René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"diff panics (`into_string().unwrap()`) on a non-UTF-8 argument ending in `--width=N`","articleBody":"## Steps to reproduce\n\n```console\n$ printf 'a\\nb\\nc\\n' \u003e A; printf 'a\\nX\\nc\\n' \u003e B\n$ diffutils diff $'\\xff--width=5' A B\nthread 'main' panicked at src/params.rs:116:45:\ncalled `Result::unwrap()` on an `Err` value: \"\\xFF--width=5\"\n$ echo $?\n134\n```\n\n`diff` aborts (panic, exit 134) when given a non-UTF-8 argument whose lossy form ends in `--width=\u003cdigits\u003e` — e.g. an argument with a leading invalid byte like `$'\\xff--width=5'`.\n\n## Expected behavior\n\nMatch GNU: the unrecognized argument is a file operand; with three operands diff reports the extra operand and exits 2.\n\n```console\n$ /usr/bin/diff $'\\xff--width=5' A B\ndiff: extra operand 'B'\n$ echo $?\n2\n```\n\n## Root cause\n\nThe `--width` regex lacks a start anchor, unlike the sibling `--tabsize` one:\n\n```rust\n// src/params.rs:62-63\nlet tabsize_re = Regex::new(r\"^--tabsize=(?\u003cnum\u003e\\d+)$\").unwrap();   // anchored — safe\nlet width_re   = Regex::new(r\"--width=(?P\u003clong\u003e\\d+)$\").unwrap();    // no leading ^\n\n// src/params.rs:115-116\nif width_re.is_match(param.to_string_lossy().as_ref()) {   // matches lossy form\n    let param = param.into_string().unwrap();              // line 116: Err on non-UTF-8\n```\n\n`to_string_lossy()` maps invalid bytes to `U+FFFD`, so a non-UTF-8 argument whose tail is `--width=N` still matches; `into_string()` then fails on the real bytes.\nFix: anchor the regex at the start (`^--width=…$`, matching `tabsize_re`), and/or match on the bytes / avoid `into_string().unwrap()` so a non-UTF-8 argument falls through to the operand path. (The unanchored regex also makes `diff xyz--width=5` silently accept a width option instead of treating it as a filename — same root cause, non-panic symptom.)\n\n_Found by our static analysis tooling._","author":{"url":"https://github.com/leeewee","@type":"Person","name":"leeewee"},"datePublished":"2026-06-16T08:39:37.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/247/diffutils/issues/247"}