Adds synchronous span APIs for datagram sockets. (#51956)

* Adds synchronous span APIs for datagram sockets.

Part of #33418/#938

* Doc comments for new APIs.

* Fix review nits.

* Add 0-byte send tests.

src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs

@@ -385,6 +385,8 @@ public void Listen(int backlog) { }
         public int ReceiveFrom(byte[] buffer, int size, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP) { throw null; }
         public int ReceiveFrom(byte[] buffer, ref System.Net.EndPoint remoteEP) { throw null; }
         public int ReceiveFrom(byte[] buffer, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP) { throw null; }
+        public int ReceiveFrom(System.Span<byte> buffer, ref System.Net.EndPoint remoteEP) { throw null; }
+        public int ReceiveFrom(System.Span<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP) { throw null; }
         public System.Threading.Tasks.Task<System.Net.Sockets.SocketReceiveFromResult> ReceiveFromAsync(System.ArraySegment<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEndPoint) { throw null; }
         public System.Threading.Tasks.ValueTask<System.Net.Sockets.SocketReceiveFromResult> ReceiveFromAsync(System.Memory<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEndPoint, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public bool ReceiveFromAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
@@ -419,6 +421,8 @@ public void SendFile(string? fileName, System.ReadOnlySpan<byte> preBuffer, Syst
         public int SendTo(byte[] buffer, int size, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
         public int SendTo(byte[] buffer, System.Net.EndPoint remoteEP) { throw null; }
         public int SendTo(byte[] buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
+        public int SendTo(System.ReadOnlySpan<byte> buffer, System.Net.EndPoint remoteEP) { throw null; }
+        public int SendTo(System.ReadOnlySpan<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
         public System.Threading.Tasks.Task<int> SendToAsync(System.ArraySegment<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
         public System.Threading.Tasks.ValueTask<int> SendToAsync(System.ReadOnlyMemory<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public bool SendToAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }

src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs

@@ -1380,6 +1380,67 @@ public int SendTo(byte[] buffer, EndPoint remoteEP)
             return SendTo(buffer, 0, buffer != null ? buffer.Length : 0, SocketFlags.None, remoteEP);
         }
 
+        /// <summary>
+        /// Sends data to the specified endpoint.
+        /// </summary>
+        /// <param name="buffer">A span of bytes that contains the data to be sent.</param>
+        /// <param name="remoteEP">The <see cref="EndPoint"/> that represents the destination for the data.</param>
+        /// <returns>The number of bytes sent.</returns>
+        /// <exception cref="ArgumentNullException"><c>remoteEP</c> is <see langword="null" />.</exception>
+        /// <exception cref="SocketException">An error occurred when attempting to access the socket.</exception>
+        /// <exception cref="ObjectDisposedException">The <see cref="Socket"/> has been closed.</exception>
+        public int SendTo(ReadOnlySpan<byte> buffer, EndPoint remoteEP)
+        {
+            return SendTo(buffer, SocketFlags.None, remoteEP);
+        }
+
+        /// <summary>
+        /// Sends data to a specific endpoint using the specified <see cref="SocketFlags"/>.
+        /// </summary>
+        /// <param name="buffer">A span of bytes that contains the data to be sent.</param>
+        /// <param name="socketFlags">A bitwise combination of the <see cref="SocketFlags"/> values.</param>
+        /// <param name="remoteEP">The <see cref="EndPoint"/> that represents the destination for the data.</param>
+        /// <returns>The number of bytes sent.</returns>
+        /// <exception cref="ArgumentNullException"><c>remoteEP</c> is <see langword="null" />.</exception>
+        /// <exception cref="SocketException">An error occurred when attempting to access the socket.</exception>
+        /// <exception cref="ObjectDisposedException">The <see cref="Socket"/> has been closed.</exception>
+        public int SendTo(ReadOnlySpan<byte> buffer, SocketFlags socketFlags, EndPoint remoteEP)
+        {
+            ThrowIfDisposed();
+            if (remoteEP == null)
+            {
+                throw new ArgumentNullException(nameof(remoteEP));
+            }
+
+            ValidateBlockingMode();
+
+            Internals.SocketAddress socketAddress = Serialize(ref remoteEP);
+
+            int bytesTransferred;
+            SocketError errorCode = SocketPal.SendTo(_handle, buffer, socketFlags, socketAddress.Buffer, socketAddress.Size, out bytesTransferred);
+
+            // Throw an appropriate SocketException if the native call fails.
+            if (errorCode != SocketError.Success)
+            {
+                UpdateSendSocketErrorForDisposed(ref errorCode);
+
+                UpdateStatusAfterSocketErrorAndThrowException(errorCode);
+            }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
+
+            if (_rightEndPoint == null)
+            {
+                // Save a copy of the EndPoint so we can use it for Create().
+                _rightEndPoint = remoteEP;
+            }
+
+            return bytesTransferred;
+        }
+
         // Receives data from a connected socket.
         public int Receive(byte[] buffer, int size, SocketFlags socketFlags)
         {
@@ -1764,6 +1825,93 @@ public int ReceiveFrom(byte[] buffer, ref EndPoint remoteEP)
             return ReceiveFrom(buffer, 0, buffer != null ? buffer.Length : 0, SocketFlags.None, ref remoteEP);
         }
 
