Repro of Node loading modules twice on Windows

[Jeff-Lewis]

Branching issue #6624

Node loading a module twice on Windows

Problem:

Nodejs modules can be loaded twice on Windows due to a change in the drive letter casing.

Using only relative paths, this repo shows how the drive letter can change using require().

Uppercase require.resolve('./moduleA') C:\temp\node_6624\moduleA.js

changes to

Lowercase require.resolve('./../moduleA') c:\temp\node_6624\moduleA.js

Demonstration of how node modules can be loaded twice on Windows under the following circumstances:

1. command line launching initial node module must use uppercase drive letter, ex. C:\server.js
2. There must be a circular reference between modules somewhere along the dependency chain where
   a child module (in this example moduleB) must be require()'ed with lowercase drive letter, ex. require(path.join('dir','moduleB'))
3. When moduleB requires moduleA, it will use the lowercase drive letter in it's path.

A dirty diagram...
C:\moduleA -> c:\moduleB -> c:\moduleA

To Reproduce:

1. Using Windows, clone this repo
2. run run.bat

You will see at the end of the console output, moduleA.js was loaded twice.

*** require.cache ***
[ 'C:\\temp\\node_6624\\test.js',
  'C:\\temp\\node_6624\\moduleA.js',
  'c:\\temp\\node_6624\\childFolder\\moduleB.js',
  'c:\\temp\\node_6624\\moduleA.js' ]

See test.js for code

How often does this happen?

1. WebStorm IDE by default uses uppercase letters in the command line when debugging node.
2. Loading modules by way of path.join() is common in many frameworks.

Why should this be fixed?

The case of the drive letter on Windows should not affect the node run-time and how modules are loaded. _Once this case occurs, all require() paths will be changed causing node to potentially load ALL subsequent modules again._

References:

#6624
#6624 (comment)

• Version: 4.4
• Platform: Windows 10 64-bit
• Subsystem: none

[orangemocha]

I'll revive nodejs/node-v0.x-archive#6774, which I think is an appropriate fix for this issue.

[luisrudge]

I'm having this issue as well and is specially annoying using front end libs because you load two of them (React, for example) and everything blows up

[Jeff-Lewis]

Awesome @orangemocha. Is more needed for a PR?

[orangemocha]

I am investigating a unit test failure with those changes. It should be ready shortly.

[Jeff-Lewis]

Hi @orangemocha. How is the testing going? This issue bit be again in another project today.

[orangemocha]

I think I have all the pieces of the puzzle now:

• The test failures were because of require.cache exposes the cache key and with my change I changed the case of it. I think the solution is to make require.resolve also normalize the case and update the documentation to clarify that require.cache should always be keyed with the result of require.resolve
• I tracked down why the keys currently always have an uppercase drive letter. It is because the full path is resolved based on the requiring module __filename, and that is calculated using fs.realPath. That in turn uses GetFinalPathNameByHandleW in libuv, which performs the normalization even if I pass in FILE_NAME_OPENED.

I think the cache key normalization change can be made regardless of the __filename drive normalization, but I wanted to make sure I understood the whole picture.

I am on vacation now and unfortunately I didn't have enough time to open the PR and defend it before leaving. I am going to resume this as soon as I get back on July 1st.

[Jeff-Lewis]

ref #7175 for another discussion on changes to fs.realPath

[bruno-brant]

I just had my issues with this: I'm connecting mongoose in one place, only to have it disconnected in another. Tracking this down took a lot of time too.

Let's just hope you guys can solve this soon.

One other thing: I don't think the scenario is the one stated by @Jeff-Lewis , instead, a much broader one - at least in my case, using vscode.

The thing is that the first module loaded by node "inherits" the drive letter casing from the command line, and everything it requires ends up with the same casing. However, indirect dependencies, the ones required by the modules that the main module loads, ends up having lower case drive letter.

If this is true, the work around would be simple, just adding a proxy main module that delegates to the actual one.

I will properly test this hypothesis later and will come back with results.

Tried to confirm my hypothesis, no luck.

[orangemocha]

The real cause of this regression is documented at #7726