tls: better error message for socket disconnect

The error emitted when a connection is closed before the
TLS handshake completes seemed rather unspefic by just saying
`socket hang up`.

Use a more verbose message, that also indicates that this is
a purely client-side error, and remove a misleading comment.

PR-URL: nodejs#18989
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/_tls_wrap.js

@@ -1074,7 +1074,6 @@ function onConnectSecure() {
     this.emit('secureConnect');
   }
 
-  // Uncork incoming data
   this.removeListener('end', onConnectEnd);
 }
 
@@ -1083,7 +1082,8 @@ function onConnectEnd() {
   if (!this._hadError) {
     const options = this[kConnectOptions];
     this._hadError = true;
-    const error = new Error('socket hang up');
+    const error = new Error('Client network socket disconnected before ' +
+                            'secure TLS connection was established');
     error.code = 'ECONNRESET';
     error.path = options.path;
     error.host = options.host;

test/parallel/test-tls-empty-sni-context.js

@@ -29,6 +29,6 @@ const server = tls.createServer(options, (c) => {
   }, common.mustNotCall());
 
   c.on('error', common.mustCall((err) => {
-    assert(/socket hang up/.test(err.message));
+    assert(/Client network socket disconnected/.test(err.message));
   }));
 }));

test/parallel/test-tls-sni-option.js

@@ -175,7 +175,9 @@ process.on('exit', function() {
   ]);
   assert.deepStrictEqual(clientResults, [true, true, true, false, false]);
   assert.deepStrictEqual(clientErrors, [
-    null, null, null, null, 'socket hang up'
+    null, null, null, null,
+    'Client network socket disconnected before secure TLS ' +
+    'connection was established'
   ]);
   assert.deepStrictEqual(serverErrors, [
     null, null, null, null, 'Invalid SNI context'