Investigate flaky test-fs-copyfile

[jasnell]

Ping @cjihrig ... seeing some flakiness in the test. This is the second time I've seen this running locally on Ubuntu.

=== release test-fs-copyfile ===
Path: parallel/test-fs-copyfile
assert.js:43
 throw new errors.AssertionError({
 ^

AssertionError [ERR_ASSERTION]: 33188 === 33204
 at verify (/home/james/node/main/test/parallel/test-fs-copyfile.js:17:10)
 at Object.<anonymous> (/home/james/node/main/test/parallel/test-fs-copyfile.js:32:1)
 at Module._compile (module.js:600:30)
 at Object.Module._extensions..js (module.js:611:10)
 at Module.load (module.js:521:32)
 at tryModuleLoad (module.js:484:12)
 at Function.Module._load (module.js:476:3)
 at Function.Module.runMain (module.js:641:10)
 at startup (bootstrap_node.js:201:16)
 at bootstrap_node.js:626:3
Command: out/Release/node /home/james/node/main/test/parallel/test-fs-copyfile.js

[cjihrig]

It looks like the reported file permissions are not identical. @jasnell when you see this error, are you able to verify if the copied file has the correct permissions? I'm curious if this is a bug in the copy code, or a bug in the test.

[addaleax]

I can reproduce this; the files do get different permissions. This should be the relevant output:

mkdir("/home/sqrt/src/node/test/tmp", 0777) = 0
open("/home/sqrt/src/node/test/tmp/copyfile.out", O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0666) = 12
close(12) = 0
open("/home/sqrt/src/node/test/fixtures/a.js", O_RDONLY|O_CLOEXEC) = 12
fstat(12,{st_mode=S_IFREG|0644, st_size=1469, ...}) = 0
open("/home/sqrt/src/node/test/tmp/copyfile.out", O_WRONLY|O_CREAT|O_CLOEXEC, 0100644) = 13
sendfile(13, 12, [0] => [1469], 1469) = 1469
close(12) = 0
close(13) = 0
open("/home/sqrt/src/node/test/fixtures/a.js", O_RDONLY|O_CLOEXEC) = 12
fstat(12,{st_mode=S_IFREG|0644, st_size=1469, ...}) = 0
read(12, "// Copyright Joyent, Inc. and ot"..., 1469) = 1469
close(12) = 0
stat("/home/sqrt/src/node/test/fixtures/a.js",{st_mode=S_IFREG|0644, st_size=1469, ...}) = 0
open("/home/sqrt/src/node/test/tmp/copyfile.out", O_RDONLY|O_CLOEXEC) = 12
fstat(12,{st_mode=S_IFREG|0664, st_size=1469, ...}) = 0
read(12, "// Copyright Joyent, Inc. and ot"..., 1469) = 1469
close(12) = 0
stat("/home/sqrt/src/node/test/tmp/copyfile.out",{st_mode=S_IFREG|0664, st_size=1469, ...}) = 0

I’m not seeing any part of the copy code that would make sure the target file gets the original file mode.

[cjihrig]

Thanks @addaleax.

I’m not seeing any part of the copy code that would make sure the target file gets the original file mode.

That is done (or should be done) in libuv here. That is why you see the fstat() call before the third open() call.

[addaleax]

@cjihrig Yes, but that only applies to the case in which the file is created, not the one in which it is overwritten (i.e. the one in the test file)

[cjihrig]

Ah. Yea, it looks like a fchmod() is needed.

[cjihrig]

@addaleax does this commit fix the problem for you?

[addaleax]

@cjihrig Looks that way 👍 And makes sense, too. I think both behaviours could make sense depending on the actual use case, though…

[cjihrig]

I think both behaviours could make sense depending on the actual use case, though…

What use cases do you have in mind?

[addaleax]

@cjihrig I think I remember cases where I had applications write history files (à la .bash_history), which implemented that by writing to a new file, then copying at the end of the session instead of just appending to the original file, which always accidentally made the file mode match the one the temp file got by default rather than the one I explicitly gave to that history file…

idk, it was nothing more than a mild annoyance. I guess all I’m saying is, sometimes people give their files a certain mode for a reason, and sometimes (a lot of the time?) copying should respect that, since the semantics of a file and therefore its security properties are usually defined via its path, not where the contents were copied from.

[cjihrig]

I agree that copying should retain the original mode. You said both behaviours could make sense. I guess my question is, when would you not want to copy the mode in a standard copy operation? I know Apple's copyfile() lets you copy different aspects of the file, such as data only, but for a basic cross platform cp operation, I think we'd always want everything.

[addaleax]

@cjihrig Uh, which one are you agreeing with? The problem is that there can be two different “original” file modes, and there is no generic way to tell which mode is the desired one.

[cjihrig]

I'm only referring to the case of cp src dest, where dest should have the same mode as src. I think we're on the same page, just failing to communicate it properly :-)