From 036c6f406ccd10bc39b07607fa44879ae5c165c8 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Mon, 22 Feb 2021 13:19:14 -0800
Subject: [PATCH] fs: fixup negative length in fs.truncate

`fs.ftruncate`, `fsPromises.truncate`, and `fsPromises.ftruncate`
all adjust negative lengths to 0 before invoking the system call.
`fs.truncate()` was the one outlier.

This "fixes" https://github.com/nodejs/node/issues/35632 but in the
opposite direction than discussed in the issue -- specifically by
removing an EINVAL error from one function rather than adding it to
another.

Signed-off-by: James M Snell <jasnell@gmail.com>
Fixes: https://github.com/nodejs/node/issues/35632
---
 doc/api/fs.md                     | 4 ++++
 lib/fs.js                         | 1 +
 test/parallel/test-fs-truncate.js | 7 +++++++
 3 files changed, 12 insertions(+)

diff --git a/doc/api/fs.md b/doc/api/fs.md
index 3790cdf2bc2b22..2c0b26f2dca01e 100644
--- a/doc/api/fs.md
+++ b/doc/api/fs.md
@@ -406,6 +406,8 @@ try {
 If the file previously was shorter than `len` bytes, it is extended, and the
 extended part is filled with null bytes (`'\0'`):
 
+If `len` is negative then `0` will be used.
+
 #### `filehandle.utimes(atime, mtime)`
 <!-- YAML
 added: v10.0.0
@@ -2295,6 +2297,8 @@ open('temp.txt', 'r+', (err, fd) => {
 If the file previously was shorter than `len` bytes, it is extended, and the
 extended part is filled with null bytes (`'\0'`):
 
+If `len` is negative then `0` will be used.
+
 ### `fs.futimes(fd, atime, mtime, callback)`
 <!-- YAML
 added: v0.4.2
diff --git a/lib/fs.js b/lib/fs.js
index 31aff87d4bec86..4e48d08f07eaab 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -814,6 +814,7 @@ function truncate(path, len, callback) {
   }
 
   validateInteger(len, 'len');
+  len = MathMax(0, len);
   callback = maybeCallback(callback);
   fs.open(path, 'r+', (er, fd) => {
     if (er) return callback(er);
diff --git a/test/parallel/test-fs-truncate.js b/test/parallel/test-fs-truncate.js
index 418d56c047d4e3..aaf003431adf93 100644
--- a/test/parallel/test-fs-truncate.js
+++ b/test/parallel/test-fs-truncate.js
@@ -280,3 +280,10 @@ function testFtruncate(cb) {
     );
   });
 });
+
+{
+  const file1 = path.resolve(tmp, 'truncate-file-1.txt');
+  fs.writeFileSync(file1, 'Hi');
+  fs.truncateSync(file1, -1);  // Negative cooerced to 0, No error.
+  assert(fs.readFileSync(file1).equals(Buffer.alloc(0)));
+}