diff --git a/common/constants.cc b/common/constants.cc
index 310f1b2..5ab96b0 100644
--- a/common/constants.cc
+++ b/common/constants.cc
@@ -124,4 +124,6 @@
 // The default is 1 (always run post install).
 const char kPayloadPropertyRunPostInstall[] = "RUN_POST_INSTALL";
 
+const char kOmahaUpdaterVersion[] = "0.1.0.0";
+
 }  // namespace chromeos_update_engine
diff --git a/common/constants.h b/common/constants.h
index d5a8ae3..9b4623f 100644
--- a/common/constants.h
+++ b/common/constants.h
@@ -108,6 +108,8 @@
 extern const char kPayloadPropertySwitchSlotOnReboot[];
 extern const char kPayloadPropertyRunPostInstall[];
 
+extern const char kOmahaUpdaterVersion[];
+
 // A download source is any combination of protocol and server (that's of
 // interest to us when looking at UMA metrics) using which we may download
 // the payload.
diff --git a/omaha_request_action.cc b/omaha_request_action.cc
index deb294a..5b69ec8 100644
--- a/omaha_request_action.cc
+++ b/omaha_request_action.cc
@@ -48,6 +48,7 @@
 #include "update_engine/connection_manager_interface.h"
 #include "update_engine/metrics_reporter_interface.h"
 #include "update_engine/metrics_utils.h"
+#include "update_engine/omaha_request_builder_xml.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/p2p_manager.h"
 #include "update_engine/payload_state_interface.h"
@@ -106,8 +107,6 @@
 constexpr char kValPostInstall[] = "postinstall";
 constexpr char kValNoUpdate[] = "noupdate";
 
-constexpr char kOmahaUpdaterVersion[] = "0.1.0.0";
-
 // X-Goog-Update headers.
 constexpr char kXGoogleUpdateInteractivity[] = "X-Goog-Update-Interactivity";
 constexpr char kXGoogleUpdateAppId[] = "X-Goog-Update-AppId";
@@ -119,362 +118,6 @@
 constexpr char kAttrFirmwareVersion[] = "firmware_version";
 constexpr char kAttrKernelVersion[] = "kernel_version";
 
-namespace {
-
-// Returns an XML ping element attribute assignment with attribute
-// |name| and value |ping_days| if |ping_days| has a value that needs
-// to be sent, or an empty string otherwise.
-string GetPingAttribute(const string& name, int ping_days) {
-  if (ping_days > 0 || ping_days == OmahaRequestAction::kNeverPinged)
-    return base::StringPrintf(" %s=\"%d\"", name.c_str(), ping_days);
-  return "";
-}
-
-// Returns an XML ping element if any of the elapsed days need to be
-// sent, or an empty string otherwise.
-string GetPingXml(int ping_active_days, int ping_roll_call_days) {
-  string ping_active = GetPingAttribute("a", ping_active_days);
-  string ping_roll_call = GetPingAttribute("r", ping_roll_call_days);
-  if (!ping_active.empty() || !ping_roll_call.empty()) {
-    return base::StringPrintf("        <ping active=\"1\"%s%s></ping>\n",
-                              ping_active.c_str(),
-                              ping_roll_call.c_str());
-  }
-  return "";
-}
-
-// Returns an XML that goes into the body of the <app> element of the Omaha
-// request based on the given parameters.
-string GetAppBody(const OmahaEvent* event,
-                  OmahaRequestParams* params,
-                  bool ping_only,
-                  bool include_ping,
-                  bool skip_updatecheck,
-                  int ping_active_days,
-                  int ping_roll_call_days,
-                  PrefsInterface* prefs) {
-  string app_body;
-  if (event == nullptr) {
-    if (include_ping)
-      app_body = GetPingXml(ping_active_days, ping_roll_call_days);
-    if (!ping_only) {
-      if (!skip_updatecheck) {
-        app_body += "        <updatecheck";
-        if (!params->target_version_prefix().empty()) {
-          app_body += base::StringPrintf(
-              " targetversionprefix=\"%s\"",
-              XmlEncodeWithDefault(params->target_version_prefix(), "")
-                  .c_str());
-          // Rollback requires target_version_prefix set.
-          if (params->rollback_allowed()) {
-            app_body += " rollback_allowed=\"true\"";
-          }
-        }
-        app_body += "></updatecheck>\n";
-      }
-
-      // If this is the first update check after a reboot following a previous
-      // update, generate an event containing the previous version number. If
-      // the previous version preference file doesn't exist the event is still
-      // generated with a previous version of 0.0.0.0 -- this is relevant for
-      // older clients or new installs. The previous version event is not sent
-      // for ping-only requests because they come before the client has
-      // rebooted. The previous version event is also not sent if it was already
-      // sent for this new version with a previous updatecheck.
-      string prev_version;
-      if (!prefs->GetString(kPrefsPreviousVersion, &prev_version)) {
-        prev_version = "0.0.0.0";
-      }
-      // We only store a non-empty previous version value after a successful
-      // update in the previous boot. After reporting it back to the server,
-      // we clear the previous version value so it doesn't get reported again.
-      if (!prev_version.empty()) {
-        app_body += base::StringPrintf(
-            "        <event eventtype=\"%d\" eventresult=\"%d\" "
-            "previousversion=\"%s\"></event>\n",
-            OmahaEvent::kTypeRebootedAfterUpdate,
-            OmahaEvent::kResultSuccess,
-            XmlEncodeWithDefault(prev_version, "0.0.0.0").c_str());
-        LOG_IF(WARNING, !prefs->SetString(kPrefsPreviousVersion, ""))
-            << "Unable to reset the previous version.";
-      }
-    }
-  } else {
-    // The error code is an optional attribute so append it only if the result
-    // is not success.
