Function: isTlsProtocolError()

isTlsProtocolError(err): boolean

Detects TLS-protocol-shaped errors, failures of the TLS protocol itself, as opposed to plain TCP-level network failures.

Apply this only to errors raised on a TLS connection; MllpClient does exactly that (the predicate is consulted only when ClientOptions.tls is set). The boundary:

TLS-protocol-shaped (true):

• code starting ERR_SSL_ (Node's TLS alert codes, e.g. ERR_SSL_TLSV13_ALERT_CERTIFICATE_REQUIRED, a clientAuth: 'MUST' server rejecting the client's certificate).
• code === 'EPROTO', on a TLS connection this is OpenSSL failing the handshake (protocol version mismatch, no shared cipher, a TLS ≤1.2 mTLS rejection).
• message containing ssl or alert (/\bssl\b|\balert\b/i, "SSL routines", "tlsv13 alert certificate required", …). This message check is a heuristic backstop over the code-based checks above, not a precise boundary: it exists to catch OpenSSL errors that surface without a usable code, and MllpClient consults it only on connections where TLS is configured. An arbitrary non-TLS error whose message happens to contain those words would also match.

NOT TLS-protocol-shaped (false), plain network failures, which stay transient for the reconnect classifier: ECONNREFUSED, ETIMEDOUT, EHOSTUNREACH, ENETUNREACH, EPIPE, and a plain ECONNRESET carrying no TLS alert context, a network blip during (or after) a handshake should still auto-heal.

Certificate-verification failures are a separate class, see isTlsVerificationErrorCode; MllpClient checks that first and labels those connectionCause: 'tls-verify'.

Why this matters: under TLS 1.3 (RFC 8446 §4.4.2) a clientAuth: 'MUST' server can reject the client's certificate AFTER the client's own 'secureConnect', the rejection then surfaces as a post-connect socket error. A misconfigured mTLS client must never auto-reconnect-loop against a server that will always reject it, so MllpClient classifies TLS-protocol-shaped errors as permanent.

Parameters

err

unknown

Returns

boolean

Example

import { isTlsProtocolError, MllpConnectionError } from '@cosyte/mllp';
client.on('error', ({ error }) => {
  if (error instanceof MllpConnectionError && isTlsProtocolError(error.cause)) {
    // TLS protocol failure, a configuration problem, not a network blip.
  }
});