fix(csv-parse): trim Buffer fields without decoding

packages/csv-parse/lib/api/index.js

@@ -718,7 +718,25 @@ const transform = function (original_options = {}) {
       }
       let field = this.state.field.toString(encoding);
       if (rtrim === true && wasQuoting === false) {
-        field = field.trimRight();
+        if (encoding === null) {
+          let end = field.length;
+          trimming: while (end > 0) {
+            for (const trimChar of this.state.timchars) {
+              const start = end - trimChar.length;
+              if (
+                start >= 0 &&
+                field.compare(trimChar, 0, trimChar.length, start, end) === 0
+              ) {
+                end = start;
+                continue trimming;
+              }
+            }
+            break;
+          }
+          field = field.subarray(0, end);
+        } else {
+          field = field.trimRight();
+        }
       }
       if (cast === true) {
         const [err, f] = this.__cast(field);

packages/csv-parse/test/option.rtrim.buffer.js

@@ -0,0 +1,43 @@
+import assert from "node:assert/strict";
+import { parse } from "../lib/index.js";
+import { parse as parseSync } from "../lib/sync.js";
+
+describe("Option `rtrim` with Buffer fields", function () {
+  for (const encoding of [null, false]) {
+    for (const trimOption of ["rtrim", "trim"]) {
+      it(`preserves bytes with encoding=${encoding} and ${trimOption}`, async function () {
+        const binary = Buffer.from([0xff, 0xfe, 0xa0]);
+        const input = Buffer.concat([
+          Buffer.from(' \ta\u2003 ," b "\n'),
+          binary,
+          Buffer.from("\u00a0, \t"),
+        ]);
+        const options = { encoding, [trimOption]: true };
+        const expected = [
+          [
+            Buffer.from(trimOption === "trim" ? "a" : " \ta"),
+            Buffer.from(" b "),
+          ],
+          [binary, Buffer.alloc(0)],
+        ];
+        assert.deepEqual(parseSync(input, options), expected);
+        const records = await new Promise((resolve, reject) => {
+          const parser = parse(options, (error, result) => {
+            if (error) reject(error);
+            else resolve(result);
+          });
+          for (const byte of input) parser.write(Buffer.from([byte]));
+          parser.end();
+        });
+        assert.deepEqual(records, expected);
+      });
+    }
+
+    it(`preserves quoted whitespace with encoding=${encoding}`, function () {
+      assert.deepEqual(
+        parseSync('" a\u2003"," \t "', { encoding, rtrim: true }),
+        [[Buffer.from(" a\u2003"), Buffer.from(" \t ")]],
+      );
+    });
+  }
+});