-    string error_code;
-    if (event->result != OmahaEvent::kResultSuccess) {
-      error_code = base::StringPrintf(" errorcode=\"%d\"",
-                                      static_cast<int>(event->error_code));
-    }
-    app_body = base::StringPrintf(
-        "        <event eventtype=\"%d\" eventresult=\"%d\"%s></event>\n",
-        event->type,
-        event->result,
-        error_code.c_str());
-  }
-
-  return app_body;
-}
-
-// Returns the cohort* argument to include in the <app> tag for the passed
-// |arg_name| and |prefs_key|, if any. The return value is suitable to
-// concatenate to the list of arguments and includes a space at the end.
-string GetCohortArgXml(PrefsInterface* prefs,
-                       const string arg_name,
-                       const string prefs_key) {
-  // There's nothing wrong with not having a given cohort setting, so we check
-  // existence first to avoid the warning log message.
-  if (!prefs->Exists(prefs_key))
-    return "";
-  string cohort_value;
-  if (!prefs->GetString(prefs_key, &cohort_value) || cohort_value.empty())
-    return "";
-  // This is a sanity check to avoid sending a huge XML file back to Ohama due
-  // to a compromised stateful partition making the update check fail in low
-  // network environments envent after a reboot.
-  if (cohort_value.size() > 1024) {
-    LOG(WARNING) << "The omaha cohort setting " << arg_name
-                 << " has a too big value, which must be an error or an "
-                    "attacker trying to inhibit updates.";
-    return "";
-  }
-
-  string escaped_xml_value;
-  if (!XmlEncode(cohort_value, &escaped_xml_value)) {
-    LOG(WARNING) << "The omaha cohort setting " << arg_name
-                 << " is ASCII-7 invalid, ignoring it.";
-    return "";
-  }
-
-  return base::StringPrintf(
-      "%s=\"%s\" ", arg_name.c_str(), escaped_xml_value.c_str());
-}
-
-struct OmahaAppData {
-  string id;
-  string version;
-  string product_components;
-};
-
-bool IsValidComponentID(const string& id) {
-  for (char c : id) {
-    if (!isalnum(c) && c != '-' && c != '_' && c != '.')
-      return false;
-  }
-  return true;
-}
-
-// Returns an XML that corresponds to the entire <app> node of the Omaha
-// request based on the given parameters.
-string GetAppXml(const OmahaEvent* event,
-                 OmahaRequestParams* params,
-                 const OmahaAppData& app_data,
-                 bool ping_only,
-                 bool include_ping,
-                 bool skip_updatecheck,
-                 int ping_active_days,
-                 int ping_roll_call_days,
-                 int install_date_in_days,
-                 SystemState* system_state) {
-  string app_body = GetAppBody(event,
-                               params,
-                               ping_only,
-                               include_ping,
-                               skip_updatecheck,
-                               ping_active_days,
-                               ping_roll_call_days,
-                               system_state->prefs());
-  string app_versions;
-
-  // If we are downgrading to a more stable channel and we are allowed to do
-  // powerwash, then pass 0.0.0.0 as the version. This is needed to get the
-  // highest-versioned payload on the destination channel.
-  if (params->ShouldPowerwash()) {
-    LOG(INFO) << "Passing OS version as 0.0.0.0 as we are set to powerwash "
-              << "on downgrading to the version in the more stable channel";
-    app_versions = "version=\"0.0.0.0\" from_version=\"" +
-                   XmlEncodeWithDefault(app_data.version, "0.0.0.0") + "\" ";
-  } else {
-    app_versions = "version=\"" +
-                   XmlEncodeWithDefault(app_data.version, "0.0.0.0") + "\" ";
-  }
-
-  string download_channel = params->download_channel();
-  string app_channels =
-      "track=\"" + XmlEncodeWithDefault(download_channel, "") + "\" ";
-  if (params->current_channel() != download_channel) {
-    app_channels += "from_track=\"" +
-                    XmlEncodeWithDefault(params->current_channel(), "") + "\" ";
-  }
-
-  string delta_okay_str = params->delta_okay() ? "true" : "false";
-
-  // If install_date_days is not set (e.g. its value is -1 ), don't
-  // include the attribute.
-  string install_date_in_days_str = "";
-  if (install_date_in_days >= 0) {
-    install_date_in_days_str =
-        base::StringPrintf("installdate=\"%d\" ", install_date_in_days);
-  }
-
-  string app_cohort_args;
-  app_cohort_args +=
-      GetCohortArgXml(system_state->prefs(), "cohort", kPrefsOmahaCohort);
-  app_cohort_args += GetCohortArgXml(
-      system_state->prefs(), "cohorthint", kPrefsOmahaCohortHint);
-  app_cohort_args += GetCohortArgXml(
-      system_state->prefs(), "cohortname", kPrefsOmahaCohortName);
-
-  string fingerprint_arg;
-  if (!params->os_build_fingerprint().empty()) {
-    fingerprint_arg = "fingerprint=\"" +
-                      XmlEncodeWithDefault(params->os_build_fingerprint(), "") +
-                      "\" ";
-  }
-
-  string buildtype_arg;
-  if (!params->os_build_type().empty()) {
-    buildtype_arg = "os_build_type=\"" +
-                    XmlEncodeWithDefault(params->os_build_type(), "") + "\" ";
-  }
-
-  string product_components_args;
-  if (!params->ShouldPowerwash() && !app_data.product_components.empty()) {
-    brillo::KeyValueStore store;
-    if (store.LoadFromString(app_data.product_components)) {
-      for (const string& key : store.GetKeys()) {
-        if (!IsValidComponentID(key)) {
-          LOG(ERROR) << "Invalid component id: " << key;
-          continue;
-        }
-        string version;
-        if (!store.GetString(key, &version)) {
-          LOG(ERROR) << "Failed to get version for " << key
-                     << " in product_components.";
-          continue;
-        }
-        product_components_args +=
-            base::StringPrintf("_%s.version=\"%s\" ",
-                               key.c_str(),
-                               XmlEncodeWithDefault(version, "").c_str());
-      }
-    } else {
-      LOG(ERROR) << "Failed to parse product_components:\n"
-                 << app_data.product_components;
-    }
-  }
-
-  // clang-format off
-  string app_xml = "    <app "
-      "appid=\"" + XmlEncodeWithDefault(app_data.id, "") + "\" " +
-      app_cohort_args +
-      app_versions +
-      app_channels +
-      product_components_args +
-      fingerprint_arg +
-      buildtype_arg +
-      "lang=\"" + XmlEncodeWithDefault(params->app_lang(), "en-US") + "\" " +
-      "board=\"" + XmlEncodeWithDefault(params->os_board(), "") + "\" " +
-      "hardware_class=\"" + XmlEncodeWithDefault(params->hwid(), "") + "\" " +
-      "delta_okay=\"" + delta_okay_str + "\" "
-      "fw_version=\"" + XmlEncodeWithDefault(params->fw_version(), "") + "\" " +
-      "ec_version=\"" + XmlEncodeWithDefault(params->ec_version(), "") + "\" " +
-      install_date_in_days_str +
-      ">\n" +
-         app_body +
-      "    </app>\n";
-  // clang-format on
-  return app_xml;
-}
-
-// Returns an XML that corresponds to the entire <os> node of the Omaha
-// request based on the given parameters.
