Add overloads for C# ByteBuffer/FlatBufferBuilder to allow adding vector blocks from ArraySegments or IntPtr (#7193)

* Add overloads to Add/Put for ArraySegment and IntPtr

In order to allow using code to reduce memory allocations, add overloads to ByteBuffer's and FlatBuffersBuilder's Put/Add methods that take ArraySegment<T> or IntPtr respectively.
Also, adaptions to the c# code generator in flatc to emit corresponding CreateVectorBlock() overloads

* Add missing files generated with generate_code.py

The previous commit changed the C# code generate, but didn't contain the updated generated test files.

* Incorporate review findings

(1) Adhere to 80 characters limit.
(2) In FlatBufferBuilder.Add(IntPtr,int), move zero length check topmost and add sanity check against negative input

net/FlatBuffers/ByteBuffer.cs

@@ -225,6 +225,18 @@ namespace FlatBuffers
             return SizeOf<T>() * x.Length;
         }
 
+        /// <summary>
+        /// Get the wire-size (in bytes) of an typed array segment, taking only the
+        /// range specified by <paramref name="x"/> into account.
+        /// </summary>
+        /// <typeparam name="T">The type of the array</typeparam>
+        /// <param name="x">The array segment to get the size of</param>
+        /// <returns>The number of bytes the array segment takes on wire</returns>
+        public static int ArraySize<T>(ArraySegment<T> x)
+        {
+            return SizeOf<T>() * x.Count;
+        }
+
 #if ENABLE_SPAN_T && (UNSAFE_BYTEBUFFER || NETSTANDARD2_1)
         public static int ArraySize<T>(Span<T> x)
         {
@@ -869,7 +881,30 @@ namespace FlatBuffers
                 throw new ArgumentNullException("Cannot put a null array");
             }
 
-            if (x.Length == 0)
+            return Put(offset, new ArraySegment<T>(x));
+        }
+
+        /// <summary>
+        /// Copies an array segment of type T into this buffer, ending at the 
+        /// given offset into this buffer. The starting offset is calculated 
+        /// based on the count of the array segment and is the value returned.
+        /// </summary>
+        /// <typeparam name="T">The type of the input data (must be a struct)
+        /// </typeparam>
+        /// <param name="offset">The offset into this buffer where the copy 
+        /// will end</param>
+        /// <param name="x">The array segment to copy data from</param>
+        /// <returns>The 'start' location of this buffer now, after the copy 
+        /// completed</returns>
+        public int Put<T>(int offset, ArraySegment<T> x)
+            where T : struct
+        {
+            if (x.Equals(default(ArraySegment<T>)))
+            {
+                throw new ArgumentNullException("Cannot put a uninitialized array segment");
+            }
+
+            if (x.Count == 0)
             {
                 throw new ArgumentException("Cannot put an empty array");
             }
@@ -889,7 +924,68 @@ namespace FlatBuffers
 #if ENABLE_SPAN_T && (UNSAFE_BYTEBUFFER || NETSTANDARD2_1)
                 MemoryMarshal.Cast<T, byte>(x).CopyTo(_buffer.Span.Slice(offset, numBytes));
 #else
-                Buffer.BlockCopy(x, 0, _buffer.Buffer, offset, numBytes);
+                var srcOffset = ByteBuffer.SizeOf<T>() * x.Offset;
+                Buffer.BlockCopy(x.Array, srcOffset, _buffer.Buffer, offset, numBytes);
+#endif
+            }
+            else
+            {
+                throw new NotImplementedException("Big Endian Support not implemented yet " +
+                    "for putting typed arrays");
+                // if we are BE, we have to swap each element by itself
+                //for(int i = x.Length - 1; i >= 0; i--)
+                //{
+                //  todo: low priority, but need to genericize the Put<T>() functions
+                //}
+            }
+            return offset;
+        }
+
+        /// <summary>
+        /// Copies an array segment of type T into this buffer, ending at the 
+        /// given offset into this buffer. The starting offset is calculated 
+        /// based on the count of the array segment and is the value returned.
+        /// </summary>
+        /// <typeparam name="T">The type of the input data (must be a struct)
+        /// </typeparam>
+        /// <param name="offset">The offset into this buffer where the copy 
+        /// will end</param>
+        /// <param name="ptr">The pointer to copy data from</param>
+        /// <param name="sizeInBytes">The number of bytes to copy</param>
+        /// <returns>The 'start' location of this buffer now, after the copy 
+        /// completed</returns>
+        public int Put<T>(int offset, IntPtr ptr, int sizeInBytes)
+            where T : struct
+        {
+            if (ptr == IntPtr.Zero)
+            {
+                throw new ArgumentNullException("Cannot add a null pointer");
+            }
+
+            if(sizeInBytes <= 0)
+            {
+                throw new ArgumentException("Cannot put an empty array");
+            }
+
+            if (!IsSupportedType<T>())
+            {
+                throw new ArgumentException("Cannot put an array of type "
+                    + typeof(T) + " into this buffer");
+            }
+
+            if (BitConverter.IsLittleEndian)
+            {
+                offset -= sizeInBytes;
+                AssertOffsetAndLength(offset, sizeInBytes);
+                // if we are LE, just do a block copy
+#if ENABLE_SPAN_T && UNSAFE_BYTEBUFFER
+                unsafe
+                { 
+                    var span = new Span<byte>(ptr.ToPointer(), sizeInBytes);
+                    span.CopyTo(_buffer.Span.Slice(offset, sizeInBytes));
+                }
+#else
+                Marshal.Copy(ptr, _buffer.Buffer, offset, sizeInBytes);
 #endif
             }
             else