+        /// <summary>
+        /// Receives a datagram into the data buffer and stores the endpoint.
+        /// </summary>
+        /// <param name="buffer">A span of bytes that is the storage location for received data.</param>
+        /// <param name="remoteEP">An <see cref="EndPoint"/>, passed by reference, that represents the remote server.</param>
+        /// <returns>The number of bytes received.</returns>
+        /// <exception cref="ArgumentNullException"><c>remoteEP</c> is <see langword="null" />.</exception>
+        /// <exception cref="SocketException">An error occurred when attempting to access the socket.</exception>
+        /// <exception cref="ObjectDisposedException">The <see cref="Socket"/> has been closed.</exception>
+        public int ReceiveFrom(Span<byte> buffer, ref EndPoint remoteEP)
+        {
+            return ReceiveFrom(buffer, SocketFlags.None, ref remoteEP);
+        }
+
+        /// <summary>
+        /// Receives a datagram into the data buffer, using the specified <see cref="SocketFlags"/>, and stores the endpoint.
+        /// </summary>
+        /// <param name="buffer">A span of bytes that is the storage location for received data.</param>
+        /// <param name="socketFlags">A bitwise combination of the <see cref="SocketFlags"/> values.</param>
+        /// <param name="remoteEP">An <see cref="EndPoint"/>, passed by reference, that represents the remote server.</param>
+        /// <returns>The number of bytes received.</returns>
+        /// <exception cref="ArgumentNullException"><c>remoteEP</c> is <see langword="null" />.</exception>
+        /// <exception cref="SocketException">An error occurred when attempting to access the socket.</exception>
+        /// <exception cref="ObjectDisposedException">The <see cref="Socket"/> has been closed.</exception>
+        public int ReceiveFrom(Span<byte> buffer, SocketFlags socketFlags, ref EndPoint remoteEP)
+        {
+            ThrowIfDisposed();
+            ValidateReceiveFromEndpointAndState(remoteEP, nameof(remoteEP));
+
+            SocketPal.CheckDualModeReceiveSupport(this);
+
+            ValidateBlockingMode();
+
+            // We don't do a CAS demand here because the contents of remoteEP aren't used by
+            // WSARecvFrom; all that matters is that we generate a unique-to-this-call SocketAddress
+            // with the right address family.
+            EndPoint endPointSnapshot = remoteEP;
+            Internals.SocketAddress socketAddress = Serialize(ref endPointSnapshot);
+            Internals.SocketAddress socketAddressOriginal = IPEndPointExtensions.Serialize(endPointSnapshot);
+
+            int bytesTransferred;
+            SocketError errorCode = SocketPal.ReceiveFrom(_handle, buffer, socketFlags, socketAddress.Buffer, ref socketAddress.InternalSize, out bytesTransferred);
+
+            UpdateReceiveSocketErrorForDisposed(ref errorCode, bytesTransferred);
+            // If the native call fails we'll throw a SocketException.
+            SocketException? socketException = null;
+            if (errorCode != SocketError.Success)
+            {
+                socketException = new SocketException((int)errorCode);
+                UpdateStatusAfterSocketError(socketException);
+                if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, socketException);
+
+                if (socketException.SocketErrorCode != SocketError.MessageSize)
+                {
+                    throw socketException;
+                }
+            }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
+
+            if (!socketAddressOriginal.Equals(socketAddress))
+            {
+                try
+                {
+                    remoteEP = endPointSnapshot.Create(socketAddress);
+                }
+                catch
+                {
+                }
+                if (_rightEndPoint == null)
+                {
+                    // Save a copy of the EndPoint so we can use it for Create().
+                    _rightEndPoint = endPointSnapshot;
+                }
+            }
+
+            if (socketException != null)
+            {
+                throw socketException;
+            }
+
+            return bytesTransferred;
+        }
+
         public int IOControl(int ioControlCode, byte[]? optionInValue, byte[]? optionOutValue)
         {
             ThrowIfDisposed();

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

@@ -1203,6 +1203,19 @@ public static SocketError SendTo(SafeSocketHandle handle, byte[] buffer, int off
             return errorCode;
         }
 
+        public static SocketError SendTo(SafeSocketHandle handle, ReadOnlySpan<byte> buffer, SocketFlags socketFlags, byte[] socketAddress, int socketAddressLen, out int bytesTransferred)
+        {
+            if (!handle.IsNonBlocking)
+            {
+                return handle.AsyncContext.SendTo(buffer, socketFlags, socketAddress, socketAddressLen, handle.SendTimeout, out bytesTransferred);
+            }
+
+            bytesTransferred = 0;
+            SocketError errorCode;
+            TryCompleteSendTo(handle, buffer, socketFlags, socketAddress, socketAddressLen, ref bytesTransferred, out errorCode);
+            return errorCode;
+        }
+
         public static SocketError Receive(SafeSocketHandle handle, IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, out int bytesTransferred)
         {
             SocketError errorCode;
@@ -1311,6 +1324,18 @@ public static SocketError ReceiveFrom(SafeSocketHandle handle, byte[] buffer, in
             return completed ? errorCode : SocketError.WouldBlock;
         }
 
