Saving a file by overwriting its content is unsafe

[core-ai-bot]

Issue by jiangyy
Wednesday Jan 20, 2016 at 05:25 GMT
Originally opened as adobe/brackets#12103

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We have traced down that when saving a file, the library finally invokes a sequence like the following (we believe that is called by brackets/src/file/FileUtils.js:110):

(1) fd = open(somefile, O_TRUNC)
(2) write(fd, something)
(3) ...
(4) close(fd)

When the system crashes in between, there may be only partial data persisted in the file system (remaining is lost). The recommended way is to save a file is first write to a temporary file, and then rename it to replace the original file, to ensure that every user-data is manipulated atomically.

This problem is discovered by an automated tool, and this generally affects almost any Linux distribution. I did not find the exact reference material for Node, but here are some arguments for POSIXly correct ways to overwrite a file: http://stackoverflow.com/questions/1812115/how-to-safely-write-to-a-file.

[core-ai-bot]

Comment by petetnt
Wednesday Jan 20, 2016 at 07:06 GMT

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I was thinking about this when debugging adobe/brackets#11826 yesterday. It wasn't the cause for that particular issue, but what@jiangyy states good to me.