From 94fe016af5de016ca4d0fc7882df940e7dd49d9b Mon Sep 17 00:00:00 2001
From: Wes McKinney <wesm@apache.org>
Date: Fri, 1 Apr 2016 13:33:08 -0700
Subject: [PATCH] Fix BufferBuilder edge case where all inputs were length-0

---
 cpp/src/feather/buffer.h            | 13 ++++++++++---
 cpp/src/feather/tests/io-test.cc    | 13 +++++++++++++
 python/feather/tests/test_reader.py |  4 ++++
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/cpp/src/feather/buffer.h b/cpp/src/feather/buffer.h
index 783121a..76af78a 100644
--- a/cpp/src/feather/buffer.h
+++ b/cpp/src/feather/buffer.h
@@ -129,13 +129,20 @@ class BufferBuilder {
       RETURN_NOT_OK(buffer_->Resize(capacity_));
       data_ = buffer_->mutable_data();
     }
-    memcpy(data_ + size_, data, length);
-    size_ += length;
+    if (length > 0) {
+      memcpy(data_ + size_, data, length);
+      size_ += length;
+    }
     return Status::OK();
   }
 
   std::shared_ptr<Buffer> Finish() {
-    auto result = buffer_;
+    std::shared_ptr<Buffer> result;
+    if (data_ == nullptr) {
+      result = std::make_shared<Buffer>(nullptr, 0);
+    } else {
+      result = buffer_;
+    }
     buffer_ = nullptr;
     return result;
   }
diff --git a/cpp/src/feather/tests/io-test.cc b/cpp/src/feather/tests/io-test.cc
index b119a56..2ad747e 100644
--- a/cpp/src/feather/tests/io-test.cc
+++ b/cpp/src/feather/tests/io-test.cc
@@ -73,4 +73,17 @@ TEST(FileOutputStream, NonExistentDirectory) {
   ASSERT_TRUE(s.IsIOError());
 }
 
+TEST(BufferBuilder, EmptyStrings) {
+  BufferBuilder builder;
+
+  builder.Append(nullptr, 0);
+  builder.Append(nullptr, 0);
+  builder.Append(nullptr, 0);
+
+  std::shared_ptr<Buffer> result = builder.Finish();
+
+  ASSERT_EQ(nullptr, result->data());
+  ASSERT_EQ(0, result->size());
+}
+
 } // namespace feather
diff --git a/python/feather/tests/test_reader.py b/python/feather/tests/test_reader.py
index 0d0eb11..7ec585d 100644
--- a/python/feather/tests/test_reader.py
+++ b/python/feather/tests/test_reader.py
@@ -204,6 +204,10 @@ def test_strings(self):
         expected = pd.DataFrame({'strings': values * repeats})
         self._check_pandas_roundtrip(df, expected)
 
+    def test_empty_strings(self):
+        df = pd.DataFrame({'strings': [''] * 10})
+        self._check_pandas_roundtrip(df)
+
     def test_nan_as_null(self):
         # Create a nan that is not numpy.nan
         values = np.array(['foo', np.nan, np.nan * 2, 'bar'] * 10)