[MSF] Move MSF unit tests to their own unittest target.

llvm-svn: 309895
diff --git a/llvm/unittests/DebugInfo/MSF/MappedBlockStreamTest.cpp b/llvm/unittests/DebugInfo/MSF/MappedBlockStreamTest.cpp
new file mode 100644
index 0000000..94cd347
--- /dev/null
+++ b/llvm/unittests/DebugInfo/MSF/MappedBlockStreamTest.cpp
@@ -0,0 +1,498 @@
+//===- llvm/unittest/DebugInfo/MSF/MappedBlockStreamTest.cpp --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/DebugInfo/MSF/MappedBlockStream.h"
+#include "llvm/DebugInfo/MSF/IMSFFile.h"
+#include "llvm/DebugInfo/MSF/MSFError.h"
+#include "llvm/Support/BinaryByteStream.h"
+#include "llvm/Support/BinaryStreamReader.h"
+#include "llvm/Support/BinaryStreamRef.h"
+#include "llvm/Support/BinaryStreamWriter.h"
+#include "llvm/Testing/Support/Error.h"
+
+#include "gtest/gtest.h"
+
+#include <unordered_map>
+
+using namespace llvm;
+using namespace llvm::msf;
+using namespace llvm::support;
+
+namespace {
+
+static const uint32_t BlocksAry[] = {0, 1, 2, 5, 4, 3, 6, 7, 8, 9};
+static uint8_t DataAry[] = {'A', 'B', 'C', 'F', 'E', 'D', 'G', 'H', 'I', 'J'};
+
+class DiscontiguousStream : public WritableBinaryStream {
+public:
+  DiscontiguousStream(ArrayRef<uint32_t> Blocks, MutableArrayRef<uint8_t> Data)
+      : Blocks(Blocks.begin(), Blocks.end()), Data(Data.begin(), Data.end()) {}
+
+  uint32_t block_size() const { return 1; }
+  uint32_t block_count() const { return Blocks.size(); }
+
+  endianness getEndian() const override { return little; }
+
+  Error readBytes(uint32_t Offset, uint32_t Size,
+                  ArrayRef<uint8_t> &Buffer) override {
+    if (auto EC = checkOffset(Offset, Size))
+      return EC;
+    Buffer = Data.slice(Offset, Size);
+    return Error::success();
+  }
+
+  Error readLongestContiguousChunk(uint32_t Offset,
+                                   ArrayRef<uint8_t> &Buffer) override {
+    if (auto EC = checkOffset(Offset, 1))
+      return EC;
+    Buffer = Data.drop_front(Offset);
+    return Error::success();
+  }
+
+  uint32_t getLength() override { return Data.size(); }
+
+  Error writeBytes(uint32_t Offset, ArrayRef<uint8_t> SrcData) override {
+    if (auto EC = checkOffset(Offset, SrcData.size()))
+      return EC;
+    ::memcpy(&Data[Offset], SrcData.data(), SrcData.size());
+    return Error::success();
+  }
+  Error commit() override { return Error::success(); }
+
+  MSFStreamLayout layout() const {
+    return MSFStreamLayout{static_cast<uint32_t>(Data.size()), Blocks};
+  }
+
+  BumpPtrAllocator Allocator;
+
+private:
+  std::vector<support::ulittle32_t> Blocks;
+  MutableArrayRef<uint8_t> Data;
+};
+
+TEST(MappedBlockStreamTest, NumBlocks) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  EXPECT_EQ(F.block_size(), S->getBlockSize());
+  EXPECT_EQ(F.layout().Blocks.size(), S->getNumBlocks());
+}
+
+// Tests that a read which is entirely contained within a single block works
+// and does not allocate.
+TEST(MappedBlockStreamTest, ReadBeyondEndOfStreamRef) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+
+  BinaryStreamReader R(*S);
+  BinaryStreamRef SR;
+  EXPECT_THAT_ERROR(R.readStreamRef(SR, 0U), Succeeded());
+  ArrayRef<uint8_t> Buffer;
+  EXPECT_THAT_ERROR(SR.readBytes(0U, 1U, Buffer), Failed());
+  EXPECT_THAT_ERROR(R.readStreamRef(SR, 1U), Succeeded());
+  EXPECT_THAT_ERROR(SR.readBytes(1U, 1U, Buffer), Failed());
+}
+
+// Tests that a read which outputs into a full destination buffer works and
+// does not fail due to the length of the output buffer.
