[C++] Use proper gRPC C++ API when using MemoryBuffer Slice (#6756)

* Use ByteBuffer

* Use Slice

* Upgrade gRPC to 1.39.0

* Update gRPC build script

* Reformat

* Added CMAKE_CXX_STANDARD=11 when building Abseil

* Enabled ABSL_ENABLE_INSTALL

* Added absl to grpctest deps

3 files changed, 8 insertions, 15 deletions

diff --git a/grpc/README.md b/grpc/README.md
index 685003f9..f46258fc 100644
--- a/grpc/README.md
+++ b/grpc/README.md
@@ -32,9 +32,8 @@ $bazel test src/compiler/...
 
 ### Linux
 
-1. `ln -s ${GRPC_INSTALL_PATH}/lib/libgrpc++_unsecure.so.6 ${GRPC_INSTALL_PATH}/lib/libgrpc++_unsecure.so.1`
-2. `export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:${GRPC_INSTALL_PATH}/lib`
-3. `make test ARGS=-V` 
+1. `export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:${GRPC_INSTALL_PATH}/lib`
+2. `make test ARGS=-V`
 
 For Bazel users:
 
diff --git a/grpc/build_grpc.sh b/grpc/build_grpc.sh
index 190a1ef9..49c5a60f 100755
--- a/grpc/build_grpc.sh
+++ b/grpc/build_grpc.sh
@@ -1,11 +1,11 @@
 #!/bin/bash
 
-grpc_1_36_0_githash=736e3758351ced3cd842bad3ba4e2540f01bbc48
+grpc_1_39_0_githash=58602e20a3f3e48f24a4114c757099b25b947f7b
 
 function build_grpc () {
   git clone https://github.com/grpc/grpc.git google/grpc
   cd google/grpc
-  git checkout ${grpc_1_36_0_githash}
+  git checkout ${grpc_1_39_0_githash}
   git submodule update --init
   # Apply boringssl build patch
   cd third_party/boringssl-with-bazel
@@ -13,11 +13,8 @@ function build_grpc () {
   cd ../..
   mkdir ../grpc_build
   cd ../grpc_build
-  cmake ../grpc -DgRPC_INSTALL=ON -DgRPC_BUILD_TESTS=OFF -DBUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX=`pwd`/../grpc/install
+  cmake ../grpc -DgRPC_INSTALL=ON -DgRPC_BUILD_TESTS=OFF -DABSL_ENABLE_INSTALL=ON -DBUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX=`pwd`/../grpc/install
   cmake --build . --target install ${JOBS:+-j$JOBS}
-  if [ ! -f ${GRPC_INSTALL_PATH}/lib/libgrpc++_unsecure.so.1 ]; then
-    ln -s ${GRPC_INSTALL_PATH}/lib/libgrpc++_unsecure.so.6 ${GRPC_INSTALL_PATH}/lib/libgrpc++_unsecure.so.1
-  fi
   cd ../..
 }
 
diff --git a/grpc/tests/message_builder_test.cpp b/grpc/tests/message_builder_test.cpp
index 3ce33a98..8af0c214 100644
--- a/grpc/tests/message_builder_test.cpp
+++ b/grpc/tests/message_builder_test.cpp
@@ -28,7 +28,7 @@ void builder_move_assign_after_releaseraw_test(
   auto root_offset1 = populate1(dst);
   dst.Finish(root_offset1);
   size_t size, offset;
-  grpc_slice slice;
+  ::grpc::Slice slice;
   dst.ReleaseRaw(size, offset, slice);
   flatbuffers::FlatBufferBuilder src;
   auto root_offset2 = populate2(src);
@@ -39,7 +39,6 @@ void builder_move_assign_after_releaseraw_test(
   TEST_EQ(dst.GetSize(), src_size);
   TEST_ASSERT(release_n_verify(dst, m2_name(), m2_color()));
   TEST_EQ(src.GetSize(), 0);
-  grpc_slice_unref(slice);
 }
 
 template<class SrcBuilder>
@@ -82,10 +81,9 @@ struct BuilderReuseTests<flatbuffers::grpc::MessageBuilder, SrcBuilder> {
       auto root_offset1 = populate1(mb);
       mb.Finish(root_offset1);
       size_t size, offset;
-      grpc_slice slice;
+      ::grpc::Slice slice;
       const uint8_t *buf = mb.ReleaseRaw(size, offset, slice);
       TEST_ASSERT_FUNC(verify(buf, offset, m1_name(), m1_color()));
-      grpc_slice_unref(slice);
     }
   }
 
@@ -146,10 +144,9 @@ struct BuilderReuseTests<flatbuffers::grpc::MessageBuilder, SrcBuilder> {
       auto root_offset1 = populate1(dst);
       dst.Finish(root_offset1);
       size_t size, offset;
-      grpc_slice slice = grpc_empty_slice();
+      ::grpc::Slice slice;
       const uint8_t *buf = dst.ReleaseRaw(size, offset, slice);
       TEST_ASSERT_FUNC(verify(buf, offset, m1_name(), m1_color()));
-      grpc_slice_unref(slice);
 
       SrcBuilder src;
       dst = std::move(src);