From d06839811d31b376d35dd373082ccce21666f44d Mon Sep 17 00:00:00 2001
From: Kyle Nekritz <knekritz@fb.com>
Date: Mon, 27 Feb 2017 10:48:39 -0800
Subject: [PATCH] Don't call memcpy with empty buffer in IOBuf::copyBuffer().

Summary: Fixes "undefined behavior" in ubsan builds when using an empty ByteRange.

Reviewed By: siyengar

Differential Revision: D4613663

fbshipit-source-id: 4b53ba764609acc986340f10613f84585fa697cf
---
 folly/io/IOBuf.h            | 4 +++-
 folly/io/test/IOBufTest.cpp | 5 +++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/folly/io/IOBuf.h b/folly/io/IOBuf.h
index 621d3933..87a3ec9e 100644
--- a/folly/io/IOBuf.h
+++ b/folly/io/IOBuf.h
@@ -1439,7 +1439,9 @@ inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
   uint64_t capacity = headroom + size + minTailroom;
   std::unique_ptr<IOBuf> buf = create(capacity);
   buf->advance(headroom);
-  memcpy(buf->writableData(), data, size);
+  if (size != 0) {
+    memcpy(buf->writableData(), data, size);
+  }
   buf->append(size);
   return buf;
 }
diff --git a/folly/io/test/IOBufTest.cpp b/folly/io/test/IOBufTest.cpp
index 85b9dcb3..6e0cf441 100644
--- a/folly/io/test/IOBufTest.cpp
+++ b/folly/io/test/IOBufTest.cpp
@@ -717,6 +717,11 @@ TEST(IOBuf, maybeCopyBuffer) {
   EXPECT_EQ(nullptr, buf.get());
 }
 
+TEST(IOBuf, copyEmptyBuffer) {
+  auto buf = IOBuf::copyBuffer(nullptr, 0);
+  EXPECT_EQ(buf->length(), 0);
+}
+
 namespace {
 
 int customDeleterCount = 0;
-- 
2.34.1