diff --git a/download_action.cc b/download_action.cc
new file mode 100644
index 0000000..10dffd2
--- /dev/null
+++ b/download_action.cc
@@ -0,0 +1,468 @@
+//
+// Copyright (C) 2011 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "update_engine/common/download_action.h"
+
+#include <errno.h>
+
+#include <algorithm>
+#include <string>
+
+#include <base/files/file_path.h>
+#include <base/metrics/statistics_recorder.h>
+#include <base/strings/stringprintf.h>
+
+#include "update_engine/common/action_pipe.h"
+#include "update_engine/common/boot_control_interface.h"
+#include "update_engine/common/error_code_utils.h"
+#include "update_engine/common/multi_range_http_fetcher.h"
+#include "update_engine/common/utils.h"
+#include "update_engine/cros/omaha_request_params.h"
+#include "update_engine/cros/p2p_manager.h"
+#include "update_engine/cros/payload_state_interface.h"
+
+using base::FilePath;
+using std::string;
+
+namespace chromeos_update_engine {
+
+DownloadAction::DownloadAction(PrefsInterface* prefs,
+                               BootControlInterface* boot_control,
+                               HardwareInterface* hardware,
+                               SystemState* system_state,
+                               HttpFetcher* http_fetcher,
+                               bool interactive)
+    : prefs_(prefs),
+      boot_control_(boot_control),
+      hardware_(hardware),
+      system_state_(system_state),
+      http_fetcher_(new MultiRangeHttpFetcher(http_fetcher)),
+      interactive_(interactive),
+      writer_(nullptr),
+      code_(ErrorCode::kSuccess),
+      delegate_(nullptr),
+      p2p_sharing_fd_(-1),
+      p2p_visible_(true) {}
+
+DownloadAction::~DownloadAction() {}
+
+void DownloadAction::CloseP2PSharingFd(bool delete_p2p_file) {
+  if (p2p_sharing_fd_ != -1) {
+    if (close(p2p_sharing_fd_) != 0) {
+      PLOG(ERROR) << "Error closing p2p sharing fd";
+    }
+    p2p_sharing_fd_ = -1;
+  }
+
+  if (delete_p2p_file) {
+    FilePath path = system_state_->p2p_manager()->FileGetPath(p2p_file_id_);
+    if (unlink(path.value().c_str()) != 0) {
+      PLOG(ERROR) << "Error deleting p2p file " << path.value();
+    } else {
+      LOG(INFO) << "Deleted p2p file " << path.value();
+    }
+  }
+
+  // Don't use p2p from this point onwards.
+  p2p_file_id_.clear();
+}
+
+bool DownloadAction::SetupP2PSharingFd() {
+  P2PManager* p2p_manager = system_state_->p2p_manager();
+
+  if (!p2p_manager->FileShare(p2p_file_id_, payload_->size)) {
+    LOG(ERROR) << "Unable to share file via p2p";
+    CloseP2PSharingFd(true);  // delete p2p file
+    return false;
+  }
+
+  // File has already been created (and allocated, xattrs been
+  // populated etc.) by FileShare() so just open it for writing.
+  FilePath path = p2p_manager->FileGetPath(p2p_file_id_);
+  p2p_sharing_fd_ = open(path.value().c_str(), O_WRONLY);
+  if (p2p_sharing_fd_ == -1) {
+    PLOG(ERROR) << "Error opening file " << path.value();
+    CloseP2PSharingFd(true);  // Delete p2p file.
+    return false;
+  }
+
+  // Ensure file to share is world-readable, otherwise
+  // p2p-server and p2p-http-server can't access it.
+  //
+  // (Q: Why doesn't the file have mode 0644 already? A: Because
+  // the process-wide umask is set to 0700 in main.cc.)
+  if (fchmod(p2p_sharing_fd_, 0644) != 0) {
+    PLOG(ERROR) << "Error setting mode 0644 on " << path.value();
+    CloseP2PSharingFd(true);  // Delete p2p file.
+    return false;
+  }
+
+  // All good.
+  LOG(INFO) << "Writing payload contents to " << path.value();
+  p2p_manager->FileGetVisible(p2p_file_id_, &p2p_visible_);
+  return true;
+}
+
+void DownloadAction::WriteToP2PFile(const void* data,
+                                    size_t length,
+                                    off_t file_offset) {
+  if (p2p_sharing_fd_ == -1) {
+    if (!SetupP2PSharingFd())
+      return;
+  }
+
+  // Check that the file is at least |file_offset| bytes long - if
+  // it's not something is wrong and we must immediately delete the
+  // file to avoid propagating this problem to other peers.
