[jira] [Work logged] (SSHD-1220) SFTP: too many LSTAT calls

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SSHD-1220?focusedWorklogId=672571&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-672571 ]

ASF GitHub Bot logged work on SSHD-1220:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 01/Nov/21 08:02
            Start Date: 01/Nov/21 08:02
    Worklog Time Spent: 10m 
      Work Description: tomaswolf commented on a change in pull request #207:
URL: https://github.com/apache/mina-sshd/pull/207#discussion_r740020319



##########
File path: docs/sftp.md
##########
@@ -532,7 +530,27 @@ if (directoryPath instanceof SftpPath) {
   // Not an SFTP path -- get the directory listing in whatever other way is appropriate.
 }
 ```
-So even if an `SftpFileSystem` fulfills the general contract of a `FileSystem`, a client still has to be aware that
+Alternatively, one can also use the fact that Apache MINA sshd caches the SFTP file attributes on the `SftpPath` objects it
+returns from a `DirectoryStream`:
+
+```java
+public void processSftpDirectory(SftpPath directoryPath, BiConsumer<Path, SftpClient.Attributes> process) throws IOException {
+  try (DirectoryStream<Path> dir = Files.newDirectoryStream(directoryPath)) {
+    for (Path path : dir) {
+      if (path instanceof SftpPath) {
+        SftpClient.Attributes attributes = ((SftpPath) path).getAttributes();
+        process.accept(path, attributes);
+      } else {
+        // A DirectoryStream on a directory given by an SftpPath always returns SftpPath instances as elements.
+        throw new IllegalStateException();

Review comment:
       Done.




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Issue Time Tracking
-------------------

    Worklog Id:     (was: 672571)
    Time Spent: 2h 40m  (was: 2.5h)

> SFTP: too many LSTAT calls
> --------------------------
>
>                 Key: SSHD-1220
>                 URL: https://issues.apache.org/jira/browse/SSHD-1220
>             Project: MINA SSHD
>          Issue Type: Improvement
>    Affects Versions: 2.7.0
>            Reporter: Thomas Wolf
>            Assignee: Thomas Wolf
>            Priority: Major
>          Time Spent: 2h 40m
>  Remaining Estimate: 0h
>
> While looking at an alternate solution for SSHD-1217 I noticed that the {{AbstractSftpSubsystemHelper}} makes several LSTAT calls for a single {{FileSystem.readAttributes()}} invocation.
> Basically it makes one LSTAT call per supported attributes view; only to collect the returned items then in one single map anyway.
> This doesn't make any sense. SFTP file attributes are a single, defined structure. If {{AbstractSftpSubsystemHelper.getAttributes()}} needs to collect all these different views ({{BasicFileAttributes}}, {{PosixFileAttributes}}, and so on) on these underlying SFTP attributes, then all these views should build upon the same single {{SftpClient.Attributes}} gotten exactly _once_.
> This could be solved with careful temporary caching of SFTP attributes on the {{SftpPath}} once read while in {{AbstractSftpSubsystemHelper.getAttributes()}} and clearing that cache at the end.
> The problem is more general, though. The code in several places makes up-front checks whether a file exists, is a directory, and so on. This is a questionable pattern anyway, since the result of a {{Files.exists()}} is outdated immediately; one cannot rely on the file being still there on the next access. With an {{SftpPath}}, this {{exists()}} call is an (L)STAT remote call getting the attributes. Now look at {{AbstractSftpSubsystemHelper.resolveFileAttributes}}: here getting the attributes themselves is so guarded, so it makes at least _two_ LSTAT calls.
> This should also be improved.



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