From 7ca49a10420587452ffd63c818dc10d60387fc33 Mon Sep 17 00:00:00 2001
From: Zihan Dai <dzh1436286758@gmail.com>
Date: Fri, 2 Oct 2026 18:02:33 +1000
Subject: [PATCH] fix(csv-parse): preserve data when trimming single-byte
 encodings

---
 packages/csv-parse/lib/api/init_state.js | 14 +++--
 packages/csv-parse/test/option.trim.ts   | 65 ++++++++++++++++++++++++
 2 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/packages/csv-parse/lib/api/init_state.js b/packages/csv-parse/lib/api/init_state.js
index 50b9e025c..f53d41874 100644
--- a/packages/csv-parse/lib/api/init_state.js
+++ b/packages/csv-parse/lib/api/init_state.js
@@ -6,9 +6,9 @@ const init_state = function (options) {
   // https://tc39.es/ecma262/#sec-white-space
   // https://tc39.es/ecma262/#sec-line-terminators
   //
-  // Codepoints unrepresentable in the target encoding are dropped: Node's
-  // Buffer substitutes them with `?` (0x3F), and including those would cause
-  // literal `?` bytes in the input to be trimmed under `latin1`/`ascii`.
+  // Drop codepoints that do not round-trip through the target encoding.
+  // Single-byte encodings truncate them and could otherwise trim ordinary
+  // input bytes, e.g. U+205F becomes `_` under `latin1` and `ascii`.
   const timchars = [
     // Basic Latin
     0x0020, // [Space](https://www.fileformat.info/info/unicode/char/0020/index.htm)
@@ -40,11 +40,9 @@ const init_state = function (options) {
     0x3000, // [IDEOGRAPHIC SPACE](https://www.fileformat.info/info/unicode/char/3000/index.htm)
     0xfeff, // [ZERO WIDTH NO-BREAK SPACE (BOM)](https://www.fileformat.info/info/unicode/char/feff/index.htm)
   ].reduce((acc, codepoint) => {
-    const encoded = Buffer.from(
-      String.fromCharCode(codepoint),
-      options.encoding,
-    );
-    if (codepoint !== 0x3f && encoded.length === 1 && encoded[0] === 0x3f) {
+    const character = String.fromCharCode(codepoint);
+    const encoded = Buffer.from(character, options.encoding);
+    if (encoded.toString(options.encoding || "utf8") !== character) {
       return acc;
     }
     acc.push(encoded);
diff --git a/packages/csv-parse/test/option.trim.ts b/packages/csv-parse/test/option.trim.ts
index 8975f8100..a04727d09 100644
--- a/packages/csv-parse/test/option.trim.ts
+++ b/packages/csv-parse/test/option.trim.ts
@@ -1,6 +1,7 @@
 import "should";
 import dedent from "dedent";
 import { parse } from "../lib/index.js";
+import { parse as parseSync } from "../lib/sync.js";
 
 describe("Option `trim`", function () {
   it("validation", function () {
@@ -385,4 +386,68 @@ describe("Option `trim`", function () {
       parser.end();
     });
   });
+  describe("single-byte encodings", function () {
+    for (const encoding of ["ascii", "latin1", "binary"] as const) {
+      for (const option of ["trim", "ltrim"] as const) {
+        it(`preserves field data with ${option} and ${encoding}`, function () {
+          const input = " _alice_, /home/user, (draft), ?value?";
+          parseSync(Buffer.from(input, encoding), {
+            encoding,
+            [option]: true,
+          }).should.eql([["_alice_", "/home/user", "(draft)", "?value?"]]);
+        });
+
+        it(`preserves column names with ${option} and ${encoding}`, function () {
+          const input = " _id, /path, (status)\n _alice, /home, (active)";
+          parseSync(Buffer.from(input, encoding), {
+            encoding,
+            columns: true,
+            [option]: true,
+          }).should.eql([
+            { _id: "_alice", "/path": "/home", "(status)": "(active)" },
+          ]);
+        });
+
+        it(`preserves data across writes with ${option} and ${encoding}`, function (next) {
+          const input = Buffer.from(" _alice_, /home, (draft)", encoding);
+          const parser = parse({ encoding, [option]: true }, (err, records) => {
+            if (err) return next(err);
+            records.should.eql([["_alice_", "/home", "(draft)"]]);
+            next();
+          });
+          for (let i = 0; i < input.length; i++) {
+            parser.write(input.subarray(i, i + 1));
+          }
+          parser.end();
+        });
+      }
+
+      it(`trims representable whitespace with ${encoding}`, function () {
+        const whitespace =
+          encoding === "ascii" ? " \t\r\n\v\f" : " \t\r\n\v\f\u00a0";
+        const input = `${whitespace}_alice_${whitespace},${whitespace}/home${whitespace}`;
+        parseSync(Buffer.from(input, encoding), {
+          encoding,
+          trim: true,
+          record_delimiter: "|",
+        }).should.eql([["_alice_", "/home"]]);
+      });
+
+      it(`preserves quoted whitespace and data with ${encoding}`, function () {
+        parseSync(Buffer.from(' " _alice_ ", " /home "', encoding), {
+          encoding,
+          trim: true,
+        }).should.eql([[" _alice_ ", " /home "]]);
+      });
+
+      it(`rejects non-whitespace after closing quotes with ${encoding}`, function () {
+        (() => {
+          parseSync(Buffer.from('"value" _', encoding), {
+            encoding,
+            trim: true,
+          });
+        }).should.throw({ code: "CSV_NON_TRIMABLE_CHAR_AFTER_CLOSING_QUOTE" });
+      });
+    }
+  });
 });