+        public static SocketError ReceiveFrom(SafeSocketHandle handle, Span<byte> buffer, SocketFlags socketFlags, byte[] socketAddress, ref int socketAddressLen, out int bytesTransferred)
+        {
+            if (!handle.IsNonBlocking)
+            {
+                return handle.AsyncContext.ReceiveFrom(buffer, ref socketFlags, socketAddress, ref socketAddressLen, handle.ReceiveTimeout, out bytesTransferred);
+            }
+
+            SocketError errorCode;
+            bool completed = TryCompleteReceiveFrom(handle, buffer, socketFlags, socketAddress, ref socketAddressLen, out bytesTransferred, out socketFlags, out errorCode);
+            return completed ? errorCode : SocketError.WouldBlock;
+        }
+
         public static SocketError WindowsIoctl(SafeSocketHandle handle, int ioControlCode, byte[]? optionInValue, byte[]? optionOutValue, out int optionLength)
         {
             // Three codes are called out in the Winsock IOCTLs documentation as "The following Unix IOCTL codes (commands) are supported." They are

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs

@@ -300,31 +300,15 @@ public static unsafe SocketError SendFile(SafeSocketHandle handle, SafeFileHandl
             }
         }
 
-        public static unsafe SocketError SendTo(SafeSocketHandle handle, byte[] buffer, int offset, int size, SocketFlags socketFlags, byte[] peerAddress, int peerAddressSize, out int bytesTransferred)
+        public static SocketError SendTo(SafeSocketHandle handle, byte[] buffer, int offset, int size, SocketFlags socketFlags, byte[] peerAddress, int peerAddressSize, out int bytesTransferred) =>
+            SendTo(handle, buffer.AsSpan(offset, size), socketFlags, peerAddress, peerAddressSize, out bytesTransferred);
+
+        public static unsafe SocketError SendTo(SafeSocketHandle handle, ReadOnlySpan<byte> buffer, SocketFlags socketFlags, byte[] peerAddress, int peerAddressSize, out int bytesTransferred)
         {
             int bytesSent;
-            if (buffer.Length == 0)
+            fixed (byte* bufferPtr = &MemoryMarshal.GetReference(buffer))
             {
-                bytesSent = Interop.Winsock.sendto(
-                    handle,
-                    null,
-                    0,
-                    socketFlags,
-                    peerAddress,
-                    peerAddressSize);
-            }
-            else
-            {
-                fixed (byte* pinnedBuffer = &buffer[0])
-                {
-                    bytesSent = Interop.Winsock.sendto(
-                        handle,
-                        pinnedBuffer + offset,
-                        size,
-                        socketFlags,
-                        peerAddress,
-                        peerAddressSize);
-                }
+                bytesSent = Interop.Winsock.sendto(handle, bufferPtr, buffer.Length, socketFlags, peerAddress, peerAddressSize);
             }
 
             if (bytesSent == (int)SocketError.SocketError)
@@ -528,19 +512,16 @@ public static unsafe SocketError ReceiveMessageFrom(Socket socket, SafeSocketHan
             return SocketError.Success;
         }
 
-        public static unsafe SocketError ReceiveFrom(SafeSocketHandle handle, byte[] buffer, int offset, int size, SocketFlags socketFlags, byte[] socketAddress, ref int addressLength, out int bytesTransferred)
+        public static unsafe SocketError ReceiveFrom(SafeSocketHandle handle, byte[] buffer, int offset, int size, SocketFlags socketFlags, byte[] socketAddress, ref int addressLength, out int bytesTransferred) =>
+            ReceiveFrom(handle, buffer.AsSpan(offset, size), SocketFlags.None, socketAddress, ref addressLength, out bytesTransferred);
+
+        public static unsafe SocketError ReceiveFrom(SafeSocketHandle handle, Span<byte> buffer, SocketFlags socketFlags, byte[] socketAddress, ref int addressLength, out int bytesTransferred)
         {
             int bytesReceived;
-            if (buffer.Length == 0)
-            {
-                bytesReceived = Interop.Winsock.recvfrom(handle, null, 0, socketFlags, socketAddress, ref addressLength);
-            }
-            else
+
+            fixed (byte* bufferPtr = &MemoryMarshal.GetReference(buffer))
             {
-                fixed (byte* pinnedBuffer = &buffer[0])
-                {
-                    bytesReceived = Interop.Winsock.recvfrom(handle, pinnedBuffer + offset, size, socketFlags, socketAddress, ref addressLength);
-                }
+                bytesReceived = Interop.Winsock.recvfrom(handle, bufferPtr, buffer.Length, socketFlags, socketAddress, ref addressLength);
             }
 
             if (bytesReceived == (int)SocketError.SocketError)