Use util.inspect.custom symbol if available.

Ports the `buffer-inspect` test from Node core.
Adds a `Buffer.prototype[util.inspect.custom]` method, which is an alias
to `Buffer.prototype.inspect`. Node already doesn't have an `.inspect`
method on Buffers anymore, but since this module has to work in browsers
that do not have Symbols, it seems better to keep it around.

In Node, this will use the builtin `util.inspect.custom` symbol. In the
browser, it will use `Symbol.for('util.inspect.custom')`. The browser
version of `util` will also use the `inspect-custom-symbol` module in
the near future.

If nodejs/node#20857 gets merged,
`Symbol.for('util.inspect.custom')` will be used everywhere and the
dependency on `inspect-custom-symbol` could probably be dropped.

The motivation for this is API parity and the fact that Node is
removing support for the old `.inspect` method:
nodejs/node#20722

index.js

@@ -10,6 +10,7 @@
 
 var base64 = require('base64-js')
 var ieee754 = require('ieee754')
+var customInspectSymbol = typeof Symbol === 'function' ? require('inspect-custom-symbol') : null
 
 exports.Buffer = Buffer
 exports.SlowBuffer = SlowBuffer
@@ -604,6 +605,9 @@ Buffer.prototype.inspect = function inspect () {
   if (this.length > max) str += ' ... '
   return '<Buffer ' + str + '>'
 }
+if (customInspectSymbol) {
+  Buffer.prototype[customInspectSymbol] = Buffer.prototype.inspect
+}
 
 Buffer.prototype.compare = function compare (target, start, end, thisStart, thisEnd) {
   if (isInstance(target, Uint8Array)) {

package.json

@@ -16,7 +16,8 @@
   ],
   "dependencies": {
     "base64-js": "^1.0.2",
-    "ieee754": "^1.1.4"
+    "ieee754": "^1.1.4",
+    "inspect-custom-symbol": "^1.1.0"
   },
   "devDependencies": {
     "airtap": "0.0.5",

test/node/test-buffer-inspect.js

@@ -0,0 +1,60 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+'use strict';
+var Buffer = require('../../').Buffer;
+
+require('./common');
+const assert = require('assert');
+const util = require('util');
+const buffer = require('../../');
+
+buffer.INSPECT_MAX_BYTES = 2;
+
+let b = Buffer.allocUnsafe(4);
+b.fill('1234');
+
+let s = buffer.SlowBuffer(4);
+s.fill('1234');
+
+let expected = '<Buffer 31 32 ... >';
+
+assert.strictEqual(util.inspect(b), expected);
+assert.strictEqual(util.inspect(s), expected);
+
+b = Buffer.allocUnsafe(2);
+b.fill('12');
+
+s = buffer.SlowBuffer(2);
+s.fill('12');
+
+expected = '<Buffer 31 32>';
+
+assert.strictEqual(util.inspect(b), expected);
+assert.strictEqual(util.inspect(s), expected);
+
+buffer.INSPECT_MAX_BYTES = Infinity;
+
+assert.strictEqual(util.inspect(b), expected);
+assert.strictEqual(util.inspect(s), expected);
+
+b.inspect = undefined;
+assert.strictEqual(util.inspect(b), expected);