'_placeholder' in ESM module is replaced with 'it' which breaks binary data

[digulla]

Describe the bug
The file socket.io.esm.min.js from the NPM package socket.io-client 4.8.0 contains a bug which breaks binary data when talking to other SocketIO implementations (for example python-socjetio).

Instead of {_placeholder: true, num: 0}, the code produces {it: true, num: 0}. It's correct in the source. The problem is somewhere in the ESM build.

To Reproduce
Search for function _deconstructPacket in socket.io.js. It looks like this:

  function _deconstructPacket(data, buffers) {
    if (!data) return data;
    if (isBinary(data)) {
      var placeholder = {
        _placeholder: true,
        num: buffers.length
      };

In the ESM, it gets compiled into this code:

function ot(t, s) {
    if (!t)
        return t;
    if (et(t)) {
        const i = {
            it: !0,
            num: s.length
        };
        return s.push(t),
        i
    }

The same happens in _reconstructPacket. Source:

  function _reconstructPacket(data, buffers) {
    if (!data) return data;
    if (data && data._placeholder === true) {
      var isIndexValid = typeof data.num === "number" && data.num >= 0 && data.num < buffers.length;

which is compiled into

function ct(t, s) {
    if (!t)
        return t;
    if (t && !0 === t.it) {
        if ("number" == typeof t.num && t.num >= 0 && t.num < s.length)

Expected behavior
The binary representation in the serialized message must be correct.

Platform:

• Device: any
• OS: any

Additional context
n.a.

[darrachequesne]

I could indeed reproduce the issue, I'm digging into this.

[digulla]

Thanks for the quick response. My workaround is to use a unit test to copy the file into the production folder and patch the two places. So it's not a killer at the moment.

[darrachequesne]

@digulla this should be fixed in version 4.8.1. Could you please check?