+TEST(MappedBlockStreamTest, ReadOntoNonEmptyBuffer) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+
+  BinaryStreamReader R(*S);
+  StringRef Str = "ZYXWVUTSRQPONMLKJIHGFEDCBA";
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 1), Succeeded());
+  EXPECT_EQ(Str, StringRef("A"));
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+}
+
+// Tests that a read which crosses a block boundary, but where the subsequent
+// blocks are still contiguous in memory to the previous block works and does
+// not allocate memory.
+TEST(MappedBlockStreamTest, ZeroCopyReadContiguousBreak) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str;
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 2), Succeeded());
+  EXPECT_EQ(Str, StringRef("AB"));
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+
+  R.setOffset(6);
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 4), Succeeded());
+  EXPECT_EQ(Str, StringRef("GHIJ"));
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+}
+
+// Tests that a read which crosses a block boundary and cannot be referenced
+// contiguously works and allocates only the precise amount of bytes
+// requested.
+TEST(MappedBlockStreamTest, CopyReadNonContiguousBreak) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str;
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 10), Succeeded());
+  EXPECT_EQ(Str, StringRef("ABCDEFGHIJ"));
+  EXPECT_EQ(10U, F.Allocator.getBytesAllocated());
+}
+
+// Test that an out of bounds read which doesn't cross a block boundary
+// fails and allocates no memory.
+TEST(MappedBlockStreamTest, InvalidReadSizeNoBreak) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str;
+
+  R.setOffset(10);
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 1), Failed());
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+}
+
+// Test that an out of bounds read which crosses a contiguous block boundary
+// fails and allocates no memory.
+TEST(MappedBlockStreamTest, InvalidReadSizeContiguousBreak) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str;
+
+  R.setOffset(6);
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 5), Failed());
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+}
+
+// Test that an out of bounds read which crosses a discontiguous block
+// boundary fails and allocates no memory.
+TEST(MappedBlockStreamTest, InvalidReadSizeNonContiguousBreak) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str;
+
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 11), Failed());
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+}
+
+// Tests that a read which is entirely contained within a single block but
+// beyond the end of a StreamRef fails.
+TEST(MappedBlockStreamTest, ZeroCopyReadNoBreak) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str;
+  EXPECT_THAT_ERROR(R.readFixedString(Str, 1), Succeeded());
+  EXPECT_EQ(Str, StringRef("A"));
+  EXPECT_EQ(0U, F.Allocator.getBytesAllocated());
+}
+
+// Tests that a read which is not aligned on the same boundary as a previous
+// cached request, but which is known to overlap that request, shares the
+// previous allocation.
+TEST(MappedBlockStreamTest, UnalignedOverlappingRead) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str1;
+  StringRef Str2;
+  EXPECT_THAT_ERROR(R.readFixedString(Str1, 7), Succeeded());
+  EXPECT_EQ(Str1, StringRef("ABCDEFG"));
+  EXPECT_EQ(7U, F.Allocator.getBytesAllocated());
+
+  R.setOffset(2);
+  EXPECT_THAT_ERROR(R.readFixedString(Str2, 3), Succeeded());
+  EXPECT_EQ(Str2, StringRef("CDE"));
+  EXPECT_EQ(Str1.data() + 2, Str2.data());
+  EXPECT_EQ(7U, F.Allocator.getBytesAllocated());
+}
+
+// Tests that a read which is not aligned on the same boundary as a previous
+// cached request, but which only partially overlaps a previous cached request,
+// still works correctly and allocates again from the shared pool.
