines 1811 to 1812 in 84c1f62

	public static SocketError SendFileAsync(SafeSocketHandle handle, FileStream fileStream, Action<long, SocketError> callback) =>
	SendFileAsync(handle, fileStream, 0, (int)fileStream.Length, callback);

This would fail for any files greater than 2GiB in length.

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[geoffkizer]

On Windows, TransmitFile is limited to 2GB. See https://docs.microsoft.com/en-us/windows/win32/api/mswsock/nf-mswsock-transmitfile

We may not need the same limitation for Linux, though.

[wfurt]

Would it make sense to check file size and fall-back to some internal implementation if file is too big? That would give us consistency while preserving perf benefits when possible...

[geoffkizer]

Possibly, yeah.

At the very least we should give a good exception here instead of just casting and losing the actual file length...

[wfurt]

actually

The maximum number of bytes that can be transmitted using a single call to the TransmitFile function is 2,147,483,646, the maximum value for a 32-bit integer minus 1. The maximum number of bytes to send in a single call includes any data sent before or after the file data pointed to by the lpTransmitBuffers parameter plus the value specified in the nNumberOfBytesToWrite parameter for the length of file data to send. If an application needs to transmit a file larger than 2,147,483,646 bytes, then multiple calls to the TransmitFile function can be used with each call transferring no more than 2,147,483,646 bytes.

it seems like the correct way is to make multiple calls - and I'm not sure we do.

[stephentoub]

it seems like the correct way is to make multiple calls - and I'm not sure we do.

I separated this out into #42534.