net/FlatBuffers/FlatBufferBuilder.cs

@@ -210,6 +210,31 @@ namespace FlatBuffers
             _space = _bb.Put(_space, x);
         }
 
+        /// <summary>
+        /// Puts an array of type T into this builder at the
+        /// current offset
+        /// </summary>
+        /// <typeparam name="T">The type of the input data </typeparam>
+        /// <param name="x">The array segment to copy data from</param>
+        public void Put<T>(ArraySegment<T> x)
+            where T : struct
+        {
+            _space = _bb.Put(_space, x);
+        }
+
+        /// <summary>
+        /// Puts data of type T into this builder at the
+        /// current offset
+        /// </summary>
+        /// <typeparam name="T">The type of the input data </typeparam>
+        /// <param name="ptr">The pointer to copy data from</param>
+        /// <param name="sizeInBytes">The length of the data in bytes</param>
+        public void Put<T>(IntPtr ptr, int sizeInBytes)
+            where T : struct
+        {
+            _space = _bb.Put<T>(_space, ptr, sizeInBytes);
+        }
+
 #if ENABLE_SPAN_T && (UNSAFE_BYTEBUFFER || NETSTANDARD2_1)
         /// <summary>
         /// Puts a span of type T into this builder at the
@@ -297,13 +322,24 @@ namespace FlatBuffers
         /// <param name="x">The array to copy data from</param>
         public void Add<T>(T[] x)
             where T : struct
+        {
+            Add(new ArraySegment<T>(x));
+        }
+
+        /// <summary>
+        /// Add an array of type T to the buffer (aligns the data and grows if necessary).
+        /// </summary>
+        /// <typeparam name="T">The type of the input data</typeparam>
+        /// <param name="x">The array segment to copy data from</param>
+        public void Add<T>(ArraySegment<T> x)
+            where T : struct
         {
             if (x == null)
             {
                 throw new ArgumentNullException("Cannot add a null array");
             }
 
-            if( x.Length == 0)
+            if( x.Count == 0)
             {
                 // don't do anything if the array is empty
                 return;
@@ -317,10 +353,52 @@ namespace FlatBuffers
             int size = ByteBuffer.SizeOf<T>();
             // Need to prep on size (for data alignment) and then we pass the
             // rest of the length (minus 1) as additional bytes
-            Prep(size, size * (x.Length - 1));
+            Prep(size, size * (x.Count - 1));
             Put(x);
         }
 
+        /// <summary>
+        /// Adds the data of type T pointed to by the given pointer to the buffer (aligns the data and grows if necessary).
+        /// </summary>
+        /// <typeparam name="T">The type of the input data</typeparam>
+        /// <param name="ptr">The pointer to copy data from</param>
+        /// <param name="sizeInBytes">The data size in bytes</param>
+        public void Add<T>(IntPtr ptr, int sizeInBytes)
+            where T : struct
+        {
+            if(sizeInBytes == 0)
+            {
+                // don't do anything if the array is empty
+                return;
+            }
+
+            if (ptr == IntPtr.Zero)
+            {
+                throw new ArgumentNullException("Cannot add a null pointer");
+            }
+
+            if(sizeInBytes < 0)
+            {
+                throw new ArgumentOutOfRangeException("sizeInBytes", "sizeInBytes cannot be negative");
+            }
+
+            if(!ByteBuffer.IsSupportedType<T>())
+            {
+                throw new ArgumentException("Cannot add this Type array to the builder");
+            }
+
+            int size = ByteBuffer.SizeOf<T>();
+            if((sizeInBytes % size) != 0)
+            {
+                throw new ArgumentException("The given size in bytes " + sizeInBytes + " doesn't match the element size of T ( " + size + ")", "sizeInBytes");
+            }
+
+            // Need to prep on size (for data alignment) and then we pass the
+            // rest of the length (minus 1) as additional bytes
+            Prep(size, sizeInBytes - size);
+            Put<T>(ptr, sizeInBytes);
+        }
+
 #if ENABLE_SPAN_T && (UNSAFE_BYTEBUFFER || NETSTANDARD2_1)
         /// <summary>
         /// Add a span of type T to the buffer (aligns the data and grows if necessary).