Update Shell.rootAccess() implementation

core/src/main/java/com/topjohnwu/superuser/Shell.java

@@ -28,6 +28,7 @@ import androidx.annotation.Nullable;
 import com.topjohnwu.superuser.internal.BuilderImpl;
 import com.topjohnwu.superuser.internal.MainShell;
 import com.topjohnwu.superuser.internal.UiThreadHandler;
+import com.topjohnwu.superuser.internal.Utils;
 
 import java.io.Closeable;
 import java.io.IOException;
@@ -206,17 +207,17 @@ public abstract class Shell implements Closeable {
     }
 
     /**
-     * {@code Shell.getShell().isRoot()}
+     * Whether the application has access to root.
      * <p>
-     * Please refer to {@link #getShell()} for info about concerns on blocking.
+     * This method would NEVER produce false negatives, but false positives can be returned before
+     * actually constructing a root shell. A {@code false} returned is guaranteed to be
+     * 100% accurate, while {@code true} may be returned if the device is rooted, but the user
+     * did not grant root access to your application. However, after any root shell is constructed,
+     * this method will accurately return {@code true}.
+     * @return whether the application has access to root.
      */
     public static boolean rootAccess() {
-        try {
-            return getShell().isRoot();
-        } catch (NoShellException e) {
-            return false;
-        }
-
+        return Utils.isAppGrantedRoot();
     }
 
     /* ************

core/src/main/java/com/topjohnwu/superuser/internal/BuilderImpl.java

@@ -89,8 +89,12 @@ public final class BuilderImpl extends Shell.Builder {
         if (shell == null && !hasFlags(FLAG_NON_ROOT_SHELL)) {
             try {
                 shell = build("su");
-                if (shell.getStatus() != ROOT_SHELL)
+                if (shell.getStatus() != ROOT_SHELL) {
                     shell = null;
+                    synchronized (Utils.class) {
+                        Utils.confirmedRootState = false;
+                    }
+                }
             } catch (NoShellException ignore) {}
         }
 

core/src/main/java/com/topjohnwu/superuser/internal/ShellImpl.java

@@ -141,8 +141,12 @@ class ShellImpl extends Shell {
             STDIN.write(("id\n").getBytes(UTF_8));
             STDIN.flush();
             s = br.readLine();
-            if (!TextUtils.isEmpty(s) && s.contains("uid=0"))
+            if (!TextUtils.isEmpty(s) && s.contains("uid=0")) {
                 status = ROOT_SHELL;
+                synchronized (Utils.class) {
+                    Utils.confirmedRootState = true;
+                }
+            }
 
             if (status == ROOT_SHELL) {
                 STDIN.write(("readlink /proc/self/ns/mnt\n").getBytes(UTF_8));

core/src/main/java/com/topjohnwu/superuser/internal/Utils.java

@@ -20,6 +20,7 @@ import android.annotation.SuppressLint;
 import android.content.Context;
 import android.content.ContextWrapper;
 import android.os.Build;
+import android.os.Process;
 import android.util.ArraySet;
 import android.util.Log;
 
@@ -42,6 +43,7 @@ public final class Utils {
     public static Context context;
     private static Class<?> synchronizedCollectionClass;
     private static final String TAG = "LIBSU";
+    static Boolean confirmedRootState = null;
 
     public static void log(Object log) {
         log(TAG, log);
@@ -123,4 +125,28 @@ public final class Utils {
             return new HashSet<>();
         }
     }
+
+    public synchronized static boolean isAppGrantedRoot() {
+        if (confirmedRootState != null) {
+            // This confirmed root state will also be set in BuilderImpl
+            // and ShellImpl when new shells are getting constructed.
+            return confirmedRootState;
+        }
+        if (Process.myUid() == 0) {
+            // The current process is a root service
+            confirmedRootState = true;
+            return true;
+        }
+        try {
+            Runtime.getRuntime().exec("su --version");
+            // Even if the execution worked, we don't actually know whether the app has
+            // been granted root access. As a heuristic, let's return true here,
+            // but do NOT set the value as a confirmed state.
+            return true;
+        } catch (IOException e) {
+            // Cannot run program "su": error=2, No such file or directory
+            confirmedRootState = false;
+            return false;
+        }
+    }
 }