http2: optimize the altsvc Max bytes limit, define and use constants

PR-URL: #29673
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/http2/core.js

@@ -162,6 +162,7 @@ function debugSessionObj(session, message, ...args) {
 const kMaxFrameSize = (2 ** 24) - 1;
 const kMaxInt = (2 ** 32) - 1;
 const kMaxStreams = (2 ** 31) - 1;
+const kMaxALTSVC = (2 ** 14) - 2;
 
 // eslint-disable-next-line no-control-regex
 const kQuotedString = /^[\x09\x20-\x5b\x5d-\x7e\x80-\xff]*$/;
@@ -1498,7 +1499,7 @@ class ServerHttp2Session extends Http2Session {
       throw new ERR_INVALID_CHAR('alt');
 
     // Max length permitted for ALTSVC
-    if ((alt.length + (origin !== undefined ? origin.length : 0)) > 16382)
+    if ((alt.length + (origin !== undefined ? origin.length : 0)) > kMaxALTSVC)
       throw new ERR_HTTP2_ALTSVC_LENGTH();
 
     this[kHandle].altsvc(stream, origin || '', alt);
@@ -1530,7 +1531,7 @@ class ServerHttp2Session extends Http2Session {
       len += origin.length;
     }
 
-    if (len > 16382)
+    if (len > kMaxALTSVC)
       throw new ERR_HTTP2_ORIGIN_LENGTH();
 
     this[kHandle].origin(arr, count);