Maximus Maximus - 1 month ago 4
Javascript Question

Why is using fstat not recommended

I'm reading the manual for

stat
method here and it says:


Using fs.stat() to check for the existence of a file before calling
fs.open(), fs.readFile() or fs.writeFile() is not recommended.
Instead, user code should open/read/write the file directly and handle
the error raised if the file is not available.

To check if a file exists without manipulating it afterwards,
fs.access() is recommended.


So, I've got two questions:


  • Why using error handler is preferred way over
    fs.stat()
    to check for file existence?

  • And since I can use
    fs.access()
    to check for file existence, is using
    error handler
    mechanism still preferred way to ensure file is open?



I think I have found an answer to the second question:


Using fs.access() to check for the accessibility of a file before
calling fs.open(), fs.readFile() or fs.writeFile() is not recommended.
Doing so introduces a race condition, since other processes may change
the file's state between the two calls. Instead, user code should
open/read/write the file directly and handle the error raised if the
file is not accessible.


So probably
fs.open()
blocks file for other processes, while
fs.stat()
and
fs.access()
simply request information and other processes still can change/delete the file.

Answer

I believe that what should be made clear here is that both fs.stat and fs.access are not recommended for the particular case of checking for the accessibility of a file before opening it. As well mentioned in the question, this can trigger race conditions. The functions exists() and existsSync() were deprecated (around version 4) for this reason (and a few others related to the API): they were often exploited for this purpose.

When seeking to open a file, the operation will already trigger an error if the file is inaccessible. Therefore, such checks should be handled here. Otherwise, there is more than one reasonable way to check if a file exists.

Also note that, as of version 6.8.0, existsSync() is undeprecated! See discussion and the 6.8.0 changelog. The same rules above apply: only use it if you do not intend to open the file afterwards.

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