access mode of files created by output_file is surprising

[berthubert]

Hi,

In 8.0.1 at least, on POSIX, files created by fmt::output_file explicitly set themselves to be readable and writable by the user only.

This led to some issues after I moved to fmt::output_file since all of a sudden my files could no longer be read by the web server.

POSIX custom is to set a broader default permission (0660 for example), and let the operator tone that down using their umask setting.

Now it may be that fmt has a good reason for 0600 of course, but it is a bit surprising. There is also no way to change this mode.

Thoughts? Can I help?

Bert (formerly powerdns_bert)

[vitaut]

Fixed in 4a85db1, now the default mode is -rw-r--r-- which is consistent with fopen. Thanks for reporting.

[berthubert]

Thanks!

[arogge]

Sorry for digging this one up again.
If the intent is to mimic behaviour of fopen() then the patch is wrong.
While libfmt is setting S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH, POSIX mandates that it should be S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH.

fopen() in the Open Group Specification reads:

If mode is w, wb, a, ab, w+, wb+, w+b, a+, ab+, or a+b, and the file did not previously exist, the fopen() function shall create a file as if it called the creat() function with a value appropriate for the path argument interpreted from pathname and a value of S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH for the mode argument.

The system will usually strip S_IWGRP and S_IWOTH based on the process' umask, which will result in the observed -rw-r--r-- if umask was set to 022. However with a umask of 002 fopen() would produce -rw-rw-r-- and libfmt should probably do the same.

I can do a pull request for that if you want.

[vitaut]

@arogge, good catch, thanks.

I can do a pull request for that if you want.

Please, do.

[arogge]

See PR #2733