From 9947655df16d216816761c234800fea5c38cfef7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20Zim=C3=A1nyi?= <estebanzimanyi@gmail.com>
Date: Thu, 3 Sep 2026 17:58:19 +0200
Subject: [PATCH] Answer the extended WKB of a geometry as the buffer it is
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The catalog states `size` as the parameter MEOS writes the length of
`geo_as_ewkb`'s buffer into, so the method reads it: `AsEWKB(string endian)`
answers a `byte[]` exactly as long as the data, joining the twenty-eight other
buffers the layer already folds that way. The length is the whole of it — an
extended WKB buffer carries no terminator and no length of its own, so a caller
holding the pointer without it has no way to say where the geometry ends.

The layer emits 1353 methods over 115 classes with 7 deferred. Its own test
reads the hex form of the same geometry as an independent statement of the same
length: `AsHexewkb` answers a string of exactly twice as many characters, and
hex-encoding the buffer reproduces it character for character, so a buffer of
the wrong length fails on the count before it fails on the content. The second
test round-trips the bytes back through `FromEWKB` to the value they came from.
---
 MEOS.NET.Tests/ExtendedWkbTests.cs | 39 ++++++++++++++++++++++++++++++
 MEOS.NET/Types/Geo.g.cs            | 21 ++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 MEOS.NET.Tests/ExtendedWkbTests.cs

diff --git a/MEOS.NET.Tests/ExtendedWkbTests.cs b/MEOS.NET.Tests/ExtendedWkbTests.cs
new file mode 100644
index 0000000..8ad4b43
--- /dev/null
+++ b/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());
+        }
+    }
+}
diff --git a/MEOS.NET/Types/Geo.g.cs b/MEOS.NET/Types/Geo.g.cs
index 266d0e7..0b31382 100644
--- a/MEOS.NET/Types/Geo.g.cs
+++ b/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);