tls: runtime-deprecate tls.convertNPNProtocols()

Fixes: #14602
PR-URL: #19403
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

Author: bnoordhuis

doc/api/deprecations.md

@@ -971,6 +971,14 @@ initialization vectors. It is recommended to derive a key using
 [`crypto.createDecipheriv()`][] to obtain the [`Cipher`][] and [`Decipher`][]
 objects respectively.
 
+<a id="DEP0107"></a>
+### DEP0107: tls.convertNPNProtocols()
+
+Type: Runtime
+
+This was an undocumented helper function not intended for use outside Node.js
+core and obsoleted by the removal of NPN (Next Protocol Negotiation) support.
+
 [`--pending-deprecation`]: cli.html#cli_pending_deprecation
 [`Buffer.allocUnsafeSlow(size)`]: buffer.html#buffer_class_method_buffer_allocunsafeslow_size
 [`Buffer.from(array)`]: buffer.html#buffer_class_method_buffer_from_array

lib/tls.js

@@ -73,15 +73,15 @@ function convertProtocols(protocols) {
   return buff;
 }
 
-exports.convertNPNProtocols = function(protocols, out) {
+exports.convertNPNProtocols = internalUtil.deprecate(function(protocols, out) {
   // If protocols is Array - translate it into buffer
   if (Array.isArray(protocols)) {
     out.NPNProtocols = convertProtocols(protocols);
   } else if (isUint8Array(protocols)) {
     // Copy new buffer not to be modified by user.
     out.NPNProtocols = Buffer.from(protocols);
   }
-};
+}, 'tls.convertNPNProtocols() is deprecated.', 'DEP0107');
 
 exports.convertALPNProtocols = function(protocols, out) {
   // If protocols is Array - translate it into buffer