diff --git a/llvm/lib/DebugInfo/Msf/StreamWriter.cpp b/llvm/lib/DebugInfo/Msf/StreamWriter.cpp
new file mode 100644
index 0000000..40bc0394
--- /dev/null
+++ b/llvm/lib/DebugInfo/Msf/StreamWriter.cpp
@@ -0,0 +1,78 @@
+//===- StreamWrite.cpp - Writes bytes and objects to a stream -------------===//
+//
+//                     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/StreamWriter.h"
+
+#include "llvm/DebugInfo/Msf/MsfError.h"
+#include "llvm/DebugInfo/Msf/StreamReader.h"
+#include "llvm/DebugInfo/Msf/StreamRef.h"
+
+using namespace llvm;
+using namespace llvm::msf;
+
+StreamWriter::StreamWriter(WritableStreamRef S) : Stream(S), Offset(0) {}
+
+Error StreamWriter::writeBytes(ArrayRef<uint8_t> Buffer) {
+  if (auto EC = Stream.writeBytes(Offset, Buffer))
+    return EC;
+  Offset += Buffer.size();
+  return Error::success();
+}
+
+Error StreamWriter::writeInteger(uint16_t Int) {
+  return writeObject(support::ulittle16_t(Int));
+}
+
+Error StreamWriter::writeInteger(uint32_t Int) {
+  return writeObject(support::ulittle32_t(Int));
+}
+
+Error StreamWriter::writeZeroString(StringRef Str) {
+  if (auto EC = writeFixedString(Str))
+    return EC;
+  if (auto EC = writeObject('\0'))
+    return EC;
+
+  return Error::success();
+}
+
+Error StreamWriter::writeFixedString(StringRef Str) {
+  ArrayRef<uint8_t> Bytes(Str.bytes_begin(), Str.bytes_end());
+  if (auto EC = Stream.writeBytes(Offset, Bytes))
+    return EC;
+
+  Offset += Str.size();
+  return Error::success();
+}
+
+Error StreamWriter::writeStreamRef(ReadableStreamRef Ref) {
+  if (auto EC = writeStreamRef(Ref, Ref.getLength()))
+    return EC;
+  // Don't increment Offset here, it is done by the overloaded call to
+  // writeStreamRef.
+  return Error::success();
+}
+
+Error StreamWriter::writeStreamRef(ReadableStreamRef Ref, uint32_t Length) {
+  Ref = Ref.slice(0, Length);
+
+  StreamReader SrcReader(Ref);
+  // This is a bit tricky.  If we just call readBytes, we are requiring that it
+  // return us the entire stream as a contiguous buffer.  For large streams this
+  // will allocate a huge amount of space from the pool.  Instead, iterate over
+  // each contiguous chunk until we've consumed the entire stream.
+  while (SrcReader.bytesRemaining() > 0) {
+    ArrayRef<uint8_t> Chunk;
+    if (auto EC = SrcReader.readLongestContiguousChunk(Chunk))
+      return EC;
+    if (auto EC = writeBytes(Chunk))
+      return EC;
+  }
+  return Error::success();
+}