diff --git a/src/torrent-manager.cpp b/src/torrent-manager.cpp
index 305fa3b..f62491f 100644
--- a/src/torrent-manager.cpp
+++ b/src/torrent-manager.cpp
@@ -238,6 +238,25 @@
   return packets;
 }
 
+static std::pair<std::shared_ptr<fs::fstream>, std::vector<bool>>
+initializeFileState(const string& dataPath,
+                    const FileManifest& manifest)
+{
+  // construct the file name
+  const auto manifestName = manifest.name();
+  auto fileName = manifestName.getSubName(1, manifestName.size() - 2).toUri();
+  auto filePath = dataPath + fileName;
+  vector<bool> fileBitMap(manifest.catalog().size());
+  auto fbits = fs::fstream::out | fs::fstream::binary;
+  // if file exists, use in O/W use concatenate mode
+  fbits |= fs::exists(filePath) ? fs::fstream::in : fs::fstream::ate;
+  auto s = std::make_shared<fs::fstream>(filePath, fbits);
+  if (!*s) {
+    BOOST_THROW_EXCEPTION(io::Error("Cannot open: " + dataPath));
+  }
+  return std::make_pair(s, fileBitMap);
+}
+
 void TorrentManager::Initialize()
 {
   // .../<torrent_name>/torrent-file/<implicit_digest>
@@ -265,29 +284,28 @@
     }
     // construct the file name
     auto fileName = m.name().getSubName(1, m.name().size() - 2).toUri();
-    auto filePath = m_dataPath + fileName;
+    fs::path filePath = m_dataPath + fileName;
     // If there are any valid packets, add corresponding state to manager
-    auto packets = intializeDataPackets(filePath, m, *currTorrentFile_it);
+    if (!fs::exists(filePath)) {
+      boost::filesystem::create_directories(filePath.parent_path());
+      continue;
+    }
+    auto packets = intializeDataPackets(filePath.string(), m, *currTorrentFile_it);
     if (!packets.empty()) {
-      // build the bit map
-      auto catalog =  m.catalog();
-      vector<bool> fileBitMap(catalog.size());
+      m_fileStates[m.getFullName()] = initializeFileState(m_dataPath, m);
+      auto& fileBitMap = m_fileStates[m.getFullName()].second;
       auto read_it = packets.begin();
       size_t i = 0;
-      for (auto name : catalog) {
+      for (auto name : m.catalog()) {
         if (name == read_it->getFullName()) {
           ++read_it;
-          fileBitMap[i]= true;
+          fileBitMap[i] = true;
         }
         ++i;
       }
       for (const auto& d : packets) {
         seed(d);
       }
-      auto s = std::make_shared<fs::fstream>(filePath, fs::fstream::binary
-                                                     | fs::fstream::in
-                                                     | fs::fstream::out);
-      m_fileStates[m.getFullName()] = std::make_pair(s, fileBitMap);
     }
   }
   for (const auto& t : m_torrentSegments) {
@@ -296,7 +314,45 @@
   for (const auto& m : m_fileManifests) {
     seed(m);
   }
+}
 
+bool TorrentManager::writeData(const Data& packet)
+{
+  // find correct manifest
+  const auto& packetName = packet.getName();
+  auto manifest_it = std::find_if(m_fileManifests.begin(), m_fileManifests.end(),
+                                 [&packetName](const FileManifest& m) {
+                                   return m.getName().isPrefixOf(packetName);
+                                 });
+  if (m_fileManifests.end() == manifest_it) {
+    return false;
+  }
+  // get file state out
+  auto& fileState = m_fileStates[manifest_it->getFullName()];
+  // if there is no open stream to the file
+  if (nullptr == fileState.first) {
+    fileState = initializeFileState(m_dataPath, *manifest_it);
+  }
+  auto packetNum = packetName.get(packet.getName().size() - 1).toSequenceNumber();
+  // if we already have the packet, do not rewrite it.
+  if (fileState.second[packetNum]) {
+    return false;
+  }
+  auto packetOffset = packetNum * manifest_it->data_packet_size();
+  // write data to disk
+  fileState.first->seekg(packetOffset);
+  try {
+    auto content = packet.getContent();
+    std::vector<char> data(content.value_begin(), content.value_end());
+    fileState.first->write(&data[0], data.size());
+  }
+  catch (io::Error &e) {
+    std::cerr << e.what() << std::endl;
+    return false;
+  }
+  // update bitmap
+  fileState.second[packetNum] = true;
+  return true;
 }
 
 void TorrentManager::seed(const Data& data) const {
diff --git a/src/torrent-manager.hpp b/src/torrent-manager.hpp
index 3c4b923..ca83a2b 100644
--- a/src/torrent-manager.hpp
+++ b/src/torrent-manager.hpp
@@ -92,6 +92,11 @@
   // Seed the specified 'data' to the network.
 
  protected:
+  bool writeData(const Data& packet);
+  // Write the Data packet to disk, return 'true' if data successfully written to disk 'false'
+  // otherwise. Behavior is undefined unless the corresponding file manifest has already been
+  // downloaded.
+
   void onDataReceived(const Data& data);
 
   void onInterestReceived(const Name& name);
diff --git a/tests/unit-tests/torrent-manager.t.cpp b/tests/unit-tests/torrent-manager.t.cpp
index 59392aa..910704d 100644
--- a/tests/unit-tests/torrent-manager.t.cpp
+++ b/tests/unit-tests/torrent-manager.t.cpp
@@ -24,6 +24,8 @@
 #include "torrent-manager.hpp"
 #include "torrent-file.hpp"
 