+  //
+  // How can this happen? It could be that we're resuming an update
+  // after a system crash... in this case, it could be that
+  //
+  //  1. the p2p file didn't get properly synced to stable storage; or
+  //  2. the file was deleted at bootup (it's in /var/cache after all); or
+  //  3. other reasons
+  off_t p2p_size = utils::FileSize(p2p_sharing_fd_);
+  if (p2p_size < 0) {
+    PLOG(ERROR) << "Error getting file status for p2p file";
+    CloseP2PSharingFd(true);  // Delete p2p file.
+    return;
+  }
+  if (p2p_size < file_offset) {
+    LOG(ERROR) << "Wanting to write to file offset " << file_offset
+               << " but existing p2p file is only " << p2p_size << " bytes.";
+    CloseP2PSharingFd(true);  // Delete p2p file.
+    return;
+  }
+
+  off_t cur_file_offset = lseek(p2p_sharing_fd_, file_offset, SEEK_SET);
+  if (cur_file_offset != static_cast<off_t>(file_offset)) {
+    PLOG(ERROR) << "Error seeking to position " << file_offset
+                << " in p2p file";
+    CloseP2PSharingFd(true);  // Delete p2p file.
+  } else {
+    // OK, seeking worked, now write the data
+    ssize_t bytes_written = write(p2p_sharing_fd_, data, length);
+    if (bytes_written != static_cast<ssize_t>(length)) {
+      PLOG(ERROR) << "Error writing " << length << " bytes at file offset "
+                  << file_offset << " in p2p file";
+      CloseP2PSharingFd(true);  // Delete p2p file.
+    }
+  }
+}
+
+void DownloadAction::PerformAction() {
+  http_fetcher_->set_delegate(this);
+
+  // Get the InstallPlan and read it
+  CHECK(HasInputObject());
+  install_plan_ = GetInputObject();
+  install_plan_.Dump();
+
+  bytes_received_ = 0;
+  bytes_received_previous_payloads_ = 0;
+  bytes_total_ = 0;
+  for (const auto& payload : install_plan_.payloads)
+    bytes_total_ += payload.size;
+
+  if (install_plan_.is_resume) {
+    int64_t payload_index = 0;
+    if (prefs_->GetInt64(kPrefsUpdateStatePayloadIndex, &payload_index) &&
+        static_cast<size_t>(payload_index) < install_plan_.payloads.size()) {
+      // Save the index for the resume payload before downloading any previous
+      // payload, otherwise it will be overwritten.
+      resume_payload_index_ = payload_index;
+      for (int i = 0; i < payload_index; i++)
+        install_plan_.payloads[i].already_applied = true;
+    }
+  }
+  // TODO(senj): check that install plan has at least one payload.
+  if (!payload_)
+    payload_ = &install_plan_.payloads[0];
+
+  LOG(INFO) << "Marking new slot as unbootable";
+  if (!boot_control_->MarkSlotUnbootable(install_plan_.target_slot)) {
+    LOG(WARNING) << "Unable to mark new slot "
+                 << BootControlInterface::SlotName(install_plan_.target_slot)
+                 << ". Proceeding with the update anyway.";
+  }
+
+  StartDownloading();
+}
+
+bool DownloadAction::LoadCachedManifest(int64_t manifest_size) {
+  std::string cached_manifest_bytes;
+  if (!prefs_->GetString(kPrefsManifestBytes, &cached_manifest_bytes) ||
+      cached_manifest_bytes.size() <= 0) {
+    LOG(INFO) << "Cached Manifest data not found";
+    return false;
+  }
+  if (static_cast<int64_t>(cached_manifest_bytes.size()) != manifest_size) {
+    LOG(WARNING) << "Cached metadata has unexpected size: "
+                 << cached_manifest_bytes.size() << " vs. " << manifest_size;
+    return false;
+  }
+
+  ErrorCode error;
+  const bool success =
+      delta_performer_->Write(
+          cached_manifest_bytes.data(), cached_manifest_bytes.size(), &error) &&
+      delta_performer_->IsManifestValid();
+  if (success) {
+    LOG(INFO) << "Successfully parsed cached manifest";
+  } else {
+    // If parsing of cached data failed, fall back to fetch them using HTTP
+    LOG(WARNING) << "Cached manifest data fails to load, error code:"
+                 << static_cast<int>(error) << "," << error;
+  }
+  return success;
+}
+
+void DownloadAction::StartDownloading() {
+  download_active_ = true;
+  http_fetcher_->ClearRanges();
+
+  if (writer_ && writer_ != delta_performer_.get()) {
+    LOG(INFO) << "Using writer for test.";
+  } else {
+    delta_performer_.reset(new DeltaPerformer(prefs_,
+                                              boot_control_,
+                                              hardware_,
+                                              delegate_,
+                                              &install_plan_,
+                                              payload_,
+                                              interactive_));
+    writer_ = delta_performer_.get();
+  }
+
+  if (install_plan_.is_resume &&
+      payload_ == &install_plan_.payloads[resume_payload_index_]) {
+    // Resuming an update so parse the cached manifest first
+    int64_t manifest_metadata_size = 0;
+    int64_t manifest_signature_size = 0;
+    prefs_->GetInt64(kPrefsManifestMetadataSize, &manifest_metadata_size);
+    prefs_->GetInt64(kPrefsManifestSignatureSize, &manifest_signature_size);
+
+    // TODO(zhangkelvin) Add unittest for success and fallback route
+    if (!LoadCachedManifest(manifest_metadata_size + manifest_signature_size)) {
+      if (delta_performer_) {
+        // Create a new DeltaPerformer to reset all its state
+        delta_performer_ = std::make_unique<DeltaPerformer>(prefs_,
+                                                            boot_control_,
+                                                            hardware_,
+                                                            delegate_,
+                                                            &install_plan_,
+                                                            payload_,
+                                                            interactive_);
+        writer_ = delta_performer_.get();
+      }
+      http_fetcher_->AddRange(base_offset_,
+                              manifest_metadata_size + manifest_signature_size);
+    }
+
+    // If there're remaining unprocessed data blobs, fetch them. Be careful not
+    // to request data beyond the end of the payload to avoid 416 HTTP response
+    // error codes.
