os: fix netmask format check condition in getCIDR function

[HBSPS]

Modified to check the format of the netmask instead of just checking that each part of the netmask is even number.
(Ref: https://www.rfc-editor.org/rfc/rfc1878)

The result of the previous run was like this.

...
if ((binary & 1) !== 0) {
  return null;
}
...

console.log(getCIDR('127.0.0.1', '242.0.0.0', 'IPv4')); // 127.0.0.1/5
// 242 = 11110010(2)

This does not satisfy the condition in netmask, but it passes the conditional statement and returns an invalid value.

I'm not sure if that conditional is necessary(if the correct value is always passed, etc), but I think it's doing the wrong thing, so I've modified it to look like this.

...
if (StringPrototypeIncludes(binary.toString(2), '01')) {
  return null;
}

console.log(getCIDR('127.0.0.1', '242.0.0.0', 'IPv4')); // null
...

I modified the netmask to check if it satisfies the condition of containing '01', such as 11110010, since a 0 cannot be followed by a 1 according to the rules of netmask.

The benchmark results for changing conditions are shown below.

                                confidence improvement accuracy (*)   (**)  (***)
os/networkInterfaces.js n=10000                 0.19 %       ±1.17% ±1.56% ±2.03%

Be aware that when doing many comparisons the risk of a false-positive result increases.
In this case, there are 1 comparisons, you can thus expect the following amount of false-positive results:
  0.05 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.01 false positives, when considering a   1% risk acceptance (**, ***),
  0.00 false positives, when considering a 0.1% risk acceptance (***)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.22%. Comparing base (db00f94) to head (6e529a4).
Report is 39 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #57324      +/-   ##
==========================================
+ Coverage   90.20%   90.22%   +0.01%     
==========================================
  Files         630      630              
  Lines      185166   185203      +37     
  Branches    36227    36247      +20     
==========================================
+ Hits       167036   167102      +66     
+ Misses      11117    11044      -73     
- Partials     7013     7057      +44     

Files with missing lines	Coverage Δ
lib/internal/util.js	96.05% <100.00%> (+0.24%)	⬆️
lib/os.js	98.59% <100.00%> (+1.27%)	⬆️

... and 63 files with indirect coverage changes

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[lpinca]

Can you please add a test?

[HBSPS]

Can you please add a test?

@lpinca This function is only being used by networkInterfaces, which is getting it from internalBinding.

Since networkInterfaces is not a pure function and returns a value based on the current state of the system, is there any way to do mocking or something in this regard?
(I'm not familiar with this kind of testing)

If you have any references or know how to do it, I'd appreciate it :)

function networkInterfaces() {
  const data = getInterfaceAddresses();
  const result = {};

  if (data === undefined)
    return result;
  for (let i = 0; i < data.length; i += 7) {
    const name = data[i];
    const entry = {
      address: data[i + 1],
      netmask: data[i + 2],
      family: data[i + 3],
      mac: data[i + 4],
      internal: data[i + 5],
      cidr: getCIDR(data[i + 1], data[i + 2], data[i + 3]),
    };
    const scopeid = data[i + 6];
    if (scopeid !== -1)
      entry.scopeid = scopeid;

    const existing = result[name];
    if (existing !== undefined)
      ArrayPrototypePush(existing, entry);
    else
      result[name] = [entry];
  }

  return result;
}

[lpinca]

What do think about moving it to lib/internal/util.js or lib/internal/os/utils.js? The latter does not exist yet.

[HBSPS]

What do think about moving it to lib/internal/util.js or lib/internal/os/utils.js? The latter does not exist yet.

@lpinca Sounds like a good idea, I moved the getCIDR function to internal/util as you said and created a new test file to test that function.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/65661/