util: truncate inspect array and typed array

As an alternative to nodejs#5070,
set the max length of Arrays/TypedArrays in util.inspect() to
`100` and provide a `maxArrayLength` option to override.

PR-URL: nodejs#6334
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Jeremiah Senkpiel <[email protected]>
Reviewed-By: Roman Reiss <[email protected]>

doc/api/util.md

@@ -183,6 +183,10 @@ formatted string:
    will be introspected to show their `target` and `hander` objects. Defaults to
    `false`.
 
+ - `maxArrayLength` - specifies the maximum number of Array and TypedArray
+   elements to include when formatting. Defaults to `100`. Set to `null` to
+   show all array elements. Set to `0` or negative to show no array elements.
+
 Example of inspecting all properties of the `util` object:
 
 ```js

lib/util.js

@@ -6,6 +6,7 @@ const internalUtil = require('internal/util');
 const binding = process.binding('util');
 
 const isError = internalUtil.isError;
+const kDefaultMaxLength = 100;
 
 var Debug;
 
@@ -141,6 +142,8 @@ function inspect(obj, opts) {
   if (ctx.customInspect === undefined) ctx.customInspect = true;
   if (ctx.showProxy === undefined) ctx.showProxy = false;
   if (ctx.colors) ctx.stylize = stylizeWithColor;
+  if (ctx.maxArrayLength === undefined) ctx.maxArrayLength = kDefaultMaxLength;
+  if (ctx.maxArrayLength === null) ctx.maxArrayLength = Infinity;
   return formatValue(ctx, obj, ctx.depth);
 }
 exports.inspect = inspect;
@@ -579,14 +582,19 @@ function formatObject(ctx, value, recurseTimes, visibleKeys, keys) {
 
 function formatArray(ctx, value, recurseTimes, visibleKeys, keys) {
   var output = [];
-  for (var i = 0, l = value.length; i < l; ++i) {
+  const maxLength = Math.min(Math.max(0, ctx.maxArrayLength), value.length);
+  const remaining = value.length - maxLength;
+  for (var i = 0; i < maxLength; ++i) {
     if (hasOwnProperty(value, String(i))) {
       output.push(formatProperty(ctx, value, recurseTimes, visibleKeys,
           String(i), true));
     } else {
       output.push('');
     }
   }
+  if (remaining > 0) {
+    output.push(`... ${remaining} more item${remaining > 1 ? 's' : ''}`);
+  }
   keys.forEach(function(key) {
     if (typeof key === 'symbol' || !key.match(/^\d+$/)) {
       output.push(formatProperty(ctx, value, recurseTimes, visibleKeys,
@@ -598,9 +606,14 @@ function formatArray(ctx, value, recurseTimes, visibleKeys, keys) {
 
 
 function formatTypedArray(ctx, value, recurseTimes, visibleKeys, keys) {
-  var output = new Array(value.length);
-  for (var i = 0, l = value.length; i < l; ++i)
+  const maxLength = Math.min(Math.max(0, ctx.maxArrayLength), value.length);
+  const remaining = value.length - maxLength;
+  var output = new Array(maxLength);
+  for (var i = 0; i < maxLength; ++i)
     output[i] = formatNumber(ctx, value[i]);
+  if (remaining > 0) {
+    output.push(`... ${remaining} more item${remaining > 1 ? 's' : ''}`);
+  }
   for (const key of keys) {
     if (typeof key === 'symbol' || !key.match(/^\d+$/)) {
       output.push(

test/parallel/test-util-inspect.js

@@ -648,3 +648,58 @@ checkAlignment(new Map(big_array.map(function(y) { return [y, null]; })));
   const x = Object.create(null);
   assert.equal(util.inspect(x), '{}');
 }
+
+// The following maxArrayLength tests were introduced after v6.0.0 was released.
+// Do not backport to v5/v4 unless all of
+// https://github.com/nodejs/node/pull/6334 is backported.
+{
+  const x = Array(101);
+  assert(/1 more item/.test(util.inspect(x)));
+}
+
+{
+  const x = Array(101);
+  assert(!/1 more item/.test(util.inspect(x, {maxArrayLength: 101})));
+}
+
+{
+  const x = Array(101);
+  assert(/^\[ ... 101 more items \]$/.test(
+      util.inspect(x, {maxArrayLength: 0})));
+}
+
+{
+  const x = new Uint8Array(101);
+  assert(/1 more item/.test(util.inspect(x)));
+}
+
+{
+  const x = new Uint8Array(101);
+  assert(!/1 more item/.test(util.inspect(x, {maxArrayLength: 101})));
+}
+
+{
+  const x = new Uint8Array(101);
+  assert(/\[ ... 101 more items \]$/.test(
+      util.inspect(x, {maxArrayLength: 0})));
+}
+
+{
+  const x = Array(101);
+  assert(!/1 more item/.test(util.inspect(x, {maxArrayLength: null})));
+}
+
+{
+  const x = Array(101);
+  assert(!/1 more item/.test(util.inspect(x, {maxArrayLength: Infinity})));
+}
+
+{
+  const x = new Uint8Array(101);
+  assert(!/1 more item/.test(util.inspect(x, {maxArrayLength: null})));
+}
+
+{
+  const x = new Uint8Array(101);
+  assert(!/1 more item/.test(util.inspect(x, {maxArrayLength: Infinity})));
+}