From af5ed37b6f4898842d55e7db80e74ba845d00393 Mon Sep 17 00:00:00 2001
From: Otto Ebeling <otto@fb.com>
Date: Thu, 27 Apr 2017 08:49:50 -0700
Subject: [PATCH] Don't return a nullptr from IOBufQueue::split(0)

Summary: There's a gotcha case for IOBufQueue::split when  n==0, it will then return an unique_ptr wrapping a nullptr, which many call sites do not expect.

Reviewed By: meyering

Differential Revision: D4868228

fbshipit-source-id: 418256dba8ca3bcfbae420b6099baa240055b9bb
---
 folly/io/IOBufQueue.cpp          | 3 +++
 folly/io/test/IOBufQueueTest.cpp | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/folly/io/IOBufQueue.cpp b/folly/io/IOBufQueue.cpp
index ce3cb8a5..33c97bc9 100644
--- a/folly/io/IOBufQueue.cpp
+++ b/folly/io/IOBufQueue.cpp
@@ -212,6 +212,9 @@ unique_ptr<IOBuf> IOBufQueue::split(size_t n, bool throwOnUnderflow) {
       break;
     }
   }
+  if (UNLIKELY(result == nullptr)) {
+    return IOBuf::create(0);
+  }
   return result;
 }
 
diff --git a/folly/io/test/IOBufQueueTest.cpp b/folly/io/test/IOBufQueueTest.cpp
index 8050812e..3b000ea8 100644
--- a/folly/io/test/IOBufQueueTest.cpp
+++ b/folly/io/test/IOBufQueueTest.cpp
@@ -167,6 +167,13 @@ TEST(IOBufQueue, SplitAtMost) {
   EXPECT_TRUE(queue.empty());
 }
 
+TEST(IOBufQueue, SplitZero) {
+  IOBufQueue queue(clOptions);
+  queue.append(stringToIOBuf(SCL("Hello world")));
+  auto buf = queue.split(0);
+  EXPECT_EQ(buf->computeChainDataLength(), 0);
+}
+
 TEST(IOBufQueue, Preallocate) {
   IOBufQueue queue(clOptions);
   queue.append(string("Hello"));
-- 
2.34.1