Add logic for saving and retrieving session IDs

And add session_id to the metrics event file.

`GenerateUuid` copied from the recently deleted `cvd_metrics_api.cpp`.

See 4c3a2b1 for the deletion commit.

Bug: 448398451

Author: cjreynol

base/cvd/MODULE.bazel

@@ -29,6 +29,7 @@ bazel_dep(name = "libarchive", version = "3.7.9")
 bazel_dep(name = "libevent", version = "2.1.12-stable.bcr.0")
 bazel_dep(name = "libjpeg_turbo", version = "2.1.91")
 bazel_dep(name = "libpng", version = "1.6.47.bcr.1")
+bazel_dep(name = "libuuid", version = "2.39.3.bcr.1")
 bazel_dep(name = "libxml2", version = "2.13.5")
 bazel_dep(name = "libzip", version = "1.10.1")
 bazel_dep(name = "lz4", version = "1.9.4.bcr.2")

base/cvd/cuttlefish/host/libs/metrics/BUILD.bazel

@@ -47,6 +47,7 @@ cf_cc_library(
         "//cuttlefish/common/libs/utils:result",
         "//cuttlefish/host/commands/cvd/instances",
         "//cuttlefish/host/libs/metrics:metrics_writer",
+        "//cuttlefish/host/libs/metrics:session_id",
         "//libbase",
         "@fmt",
     ],
@@ -69,3 +70,18 @@ cf_cc_library(
         "@fmt",
     ],
 )
+
+cf_cc_library(
+    name = "session_id",
+    srcs = [
+        "session_id.cc",
+    ],
+    hdrs = [
+        "session_id.h",
+    ],
+    deps = [
+        "//cuttlefish/common/libs/utils:files",
+        "//cuttlefish/common/libs/utils:result",
+        "@libuuid",
+    ],
+)

base/cvd/cuttlefish/host/libs/metrics/metrics_orchestration.cc

@@ -26,6 +26,7 @@
 #include "cuttlefish/common/libs/utils/result.h"
 #include "cuttlefish/host/commands/cvd/instances/instance_group_record.h"
 #include "cuttlefish/host/libs/metrics/metrics_writer.h"
+#include "cuttlefish/host/libs/metrics/session_id.h"
 
 namespace cuttlefish {
 namespace {
@@ -46,14 +47,17 @@ std::string GetMetricsDirectoryFilepath(
 Result<void> SetUpMetrics(const std::string& metrics_directory) {
   CF_EXPECT(EnsureDirectoryExists(metrics_directory));
   CF_EXPECT(WriteNewFile(metrics_directory + "/README", kReadmeText));
+  CF_EXPECT(GenerateSessionIdFile(metrics_directory));
   return {};
 }
 
 Result<void> GatherMetrics(const std::string& metrics_directory) {
+  const std::string session_id =
+      CF_EXPECT(ReadSessionIdFile(metrics_directory));
   HostInfo host_metrics = GetHostInfo();
   // TODO: chadreynolds - gather the rest of the data (guest/flag information)
   // TODO: chadreynolds - convert data to the proto representation
-  CF_EXPECT(WriteMetricsEvent(metrics_directory, host_metrics));
+  CF_EXPECT(WriteMetricsEvent(metrics_directory, session_id, host_metrics));
   // TODO: chadreynolds - if <TBD> condition, transmit metrics event as well
   return {};
 }

base/cvd/cuttlefish/host/libs/metrics/metrics_writer.cc

@@ -18,6 +18,7 @@
 
 #include <chrono>
 #include <string>
+#include <string_view>
 
 #include <fmt/format.h>
 
@@ -37,12 +38,15 @@ std::string GenerateFilenameSuffix() {
 }  // namespace
 
 Result<void> WriteMetricsEvent(const std::string& metrics_directory,
+                               std::string_view session_id,
                                const HostInfo& host_metrics) {
   const std::string event_filepath =
       fmt::format("{}/vm-instantiation_{}_{}", metrics_directory,
                   std::chrono::system_clock::now(), GenerateFilenameSuffix());
   // TODO: chadreynolds - convert (what will be a proto) to text
-  CF_EXPECT(WriteNewFile(event_filepath, host_metrics.to_string()));
+  CF_EXPECT(WriteNewFile(
+      event_filepath,
+      fmt::format("{}\n{}\n", host_metrics.to_string(), session_id)));
   return {};
 }
 

base/cvd/cuttlefish/host/libs/metrics/metrics_writer.h

@@ -17,6 +17,7 @@
 #pragma once
 
 #include <string>
+#include <string_view>
 
 #include "cuttlefish/common/libs/utils/host_info.h"
 #include "cuttlefish/common/libs/utils/result.h"
@@ -25,6 +26,7 @@ namespace cuttlefish {
 
 // TODO: chadreynolds - add support for more fields than HostInfo
 Result<void> WriteMetricsEvent(const std::string& metrics_directory,
+                               std::string_view session_id,
                                const HostInfo& host_metrics);
 
 }  // namespace cuttlefish

base/cvd/cuttlefish/host/libs/metrics/session_id.cc

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2025 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 "cuttlefish/host/libs/metrics/session_id.h"
+
+#include <string>
+#include <string_view>
+
+#include <uuid/uuid.h>
+
+#include "cuttlefish/common/libs/utils/files.h"
+#include "cuttlefish/common/libs/utils/result.h"
+
+namespace cuttlefish {
+namespace {
+
+constexpr char kSessionIdFileName[] = "metrics_session_id.txt";
+constexpr int kUuidStringLength = 36;  // per uuid_unparse(3)
+
+std::string GenerateUuid() {
+  uuid_t uuid;
+  uuid_generate_random(uuid);
+  std::string uuid_str = std::string(kUuidStringLength, 'x');
+  uuid_unparse(uuid, uuid_str.data());
+  return uuid_str;
+}
+
+}  // namespace
+
+Result<std::string> ReadSessionIdFile(const std::string& metrics_directory) {
+  return CF_EXPECT(ReadFileContents(metrics_directory + kSessionIdFileName));
+}
+
+Result<void> GenerateSessionIdFile(const std::string& metrics_directory) {
+  const std::string session_id = GenerateUuid();
+  CF_EXPECT(WriteNewFile(metrics_directory + kSessionIdFileName, session_id));
+  return {};
+}
+
+}  // namespace cuttlefish

base/cvd/cuttlefish/host/libs/metrics/session_id.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2025 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.
+ */
+
+#pragma once
+
+#include <string>
+#include <string_view>
+
+#include "cuttlefish/common/libs/utils/result.h"
+
+namespace cuttlefish {
+
+Result<std::string> ReadSessionIdFile(const std::string& metrics_directory);
+
+Result<void> GenerateSessionIdFile(const std::string& metrics_directory);
+
+}  // namespace cuttlefish