Exception Thrown File Exists

[pbferre]

I have been going through the Emscripten tutorials and tests. I modified to hello_world_file.cpp test to use NODEFS, rather than pre-loading the text file. Here is my modified code:

#include <stdio.h>
#include <stdlib.h>
#include <emscripten.h>
#include <string.h>

int main() {
  EM_ASM(
    FS.mkdir('/tmp');
    FS.mount(NODEFS, { root: '.' }, '/tmp');
  );
  
  FILE *file = fopen("/tmp/tests/hello_world_file.txt", "rb");
  if (!file) {
    printf("Cannot open file:\n");
    return 1;
  }
  while (!feof(file)) {
    char c = fgetc(file);
    if (c != EOF) {
      putchar(c);
    }
  }
  fclose (file);
  return 0;
}

The code compiles fine, but when I run it, I get an exception thrown with an error complaining that a file already exists. Here is the output:

C:\Program Files\Emscripten\emscripten\1.35.0>node a.out.js
exception thrown: Error: File exists,Error
    at Object.FS.ensureErrnoError (C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:4169:35)
    at Object.FS.staticInit (C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:4177:12)
    at Object.<anonymous> (C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:5723:4)
    at Module._compile (module.js:434:26)
    at Object.Module._extensions..js (module.js:452:10)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Function.Module.runMain (module.js:475:10)
    at startup (node.js:117:18)
    at node.js:951:3

C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:97
      throw ex;
      ^
Error
    at Object.FS.ensureErrnoError (C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:4169:35)
    at Object.FS.staticInit (C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:4177:12)
    at Object.<anonymous> (C:\Program Files\Emscripten\emscripten\1.35.0\a.out.js:5723:4)
    at Module._compile (module.js:434:26)
    at Object.Module._extensions..js (module.js:452:10)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Function.Module.runMain (module.js:475:10)
    at startup (node.js:117:18)
    at node.js:951:3

Any ideas?

[pbferre]

I changed the name of the folder, and the program is working fine. The only thing I can see is that there is a 'tmp' folder 4 levels down in the directory tree from where the a.out.js file was created. Is that a thing, you cannot pass a name to FS.mkdir that is the same as the name of any folder in the directory tree?

[kripken]

That shouldn't happen, but it could be a weird bug. Does renaming the tmp folder 4 levels down change things?

I suspect that FS.mkdir('/tmp'); is trying to create tmp at the highest level (not a subdir), and your machine already has such a folder.

[bryangingechen]

I ran into a similar issue today except with a call to FS.mkdir('/home'). After some digging, I believe the underlying issue is that /home and /tmp are created automatically by default here: https://github.com/emscripten-core/emscripten/blob/incoming/src/library_fs.js#L1288

I'll submit a PR to document this shortly.

[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 7 days. Feel free to re-open at any time if this issue is still relevant.

[vadimkantorov]

It would be nice also if the exception listed the offending file path