+TEST(MappedBlockStreamTest, UnalignedOverlappingReadFail) {
+  DiscontiguousStream F(BlocksAry, DataAry);
+  auto S = MappedBlockStream::createStream(F.block_size(), F.layout(), F,
+                                           F.Allocator);
+  BinaryStreamReader R(*S);
+  StringRef Str1;
+  StringRef Str2;
+  EXPECT_THAT_ERROR(R.readFixedString(Str1, 6), Succeeded());
+  EXPECT_EQ(Str1, StringRef("ABCDEF"));
+  EXPECT_EQ(6U, F.Allocator.getBytesAllocated());
+
+  R.setOffset(4);
+  EXPECT_THAT_ERROR(R.readFixedString(Str2, 4), Succeeded());
+  EXPECT_EQ(Str2, StringRef("EFGH"));
+  EXPECT_EQ(10U, F.Allocator.getBytesAllocated());
+}
+
+TEST(MappedBlockStreamTest, WriteBeyondEndOfStream) {
+  static uint8_t Data[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'};
+  static uint8_t LargeBuffer[] = {'0', '1', '2', '3', '4', '5',
+                                  '6', '7', '8', '9', 'A'};
+  static uint8_t SmallBuffer[] = {'0', '1', '2'};
+  static_assert(sizeof(LargeBuffer) > sizeof(Data),
+                "LargeBuffer is not big enough");
+
+  DiscontiguousStream F(BlocksAry, Data);
+  auto S = WritableMappedBlockStream::createStream(F.block_size(), F.layout(),
+                                                   F, F.Allocator);
+  ArrayRef<uint8_t> Buffer;
+
+  EXPECT_THAT_ERROR(S->writeBytes(0, ArrayRef<uint8_t>(LargeBuffer)), Failed());
+  EXPECT_THAT_ERROR(S->writeBytes(0, ArrayRef<uint8_t>(SmallBuffer)),
+                    Succeeded());
+  EXPECT_THAT_ERROR(S->writeBytes(7, ArrayRef<uint8_t>(SmallBuffer)),
+                    Succeeded());
+  EXPECT_THAT_ERROR(S->writeBytes(8, ArrayRef<uint8_t>(SmallBuffer)), Failed());
+}
+
+TEST(MappedBlockStreamTest, TestWriteBytesNoBreakBoundary) {
+  static uint8_t Data[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'};
+  DiscontiguousStream F(BlocksAry, Data);
+  auto S = WritableMappedBlockStream::createStream(F.block_size(), F.layout(),
+                                                   F, F.Allocator);
+  ArrayRef<uint8_t> Buffer;
+
+  EXPECT_THAT_ERROR(S->readBytes(0, 1, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>('A'));
+  EXPECT_THAT_ERROR(S->readBytes(9, 1, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>('J'));
+
+  EXPECT_THAT_ERROR(S->writeBytes(0, ArrayRef<uint8_t>('J')), Succeeded());
+  EXPECT_THAT_ERROR(S->writeBytes(9, ArrayRef<uint8_t>('A')), Succeeded());
+
+  EXPECT_THAT_ERROR(S->readBytes(0, 1, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>('J'));
+  EXPECT_THAT_ERROR(S->readBytes(9, 1, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>('A'));
+
+  EXPECT_THAT_ERROR(S->writeBytes(0, ArrayRef<uint8_t>('A')), Succeeded());
+  EXPECT_THAT_ERROR(S->writeBytes(9, ArrayRef<uint8_t>('J')), Succeeded());
+
+  EXPECT_THAT_ERROR(S->readBytes(0, 1, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>('A'));
+  EXPECT_THAT_ERROR(S->readBytes(9, 1, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>('J'));
+}
+
+TEST(MappedBlockStreamTest, TestWriteBytesBreakBoundary) {
+  static uint8_t Data[] = {'0', '0', '0', '0', '0', '0', '0', '0', '0', '0'};
+  static uint8_t TestData[] = {'T', 'E', 'S', 'T', 'I', 'N', 'G', '.'};
+  static uint8_t Expected[] = {'T', 'E', 'S', 'N', 'I',
+                               'T', 'G', '.', '0', '0'};
+
+  DiscontiguousStream F(BlocksAry, Data);
+  auto S = WritableMappedBlockStream::createStream(F.block_size(), F.layout(),
+                                                   F, F.Allocator);
+  ArrayRef<uint8_t> Buffer;
+
+  EXPECT_THAT_ERROR(S->writeBytes(0, TestData), Succeeded());
+  // First just compare the memory, then compare the result of reading the
+  // string out.
