[CP-SAT] fix memory leak in C#

ortools/init/csharp/init.i

@@ -13,12 +13,19 @@
 
 %include "ortools/base/base.i"
 
+%include "stdint.i"
 %include "std_string.i"
 
 %{
 #include "ortools/init/init.h"
 %}
 
+%typemap(ctype)  uint8_t* "uint8_t*"
+%typemap(imtype) uint8_t* "System.IntPtr"
+%typemap(cstype) uint8_t* "System.IntPtr"
+%typemap(csin)   uint8_t* "$csinput"
+%typemap(in)     uint8_t* %{ $1 = $input; %}
+
 %ignoreall
 
 %unignore operations_research;
@@ -38,6 +45,7 @@
 %unignore operations_research::CppBridge::ShutdownLogging;
 %unignore operations_research::CppBridge::SetFlags;
 %unignore operations_research::CppBridge::LoadGurobiSharedLibrary;
+%unignore operations_research::CppBridge::DeleteByteArray;
 
 %unignore operations_research::OrToolsVersion;
 %unignore operations_research::OrToolsVersion::MajorNumber;

ortools/init/init.h

@@ -14,6 +14,7 @@
 #ifndef OR_TOOLS_OPEN_SOURCE_INIT_INIT_H_
 #define OR_TOOLS_OPEN_SOURCE_INIT_INIT_H_
 
+#include <cstdint>
 #include <string>
 #include <vector>
 
@@ -123,6 +124,14 @@ class CppBridge {
   static bool LoadGurobiSharedLibrary(const std::string& full_library_path) {
     return LoadGurobiDynamicLibrary({full_library_path}).ok();
   }
+
+  /**
+   * Delete a temporary C++ byte array.
+   */
+  static void DeleteByteArray(uint8_t* buffer) {
+    delete [] buffer;
+  }
+
 };
 
 class OrToolsVersion {

ortools/util/csharp/proto.i

@@ -76,10 +76,10 @@
 %typemap(csout)  CppProtoType {
     System.IntPtr data = $imcall;
     int size = System.Runtime.InteropServices.Marshal.ReadInt32(data);
-    data += sizeof(int);
+    System.IntPtr bufferStart = data + sizeof(int);
     byte[] buf = System.Buffers.ArrayPool<byte>.Shared.Rent(size);
-    System.Runtime.InteropServices.Marshal.Copy(data, buf, 0, size);
-    // TODO(user): delete the C++ buffer.
+    System.Runtime.InteropServices.Marshal.Copy(bufferStart, buf, 0, size);
+    Google.OrTools.Init.CppBridge.DeleteByteArray(data);
     try {
       return CSharpProtoType.Parser.ParseFrom(System.MemoryExtensions.AsSpan(buf, 0, size));
     } catch (Google.Protobuf.InvalidProtocolBufferException /*e*/) {
@@ -98,4 +98,5 @@
   $result[2] = (size >> 16) & 0xFF;
   $result[3] = (size >> 24) & 0xFF;
 }
+
 %enddef // end PROTO2_RETURN