-string GetOsXml(OmahaRequestParams* params) {
-  string os_xml =
-      "    <os "
-      "version=\"" +
-      XmlEncodeWithDefault(params->os_version(), "") + "\" " + "platform=\"" +
-      XmlEncodeWithDefault(params->os_platform(), "") + "\" " + "sp=\"" +
-      XmlEncodeWithDefault(params->os_sp(), "") +
-      "\">"
-      "</os>\n";
-  return os_xml;
-}
-
-// Returns an XML that corresponds to the entire Omaha request based on the
-// given parameters.
-string GetRequestXml(const OmahaEvent* event,
-                     OmahaRequestParams* params,
-                     bool ping_only,
-                     bool include_ping,
-                     int ping_active_days,
-                     int ping_roll_call_days,
-                     int install_date_in_days,
-                     SystemState* system_state) {
-  string os_xml = GetOsXml(params);
-  OmahaAppData product_app = {
-      .id = params->GetAppId(),
-      .version = params->app_version(),
-      .product_components = params->product_components()};
-  // Skips updatecheck for platform app in case of an install operation.
-  string app_xml = GetAppXml(event,
-                             params,
-                             product_app,
-                             ping_only,
-                             include_ping,
-                             params->is_install(), /* skip_updatecheck */
-                             ping_active_days,
-                             ping_roll_call_days,
-                             install_date_in_days,
-                             system_state);
-  if (!params->system_app_id().empty()) {
-    OmahaAppData system_app = {.id = params->system_app_id(),
-                               .version = params->system_version()};
-    app_xml += GetAppXml(event,
-                         params,
-                         system_app,
-                         ping_only,
-                         include_ping,
-                         false, /* skip_updatecheck */
-                         ping_active_days,
-                         ping_roll_call_days,
-                         install_date_in_days,
-                         system_state);
-  }
-  // Create APP ID according to |dlc_module_id| (sticking the current AppID to
-  // the DLC module ID with an underscode).
-  for (const auto& dlc_module_id : params->dlc_module_ids()) {
-    OmahaAppData dlc_module_app = {
-        .id = params->GetAppId() + "_" + dlc_module_id,
-        .version = params->app_version()};
-    app_xml += GetAppXml(event,
-                         params,
-                         dlc_module_app,
-                         ping_only,
-                         include_ping,
-                         false, /* skip_updatecheck */
-                         ping_active_days,
-                         ping_roll_call_days,
-                         install_date_in_days,
-                         system_state);
-  }
-
-  string request_xml = base::StringPrintf(
-      "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
-      "<request protocol=\"3.0\" updater=\"%s\" updaterversion=\"%s\""
-      " installsource=\"%s\" ismachine=\"1\">\n%s%s</request>\n",
-      constants::kOmahaUpdaterID,
-      kOmahaUpdaterVersion,
-      params->interactive() ? "ondemandupdate" : "scheduler",
-      os_xml.c_str(),
-      app_xml.c_str());
-
-  return request_xml;
-}
-
-}  // namespace
-
 // Struct used for holding data obtained when parsing the XML.
 struct OmahaParserData {
   explicit OmahaParserData(XML_Parser _xml_parser) : xml_parser(_xml_parser) {}
@@ -638,49 +281,6 @@
 
 }  // namespace
 
-bool XmlEncode(const string& input, string* output) {
-  if (std::find_if(input.begin(), input.end(), [](const char c) {
-        return c & 0x80;
-      }) != input.end()) {
-    LOG(WARNING) << "Invalid ASCII-7 string passed to the XML encoder:";
-    utils::HexDumpString(input);
-    return false;
-  }
-  output->clear();
-  // We need at least input.size() space in the output, but the code below will
-  // handle it if we need more.
