buffer: inspect extra properties

This makes sure extra properties on buffers are not ignored anymore
when inspecting the buffer.

PR-URL: nodejs#25150
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/buffer.js

@@ -38,6 +38,13 @@ const {
   kStringMaxLength
 } = internalBinding('buffer');
 const { isAnyArrayBuffer } = internalBinding('types');
+const {
+  getOwnNonIndexProperties,
+  propertyFilter: {
+    ALL_PROPERTIES,
+    ONLY_ENUMERABLE
+  }
+} = internalBinding('util');
 const {
   customInspectSymbol,
   isInsideNodeModules,
@@ -51,6 +58,11 @@ const {
 const {
   pendingDeprecation
 } = internalBinding('config');
+const {
+  formatProperty,
+  kObjectType
+} = require('internal/util/inspect');
+
 const {
   ERR_BUFFER_OUT_OF_BOUNDS,
   ERR_OUT_OF_RANGE,
@@ -670,10 +682,20 @@ Buffer.prototype.equals = function equals(otherBuffer) {
 Buffer.prototype[customInspectSymbol] = function inspect(recurseTimes, ctx) {
   const max = exports.INSPECT_MAX_BYTES;
   const actualMax = Math.min(max, this.length);
-  let str = this.hexSlice(0, actualMax).replace(/(.{2})/g, '$1 ').trim();
   const remaining = this.length - max;
+  let str = this.hexSlice(0, actualMax).replace(/(.{2})/g, '$1 ').trim();
   if (remaining > 0)
     str += ` ... ${remaining} more byte${remaining > 1 ? 's' : ''}`;
+  // Inspect special properties as well, if possible.
+  if (ctx) {
+    const filter = ctx.showHidden ? ALL_PROPERTIES : ONLY_ENUMERABLE;
+    str += getOwnNonIndexProperties(this, filter).reduce((str, key) => {
+      // Using `formatProperty()` expects an indentationLvl to be set.
+      ctx.indentationLvl = 0;
+      str += `, ${formatProperty(ctx, this, recurseTimes, key, kObjectType)}`;
+      return str;
+    }, '');
+  }
   return `<${this.constructor.name} ${str}>`;
 };
 Buffer.prototype.inspect = Buffer.prototype[customInspectSymbol];

lib/internal/util/inspect.js

@@ -1220,5 +1220,7 @@ function reduceToSingleString(ctx, output, base, braces) {
 }
 
 module.exports = {
-  inspect
+  inspect,
+  formatProperty,
+  kObjectType
 };

test/parallel/test-buffer-inspect.js

@@ -55,4 +55,4 @@ assert.strictEqual(util.inspect(b), expected);
 assert.strictEqual(util.inspect(s), expected);
 
 b.inspect = undefined;
-assert.strictEqual(util.inspect(b), expected);
+assert.strictEqual(util.inspect(b), '<Buffer 31 32, inspect: undefined>');