src: improve node::Dotenv trimming

the trimming functionality that the dotenv parsing uses currently
only takes into consideration plain spaces (' '), other type of
space characters such as tabs and newlines are not trimmed, this
can cause subtle bugs, so the changes here make sure that such
characters get trimmed as well

Author: dario-piotrowicz

src/node_dotenv.cc

@@ -107,13 +107,28 @@ Local<Object> Dotenv::ToObject(Environment* env) const {
 
 std::string_view trim_spaces(std::string_view input) {
   if (input.empty()) return "";
-  if (input.front() == ' ') {
-    input.remove_prefix(input.find_first_not_of(' '));
+
+  size_t input_size = input.size();
+
+  size_t pos_start = 0;
+  while (pos_start < input_size) {
+    const char ch = input.at(pos_start);
+    if (ch != ' ' && ch != '\t' && ch != '\n') {
+      break;
+    };
+    pos_start++;
   }
-  if (!input.empty() && input.back() == ' ') {
-    input = input.substr(0, input.find_last_not_of(' ') + 1);
+
+  size_t pos_end = input_size - 1;
+  while (pos_end > pos_start) {
+    const char ch = input.at(pos_end);
+    if (ch != ' ' && ch != '\t' && ch != '\n') {
+      break;
+    };
+    pos_end--;
   }
-  return input;
+
+  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

@@ -137,6 +137,29 @@ describe('.env supports edge cases', () => {
     assert.strictEqual(child.code, 0);
   });
 
+  it('lines containing only spaces (and tabs) should not effect values defined in the next lines', async () => {
+    // Ref: https://github.com/nodejs/node/issues/56686
+    const code = `
+      process.loadEnvFile('./lines-with-only-spaces.env');
+      console.log(\`EMPTY_LINE: "\${process.env.EMPTY_LINE}"\`);
+      console.log(\`SPACES_LINE: "\${process.env.SPACES_LINE}"\`);
+      console.log(\`TABS_LINE: "\${process.env.TABS_LINE}"\`);
+      console.log(\`SPACES_TABS_LINE: "\${process.env.SPACES_TABS_LINE}"\`);
+    `.trim();
+    const child = await common.spawnPromisified(
+      process.execPath,
+      [ '--eval', code ],
+      { cwd: fixtures.path('dotenv') },
+    );
+    const lines = child.stdout.toString().split('\n').filter(Boolean);
+    assert.deepStrictEqual(lines, [
+      '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"',
+    ]);
+  });
+
   it('should handle when --env-file is passed along with --', async () => {
     const child = await common.spawnPromisified(
       process.execPath,