exception not thrown when truncating filenames longer than 255 char

[mdh1418]

When files with a filename greater than 255 characters is being created, it is truncated, but does not throw an exception that other systems throw.

Expectation: File is truncated and created with an exception thrown.

[kripken]

Interesting, I don't remember us imposing a 255 character limit anywhere. But maybe it's a part of library_fs.js I'm not familiar with? It should be in there or maybe in library_path.js.

edit: Oh, hmm, unless it's a musl limitation and it happens there...

[akoeplinger]

The limitation probably comes from

emscripten/system/include/libc/limits.h

Line 47 in 2bca083

#define NAME_MAX 255

However it's not clear to me where exactly the truncation happens.

[mdh1418]

I looked to make a repro yesterday but didn't manage to make one demonstrating opening a file with a path basename longer than 255 characters. I suspected that the truncation happens here within the open: function which is the one I believe is called into through the pal code.

emscripten/src/library_fs.js

Line 1065 in b1a7889

FS.truncate(node, 0);

but when I tried to repro, it doesn't hit that logic because of this.

emscripten/src/library_fs.js

Line 1047 in b1a7889

if (FS.isChrdev(node.mode)) {

.

I also thought NAME_MAX was being used, but after grepping through files in this repo, its not obvious to me how the variable contributes to truncation.

[akoeplinger]

hm no, that first library_fs.js just truncated the file contents, not the name.

I think what probably happens is that when we create the inode we don't check for the length before filling this struct:

emscripten/system/lib/fetch/asmfs.cpp

Lines 37 to 38 in b9f357c

	struct inode {
	char name[NAME_MAX + 1]; // NAME_MAX actual bytes + one byte for null termination.

[akoeplinger]

ah, I just read that asmfs is a work in progress so it's probably not that: #9534 😄

[akoeplinger]

so most likely here:

emscripten/src/library_fs.js

Lines 645 to 646 in b1a7889

	// generic function for all node creation
	mknod: function(path, mode, dev) {

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 30 days. Feel free to re-open at any time if this issue is still relevant.

[akoeplinger]

From what I can see this is still an issue.