temp file api

[timotheecour]

links

• mkostemp
• We need better temporary file and dir API · Issue #9372 · nim-lang/Nim
• tempfile.nim/tempfile.nim at master · OpenSystemsLab/tempfile.nim
• tmp - How create a temporary file in shell script? - Unix & Linux Stack Exchange
• option for guaranteed auto cleanup using file descriptor trick · Issue #10 · OpenSystemsLab/tempfile.nim
• close #9372 add std/tempfiles nim-lang/Nim#17361 (merged)

example use cases

• unix - Is there anything like shm_open() without filename? - Stack Overflow

  The POSIX shm_open() function returns a file descriptor that can be used to access shared memory. This is extremely convenient because one can use all the traditional mechanisms for controlling file descriptors to also control shared memory.

note

for temporary scope / auto-cleanup there are a few options:

• defer
• deferScoped add deferScoped, library defined scoped defer by timotheecour · Pull Request #16048 · nim-lang/Nim
• in python, context managers: Comparing C++ RAII and Python Context Managers - DEV Community 👩‍💻👨‍💻
• destructors
• see also O_EXCL
• should be in std/tempfiles
• Issue 12760: Add create mode to open() - Python tracker
• 1252-open-options - The Rust RFC Book
• Contexts and structs - The Go Blog

Context provides a means of transmitting deadlines, caller cancellations, and other request-scoped values across API boundaries and between processes. It is often used when a library interacts — directly or transitively — with remote servers, such as databases, APIs, and the like.

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scratch below

O_TMPFILE

Issue 21515: Use Linux O_TMPFILE flag in tempfile.TemporaryFile? - Python tracker

python3 -c 'import os; fd=os.open(".", os.O_RDWR | os.O_TMPFILE, 0o600)’
uname -a
Linux ee83eead8c5f 4.19.121-linuxkit #1 SMP Tue Dec 1 17:50:32 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

https://man7.org/linux/man-pages/man2/openat.2.html has good explanation for O_TMPFILE

          There are two main use cases for O_TMPFILE: ...

O_BENEATH

open() flags: O_TMPFILE and O_BENEATH [LWN.net]

open2

openat2(2) - Linux manual page

• very simple O_TMPFILE usage, took me a little to figure out the requirements. O_TMPFILE requires MAY_WRITE privileges in the kernel, which can be explicitly achieved with O_RDWR flag. Requires linux >=3.11-rc2, which introduced O_TMPFILE into the mainline.
• unix - Is there anything like shm_open() without filename? - Stack Overflow
• Is there an equivalent of O_TMPFILE for directories? - DebugCN
• Chris's Wiki :: blog/unix/FileSyncProblem
• Unix’s file durability problem | Hacker News

[maxgrenderjones]

I'm a git/github newbie so please be gentle, but have just opened nim-lang#14347 to get support for mkstemps
(EDIT: this is now merged)