+#include <set>
+
 #include <boost/filesystem.hpp>
 
 #include <ndn-cxx/util/io.hpp>
@@ -53,8 +55,16 @@
   }
 
   std::vector<bool> fileState(const ndn::Name& manifestName) {
+    auto fout = m_fileStates[manifestName].first;
+    if (nullptr != fout) {
+      fout->flush();
+    }
     return m_fileStates[manifestName].second;
   }
+
+  bool writeData(const Data& data) {
+    return TorrentManager::writeData(data);
+  }
 };
 
 BOOST_AUTO_TEST_SUITE(TestTorrentManagerInitialize)
@@ -74,9 +84,7 @@
     torrentSegments = temp.first;
     auto temp1      = temp.second;
     for (const auto& ms : temp1) {
-      for (const auto& m : ms.first) {
-        manifests.push_back(m);
-      }
+      manifests.insert(manifests.end(), ms.first.begin(), ms.first.end());
     }
   }
   // write the torrent segments  and manifests to disk
@@ -177,10 +185,8 @@
     torrentSegments = temp.first;
     auto temp1      = temp.second;
     temp1.pop_back(); // remove the manifests for the last file
-    for (const auto& ms : temp1) {
-      for (const auto& m : ms.first) {
-        manifests.push_back(m);
-      }
+    for (const  auto& ms : temp1) {
+      manifests.insert(manifests.end(), ms.first.begin(), ms.first.end());
     }
   }
   // write the torrent segments  and manifests to disk
@@ -193,7 +199,6 @@
     fileNum++;
     auto filename = torrentPath + to_string(fileNum);
     io::save(t, filename);
-
   }
   fileNum = 0;
   auto manifestPath = dirPath + "manifests/";
@@ -224,6 +229,102 @@
 
 BOOST_AUTO_TEST_SUITE_END()
 
+BOOST_AUTO_TEST_SUITE(CheckTorrentManagerUtilities)
+
+BOOST_AUTO_TEST_CASE(CheckWriteDataComplete)
+{
+  vector<FileManifest> manifests;
+  vector<TorrentFile>  torrentSegments;
+  // for each file, the data packets
+  std::vector<vector<Data>> fileData;
+  std::string filePath = "tests/testdata/temp";
+  // get torrent files and manifests
+  {
+    auto temp = TorrentFile::generate("tests/testdata/foo",
+                                      1024,
+                                      1024,
+                                      1024,
+                                      true);
+    torrentSegments = temp.first;
+    auto temp1      = temp.second;
+    for (const auto& ms : temp1) {
+      manifests.insert(manifests.end(), ms.first.begin(), ms.first.end());
+      fileData.push_back(ms.second);
+    }
+  }
+  // write the torrent segments and manifests to disk
+  std::string dirPath = ".appdata/foo/";
+  boost::filesystem::create_directories(dirPath);
+  std::string torrentPath = dirPath + "torrent_files/";
+  boost::filesystem::create_directories(torrentPath);
+  auto fileNum = 0;
+  for (const auto& t : torrentSegments) {
+    fileNum++;
+    auto filename = torrentPath + to_string(fileNum);
+    io::save(t, filename);
+  }
+  fileNum = 0;
+  auto manifestPath = dirPath + "manifests/";
+  boost::filesystem::create_directory(manifestPath);
+  for (const auto& m : manifests) {
+    fileNum++;
+    auto filename = manifestPath + to_string(fileNum);
+    io::save(m, filename);
+  }
+  // Initialize manager
+  TestTorrentManager manager("/NTORRENT/foo/torrent-file/sha256digest=02c737fd4c6e7de4b4825b089f39700c2dfa8fd2bb2b91f09201e357c4463253",
+                             filePath);
+  manager.Initialize();
+  // check that initially there is no data on disk
+  for (auto m : manager.fileManifests()) {
+    auto fileState = manager.fileState(m.getFullName());
+    BOOST_CHECK(fileState.empty());
+  }
+  // write all data to disk (for each file manifest)
+  auto manifest_it = manifests.begin();
+  for (auto& data : fileData) {
+    for (auto& d : data) {
+      BOOST_CHECK(manager.writeData(d));
+    }
+    // check that the  state is updated appropriately
+    auto fileState = manager.fileState(manifest_it->getFullName());
+    for (auto s : fileState) {
+      BOOST_CHECK(s);
+    }
+    ++manifest_it;
+  }
+  // get the file names (ascending)
+  std::set<std::string> fileNames;
+  for (auto i = fs::recursive_directory_iterator(filePath + "/foo");
+       i != fs::recursive_directory_iterator();
+       ++i) {
+    fileNames.insert(i->path().string());
+  }
+  // verify file by file that the data packets are written correctly
+  auto f_it = fileData.begin();
+  for (auto f : fileNames) {
+    // read file from disk
+    std::vector<uint8_t> file_bytes;
+    fs::ifstream is(f, fs::ifstream::binary | fs::ifstream::in);
+    is >> std::noskipws;
+    std::istream_iterator<uint8_t> start(is), end;
+    file_bytes.insert(file_bytes.end(), start, end);
+    std::vector<uint8_t> data_bytes;
+    // get content from data packets
+    for (const auto& d : *f_it) {
+      auto content = d.getContent();
+      data_bytes.insert(data_bytes.end(), content.value_begin(), content.value_end());
+    }
+    BOOST_CHECK(data_bytes == file_bytes);
+    ++f_it;
+  }
+  fs::remove_all(filePath);
+  fs::remove_all(".appdata");
+}
+
+
+BOOST_AUTO_TEST_SUITE_END()
+
 } // namespace tests
 } // namespace nTorrent
 } // namespace ndn
\ No newline at end of file