-  output->reserve(input.size());
-  for (char c : input) {
-    switch (c) {
-      case '\"':
-        output->append("&quot;");
-        break;
-      case '\'':
-        output->append("&apos;");
-        break;
-      case '&':
-        output->append("&amp;");
-        break;
-      case '<':
-        output->append("&lt;");
-        break;
-      case '>':
-        output->append("&gt;");
-        break;
-      default:
-        output->push_back(c);
-    }
-  }
-  return true;
-}
-
-string XmlEncodeWithDefault(const string& input, const string& default_value) {
-  string output;
-  if (XmlEncode(input, &output))
-    return output;
-  return default_value;
-}
-
 OmahaRequestAction::OmahaRequestAction(
     SystemState* system_state,
     OmahaEvent* event,
@@ -732,8 +332,8 @@
 }
 
 bool OmahaRequestAction::ShouldPing() const {
-  if (ping_active_days_ == OmahaRequestAction::kNeverPinged &&
-      ping_roll_call_days_ == OmahaRequestAction::kNeverPinged) {
+  if (ping_active_days_ == kNeverPinged &&
+      ping_roll_call_days_ == kNeverPinged) {
     int powerwash_count = system_state_->hardware()->GetPowerwashCount();
     if (powerwash_count > 0) {
       LOG(INFO) << "Not sending ping with a=-1 r=-1 to omaha because "
diff --git a/omaha_request_action.h b/omaha_request_action.h
index 8db5fb9..8e81af9 100644
--- a/omaha_request_action.h
+++ b/omaha_request_action.h
@@ -33,6 +33,7 @@
 
 #include "update_engine/common/action.h"
 #include "update_engine/common/http_fetcher.h"
+#include "update_engine/omaha_request_builder_xml.h"
 #include "update_engine/omaha_response.h"
 #include "update_engine/system_state.h"
 
@@ -45,56 +46,6 @@
 
 namespace chromeos_update_engine {
 
-// Encodes XML entities in a given string. Input must be ASCII-7 valid. If
-// the input is invalid, the default value is used instead.
-std::string XmlEncodeWithDefault(const std::string& input,
-                                 const std::string& default_value);
-
-// Escapes text so it can be included as character data and attribute
-// values. The |input| string must be valid ASCII-7, no UTF-8 supported.
-// Returns whether the |input| was valid and escaped properly in |output|.
-bool XmlEncode(const std::string& input, std::string* output);
-
-// This struct encapsulates the Omaha event information. For a
-// complete list of defined event types and results, see
-// http://code.google.com/p/omaha/wiki/ServerProtocol#event
-struct OmahaEvent {
-  // The Type values correspond to EVENT_TYPE values of Omaha.
-  enum Type {
-    kTypeUnknown = 0,
-    kTypeDownloadComplete = 1,
-    kTypeInstallComplete = 2,
-    kTypeUpdateComplete = 3,
-    kTypeUpdateDownloadStarted = 13,
-    kTypeUpdateDownloadFinished = 14,
-    // Chromium OS reserved type sent after the first reboot following an update
-    // completed.
-    kTypeRebootedAfterUpdate = 54,
-  };
-
-  // The Result values correspond to EVENT_RESULT values of Omaha.
-  enum Result {
-    kResultError = 0,
-    kResultSuccess = 1,
-    kResultUpdateDeferred = 9,  // When we ignore/defer updates due to policy.
-  };
-
-  OmahaEvent()
-      : type(kTypeUnknown),
-        result(kResultError),
-        error_code(ErrorCode::kError) {}
-  explicit OmahaEvent(Type in_type)
-      : type(in_type),
-        result(kResultSuccess),
-        error_code(ErrorCode::kSuccess) {}
-  OmahaEvent(Type in_type, Result in_result, ErrorCode in_error_code)
-      : type(in_type), result(in_result), error_code(in_error_code) {}
-
-  Type type;
-  Result result;
-  ErrorCode error_code;
-};
-
 class NoneType;
 class OmahaRequestAction;
 class OmahaRequestParams;
@@ -116,7 +67,6 @@
 class OmahaRequestAction : public Action<OmahaRequestAction>,
                            public HttpFetcherDelegate {
  public:
-  static const int kNeverPinged = -1;
   static const int kPingTimeJump = -2;
   // We choose this value of 10 as a heuristic for a work day in trying
   // each URL, assuming we check roughly every 45 mins. This is a good time to
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index a642b5a..e7c610f 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -51,6 +51,7 @@
 #include "update_engine/metrics_reporter_interface.h"
 #include "update_engine/mock_connection_manager.h"
 #include "update_engine/mock_payload_state.h"
+#include "update_engine/omaha_request_builder_xml.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/update_manager/rollback_prefs.h"
 
@@ -1755,27 +1756,6 @@
   EXPECT_FALSE(loop.PendingTasks());
 }
 
-TEST_F(OmahaRequestActionTest, XmlEncodeTest) {
-  string output;
-  EXPECT_TRUE(XmlEncode("ab", &output));
-  EXPECT_EQ("ab", output);
-  EXPECT_TRUE(XmlEncode("a<b", &output));
-  EXPECT_EQ("a&lt;b", output);
-  EXPECT_TRUE(XmlEncode("<&>\"\'\\", &output));
-  EXPECT_EQ("&lt;&amp;&gt;&quot;&apos;\\", output);
-  EXPECT_TRUE(XmlEncode("&lt;&amp;&gt;", &output));
-  EXPECT_EQ("&amp;lt;&amp;amp;&amp;gt;", output);
-  // Check that unterminated UTF-8 strings are handled properly.
-  EXPECT_FALSE(XmlEncode("\xc2", &output));
-  // Fail with invalid ASCII-7 chars.
-  EXPECT_FALSE(XmlEncode("This is an 'n' with a tilde: \xc3\xb1", &output));
-}
-
-TEST_F(OmahaRequestActionTest, XmlEncodeWithDefaultTest) {
-  EXPECT_EQ("&lt;&amp;&gt;", XmlEncodeWithDefault("<&>", "something else"));
-  EXPECT_EQ("<not escaped>", XmlEncodeWithDefault("\xc2", "<not escaped>"));
-}
-
 TEST_F(OmahaRequestActionTest, XmlEncodeIsUsedForParams) {
   brillo::Blob post_data;
 
diff --git a/omaha_request_builder_xml.cc b/omaha_request_builder_xml.cc
new file mode 100644
index 0000000..899f17f
--- /dev/null
+++ b/omaha_request_builder_xml.cc
@@ -0,0 +1,413 @@
+//
+// Copyright (C) 2019 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/omaha_request_builder_xml.h"
+
+#include <inttypes.h>
+
+#include <string>
+
+#include <base/logging.h>
+#include <base/strings/string_number_conversions.h>
+#include <base/strings/string_util.h>
+#include <base/strings/stringprintf.h>
+#include <base/time/time.h>
+
+#include "update_engine/common/constants.h"
+#include "update_engine/common/prefs_interface.h"
+#include "update_engine/common/utils.h"
+#include "update_engine/omaha_request_params.h"
+
+using std::string;
+
+namespace chromeos_update_engine {
+
+const int kNeverPinged = -1;
+
+bool XmlEncode(const string& input, string* output) {
+  if (std::find_if(input.begin(), input.end(), [](const char c) {
+        return c & 0x80;
+      }) != input.end()) {
+    LOG(WARNING) << "Invalid ASCII-7 string passed to the XML encoder:";
+    utils::HexDumpString(input);
+    return false;
+  }
+  output->clear();
+  // We need at least input.size() space in the output, but the code below will
+  // handle it if we need more.
