src: improve node::Dotenv trimming

src/node_dotenv.cc

@@ -105,15 +105,26 @@ Local<Object> Dotenv::ToObject(Environment* env) const {
   return result;
 }
 
+// Removes space characters (spaces, tabs and newlines) from
+// the start and end of a given input string
 std::string_view trim_spaces(std::string_view input) {
   if (input.empty()) return "";
-  if (input.front() == ' ') {
-    input.remove_prefix(input.find_first_not_of(' '));
+
+  auto pos_start = input.find_first_not_of(" \t\n");
+  if (pos_start == std::string_view::npos) {
+    return "";
   }
-  if (!input.empty() && input.back() == ' ') {
-    input = input.substr(0, input.find_last_not_of(' ') + 1);
+
+  auto pos_end = input.find_last_not_of(" \t\n");
+  if (pos_end == std::string_view::npos) {
+    return input.substr(pos_start);
   }
-  return input;
+
+  if (pos_start == pos_end) {
+    return "";
+  }
+
+  return input.substr(pos_start, pos_end - pos_start + 1);
 }
 
 void Dotenv::ParseContent(const std::string_view input) {

test/fixtures/dotenv/lines-with-only-spaces.env

@@ -0,0 +1,8 @@
+
+EMPTY_LINE='value after an empty line'
+
+SPACES_LINE='value after a line with just some spaces'
+
+TABS_LINE='value after a line with just some tabs'
+
+SPACES_TABS_LINE='value after a line with just some spaces and tabs'

test/parallel/test-dotenv-edge-cases.js

@@ -31,7 +31,7 @@
         ],
         { cwd: __dirname },
       )));
     assert.deepStrictEqual(children, Array.from({ length: 4 }, () => ({
       code: 0,
       signal: null,
       stdout: '',
@@ -137,6 +137,25 @@
     assert.strictEqual(child.code, 0);
   });
 
+  it('should handle lines that come after lines with only spaces (and tabs)', async () => {
+    // Ref: https://github.com/nodejs/node/issues/56686
+    const code = `
+      process.loadEnvFile('./lines-with-only-spaces.env');
+      assert.strictEqual(process.env.EMPTY_LINE, 'value after an empty line');
+      assert.strictEqual(process.env.SPACES_LINE, 'value after a line with just some spaces');
+      assert.strictEqual(process.env.TABS_LINE, 'value after a line with just some tabs');
+      assert.strictEqual(process.env.SPACES_TABS_LINE, 'value after a line with just some spaces and tabs');
+    `.trim();
+    const child = await common.spawnPromisified(
+      process.execPath,
+      [ '--eval', code ],
+      { cwd: fixtures.path('dotenv') },
+    );
+    assert.strictEqual(child.stdout, '');
+    assert.strictEqual(child.stderr, '');
+    assert.strictEqual(child.code, 0);
+  });
+
   it('should handle when --env-file is passed along with --', async () => {
     const child = await common.spawnPromisified(
       process.execPath,