node: Provide fallback for MachineIdentifier, in case shell is not available

[steilerDev]

In a hardened environment, where shell access has been restricted, spinning up Backtrace leads to an unhandled exception:

node:internal/child_process:1120
    at new AttributeManager (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/sdk-core/lib/bundle.cjs:572:18)
    result.error = new ErrnoException(result.error, 'spawnSync ' + options.file);
                   ^
<ref *1> Error: spawnSync /bin/sh ENOENT
    at Object.spawnSync (node:internal/child_process:1120:20)
    at spawnSync (node:child_process:902:24)
    at Object.execSync (node:child_process:983:15)
    at MachineIdentitfierAttributeProvider.get (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/node/lib/bundle.cjs:878:33)
    at MachineIdentitfierAttributeProvider.generateGuid (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/node/lib/bundle.cjs:901:38)
    at AttributeManager.addProvider (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/sdk-core/lib/bundle.cjs:598:50)
    at new BacktraceCoreClient (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/sdk-core/lib/bundle.cjs:3042:33)
    at new BacktraceClient (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/node/lib/bundle.cjs:1162:9)
    at BacktraceClientBuilder.build (/usr/local/lib/node_modules/icloud-photos-sync/node_modules/@backtrace/node/lib/bundle.cjs:977:26) {
  errno: -2,
  code: 'ENOENT',
  syscall: 'spawnSync /bin/sh',
    '-c',
  spawnargs: [
  path: '/bin/sh',
    '( cat /var/lib/dbus/machine-id /etc/machine-id 2> /dev/null || hostname ) | head -n 1 || :'
  error: [Circular *1],
  ],
  status: null,
  output: null,
  signal: null,
  pid: 0,
  stdout: undefined,
  stderr: undefined
}
Node.js v22.20.0

The proposed change handles any exception thrown, to return null and triggering the existing fallback case const guid = this.generateGuid() ?? IdGenerator.uuid();

[rick-bt]

Hi @steilerDev! This would mask multiple exception types which is risky. Can't take this into main as-is. A good alt would be to not punch out to shell to get a consistent identifier, if you want to give that a try. Compose a few machine-stable identifiers and hash it to a uuid.

[steilerDev]

Hey @rick-bt - I fully understand your input, my proposal is a very quick and dirty "fix".

However, the challenge I'm facing in my execution environment is that it's a hardened, ephemeral Docker container: No system tools or shell available, besides nodejs. Therefore any fingerprint created, would probably not survive a container restart.

I do have a user identifier available - maybe the 'correct' solution would be an option to allow the dev to supply a MachineIdentifier to the lib as a configuration option?