+  EXPECT_EQ(ArrayRef<uint8_t>(Data), ArrayRef<uint8_t>(Expected));
+
+  EXPECT_THAT_ERROR(S->readBytes(0, 8, Buffer), Succeeded());
+  EXPECT_EQ(Buffer, ArrayRef<uint8_t>(TestData));
+}
+
+TEST(MappedBlockStreamTest, TestWriteThenRead) {
+  std::vector<uint8_t> DataBytes(10);
+  MutableArrayRef<uint8_t> Data(DataBytes);
+  const uint32_t Blocks[] = {2, 1, 0, 6, 3, 4, 5, 7, 9, 8};
+
+  DiscontiguousStream F(Blocks, Data);
+  auto S = WritableMappedBlockStream::createStream(F.block_size(), F.layout(),
+                                                   F, F.Allocator);
+
+  enum class MyEnum : uint32_t { Val1 = 2908234, Val2 = 120891234 };
+  using support::ulittle32_t;
+
+  uint16_t u16[] = {31468, 0};
+  uint32_t u32[] = {890723408, 0};
+  MyEnum Enum[] = {MyEnum::Val1, MyEnum::Val2};
+  StringRef ZStr[] = {"Zero Str", ""};
+  StringRef FStr[] = {"Fixed Str", ""};
+  uint8_t byteArray0[] = {'1', '2'};
+  uint8_t byteArray1[] = {'0', '0'};
+  ArrayRef<uint8_t> byteArrayRef0(byteArray0);
+  ArrayRef<uint8_t> byteArrayRef1(byteArray1);
+  ArrayRef<uint8_t> byteArray[] = {byteArrayRef0, byteArrayRef1};
+  uint32_t intArr0[] = {890723408, 29082234};
+  uint32_t intArr1[] = {890723408, 29082234};
+  ArrayRef<uint32_t> intArray[] = {intArr0, intArr1};
+
+  BinaryStreamReader Reader(*S);
+  BinaryStreamWriter Writer(*S);
+  EXPECT_THAT_ERROR(Writer.writeInteger(u16[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readInteger(u16[1]), Succeeded());
+  EXPECT_EQ(u16[0], u16[1]);
+  EXPECT_EQ(std::vector<uint8_t>({0, 0x7A, 0xEC, 0, 0, 0, 0, 0, 0, 0}),
+            DataBytes);
+
+  Reader.setOffset(0);
+  Writer.setOffset(0);
+  ::memset(DataBytes.data(), 0, 10);
+  EXPECT_THAT_ERROR(Writer.writeInteger(u32[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readInteger(u32[1]), Succeeded());
+  EXPECT_EQ(u32[0], u32[1]);
+  EXPECT_EQ(std::vector<uint8_t>({0x17, 0x5C, 0x50, 0, 0, 0, 0x35, 0, 0, 0}),
+            DataBytes);
+
+  Reader.setOffset(0);
+  Writer.setOffset(0);
+  ::memset(DataBytes.data(), 0, 10);
+  EXPECT_THAT_ERROR(Writer.writeEnum(Enum[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readEnum(Enum[1]), Succeeded());
+  EXPECT_EQ(Enum[0], Enum[1]);
+  EXPECT_EQ(std::vector<uint8_t>({0x2C, 0x60, 0x4A, 0, 0, 0, 0, 0, 0, 0}),
+            DataBytes);
+
+  Reader.setOffset(0);
+  Writer.setOffset(0);
+  ::memset(DataBytes.data(), 0, 10);
+  EXPECT_THAT_ERROR(Writer.writeCString(ZStr[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readCString(ZStr[1]), Succeeded());
+  EXPECT_EQ(ZStr[0], ZStr[1]);
+  EXPECT_EQ(
+      std::vector<uint8_t>({'r', 'e', 'Z', ' ', 'S', 't', 'o', 'r', 0, 0}),
+      DataBytes);
+
+  Reader.setOffset(0);
+  Writer.setOffset(0);
+  ::memset(DataBytes.data(), 0, 10);
+  EXPECT_THAT_ERROR(Writer.writeFixedString(FStr[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readFixedString(FStr[1], FStr[0].size()),
+                    Succeeded());
+  EXPECT_EQ(FStr[0], FStr[1]);
+  EXPECT_EQ(
+      std::vector<uint8_t>({'x', 'i', 'F', 'd', ' ', 'S', 'e', 't', 0, 'r'}),
+      DataBytes);
+
+  Reader.setOffset(0);
+  Writer.setOffset(0);
+  ::memset(DataBytes.data(), 0, 10);
+  EXPECT_THAT_ERROR(Writer.writeArray(byteArray[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readArray(byteArray[1], byteArray[0].size()),
+                    Succeeded());
+  EXPECT_EQ(byteArray[0], byteArray[1]);
+  EXPECT_EQ(std::vector<uint8_t>({0, 0x32, 0x31, 0, 0, 0, 0, 0, 0, 0}),
+            DataBytes);
+
+  Reader.setOffset(0);
+  Writer.setOffset(0);
+  ::memset(DataBytes.data(), 0, 10);
+  EXPECT_THAT_ERROR(Writer.writeArray(intArray[0]), Succeeded());
+  EXPECT_THAT_ERROR(Reader.readArray(intArray[1], intArray[0].size()),
+                    Succeeded());
+  EXPECT_EQ(intArray[0], intArray[1]);
+}
+
+TEST(MappedBlockStreamTest, TestWriteContiguousStreamRef) {
+  std::vector<uint8_t> DestDataBytes(10);
+  MutableArrayRef<uint8_t> DestData(DestDataBytes);
+  const uint32_t DestBlocks[] = {2, 1, 0, 6, 3, 4, 5, 7, 9, 8};
+
+  std::vector<uint8_t> SrcDataBytes(10);
+  MutableArrayRef<uint8_t> SrcData(SrcDataBytes);
+
+  DiscontiguousStream F(DestBlocks, DestData);
+  auto DestStream = WritableMappedBlockStream::createStream(
+      F.block_size(), F.layout(), F, F.Allocator);
+
+  // First write "Test Str" into the source stream.
