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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"diff panics (broken-pipe unwrap) when its stdout is closed early","articleBody":"## Summary\n\nWhen `diff`'s standard output is a pipe whose reader closes early (e.g. `diff … | head`), uutils `diff` aborts with a panic (exit 134, core dump)\ninstead of dying cleanly to `SIGPIPE` like GNU (exit 141). The output is written with a bare `.unwrap()` on the `write_all`/`push_output` result; the `BrokenPipe` error is unwrapped and, under `panic=\"abort\"`, aborts the process. This affects every output mode: the normal/context/unified/ed path writes the buffered result in `src/diff.rs:94`, and the side-by-side (`-y`) path writes each line in `src/side_diff.rs:353-356`.\n\n## Steps to reproduce\n\n```console\n$ seq 1 100000 \u003e b1; seq 1 100000 | sed 's/5/X/' \u003e b2\n$ diffutils diff b1 b2 | head -1\nthread 'main' panicked at src/diff.rs:94:41:\ncalled `Result::unwrap()` on an `Err` value: Os { code: 32, kind: BrokenPipe, message: \"Broken pipe\" }\n$ echo \"${PIPESTATUS[0]}\"\n134\n```\n\nSide-by-side mode hits the sibling site `src/side_diff.rs:353`:\n\n```console\n$ diffutils diff -y b1 b2 | head -1\nthread 'main' panicked at src/side_diff.rs:353:87:\ncalled `Result::unwrap()` on an `Err` value: Os { code: 32, kind: BrokenPipe, message: \"Broken pipe\" }\n$ echo \"${PIPESTATUS[0]}\"\n134\n```\n\n## Expected behavior\n\nMatch GNU: a closed output pipe terminates the program via `SIGPIPE` (exit 141) with no error message and no core dump.\n\n```console\n$ /usr/bin/diff b1 b2 | head -1\n1c1\n$ echo \"${PIPESTATUS[0]}\"\n141\n$ /usr/bin/diff -y b1 b2 | head -1\n1                            \u003c      1\n$ echo \"${PIPESTATUS[0]}\"\n141\n```\n\n## Root cause\n\nThe full diff output (normal/context/unified/ed) is buffered and written once:\n\n```rust\n// src/diff.rs:94\nio::stdout().write_all(\u0026result).unwrap();\n```\n\nSide-by-side writes each line straight to the locked stdout and unwraps every\nwrite:\n\n```rust\n// src/side_diff.rs:353-356\npush_output(...).unwrap();   // and the sibling unwraps at :354, :356\n```\n\nAny `write_all`/`push_output` error — `BrokenPipe` in the common pipe-closed case — is unwrapped and aborts. \n\n_Found by our static analysis tooling._","author":{"url":"https://github.com/leeewee","@type":"Person","name":"leeewee"},"datePublished":"2026-06-10T04:50:40.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/244/diffutils/issues/244"}