Add InputMethodService#exposeContent()

This is a follow up CL to my previous CLs [1][2] that introduced
InputConnection#commitContent(InputContentInfo, Bundle) API to enable
IMEs to send a content to the target application.

With this CL, IME developers are able to temporarily expose
InputContentInfo object to the target package without permanently
granting URI permission.  Although calling IMS#exposeContent() is
allowed only for the IME that is currently selected, the client is able
to request a temporary read-only access even after the current IME is
switched to any other IME as long as the client keeps InputContentInfo
object.

Here is a sample code snippet about how to use this mechanism.

  [IME]
  InputContentInfo contentInfo = new InputContentInfo(
          contentUri,
          new ClipDescription(description, new String[]{mimeType}),
          linkUrl);
  exposeContent(contentInfo, getCurrentInputEditorInfo());
  getCurrentInputConnection().commitContent(inputContentInfo, null);

  [App]
  try {
      contentInfo.requestPermission();
      // Load inputContentInfo.getContentUri() here.
  } finally {
      contentInfo.releasePermission();
  }

 [1]: Iaadf934a997ffcd6000a516cc3c1873db56e60ad
      152944f4909c47917473293b258d266435c6ab35
 [2]: Ica1ba3154795c1bf44e140dfe639b299f83cd8af
      adebb52588b098a1af678d4e33a234ef1ce783b2

Bug: 29450031
Change-Id: I2772889ca01f2ecb2cdeed4e04a9319bdf7bc5a6
diff --git a/services/core/java/com/android/server/InputMethodManagerService.java b/services/core/java/com/android/server/InputMethodManagerService.java
index 5d8fe7c..e0d89f2 100644
--- a/services/core/java/com/android/server/InputMethodManagerService.java
+++ b/services/core/java/com/android/server/InputMethodManagerService.java
@@ -18,6 +18,7 @@
 import static java.lang.annotation.RetentionPolicy.SOURCE;
 
 import com.android.internal.content.PackageMonitor;
+import com.android.internal.inputmethod.IInputContentUriToken;
 import com.android.internal.inputmethod.InputMethodSubtypeSwitchingController;
 import com.android.internal.inputmethod.InputMethodSubtypeSwitchingController.ImeSubtypeListItem;
 import com.android.internal.inputmethod.InputMethodUtils;
@@ -137,6 +138,7 @@
 import java.io.PrintWriter;
 import java.lang.annotation.Retention;
 import java.nio.charset.StandardCharsets;
+import java.security.InvalidParameterException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
@@ -3911,6 +3913,52 @@
     }
 
     @Override
+    public IInputContentUriToken createInputContentUriToken(@Nullable IBinder token,
+            @Nullable Uri contentUri, @Nullable String packageName) {
+        if (!calledFromValidUser()) {
+            return null;
+        }
+
+        if (token == null) {
+            throw new NullPointerException("token");
+        }
+        if (packageName == null) {
+            throw new NullPointerException("packageName");
+        }
+        if (contentUri == null) {
+            throw new NullPointerException("contentUri");
+        }
+        final String contentUriScheme = contentUri.getScheme();
+        if (!"content".equals(contentUriScheme)) {
+            throw new InvalidParameterException("contentUri must have content scheme");
+        }
+
+        synchronized (mMethodMap) {
+            final int uid = Binder.getCallingUid();
+            if (mCurMethodId == null) {
+                return null;
+            }
+            if (mCurToken != token) {
+                Slog.e(TAG, "Ignoring createInputContentUriToken mCurToken=" + mCurToken
+                        + " token=" + token);
+                return null;
+            }
+            // We cannot simply distinguish a bad IME that reports an arbitrary package name from
+            // an unfortunate IME whose internal state is already obsolete due to the asynchronous
+            // nature of our system.  Let's compare it with our internal record.
+            if (!TextUtils.equals(mCurAttribute.packageName, packageName)) {
+                Slog.e(TAG, "Ignoring createInputContentUriToken mCurAttribute.packageName="
+                    + mCurAttribute.packageName + " packageName=" + packageName);
+                return null;
+            }
+            final int imeUserId = UserHandle.getUserId(uid);
+            final int appUserId = UserHandle.getUserId(mCurClient.uid);
+            return new InputContentUriTokenHandler(contentUri, uid, packageName, imeUserId,
+                    appUserId);
+        }
+    }
+
+    @Override
     protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
         if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.DUMP)
                 != PackageManager.PERMISSION_GRANTED) {