+    int64_t next_data_offset = 0;
+    prefs_->GetInt64(kPrefsUpdateStateNextDataOffset, &next_data_offset);
+    uint64_t resume_offset =
+        manifest_metadata_size + manifest_signature_size + next_data_offset;
+    if (!payload_->size) {
+      http_fetcher_->AddRange(base_offset_ + resume_offset);
+    } else if (resume_offset < payload_->size) {
+      http_fetcher_->AddRange(base_offset_ + resume_offset,
+                              payload_->size - resume_offset);
+    }
+  } else {
+    if (payload_->size) {
+      http_fetcher_->AddRange(base_offset_, payload_->size);
+    } else {
+      // If no payload size is passed we assume we read until the end of the
+      // stream.
+      http_fetcher_->AddRange(base_offset_);
+    }
+  }
+
+  if (system_state_ != nullptr) {
+    const PayloadStateInterface* payload_state = system_state_->payload_state();
+    string file_id = utils::CalculateP2PFileId(payload_->hash, payload_->size);
+    if (payload_state->GetUsingP2PForSharing()) {
+      // If we're sharing the update, store the file_id to convey
+      // that we should write to the file.
+      p2p_file_id_ = file_id;
+      LOG(INFO) << "p2p file id: " << p2p_file_id_;
+    } else {
+      // Even if we're not sharing the update, it could be that
+      // there's a partial file from a previous attempt with the same
+      // hash. If this is the case, we NEED to clean it up otherwise
+      // we're essentially timing out other peers downloading from us
+      // (since we're never going to complete the file).
+      FilePath path = system_state_->p2p_manager()->FileGetPath(file_id);
+      if (!path.empty()) {
+        if (unlink(path.value().c_str()) != 0) {
+          PLOG(ERROR) << "Error deleting p2p file " << path.value();
+        } else {
+          LOG(INFO) << "Deleting partial p2p file " << path.value()
+                    << " since we're not using p2p to share.";
+        }
+      }
+    }
+
+    // Tweak timeouts on the HTTP fetcher if we're downloading from a
+    // local peer.
+    if (payload_state->GetUsingP2PForDownloading() &&
+        payload_state->GetP2PUrl() == install_plan_.download_url) {
+      LOG(INFO) << "Tweaking HTTP fetcher since we're downloading via p2p";
+      http_fetcher_->set_low_speed_limit(kDownloadP2PLowSpeedLimitBps,
+                                         kDownloadP2PLowSpeedTimeSeconds);
+      http_fetcher_->set_max_retry_count(kDownloadP2PMaxRetryCount);
+      http_fetcher_->set_connect_timeout(kDownloadP2PConnectTimeoutSeconds);
+    }
+  }
+
+  http_fetcher_->BeginTransfer(install_plan_.download_url);
+}
+
+void DownloadAction::SuspendAction() {
+  http_fetcher_->Pause();
+}
+
+void DownloadAction::ResumeAction() {
+  http_fetcher_->Unpause();
+}
+
+void DownloadAction::TerminateProcessing() {
+  if (writer_) {
+    writer_->Close();
+    writer_ = nullptr;
+  }
+  download_active_ = false;
+  CloseP2PSharingFd(false);  // Keep p2p file.
+  // Terminates the transfer. The action is terminated, if necessary, when the
+  // TransferTerminated callback is received.
