fs: accept all valid utf8 values in fast paths

lib/fs.js

@@ -59,6 +59,13 @@ const {
   O_SYMLINK,
 } = constants;
 
+function isUtf8Encoding(encoding) {
+  return encoding === 'utf8' ||
+         encoding === 'utf-8' ||
+         encoding === 'UTF8' ||
+         encoding === 'UTF-8';
+}
+
 const pathModule = require('path');
 const { isArrayBufferView } = require('internal/util/types');
 
@@ -531,8 +538,7 @@ function readFileSync(path, options) {
   validateReadFileBufferOptions(options);
   const hasUserBuffer = options.buffer !== undefined;
 
-  if ((options.encoding === 'utf8' || options.encoding === 'utf-8') &&
-      !hasUserBuffer) {
+  if (isUtf8Encoding(options.encoding) && !hasUserBuffer) {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }
@@ -2906,7 +2912,7 @@ function writeFileSync(path, data, options) {
   const flag = options.flag || 'w';
 
   // C++ fast path for string data and UTF8 encoding
-  if (typeof data === 'string' && (options.encoding === 'utf8' || options.encoding === 'utf-8')) {
+  if (typeof data === 'string' && isUtf8Encoding(options.encoding)) {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }
@@ -3197,7 +3203,7 @@ if (isWindows) {
 }
 
 function encodeRealpathResult(result, options) {
-  if (!options || !options.encoding || options.encoding === 'utf8')
+  if (!options || !options.encoding || isUtf8Encoding(options.encoding))
     return result;
   const asBuffer = Buffer.from(result);
   if (options.encoding === 'buffer') {

lib/internal/util/inspect.js

@@ -2624,6 +2624,14 @@ function isBelowBreakLength(ctx, output, start, base) {
   // TODO(BridgeAR): Add unicode support. Use the readline getStringWidth
   // function. Check the performance overhead and make it an opt-in in case it's
   // significant.
+  // allow the single-line format if the length limit is infinite and no items have newlines
+  if (ctx.breakLength === Infinity) {
+    if (base !== '' && StringPrototypeIncludes(base, '\n')) return false;
+    for (let i = 0; i < output.length; i++) {
+      if (typeof output[i] === 'string' && StringPrototypeIncludes(output[i], '\n')) return false;
+    }
+    return true;
+  }
   let totalLength = output.length + start;
   if (totalLength + output.length > ctx.breakLength)
     return false;

test/parallel/test-util-inspect.js

@@ -4058,3 +4058,9 @@ ${error.stack.split('\n').slice(1).join('\n')}`,
   assert.match(inspect(DOMException.prototype), /^\[object DOMException\] \{/);
   delete Error[Symbol.hasInstance];
 }
+
+{
+  const obj = { a: 'short string', b: [1, 2], c: { d: true } };
+  const expected = "{ a: 'short string', b: [ 1, 2 ], c: { d: true } }";
+  assert.strictEqual(util.inspect(obj, { breakLength: Infinity }), expected);
+}