Improve efficiency of checking for access to authority documents

* java/org/gnu/emacs/EmacsService.java (checkContentUri): Take a
string instead of a byte array.  Then, use
checkCallingUriPermission, in lieu of opening the file.
* src/android.c (android_check_content_access): Delete unused
function.
(android_init_emacs_service): Adjust for changes to
checkContentUri's signature.
* src/androidvfs.c (android_get_content_name): Return the file
name in a new buffer.
(android_check_content_access): Adjust correspondingly.
(android_authority_name): Verify NAME is a valid JNI string.

java/org/gnu/emacs/EmacsService.java

@@ -960,44 +960,30 @@ invocation of app_process (through android-emacs) can
       }
   }
 
+  /* Return whether Emacs is directly permitted to access the
+     content:// URI NAME.  This is not a suitable test for files which
+     Emacs can access by virtue of their containing document
+     trees.  */
+
   public boolean
-  checkContentUri (byte[] string, boolean readable, boolean writable)
+  checkContentUri (String name, boolean readable, boolean writable)
   {
-    String mode, name;
+    String mode;
     ParcelFileDescriptor fd;
+    Uri uri;
+    int rc, flags;
 
-    /* Decode this into a URI.  */
+    uri = Uri.parse (name);
+    flags = 0;
 
-    try
-      {
-	/* The usual file name encoding question rears its ugly head
-	   again.  */
-	name = new String (string, "UTF-8");
-      }
-    catch (UnsupportedEncodingException exception)
-      {
-	name = null;
-	throw new RuntimeException (exception);
-      }
-
-    mode = "r";
+    if (readable)
+      flags |= Intent.FLAG_GRANT_READ_URI_PERMISSION;
 
     if (writable)
-      mode += "w";
+      flags |= Intent.FLAG_GRANT_WRITE_URI_PERMISSION;
 
-    try
-      {
-	fd = resolver.openFileDescriptor (Uri.parse (name), mode);
-	fd.close ();
-
-	return true;
-      }
-    catch (Exception exception)
-      {
-	/* Fall through.  */
-      }
-
-    return false;
+    rc = checkCallingUriPermission (uri, flags);
+    return rc == PackageManager.PERMISSION_GRANTED;
   }
 
   /* Build a content file name for URI.

src/android.c

@@ -1107,41 +1107,6 @@ android_get_content_name (const char *filename)
   return NULL;
 }
 
-/* Return whether or not the specified FILENAME is an accessible
-   content URI.  MODE specifies what to check.  */
-
-static bool
-android_check_content_access (const char *filename, int mode)
-{
-  const char *name;
-  jobject string;
-  size_t length;
-  jboolean rc;
-
-  name = android_get_content_name (filename);
-  length = strlen (name);
-
-  string = (*android_java_env)->NewByteArray (android_java_env,
-					      length);
-  android_exception_check ();
-
-  (*android_java_env)->SetByteArrayRegion (android_java_env,
-					   string, 0, length,
-					   (jbyte *) name);
-  rc = (*android_java_env)->CallBooleanMethod (android_java_env,
-					       emacs_service,
-					       service_class.check_content_uri,
-					       string,
-					       (jboolean) ((mode & R_OK)
-							   != 0),
-					       (jboolean) ((mode & W_OK)
-							   != 0));
-  android_exception_check_1 (string);
-  ANDROID_DELETE_LOCAL_REF (string);
-
-  return rc;
-}
-
 #endif /* 0 */
 
 /* Return the current user's ``home'' directory, which is actually the
@@ -1549,7 +1514,7 @@ android_init_emacs_service (void)
   FIND_METHOD (open_content_uri, "openContentUri",
 	       "([BZZZ)I");
   FIND_METHOD (check_content_uri, "checkContentUri",
-	       "([BZZ)Z");
+	       "(Ljava/lang/String;ZZ)Z");
   FIND_METHOD (query_battery, "queryBattery", "()[J");
   FIND_METHOD (update_extracted_text, "updateExtractedText",
 	       "(Lorg/gnu/emacs/EmacsWindow;"

src/androidvfs.c

@@ -2765,14 +2765,13 @@ android_content_initial (char *name, size_t length)
 /* Return the content URI corresponding to a `/content/by-authority'
    file name, or NULL if it is invalid for some reason.  FILENAME
    should be relative to /content/by-authority, with no leading
-   directory separator character.
+   directory separator character.  */
 
