util: add maxStrLength option to inspect function

Refs: #25478

PR-URL: #32392
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/util.md

@@ -398,6 +398,9 @@ stream.write('With ES6');
 <!-- YAML
 added: v0.3.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/32392
+    description: The `maxStringLength` option is supported now.
   - version: v12.16.0
     pr-url: https://github.com/nodejs/node/pull/30768
     description: User defined prototype properties are inspected in case
@@ -480,6 +483,9 @@ changes:
     [`TypedArray`][], [`WeakMap`][] and [`WeakSet`][] elements to include when
     formatting. Set to `null` or `Infinity` to show all elements. Set to `0` or
     negative to show no elements. **Default:** `100`.
+  * `maxStringLength` {integer} Specifies the maximum number of characters to
+    include when formatting. Set to `null` or `Infinity` to show all elements.
+    Set to `0` or negative to show no characters. **Default:** `Infinity`.
   * `breakLength` {integer} The length at which input values are split across
     multiple lines. Set to `Infinity` to format the input as a single line
     (in combination with `compact` set to `true` or any number >= `1`).

lib/internal/util/inspect.js

@@ -146,6 +146,7 @@ const inspectDefaultOptions = ObjectSeal({
   customInspect: true,
   showProxy: false,
   maxArrayLength: 100,
+  maxStringLength: Infinity,
   breakLength: 80,
   compact: 3,
   sorted: false,
@@ -213,6 +214,7 @@ function getUserOptions(ctx) {
     customInspect: ctx.customInspect,
     showProxy: ctx.showProxy,
     maxArrayLength: ctx.maxArrayLength,
+    maxStringLength: ctx.maxStringLength,
     breakLength: ctx.breakLength,
     compact: ctx.compact,
     sorted: ctx.sorted,
@@ -243,6 +245,7 @@ function inspect(value, opts) {
     customInspect: inspectDefaultOptions.customInspect,
     showProxy: inspectDefaultOptions.showProxy,
     maxArrayLength: inspectDefaultOptions.maxArrayLength,
+    maxStringLength: inspectDefaultOptions.maxStringLength,
     breakLength: inspectDefaultOptions.breakLength,
     compact: inspectDefaultOptions.compact,
     sorted: inspectDefaultOptions.sorted,
@@ -280,6 +283,7 @@ function inspect(value, opts) {
   }
   if (ctx.colors) ctx.stylize = stylizeWithColor;
   if (ctx.maxArrayLength === null) ctx.maxArrayLength = Infinity;
+  if (ctx.maxStringLength === null) ctx.maxStringLength = Infinity;
   return formatValue(ctx, value, 0);
 }
 inspect.custom = customInspectSymbol;
@@ -1293,6 +1297,12 @@ function formatBigInt(fn, value) {
 
 function formatPrimitive(fn, value, ctx) {
   if (typeof value === 'string') {
+    let trailer = '';
+    if (value.length > ctx.maxStringLength) {
+      const remaining = value.length - ctx.maxStringLength;
+      value = value.slice(0, ctx.maxStringLength);
+      trailer = `... ${remaining} more character${remaining > 1 ? 's' : ''}`;
+    }
     if (ctx.compact !== true &&
         // TODO(BridgeAR): Add unicode support. Use the readline getStringWidth
         // function.
@@ -1301,9 +1311,9 @@ function formatPrimitive(fn, value, ctx) {
       return value
         .split(/(?<=\n)/)
         .map((line) => fn(strEscape(line), 'string'))
-        .join(` +\n${' '.repeat(ctx.indentationLvl + 2)}`);
+        .join(` +\n${' '.repeat(ctx.indentationLvl + 2)}`) + trailer;
     }
-    return fn(strEscape(value), 'string');
+    return fn(strEscape(value), 'string') + trailer;
   }
   if (typeof value === 'number')
     return formatNumber(fn, value);

test/parallel/test-util-inspect.js

@@ -2778,3 +2778,11 @@ assert.strictEqual(
   v8.setFlagsFromString('--no-allow-natives-syntax');
   assert.strictEqual(inspect(undetectable), '{}');
 }
+
+{
+  const x = 'a'.repeat(1e6);
+  assert.strictEqual(
+    util.inspect(x, { maxStringLength: 4 }),
+    "'aaaa'... 999996 more characters"
+  );
+}