+  output->reserve(input.size());
+  for (char c : input) {
+    switch (c) {
+      case '\"':
+        output->append("&quot;");
+        break;
+      case '\'':
+        output->append("&apos;");
+        break;
+      case '&':
+        output->append("&amp;");
+        break;
+      case '<':
+        output->append("&lt;");
+        break;
+      case '>':
+        output->append("&gt;");
+        break;
+      default:
+        output->push_back(c);
+    }
+  }
+  return true;
+}
+
+string XmlEncodeWithDefault(const string& input, const string& default_value) {
+  string output;
+  if (XmlEncode(input, &output))
+    return output;
+  return default_value;
+}
+
+string GetPingAttribute(const string& name, int ping_days) {
+  if (ping_days > 0 || ping_days == kNeverPinged)
+    return base::StringPrintf(" %s=\"%d\"", name.c_str(), ping_days);
+  return "";
+}
+
+string GetPingXml(int ping_active_days, int ping_roll_call_days) {
+  string ping_active = GetPingAttribute("a", ping_active_days);
+  string ping_roll_call = GetPingAttribute("r", ping_roll_call_days);
+  if (!ping_active.empty() || !ping_roll_call.empty()) {
+    return base::StringPrintf("        <ping active=\"1\"%s%s></ping>\n",
+                              ping_active.c_str(),
+                              ping_roll_call.c_str());
+  }
+  return "";
+}
+
+string GetAppBody(const OmahaEvent* event,
+                  OmahaRequestParams* params,
+                  bool ping_only,
+                  bool include_ping,
+                  bool skip_updatecheck,
+                  int ping_active_days,
+                  int ping_roll_call_days,
+                  PrefsInterface* prefs) {
+  string app_body;
+  if (event == nullptr) {
+    if (include_ping)
+      app_body = GetPingXml(ping_active_days, ping_roll_call_days);
+    if (!ping_only) {
+      if (!skip_updatecheck) {
+        app_body += "        <updatecheck";
+        if (!params->target_version_prefix().empty()) {
+          app_body += base::StringPrintf(
+              " targetversionprefix=\"%s\"",
+              XmlEncodeWithDefault(params->target_version_prefix(), "")
+                  .c_str());
+          // Rollback requires target_version_prefix set.
+          if (params->rollback_allowed()) {
+            app_body += " rollback_allowed=\"true\"";
+          }
+        }
+        app_body += "></updatecheck>\n";
+      }
+
+      // If this is the first update check after a reboot following a previous
+      // update, generate an event containing the previous version number. If
+      // the previous version preference file doesn't exist the event is still
+      // generated with a previous version of 0.0.0.0 -- this is relevant for
+      // older clients or new installs. The previous version event is not sent
+      // for ping-only requests because they come before the client has
+      // rebooted. The previous version event is also not sent if it was already
+      // sent for this new version with a previous updatecheck.
+      string prev_version;
+      if (!prefs->GetString(kPrefsPreviousVersion, &prev_version)) {
+        prev_version = "0.0.0.0";
+      }
+      // We only store a non-empty previous version value after a successful
+      // update in the previous boot. After reporting it back to the server,
+      // we clear the previous version value so it doesn't get reported again.
+      if (!prev_version.empty()) {
+        app_body += base::StringPrintf(
+            "        <event eventtype=\"%d\" eventresult=\"%d\" "
+            "previousversion=\"%s\"></event>\n",
+            OmahaEvent::kTypeRebootedAfterUpdate,
+            OmahaEvent::kResultSuccess,
+            XmlEncodeWithDefault(prev_version, "0.0.0.0").c_str());
+        LOG_IF(WARNING, !prefs->SetString(kPrefsPreviousVersion, ""))
+            << "Unable to reset the previous version.";
+      }
+    }
+  } else {
+    // The error code is an optional attribute so append it only if the result
+    // is not success.
+    string error_code;
+    if (event->result != OmahaEvent::kResultSuccess) {
+      error_code = base::StringPrintf(" errorcode=\"%d\"",
+                                      static_cast<int>(event->error_code));
+    }
+    app_body = base::StringPrintf(
+        "        <event eventtype=\"%d\" eventresult=\"%d\"%s></event>\n",
+        event->type,
+        event->result,
+        error_code.c_str());
+  }
+
+  return app_body;
+}
+
+string GetCohortArgXml(PrefsInterface* prefs,
+                       const string arg_name,
+                       const string prefs_key) {
+  // There's nothing wrong with not having a given cohort setting, so we check
+  // existence first to avoid the warning log message.
+  if (!prefs->Exists(prefs_key))
+    return "";
+  string cohort_value;
+  if (!prefs->GetString(prefs_key, &cohort_value) || cohort_value.empty())
+    return "";
+  // This is a sanity check to avoid sending a huge XML file back to Ohama due
+  // to a compromised stateful partition making the update check fail in low
+  // network environments envent after a reboot.
