fs: complete error message for validate function

PR-URL: #19909
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: ah-yu

lib/internal/fs.js

@@ -350,11 +350,13 @@ function validateLen(len) {
   let err;
 
   if (!isInt32(len)) {
-    if (typeof value !== 'number') {
+    if (typeof len !== 'number') {
       err = new ERR_INVALID_ARG_TYPE('len', 'number', len);
-    } else {
-      // TODO(BridgeAR): Improve this error message.
+    } else if (!Number.isInteger(len)) {
       err = new ERR_OUT_OF_RANGE('len', 'an integer', len);
+    } else {
+      // 2 ** 31 === 2147483648
+      err = new ERR_OUT_OF_RANGE('len', '> -2147483649 && < 2147483648', len);
     }
   }
 

test/parallel/test-fs-truncate.js

@@ -190,6 +190,31 @@ function testFtruncate(cb) {
     );
   });
 
+  [-1.5, 1.5].forEach((input) => {
+    assert.throws(
+      () => fs.ftruncate(fd, input),
+      {
+        code: 'ERR_OUT_OF_RANGE',
+        name: 'RangeError [ERR_OUT_OF_RANGE]',
+        message: 'The value of "len" is out of range. It must be ' +
+                  `an integer. Received ${input}`
+      }
+    );
+  });
+
+  // 2 ** 31 = 2147483648
+  [2147483648, -2147483649].forEach((input) => {
+    assert.throws(
+      () => fs.ftruncate(fd, input),
+      {
+        code: 'ERR_OUT_OF_RANGE',
+        name: 'RangeError [ERR_OUT_OF_RANGE]',
+        message: 'The value of "len" is out of range. It must be ' +
+                  `> -2147483649 && < 2147483648. Received ${input}`
+      }
+    );
+  });
+
   fs.ftruncate(fd, undefined, common.mustCall(function(err) {
     assert.ifError(err);
     assert(fs.readFileSync(file5).equals(Buffer.from('')));