-   This function is not reentrant.  */
-
-static const char *
+static char *
 android_get_content_name (const char *filename)
 {
-  static char buffer[PATH_MAX + 1], *fill;
+  char *fill, *buffer;
+  size_t length;
 
   /* Make sure FILENAME isn't obviously invalid: it must contain an
      authority name and a file name component.  */
@@ -2784,48 +2783,53 @@ android_get_content_name (const char *filename)
       return NULL;
     }
 
-  /* FILENAME must also not be a directory.  */
+  /* FILENAME must also not be a directory.  Accessing content
+     provider directories is not supported by this interface.  */
 
-  if (filename[strlen (filename)] == '/')
+  length = strlen (filename);
+  if (filename[length] == '/')
     {
       errno = ENOTDIR;
       return NULL;
     }
 
-  snprintf (buffer, PATH_MAX + 1, "content://%s", filename);
+  /* Prefix FILENAME with content:// and return the buffer containing
+     that URI.  */
+
+  buffer = xmalloc (sizeof "content://" + length);
+  sprintf (buffer, "content://%s", filename);
   return buffer;
 }
 
 /* Return whether or not the specified URI is an accessible content
-   URI.  MODE specifies what to check.  */
+   URI.  MODE specifies what to check.
+
+   URI must be a string in the JVM's extended UTF-8 format.  */
 
 static bool
 android_check_content_access (const char *uri, int mode)
 {
   jobject string;
   size_t length;
-  jboolean rc;
+  jboolean rc, read, write;
 
   length = strlen (uri);
 
-  string = (*android_java_env)->NewByteArray (android_java_env,
-					      length);
+  string = (*android_java_env)->NewStringUTF (android_java_env, uri);
   android_exception_check ();
 
-  (*android_java_env)->SetByteArrayRegion (android_java_env,
-					   string, 0, length,
-					   (jbyte *) uri);
+  /* Establish what is being checked.  Checking for read access is
+     identical to checking if the file exists.  */
+
+  read = (bool) (mode & R_OK || (mode == F_OK));
+  write = (bool) (mode & W_OK);
+
   rc = (*android_java_env)->CallBooleanMethod (android_java_env,
 					       emacs_service,
 					       service_class.check_content_uri,
-					       string,
-					       (jboolean) ((mode & R_OK)
-							   != 0),
-					       (jboolean) ((mode & W_OK)
-							   != 0));
+					       string, read, write);
   android_exception_check_1 (string);
   ANDROID_DELETE_LOCAL_REF (string);
-
   return rc;
 }
 
@@ -2889,7 +2893,7 @@ android_authority_name (struct android_vnode *vnode, char *name,
 			size_t length)
 {
   struct android_authority_vnode *vp;
-  const char *uri_name;
+  char *uri_name;
 
   if (!android_init_gui)
     {
@@ -2922,6 +2926,12 @@ android_authority_name (struct android_vnode *vnode, char *name,
       if (*name == '/')
 	name++, length -= 1;
 
+      /* NAME must be a valid JNI string, so that it can be encoded
+	 properly.  */
+
+      if (android_verify_jni_string (name))
+	goto no_entry;
+
       uri_name = android_get_content_name (name);
       if (!uri_name)
 	goto error;
@@ -2931,11 +2941,12 @@ android_authority_name (struct android_vnode *vnode, char *name,
       vp->vnode.ops = &authority_vfs_ops;
       vp->vnode.type = ANDROID_VNODE_CONTENT_AUTHORITY;
       vp->vnode.flags = 0;
-      vp->uri = xstrdup (uri_name);
+      vp->uri = uri_name;
       return &vp->vnode;
     }
 
   /* Content files can't have children.  */
+ no_entry:
   errno = ENOENT;
  error:
   return NULL;