+  if (cohort_value.size() > 1024) {
+    LOG(WARNING) << "The omaha cohort setting " << arg_name
+                 << " has a too big value, which must be an error or an "
+                    "attacker trying to inhibit updates.";
+    return "";
+  }
+
+  string escaped_xml_value;
+  if (!XmlEncode(cohort_value, &escaped_xml_value)) {
+    LOG(WARNING) << "The omaha cohort setting " << arg_name
+                 << " is ASCII-7 invalid, ignoring it.";
+    return "";
+  }
+
+  return base::StringPrintf(
+      "%s=\"%s\" ", arg_name.c_str(), escaped_xml_value.c_str());
+}
+
+bool IsValidComponentID(const string& id) {
+  for (char c : id) {
+    if (!isalnum(c) && c != '-' && c != '_' && c != '.')
+      return false;
+  }
+  return true;
+}
+
+string GetAppXml(const OmahaEvent* event,
+                 OmahaRequestParams* params,
+                 const OmahaAppData& app_data,
+                 bool ping_only,
+                 bool include_ping,
+                 bool skip_updatecheck,
+                 int ping_active_days,
+                 int ping_roll_call_days,
+                 int install_date_in_days,
+                 SystemState* system_state) {
+  string app_body = GetAppBody(event,
+                               params,
+                               ping_only,
+                               include_ping,
+                               skip_updatecheck,
+                               ping_active_days,
+                               ping_roll_call_days,
+                               system_state->prefs());
+  string app_versions;
+
+  // If we are downgrading to a more stable channel and we are allowed to do
+  // powerwash, then pass 0.0.0.0 as the version. This is needed to get the
+  // highest-versioned payload on the destination channel.
+  if (params->ShouldPowerwash()) {
+    LOG(INFO) << "Passing OS version as 0.0.0.0 as we are set to powerwash "
+              << "on downgrading to the version in the more stable channel";
+    app_versions = "version=\"0.0.0.0\" from_version=\"" +
+                   XmlEncodeWithDefault(app_data.version, "0.0.0.0") + "\" ";
+  } else {
+    app_versions = "version=\"" +
+                   XmlEncodeWithDefault(app_data.version, "0.0.0.0") + "\" ";
+  }
+
+  string download_channel = params->download_channel();
+  string app_channels =
+      "track=\"" + XmlEncodeWithDefault(download_channel, "") + "\" ";
+  if (params->current_channel() != download_channel) {
+    app_channels += "from_track=\"" +
+                    XmlEncodeWithDefault(params->current_channel(), "") + "\" ";
+  }
+
+  string delta_okay_str = params->delta_okay() ? "true" : "false";
+
+  // If install_date_days is not set (e.g. its value is -1 ), don't
+  // include the attribute.
+  string install_date_in_days_str = "";
+  if (install_date_in_days >= 0) {
+    install_date_in_days_str =
+        base::StringPrintf("installdate=\"%d\" ", install_date_in_days);
+  }
+
+  string app_cohort_args;
+  app_cohort_args +=
+      GetCohortArgXml(system_state->prefs(), "cohort", kPrefsOmahaCohort);
+  app_cohort_args += GetCohortArgXml(
+      system_state->prefs(), "cohorthint", kPrefsOmahaCohortHint);
+  app_cohort_args += GetCohortArgXml(
+      system_state->prefs(), "cohortname", kPrefsOmahaCohortName);
+
+  string fingerprint_arg;
+  if (!params->os_build_fingerprint().empty()) {
+    fingerprint_arg = "fingerprint=\"" +
+                      XmlEncodeWithDefault(params->os_build_fingerprint(), "") +
+                      "\" ";
+  }
+
+  string buildtype_arg;
+  if (!params->os_build_type().empty()) {
+    buildtype_arg = "os_build_type=\"" +
+                    XmlEncodeWithDefault(params->os_build_type(), "") + "\" ";
+  }
+
+  string product_components_args;
+  if (!params->ShouldPowerwash() && !app_data.product_components.empty()) {
+    brillo::KeyValueStore store;
+    if (store.LoadFromString(app_data.product_components)) {
+      for (const string& key : store.GetKeys()) {
+        if (!IsValidComponentID(key)) {
+          LOG(ERROR) << "Invalid component id: " << key;
+          continue;
+        }
+        string version;
+        if (!store.GetString(key, &version)) {
+          LOG(ERROR) << "Failed to get version for " << key
+                     << " in product_components.";
+          continue;
+        }
+        product_components_args +=
+            base::StringPrintf("_%s.version=\"%s\" ",
+                               key.c_str(),
+                               XmlEncodeWithDefault(version, "").c_str());
+      }
+    } else {
+      LOG(ERROR) << "Failed to parse product_components:\n"
+                 << app_data.product_components;
+    }
+  }
+
+  // clang-format off
+  string app_xml = "    <app "
+      "appid=\"" + XmlEncodeWithDefault(app_data.id, "") + "\" " +
+      app_cohort_args +
+      app_versions +
+      app_channels +
+      product_components_args +
+      fingerprint_arg +
+      buildtype_arg +
+      "lang=\"" + XmlEncodeWithDefault(params->app_lang(), "en-US") + "\" " +
+      "board=\"" + XmlEncodeWithDefault(params->os_board(), "") + "\" " +
+      "hardware_class=\"" + XmlEncodeWithDefault(params->hwid(), "") + "\" " +
+      "delta_okay=\"" + delta_okay_str + "\" "
+      "fw_version=\"" + XmlEncodeWithDefault(params->fw_version(), "") + "\" " +
+      "ec_version=\"" + XmlEncodeWithDefault(params->ec_version(), "") + "\" " +
+      install_date_in_days_str +
+      ">\n" +
+         app_body +
+      "    </app>\n";
+  // clang-format on
+  return app_xml;
+}
+
+string GetOsXml(OmahaRequestParams* params) {
+  string os_xml =
+      "    <os "
+      "version=\"" +
+      XmlEncodeWithDefault(params->os_version(), "") + "\" " + "platform=\"" +
+      XmlEncodeWithDefault(params->os_platform(), "") + "\" " + "sp=\"" +
+      XmlEncodeWithDefault(params->os_sp(), "") +
+      "\">"
+      "</os>\n";
+  return os_xml;
+}
+
+string GetRequestXml(const OmahaEvent* event,
+                     OmahaRequestParams* params,
+                     bool ping_only,
+                     bool include_ping,
+                     int ping_active_days,
+                     int ping_roll_call_days,
+                     int install_date_in_days,
+                     SystemState* system_state) {
+  string os_xml = GetOsXml(params);
+  OmahaAppData product_app = {
+      .id = params->GetAppId(),
+      .version = params->app_version(),
+      .product_components = params->product_components()};
+  // Skips updatecheck for platform app in case of an install operation.
