From a4d8d01064780d2325554aa824f7e359af582f02 Mon Sep 17 00:00:00 2001
From: Ajit Banerjee <ajitb@fb.com>
Date: Thu, 2 Jan 2014 16:30:59 -0800
Subject: [PATCH] Fix cursor insert inconsistency

Summary:
The invariant after Cursor::insert is that the cursor points to the buffer
after the insert. That invariant was not followed in the branch where the
new buffer was just prepended. This change fixes the bug.

Test Plan:
Unit test modified, all tests run with
fbconfig -r folly && fbmake runtests_opt

Reviewed By: davejwatson@fb.com

FB internal diff: D1114749
---
 folly/io/Cursor.h                 |  4 ++--
 folly/io/test/IOBufCursorTest.cpp | 12 +++++++-----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/folly/io/Cursor.h b/folly/io/Cursor.h
index 0b79c23f..5f65fb0e 100644
--- a/folly/io/Cursor.h
+++ b/folly/io/Cursor.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2014 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -501,7 +501,7 @@ class RWCursor
     folly::IOBuf* nextBuf;
     if (this->offset_ == 0) {
       // Can just prepend
-      nextBuf = buf.get();
+      nextBuf = this->crtBuf_;
       this->crtBuf_->prependChain(std::move(buf));
     } else {
       std::unique_ptr<folly::IOBuf> remaining;
diff --git a/folly/io/test/IOBufCursorTest.cpp b/folly/io/test/IOBufCursorTest.cpp
index 5cc68967..e0bf5a5a 100644
--- a/folly/io/test/IOBufCursorTest.cpp
+++ b/folly/io/test/IOBufCursorTest.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2014 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -315,9 +315,11 @@ TEST(IOBuf, cloneAndInsert) {
     cursor.skip(1);
 
     cursor.insert(std::move(cloned));
-    EXPECT_EQ(6, iobuf1->countChainElements());
+    cursor.insert(folly::IOBuf::create(0));
+    EXPECT_EQ(7, iobuf1->countChainElements());
     EXPECT_EQ(14, iobuf1->computeChainDataLength());
-    // Check that nextBuf got set correctly
+    // Check that nextBuf got set correctly to the buffer with 1 byte left
+    EXPECT_EQ(1, cursor.peek().second);
     cursor.read<uint8_t>();
   }
 
@@ -331,7 +333,7 @@ TEST(IOBuf, cloneAndInsert) {
     cursor.skip(1);
 
     cursor.insert(std::move(cloned));
-    EXPECT_EQ(7, iobuf1->countChainElements());
+    EXPECT_EQ(8, iobuf1->countChainElements());
     EXPECT_EQ(15, iobuf1->computeChainDataLength());
     // Check that nextBuf got set correctly
     cursor.read<uint8_t>();
@@ -344,7 +346,7 @@ TEST(IOBuf, cloneAndInsert) {
     EXPECT_EQ(1, cloned->computeChainDataLength());
 
     cursor.insert(std::move(cloned));
-    EXPECT_EQ(8, iobuf1->countChainElements());
+    EXPECT_EQ(9, iobuf1->countChainElements());
     EXPECT_EQ(16, iobuf1->computeChainDataLength());
     // Check that nextBuf got set correctly
     cursor.read<uint8_t>();
-- 
2.34.1