From 64b110942d0c88bd7e16f72cddd060d2bcff4f3f Mon Sep 17 00:00:00 2001
From: mwish <maplewish117@gmail.com>
Date: Wed, 12 Jun 2024 00:33:11 +0800
Subject: [PATCH] GH-41899: [C++]  IPC: Minor enhance the code of writer
 (#41900)

### Rationale for this change

Enhance the code of IPC writer

### What changes are included in this PR?

1. memcpy rather than reinterpret_cast
2. move the buffer rather than copying

### Are these changes tested?

Covered by existing

### Are there any user-facing changes?

No

* GitHub Issue: #41899

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: mwish <maplewish117@gmail.com>
---
 cpp/src/arrow/ipc/writer.cc | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/cpp/src/arrow/ipc/writer.cc b/cpp/src/arrow/ipc/writer.cc
index e3dd36efe0543..549fb34a2e880 100644
--- a/cpp/src/arrow/ipc/writer.cc
+++ b/cpp/src/arrow/ipc/writer.cc
@@ -164,7 +164,7 @@ class RecordBatchSerializer {
         std::shared_ptr<Buffer> bitmap;
         RETURN_NOT_OK(GetTruncatedBitmap(arr.offset(), arr.length(), arr.null_bitmap(),
                                          options_.memory_pool, &bitmap));
-        out_->body_buffers.emplace_back(bitmap);
+        out_->body_buffers.emplace_back(std::move(bitmap));
       } else {
         // Push a dummy zero-length buffer, not to be copied
         out_->body_buffers.emplace_back(kNullBuffer);
@@ -222,8 +222,9 @@ class RecordBatchSerializer {
       RETURN_NOT_OK(
           result->Resize(actual_length + sizeof(int64_t), /* shrink_to_fit= */ true));
     }
-    *reinterpret_cast<int64_t*>(result->mutable_data()) =
-        bit_util::ToLittleEndian(prefixed_length);
+    int64_t prefixed_length_little_endian = bit_util::ToLittleEndian(prefixed_length);
+    util::SafeStore(result->mutable_data(), prefixed_length_little_endian);
+
     *out = SliceBuffer(std::move(result), /*offset=*/0, actual_length + sizeof(int64_t));
 
     return Status::OK();
@@ -415,7 +416,7 @@ class RecordBatchSerializer {
     std::shared_ptr<Buffer> data;
     RETURN_NOT_OK(GetTruncatedBitmap(array.offset(), array.length(), array.values(),
                                      options_.memory_pool, &data));
-    out_->body_buffers.emplace_back(data);
+    out_->body_buffers.emplace_back(std::move(data));
     return Status::OK();
   }
 
@@ -442,7 +443,7 @@ class RecordBatchSerializer {
                    data->size() - byte_offset);
       data = SliceBuffer(data, byte_offset, buffer_length);
     }
-    out_->body_buffers.emplace_back(data);
+    out_->body_buffers.emplace_back(std::move(data));
     return Status::OK();
   }
 
@@ -464,8 +465,8 @@ class RecordBatchSerializer {
       data = SliceBuffer(data, start_offset, slice_length);
     }
 
-    out_->body_buffers.emplace_back(value_offsets);
-    out_->body_buffers.emplace_back(data);
+    out_->body_buffers.emplace_back(std::move(value_offsets));
+    out_->body_buffers.emplace_back(std::move(data));
     return Status::OK();
   }
 
@@ -566,7 +567,7 @@ class RecordBatchSerializer {
     RETURN_NOT_OK(GetTruncatedBuffer(
         offset, length, static_cast<int32_t>(sizeof(UnionArray::type_code_t)),
         array.type_codes(), options_.memory_pool, &type_codes));
-    out_->body_buffers.emplace_back(type_codes);
+    out_->body_buffers.emplace_back(std::move(type_codes));
 
     --max_recursion_depth_;
     for (int i = 0; i < array.num_fields(); ++i) {
@@ -585,7 +586,7 @@ class RecordBatchSerializer {
     RETURN_NOT_OK(GetTruncatedBuffer(
         offset, length, static_cast<int32_t>(sizeof(UnionArray::type_code_t)),
         array.type_codes(), options_.memory_pool, &type_codes));
-    out_->body_buffers.emplace_back(type_codes);
+    out_->body_buffers.emplace_back(std::move(type_codes));
 
     --max_recursion_depth_;
     const auto& type = checked_cast<const UnionType&>(*array.type());
@@ -640,7 +641,7 @@ class RecordBatchSerializer {
 
       value_offsets = std::move(shifted_offsets_buffer);
     }
-    out_->body_buffers.emplace_back(value_offsets);
+    out_->body_buffers.emplace_back(std::move(value_offsets));
 
     // Visit children and slice accordingly
     for (int i = 0; i < type.num_fields(); ++i) {