+  string app_xml = GetAppXml(event,
+                             params,
+                             product_app,
+                             ping_only,
+                             include_ping,
+                             params->is_install(), /* skip_updatecheck */
+                             ping_active_days,
+                             ping_roll_call_days,
+                             install_date_in_days,
+                             system_state);
+  if (!params->system_app_id().empty()) {
+    OmahaAppData system_app = {.id = params->system_app_id(),
+                               .version = params->system_version()};
+    app_xml += GetAppXml(event,
+                         params,
+                         system_app,
+                         ping_only,
+                         include_ping,
+                         false, /* skip_updatecheck */
+                         ping_active_days,
+                         ping_roll_call_days,
+                         install_date_in_days,
+                         system_state);
+  }
+  // Create APP ID according to |dlc_module_id| (sticking the current AppID to
+  // the DLC module ID with an underscode).
+  for (const auto& dlc_module_id : params->dlc_module_ids()) {
+    OmahaAppData dlc_module_app = {
+        .id = params->GetAppId() + "_" + dlc_module_id,
+        .version = params->app_version()};
+    app_xml += GetAppXml(event,
+                         params,
+                         dlc_module_app,
+                         ping_only,
+                         include_ping,
+                         false, /* skip_updatecheck */
+                         ping_active_days,
+                         ping_roll_call_days,
+                         install_date_in_days,
+                         system_state);
+  }
+
+  string request_xml = base::StringPrintf(
+      "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
+      "<request protocol=\"3.0\" updater=\"%s\" updaterversion=\"%s\""
+      " installsource=\"%s\" ismachine=\"1\">\n%s%s</request>\n",
+      constants::kOmahaUpdaterID,
+      kOmahaUpdaterVersion,
+      params->interactive() ? "ondemandupdate" : "scheduler",
+      os_xml.c_str(),
+      app_xml.c_str());
+
+  return request_xml;
+}
+
+}  // namespace chromeos_update_engine
diff --git a/omaha_request_builder_xml.h b/omaha_request_builder_xml.h
new file mode 100644
index 0000000..011c592
--- /dev/null
+++ b/omaha_request_builder_xml.h
@@ -0,0 +1,161 @@
+//
+// Copyright (C) 2019 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.
+//
+
+#ifndef UPDATE_ENGINE_OMAHA_REQUEST_BUILDER_XML_H_
+#define UPDATE_ENGINE_OMAHA_REQUEST_BUILDER_XML_H_
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest_prod.h>  // for FRIEND_TEST
+
+#include <brillo/secure_blob.h>
+#include <curl/curl.h>
+
+#include "update_engine/common/action.h"
+#include "update_engine/common/http_fetcher.h"
+#include "update_engine/omaha_response.h"
+#include "update_engine/system_state.h"
+
+// TODO(ahassani): Make the xml builder into a class of its own so we don't have
+// to pass all these parameters around.
+
+namespace chromeos_update_engine {
+
+extern const int kNeverPinged;
+
+// This struct encapsulates the Omaha event information. For a
+// complete list of defined event types and results, see
+// http://code.google.com/p/omaha/wiki/ServerProtocol#event
+struct OmahaEvent {
+  // The Type values correspond to EVENT_TYPE values of Omaha.
+  enum Type {
+    kTypeUnknown = 0,
+    kTypeDownloadComplete = 1,
+    kTypeInstallComplete = 2,
+    kTypeUpdateComplete = 3,
+    kTypeUpdateDownloadStarted = 13,
+    kTypeUpdateDownloadFinished = 14,
+    // Chromium OS reserved type sent after the first reboot following an update
+    // completed.
+    kTypeRebootedAfterUpdate = 54,
+  };
+
+  // The Result values correspond to EVENT_RESULT values of Omaha.
+  enum Result {
+    kResultError = 0,
+    kResultSuccess = 1,
+    kResultUpdateDeferred = 9,  // When we ignore/defer updates due to policy.
+  };
+
+  OmahaEvent()
+      : type(kTypeUnknown),
+        result(kResultError),
+        error_code(ErrorCode::kError) {}
+  explicit OmahaEvent(Type in_type)
+      : type(in_type),
+        result(kResultSuccess),
+        error_code(ErrorCode::kSuccess) {}
+  OmahaEvent(Type in_type, Result in_result, ErrorCode in_error_code)
+      : type(in_type), result(in_result), error_code(in_error_code) {}
+
+  Type type;
+  Result result;
+  ErrorCode error_code;
+};
+
+struct OmahaAppData {
+  std::string id;
+  std::string version;
+  std::string product_components;
+};
+
+// Encodes XML entities in a given string. Input must be ASCII-7 valid. If
+// the input is invalid, the default value is used instead.
+std::string XmlEncodeWithDefault(const std::string& input,
+                                 const std::string& default_value);
+
+// Escapes text so it can be included as character data and attribute
+// values. The |input| string must be valid ASCII-7, no UTF-8 supported.
+// Returns whether the |input| was valid and escaped properly in |output|.
+bool XmlEncode(const std::string& input, std::string* output);
+
+// Returns an XML ping element attribute assignment with attribute
+// |name| and value |ping_days| if |ping_days| has a value that needs
+// to be sent, or an empty string otherwise.
