libbrillo: policy: Increase resilience for policy readandroid-wear-8.0.0_r1

The policy files will be stored with indexes as suffix to improve
resilience to disk corruptions. This change makes it possible to
read the policy data from new files and validate them.

Design doc:
https://docs.google.com/document/d/1RdUKb-deQCBiyc6Dpdf4RDBEPV-feb5WHu7uzY1YozQ/edit#heading=h.h0q5njx6l4xf

BUG=chromium:764337
TEST=Manual
CQ-DEPEND=CL:681939, CL:819250, CL:819353, CL:819412

Change-Id: I10f31d307925c6ccef3cfd0887a71b7c774139e2
Reviewed-on: https://chromium-review.googlesource.com/674935
Commit-Ready: Igor <igorcov@chromium.org>
Tested-by: Igor <igorcov@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
(cherry picked from commit d213a401f639649b3e38f6def5782ae2f1322fce)
Merged-In: I10f31d307925c6ccef3cfd0887a71b7c774139e2

1 files changed, 41 insertions, 0 deletions

diff --git a/policy/policy_util.cc b/policy/policy_util.cc
new file mode 100644
index 0000000..8c17fc2
--- /dev/null
+++ b/policy/policy_util.cc
@@ -0,0 +1,41 @@
+// Copyright 2017 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "policy/policy_util.h"
+
+#include <base/files/file_util.h>
+#include <base/logging.h>
+
+namespace policy {
+
+LoadPolicyResult LoadPolicyFromPath(
+    const base::FilePath& policy_path,
+    std::string* policy_data_str_out,
+    enterprise_management::PolicyFetchResponse* policy_out) {
+  DCHECK(policy_data_str_out);
+  DCHECK(policy_out);
+  if (!base::PathExists(policy_path)) {
+    return LoadPolicyResult::kFileNotFound;
+  }
+
+  if (!base::ReadFileToString(policy_path, policy_data_str_out)) {
+    PLOG(ERROR) << "Could not read policy off disk at " << policy_path.value();
+    return LoadPolicyResult::kFailedToReadFile;
+  }
+
+  if (policy_data_str_out->empty()) {
+    LOG(ERROR) << "Empty policy file at " << policy_path.value();
+    return LoadPolicyResult::kEmptyFile;
+  }
+
+  if (!policy_out->ParseFromString(*policy_data_str_out)) {
+    LOG(ERROR) << "Policy on disk could not be parsed, file: "
+               << policy_path.value();
+    return LoadPolicyResult::kInvalidPolicyData;
+  }
+
+  return LoadPolicyResult::kSuccess;
+}
+
+}  // namespace policy