From: "rhenium (Kazuki Yamaguchi) via ruby-core" <ruby-core@...>
Date: 2026-09-22T16:22:12+00:00
Subject: [ruby-core:126829] [Ruby Bug#22342] IO#gets can ignore the limit argument in some edge cases

Issue #22342 has been updated by rhenium (Kazuki Yamaguchi).


I've opened a GitHub PR for this: https://github.com/ruby/ruby/pull/18961

----------------------------------------
Bug #22342: IO#gets can ignore the limit argument in some edge cases
https://bugs.ruby-lang.org/issues/22342#change-119140

* Author: rhenium (Kazuki Yamaguchi)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: REQUIRED, 4.0: REQUIRED
----------------------------------------
`io.gets(rs, limit)` ignores the `limit` value and reads until `rs` is found or EOF, if the `limit`-th byte of the stream matches `rs`'s last byte and:

1. The potential start of the record separator, the `limit-rs.bytesize`-th byte of the stream is not at a character boundary

```ruby
str = "\x83\\xxx".force_encoding("Windows-31J") # "���xxx".encode("Windows-31J")
IO.pipe("Windows-31J"){|r,w|w.write(str); w.close_write; p r.gets("\\", 2); p r.read}

# Expected:
"\x{835C}"
"xxx"

# Actual:
"\x{835C}xxx"
""
```

2. Or, `limit < rs.bytesize`

```ruby
IO.pipe{|r,w|w.write("a:bc"); w.close_write; p r.gets(":::", 2); p r.read}

# Expected:
"a:"
"bc"

# Actual:
"a:bc"
""
```

This behavior appears to date back to Ruby 1.9.x.



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