Adding ApexInfo utility

This is to get name/version when the HAL is started from an APEX. This
is the initial work and just prints name/version on startup.

Bug: 268439003
Test: adb logcat | grep com.google.android.widevine
Change-Id: I756c042d544f973999738f7d17022d916b9712cd

libwvdrmengine/apex/proto/widevine_apex_info.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2023 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 "widevine_apex_info.h"
+
+#include <android-base/file.h>
+#include <android-base/strings.h>
+
+#include "apex_manifest_minimal.pb.h"
+
+using android::base::ConsumePrefix;
+using android::base::ErrnoError;
+using android::base::Error;
+using android::base::GetExecutablePath;
+using android::base::ReadFileToString;
+using android::base::Result;
+using apex::proto::ApexManifest;
+
+namespace widevine::apex {
+
+namespace {
+
+Result<std::string> GetApexNameFromPath(const std::string& path) {
+  std::string_view sv{path};
+  if (!ConsumePrefix(&sv, "/apex/")) {
+    return Error() << "Not found an apex name: " << path;
+  }
+  return std::string{sv.substr(0, sv.find('/'))};
+}
+
+Result<ApexManifest> ParseApexManifest(const std::string& manifest_path) {
+  std::string content;
+  if (!ReadFileToString(manifest_path, &content)) {
+    return ErrnoError() << "Failed to read manifest file: " << manifest_path;
+  }
+  ApexManifest manifest;
+  if (!manifest.ParseFromString(content)) {
+    return Error() << "Can't parse APEX manifest: " << manifest_path;
+  }
+  return manifest;
+}
+
+}
+
+Result<ApexInfo> GetApexInfo() {
+  auto exe_path = GetExecutablePath();
+  auto apex_name = GetApexNameFromPath(exe_path);
+  if (!apex_name.ok()) {
+    return apex_name.error();
+  }
+  auto manifest_path = fmt::format("/apex/{}/apex_manifest.pb", *apex_name);
+  auto apex_manifest = ParseApexManifest(manifest_path);
+  if (!apex_manifest.ok()) {
+    return apex_manifest.error();
+  }
+  return ApexInfo {
+    apex_manifest->name(),
+    apex_manifest->version(),
+  };
+}
+
+}  // namespace widevine::apex