Add a hostside Java lib to read proto paths

Bug: 365157972
Test: m aconfig_host_device_paths_java
Change-Id: I858cda31e1e20b7df95bd0e6883694f0dd1cdef0

tools/aconfig/aconfig_device_paths/Android.bp

@@ -56,3 +56,16 @@ java_library {
         "//apex_available:platform",
     ],
 }
+
+genrule {
+    name: "libaconfig_java_host_device_paths_src",
+    srcs: ["src/HostDeviceProtosTemplate.java"],
+    out: ["HostDeviceProtos.java"],
+    tool_files: ["partition_aconfig_flags_paths.txt"],
+    cmd: "sed -e '/TEMPLATE/{r$(location partition_aconfig_flags_paths.txt)' -e 'd}' $(in) > $(out)",
+}
+
+java_library_host {
+    name: "aconfig_host_device_paths_java",
+    srcs: [":libaconfig_java_host_device_paths_src"],
+}

tools/aconfig/aconfig_device_paths/src/HostDeviceProtosTemplate.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2024 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.
+ */
+package android.aconfig;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * A host lib that can read all aconfig proto file paths on a given device.
+ */
+public class HostDeviceProtos {
+    /**
+     * An interface that executes ADB command and return the result.
+     */
+    public static interface AdbCommandExecutor {
+        /** Executes the ADB command. */
+        String executeAdbCommand(String command);
+    }
+
+    static final String[] PATHS = {
+        TEMPLATE
+    };
+
+    private static final String APEX_DIR = "/apex";
+    private static final String RECURSIVELY_LIST_APEX_DIR_COMMAND = "shell find /apex | grep aconfig_flags";
+    private static final String APEX_ACONFIG_PATH_SUFFIX = "/etc/aconfig_flags.pb";
+
+
+    /**
+     * Returns the list of all on-device aconfig proto paths from host side.
+     */
+    public static List<String> parsedFlagsProtoPaths(AdbCommandExecutor adbCommandExecutor) {
+        ArrayList<String> paths = new ArrayList(Arrays.asList(PATHS));
+
+        String adbCommandOutput = adbCommandExecutor.executeAdbCommand(
+            RECURSIVELY_LIST_APEX_DIR_COMMAND);
+
+        if (adbCommandOutput == null) {
+            return paths;
+        }
+
+        Set<String> allFiles = new HashSet<>(Arrays.asList(adbCommandOutput.split("\n")));
+
+        Set<String> subdirs = allFiles.stream().map(file -> {
+            String[] filePaths = file.split("/");
+            // The first element is "", the second element is "apex".
+            return filePaths.length > 2 ? filePaths[2] : "";
+        }).collect(Collectors.toSet());
+
+        for (String prefix : subdirs) {
+            // For each mainline modules, there are two directories, one <modulepackage>/,
+            // and one <modulepackage>@<versioncode>/. Just read the former.
+            if (prefix.contains("@")) {
+                continue;
+            }
+
+            String protoPath = APEX_DIR + "/" + prefix + APEX_ACONFIG_PATH_SUFFIX;
+            if (allFiles.contains(protoPath)) {
+                paths.add(protoPath);
+            }
+        }
+        return paths;
+    }
+}