From ce399ac28af7023b1aff0ede4986cb6d89b3c0b5 Mon Sep 17 00:00:00 2001
From: cmumford <cmumford@google.com>
Date: Tue, 19 Mar 2019 17:10:56 -0700
Subject: [PATCH] Always copy bytes to scratch buffer when reading w/MemEnv.

FileState::Read (used by InMemoryEnv) creates a new Slice when reading.
If all the bytes for the read are in the first block then the Slice
points to the private block data in FileState and is not copied to the
|scratch| buffer.

A recent change allows files in InMemEnv to be overwritten which deletes
these blocks and in this case can result in a Slice having a dangling
pointer. This change fixes this bug by always copying to the |scratch|
buffer.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=239301930
---
 helpers/memenv/memenv.cc | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/helpers/memenv/memenv.cc b/helpers/memenv/memenv.cc
index b78a998..ff384e4 100644
--- a/helpers/memenv/memenv.cc
+++ b/helpers/memenv/memenv.cc
@@ -82,13 +82,6 @@ class FileState {
     assert(offset / kBlockSize <= std::numeric_limits<size_t>::max());
     size_t block = static_cast<size_t>(offset / kBlockSize);
     size_t block_offset = offset % kBlockSize;
-
-    if (n <= kBlockSize - block_offset) {
-      // The requested bytes are all in the first block.
-      *result = Slice(blocks_[block] + block_offset, n);
-      return Status::OK();
-    }
-
     size_t bytes_to_copy = n;
     char* dst = scratch;