From 7873369338ee0159ca285153fd4592cbcff65d7a Mon Sep 17 00:00:00 2001
From: Po Lu
Date: Sun, 6 Aug 2023 21:45:29 +0800
Subject: Update Android port

* java/org/gnu/emacs/EmacsNative.java: Declare ftruncate.

* java/org/gnu/emacs/EmacsSafThread.java (openDocument1): If
initially opening with rwt, verify the file descriptor is really
writable; if not, resort to rw and truncating the file descriptor
by hand instead.

* src/androidvfs.c (NATIVE_NAME (ftruncate)): New function.
Truncate file descriptor and return whether that was successful.
---
 java/org/gnu/emacs/EmacsNative.java    |  4 ++++
 java/org/gnu/emacs/EmacsSafThread.java | 37 ++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

(limited to 'java')

diff --git a/java/org/gnu/emacs/EmacsNative.java b/java/org/gnu/emacs/EmacsNative.java
index 7d72a9f192e..fae0ba98f86 100644
--- a/java/org/gnu/emacs/EmacsNative.java
+++ b/java/org/gnu/emacs/EmacsNative.java
@@ -274,6 +274,10 @@ public final class EmacsNative
      operations.  */
   public static native void safPostRequest ();
 
+  /* Detect and return FD is writable.  FD may be truncated to 0 bytes
+     in the process.  */
+  public static native boolean ftruncate (int fd);
+
   static
   {
     /* Older versions of Android cannot link correctly with shared
diff --git a/java/org/gnu/emacs/EmacsSafThread.java b/java/org/gnu/emacs/EmacsSafThread.java
index 29cd3fa6bc7..3ae3c0839ce 100644
--- a/java/org/gnu/emacs/EmacsSafThread.java
+++ b/java/org/gnu/emacs/EmacsSafThread.java
@@ -24,6 +24,7 @@ import java.util.HashMap;
 import java.util.Iterator;
 
 import java.io.FileNotFoundException;
+import java.io.IOException;
 
 import android.content.ContentResolver;
 import android.database.Cursor;
@@ -1597,6 +1598,42 @@ public final class EmacsSafThread extends HandlerThread
       = resolver.openFileDescriptor (documentUri, mode,
 				     signal);
 
+    /* If a writable file descriptor is requested and TRUNCATE is set,
+       then probe the file descriptor to detect if it is actually
+       readable.  If not, close this file descriptor and reopen it
+       with MODE set to rw; some document providers granting access to
+       Samba shares don't implement rwt, but these document providers
+       invariably truncate the file opened even when the mode is
+       merely rw.
+
+       This may be ascribed to a mix-up in Android's documentation
+       regardin DocumentsProvider: the `openDocument' function is only
+       documented to accept r or rw, whereas the default
+       implementation of the `openFile' function (which documents rwt)
+       delegates to `openDocument'.  */
+
+    if (write && truncate && fileDescriptor != null
+	&& !EmacsNative.ftruncate (fileDescriptor.getFd ()))
+      {
+	try
+	  {
+	    fileDescriptor.closeWithError ("File descriptor requested"
+					   + " is not writable");
+	  }
+	catch (IOException e)
+	  {
+	    Log.w (TAG, "Leaking unclosed file descriptor " + e);
+	  }
+
+	fileDescriptor
+	  = resolver.openFileDescriptor (documentUri, "rw", signal);
+
+	/* Try to truncate fileDescriptor just to stay on the safe
+	   side.  */
+	if (fileDescriptor != null)
+	  EmacsNative.ftruncate (fileDescriptor.getFd ());
+      }
+
     /* Every time a document is opened, remove it from the file status
        cache.  */
     toplevel = getCache (treeUri);
-- 
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