+  http_fetcher_->TerminateTransfer();
+}
+
+void DownloadAction::SeekToOffset(off_t offset) {
+  bytes_received_ = offset;
+}
+
+bool DownloadAction::ReceivedBytes(HttpFetcher* fetcher,
+                                   const void* bytes,
+                                   size_t length) {
+  // Note that bytes_received_ is the current offset.
+  if (!p2p_file_id_.empty()) {
+    WriteToP2PFile(bytes, length, bytes_received_);
+  }
+
+  bytes_received_ += length;
+  uint64_t bytes_downloaded_total =
+      bytes_received_previous_payloads_ + bytes_received_;
+  if (delegate_ && download_active_) {
+    delegate_->BytesReceived(length, bytes_downloaded_total, bytes_total_);
+  }
+  if (writer_ && !writer_->Write(bytes, length, &code_)) {
+    if (code_ != ErrorCode::kSuccess) {
+      LOG(ERROR) << "Error " << utils::ErrorCodeToString(code_) << " (" << code_
+                 << ") in DeltaPerformer's Write method when "
+                 << "processing the received payload -- Terminating processing";
+    }
+    // Delete p2p file, if applicable.
+    if (!p2p_file_id_.empty())
+      CloseP2PSharingFd(true);
+    // Don't tell the action processor that the action is complete until we get
+    // the TransferTerminated callback. Otherwise, this and the HTTP fetcher
+    // objects may get destroyed before all callbacks are complete.
+    TerminateProcessing();
+    return false;
+  }
+
+  // Call p2p_manager_->FileMakeVisible() when we've successfully
+  // verified the manifest!
+  if (!p2p_visible_ && system_state_ && delta_performer_.get() &&
+      delta_performer_->IsManifestValid()) {
+    LOG(INFO) << "Manifest has been validated. Making p2p file visible.";
+    system_state_->p2p_manager()->FileMakeVisible(p2p_file_id_);
+    p2p_visible_ = true;
+  }
+  return true;
+}
+
+void DownloadAction::TransferComplete(HttpFetcher* fetcher, bool successful) {
+  if (writer_) {
+    LOG_IF(WARNING, writer_->Close() != 0) << "Error closing the writer.";
+    if (delta_performer_.get() == writer_) {
+      // no delta_performer_ in tests, so leave the test writer in place
+      writer_ = nullptr;
+    }
+  }
+  download_active_ = false;
+  ErrorCode code =
+      successful ? ErrorCode::kSuccess : ErrorCode::kDownloadTransferError;
+  if (code == ErrorCode::kSuccess) {
+    if (delta_performer_ && !payload_->already_applied)
+      code = delta_performer_->VerifyPayload(payload_->hash, payload_->size);
+    if (code == ErrorCode::kSuccess) {
+      if (payload_ < &install_plan_.payloads.back() &&
+          system_state_->payload_state()->NextPayload()) {
+        LOG(INFO) << "Incrementing to next payload";
+        // No need to reset if this payload was already applied.
+        if (delta_performer_ && !payload_->already_applied)
+          DeltaPerformer::ResetUpdateProgress(prefs_, false);
+        // Start downloading next payload.
+        bytes_received_previous_payloads_ += payload_->size;
+        payload_++;
+        install_plan_.download_url =
+            system_state_->payload_state()->GetCurrentUrl();
+        StartDownloading();
+        return;
+      }
+
+      // All payloads have been applied and verified.
+      if (delegate_)
+        delegate_->DownloadComplete();
+
+      // Log UpdateEngine.DownloadAction.* histograms to help diagnose
+      // long-blocking operations.
+      std::string histogram_output;
+      base::StatisticsRecorder::WriteGraph("UpdateEngine.DownloadAction.",
+                                           &histogram_output);
+      LOG(INFO) << histogram_output;
+    } else {
+      LOG(ERROR) << "Download of " << install_plan_.download_url
+                 << " failed due to payload verification error.";
+      // Delete p2p file, if applicable.
+      if (!p2p_file_id_.empty())
+        CloseP2PSharingFd(true);
+    }
+  }
+
+  // Write the path to the output pipe if we're successful.
+  if (code == ErrorCode::kSuccess && HasOutputPipe())
+    SetOutputObject(install_plan_);
+  processor_->ActionComplete(this, code);
+}
+
+void DownloadAction::TransferTerminated(HttpFetcher* fetcher) {
+  if (code_ != ErrorCode::kSuccess) {
+    processor_->ActionComplete(this, code_);
+  } else if (payload_->already_applied) {
+    LOG(INFO) << "TransferTerminated with ErrorCode::kSuccess when the current "
+                 "payload has already applied, treating as TransferComplete.";
+    TransferComplete(fetcher, true);
+  }
+}
+
+}  // namespace chromeos_update_engine