+  MutableBinaryByteStream SourceStream(SrcData, little);
+  BinaryStreamWriter SourceWriter(SourceStream);
+  EXPECT_THAT_ERROR(SourceWriter.writeCString("Test Str"), Succeeded());
+  EXPECT_EQ(SrcDataBytes, std::vector<uint8_t>(
+                              {'T', 'e', 's', 't', ' ', 'S', 't', 'r', 0, 0}));
+
+  // Then write the source stream into the dest stream.
+  BinaryStreamWriter DestWriter(*DestStream);
+  EXPECT_THAT_ERROR(DestWriter.writeStreamRef(SourceStream), Succeeded());
+  EXPECT_EQ(DestDataBytes, std::vector<uint8_t>(
+                               {'s', 'e', 'T', ' ', 'S', 't', 't', 'r', 0, 0}));
+
+  // Then read the string back out of the dest stream.
+  StringRef Result;
+  BinaryStreamReader DestReader(*DestStream);
+  EXPECT_THAT_ERROR(DestReader.readCString(Result), Succeeded());
+  EXPECT_EQ(Result, "Test Str");
+}
+
+TEST(MappedBlockStreamTest, TestWriteDiscontiguousStreamRef) {
+  std::vector<uint8_t> DestDataBytes(10);
+  MutableArrayRef<uint8_t> DestData(DestDataBytes);
+  const uint32_t DestBlocks[] = {2, 1, 0, 6, 3, 4, 5, 7, 9, 8};
+
+  std::vector<uint8_t> SrcDataBytes(10);
+  MutableArrayRef<uint8_t> SrcData(SrcDataBytes);
+  const uint32_t SrcBlocks[] = {1, 0, 6, 3, 4, 5, 2, 7, 8, 9};
+
+  DiscontiguousStream DestF(DestBlocks, DestData);
+  DiscontiguousStream SrcF(SrcBlocks, SrcData);
+
+  auto Dest = WritableMappedBlockStream::createStream(
+      DestF.block_size(), DestF.layout(), DestF, DestF.Allocator);
+  auto Src = WritableMappedBlockStream::createStream(
+      SrcF.block_size(), SrcF.layout(), SrcF, SrcF.Allocator);
+
+  // First write "Test Str" into the source stream.
+  BinaryStreamWriter SourceWriter(*Src);
+  EXPECT_THAT_ERROR(SourceWriter.writeCString("Test Str"), Succeeded());
+  EXPECT_EQ(SrcDataBytes, std::vector<uint8_t>(
+                              {'e', 'T', 't', 't', ' ', 'S', 's', 'r', 0, 0}));
+
+  // Then write the source stream into the dest stream.
+  BinaryStreamWriter DestWriter(*Dest);
+  EXPECT_THAT_ERROR(DestWriter.writeStreamRef(*Src), Succeeded());
+  EXPECT_EQ(DestDataBytes, std::vector<uint8_t>(
+                               {'s', 'e', 'T', ' ', 'S', 't', 't', 'r', 0, 0}));
+
+  // Then read the string back out of the dest stream.
+  StringRef Result;
+  BinaryStreamReader DestReader(*Dest);
+  EXPECT_THAT_ERROR(DestReader.readCString(Result), Succeeded());
+  EXPECT_EQ(Result, "Test Str");
+}
+
+TEST(MappedBlockStreamTest, DataLivesAfterStreamDestruction) {
+  std::vector<uint8_t> DataBytes(10);
+  MutableArrayRef<uint8_t> Data(DataBytes);
+  const uint32_t Blocks[] = {2, 1, 0, 6, 3, 4, 5, 7, 9, 8};
+
+  StringRef Str[] = {"Zero Str", ""};
+
+  DiscontiguousStream F(Blocks, Data);
+  {
+    auto S = WritableMappedBlockStream::createStream(F.block_size(), F.layout(),
+                                                     F, F.Allocator);
+
+    BinaryStreamReader Reader(*S);
+    BinaryStreamWriter Writer(*S);
+    ::memset(DataBytes.data(), 0, 10);
+    EXPECT_THAT_ERROR(Writer.writeCString(Str[0]), Succeeded());
+    EXPECT_THAT_ERROR(Reader.readCString(Str[1]), Succeeded());
+    EXPECT_EQ(Str[0], Str[1]);
+  }
+
+  EXPECT_EQ(Str[0], Str[1]);
+}
+
+} // end anonymous namespace