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fs/promises's readFile returns truncated content for files in /proc/net/ #50437
Description
Activity
Can confirm. The bug here is that the promise-based version allocates a 64k buffer and thinks it's done when it reads less than that. That optimization is valid for regular files but not for files under /proc. It should keep reading until EOF (zero read.)
Reacted by Benjamin Gruenbaum, ExE Boss and Florian Prud'homme(rookie question) Is there a way to way to check whether the file we are reading is one of these special files? other than maybe checking the path?
Checking the path isn't enough because a procfs can be mounted anywhere; /proc is just the most common.
Checking
fs.statfsSync(path).type === 0x9FA0(PROC_SUPER_MAGIC) works but isn't race-free.I'm not 100% sure if it's okay to assume that
fs.fstatSync(fd).dev === 22means the file is on procfs.Reacted by Benjamin GruenbaumForgot to mention, linux has a
fstatfs(fd)syscall but that isn't exposed by libuv. Would IMO be okay to use in a linux-only code path though.edit: having said that... it's easier all around to simply read until EOF. Zero-sized files are rare enough that they aren't worth optimizing for. You're making at least two system calls either way.
Reacted by Benjamin Gruenbaum, ExE Boss, Juan José and CattChen@nodejs/fs
Hi! It's been a few months since any activity on this issue. I just attempted to reproduce in v22.6.0, and I was unable to do:
require("fs/promises").readFile("/proc/net/unix", "utf-8").then(x => console.log(x.length)) require("fs").readFile("/proc/net/unix", "utf-8", (_, x) => console.log(x.length))
$ node index.js 75897 75897
For that reason, I'm optimistically closing this issue, but feel free to reopen.
Version
v21.1.0
Platform
Linux ubuntu 6.2.0-35-generic #35~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Fri Oct 6 10:23:26 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
Subsystem
fs/promises
What steps will reproduce the bug?
Compare the length of the content returned by
fs/promises.readFileandfs.readFilewhen reading any file larger than 4 KiB in/proc/net.fs/promisesonly returns the first 4 KiB or so.How often does it reproduce? Is there a required condition?
Always
What is the expected behavior? Why is that the expected behavior?
fs/promises'sreadFileandfs.readFilereturn the same untruncated file contents.What do you see instead?
fs/promises'sreadFiletruncates procfs file contents to around 4 KiB.Additional information
No response