SftpInboundFileSynchronizer fails to synchronize files if the directory path is a symbolic link

[jandurovec]

In what version(s) of Spring Integration are you seeing this issue?

6.4.1

Describe the bug

After upgrading from previous version (as part of Spring Boot 2.x -> SpringBoot 3.x migration) SftpInboundFileSynchronizer stopped syncing the files. We have isolated the problem to be related to a situation where the directory to synchronize is a symlink (i.e. last element in the path is a symlink).

To Reproduce

• Create /tmp/realdir on SFTP server and place a file (eg aaa.txt there)
• Create /tmp/link on SFTP server as a symlink pointing to /tmp/realdir
• Configure SftpInboundFileSynchronizer to synchronize the content of /tmp/link

Expected behavior

aaa.txt is downloaded from SFTP to local filesystem

Analysis

SftpInboundFileSynchronizer (via its parent AbstractInboundFileSynchronizer) calls list() method to retrieve the directory content

spring-integration/spring-integration-file/src/main/java/org/springframework/integration/file/remote/synchronizer/AbstractInboundFileSynchronizer.java

Line 354 in 478409e

F[] files = session.list(remoteDirectory);

The problem is that SftpSession calls lstat on a file/directory and if it is not reported as a directory (which it isn't since it's a symbolic link), it fails silently and returns empty list.

spring-integration/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/session/SftpSession.java

Lines 104 to 107 in 478409e

	SftpClient.Attributes attributes = this.sftpClient.lstat(path);
	if (!attributes.isDirectory()) {
	return Stream.of(new SftpClient.DirEntry(remoteFile, path, attributes));
	}

I believe that SftpSession.doList(String path) method should call stat() instead of lstat() so that it resolves also symlinks.

[artembilan]

Yeah...

I even see difference in their JavaDocs:

    /**
     * Retrieve remote path meta-data - do <B>not</B> follow symbolic links
     *
     * @param  path        The remote path
     * @return             The associated {@link Attributes}
     * @throws IOException If failed to execute
     */
    Attributes lstat(String path) throws IOException;

    /**
     * Retrieve file/directory handle meta-data
     *
     * @param  handle      The {@link Handle} obtained via one of the {@code open} calls
     * @return             The associated {@link Attributes}
     * @throws IOException If failed to execute
     */
    Attributes stat(Handle handle) throws IOException;

I just changed it to stat() in our logic and all the test for SFTP are green.

If that is what you are looking for, I'm happy to push the fix.

Thanks

[jandurovec]

That would be great. This is a regression issue for us and it would be great if the retrieval of symlinked dir content worked as described above (and as it worked before migration from JSch)