Answer the extended WKB of a geometry as the buffer it is

MEOS.NET.Tests/ExtendedWkbTests.cs

@@ -0,0 +1,39 @@
+using MEOS.NET.Types;
+
+namespace MEOS.NET.Tests
+{
+    /// <summary>
+    /// The extended WKB of a geometry is a buffer whose length MEOS states
+    /// through a pointer, so the array a caller gets is exactly as long as the
+    /// data — which the hex form of the same value states independently.
+    /// </summary>
+    [TestClass]
+    public class ExtendedWkbTests : MeosTest
+    {
+        private const string Line = "SRID=4326;LINESTRING(1 1, 2 2, 3 4)";
+
+        [TestMethod]
+        public void TheBufferIsAsLongAsTheHexFormSays()
+        {
+            Geo line = Geometry.In(Line, -1)!;
+
+            byte[]? ewkb = line.AsEWKB("ndr");
+            string hex = line.AsHexewkb("ndr");
+
+            Assert.IsNotNull(ewkb);
+            Assert.AreEqual(hex.Length, ewkb!.Length * 2);
+            Assert.AreEqual(hex.ToUpperInvariant(), Convert.ToHexString(ewkb));
+        }
+
+        [TestMethod]
+        public void AGeometryRoundTripsThroughItsOwnEWKB()
+        {
+            Geo line = Geometry.In(Line, -1)!;
+
+            Geo? read = Geo.FromEWKB(line.AsEWKB("ndr")!, 4326);
+
+            Assert.IsNotNull(read);
+            Assert.AreEqual(line.ToString(), read!.ToString());
+        }
+    }
+}

MEOS.NET/Types/Geo.g.cs

@@ -18,6 +18,27 @@ internal Geo(IntPtr ptr) : base(ptr) { }
         public override string ToString()
             => this.Out();
 
+        public byte[]? AsEWKB(string endian)
+        {
+            IntPtr _size = Marshal.AllocHGlobal(sizeof(long));
+            try
+            {
+                IntPtr _bytes = Meos.GeoAsEwkb(this.Ptr, endian, _size);
+                if (_bytes == IntPtr.Zero)
+                {
+                    return null;
+                }
+
+                byte[] _wkb = new byte[Marshal.ReadInt64(_size)];
+                Marshal.Copy(_bytes, _wkb, 0, _wkb.Length);
+                return _wkb;
+            }
+            finally
+            {
+                Marshal.FreeHGlobal(_size);
+            }
+        }
+
         public string AsEWKT(int precision)
             => Meos.GeoAsEwkt(this.Ptr, precision);