+std::string GetPingAttribute(const std::string& name, int ping_days);
+
+// Returns an XML ping element if any of the elapsed days need to be
+// sent, or an empty string otherwise.
+std::string GetPingXml(int ping_active_days, int ping_roll_call_days);
+
+// Returns an XML that goes into the body of the <app> element of the Omaha
+// request based on the given parameters.
+std::string GetAppBody(const OmahaEvent* event,
+                       OmahaRequestParams* params,
+                       bool ping_only,
+                       bool include_ping,
+                       bool skip_updatecheck,
+                       int ping_active_days,
+                       int ping_roll_call_days,
+                       PrefsInterface* prefs);
+
+// Returns the cohort* argument to include in the <app> tag for the passed
+// |arg_name| and |prefs_key|, if any. The return value is suitable to
+// concatenate to the list of arguments and includes a space at the end.
+std::string GetCohortArgXml(PrefsInterface* prefs,
+                            const std::string arg_name,
+                            const std::string prefs_key);
+
+bool IsValidComponentID(const std::string& id);
+
+// Returns an XML that corresponds to the entire <app> node of the Omaha
+// request based on the given parameters.
+std::string GetAppXml(const OmahaEvent* event,
+                      OmahaRequestParams* params,
+                      const OmahaAppData& app_data,
+                      bool ping_only,
+                      bool include_ping,
+                      bool skip_updatecheck,
+                      int ping_active_days,
+                      int ping_roll_call_days,
+                      int install_date_in_days,
+                      SystemState* system_state);
+
+// Returns an XML that corresponds to the entire <os> node of the Omaha
+// request based on the given parameters.
+std::string GetOsXml(OmahaRequestParams* params);
+
+// Returns an XML that corresponds to the entire Omaha request based on the
+// given parameters.
+std::string GetRequestXml(const OmahaEvent* event,
+                          OmahaRequestParams* params,
+                          bool ping_only,
+                          bool include_ping,
+                          int ping_active_days,
+                          int ping_roll_call_days,
+                          int install_date_in_days,
+                          SystemState* system_state);
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_OMAHA_REQUEST_BUILDER_XML_H_
diff --git a/omaha_request_builder_xml_unittest.cc b/omaha_request_builder_xml_unittest.cc
new file mode 100644
index 0000000..3293c44
--- /dev/null
+++ b/omaha_request_builder_xml_unittest.cc
@@ -0,0 +1,50 @@
+//
+// Copyright (C) 2019 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/omaha_request_builder_xml.h"
+
+#include <string>
+
+#include <gtest/gtest.h>
+
+using std::string;
+
+namespace chromeos_update_engine {
+
+class OmahaRequestBuilderXmlTest : public ::testing::Test {};
+
+TEST_F(OmahaRequestBuilderXmlTest, XmlEncodeTest) {
+  string output;
+  EXPECT_TRUE(XmlEncode("ab", &output));
+  EXPECT_EQ("ab", output);
+  EXPECT_TRUE(XmlEncode("a<b", &output));
+  EXPECT_EQ("a&lt;b", output);
+  EXPECT_TRUE(XmlEncode("<&>\"\'\\", &output));
+  EXPECT_EQ("&lt;&amp;&gt;&quot;&apos;\\", output);
+  EXPECT_TRUE(XmlEncode("&lt;&amp;&gt;", &output));
+  EXPECT_EQ("&amp;lt;&amp;amp;&amp;gt;", output);
+  // Check that unterminated UTF-8 strings are handled properly.
+  EXPECT_FALSE(XmlEncode("\xc2", &output));
+  // Fail with invalid ASCII-7 chars.
+  EXPECT_FALSE(XmlEncode("This is an 'n' with a tilde: \xc3\xb1", &output));
+}
+
+TEST_F(OmahaRequestBuilderXmlTest, XmlEncodeWithDefaultTest) {
+  EXPECT_EQ("&lt;&amp;&gt;", XmlEncodeWithDefault("<&>", "something else"));
+  EXPECT_EQ("<not escaped>", XmlEncodeWithDefault("\xc2", "<not escaped>"));
+}
+
+}  // namespace chromeos_update_engine
diff --git a/update_attempter.h b/update_attempter.h
index c106001..6c25eb2 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -37,6 +37,7 @@
 #include "update_engine/common/action_processor.h"
 #include "update_engine/common/cpu_limiter.h"
 #include "update_engine/common/proxy_resolver.h"
+#include "update_engine/omaha_request_builder_xml.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/omaha_response_handler_action.h"
 #include "update_engine/payload_consumer/download_action.h"
diff --git a/update_engine.gyp b/update_engine.gyp
index 754b314..b7ccae8 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -269,6 +269,7 @@
         'metrics_reporter_omaha.cc',
         'metrics_utils.cc',
         'omaha_request_action.cc',
+        'omaha_request_builder_xml.cc',
         'omaha_request_params.cc',
         'omaha_response_handler_action.cc',
         'omaha_utils.cc',
@@ -424,8 +425,8 @@
         'payload_generator/inplace_generator.cc',
         'payload_generator/mapfile_filesystem.cc',
         'payload_generator/payload_file.cc',
-        'payload_generator/payload_generation_config_chromeos.cc',
         'payload_generator/payload_generation_config.cc',
+        'payload_generator/payload_generation_config_chromeos.cc',
         'payload_generator/payload_signer.cc',
         'payload_generator/raw_filesystem.cc',
         'payload_generator/squashfs_filesystem.cc',
@@ -564,6 +565,7 @@
             'metrics_reporter_omaha_unittest.cc',
             'metrics_utils_unittest.cc',
             'omaha_request_action_unittest.cc',
+            'omaha_request_builder_xml_unittest.cc',
             'omaha_request_params_unittest.cc',
             'omaha_response_handler_action_unittest.cc',
             'omaha_utils_unittest.cc',