nanahi 9a861c930b image_writer: fix TOCTOU in screenshot filename generation ...

The screenshot command is documented to not overwrite existing files.
However, there is a race window between the filename is generated with
gen_fname and when the file is open to write. Specifically, the
convert_image function in this window can be very time consuming
depending on video and screenshot image format and size. This results
in existing file being overwritten because the file writing functions
don't check for the existance of file.

Fix this be opening the file in exclusive mode. Add overwrite parameter to
write_image for other operations that are documented to overwrite existing
files, like screenshot-to-file. Note that for write_avif, checking
existance is used instead because avio_open does not support exclusive
open mode.

2024-03-19 19:30:27 +01:00

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