From: "ioquatix (Samuel Williams) via ruby-core" <ruby-core@...>
Date: 2022-12-24T12:13:48+00:00
Subject: [ruby-core:111416] [Ruby master Bug#19252] IO::Buffer.pread last argument is always ignored?

Issue #19252 has been updated by ioquatix (Samuel Williams).

Status changed from Open to Closed

Merged.

----------------------------------------
Bug #19252: IO::Buffer.pread last argument is always ignored?
https://bugs.ruby-lang.org/issues/19252#change-100788

* Author: zverok (Victor Shepelev)
* Status: Closed
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
I am trying to document new `IO::Buffer#pread` and `#pwrite` methods.

According to what I can guess from code and tests, this code:
```ruby
IO::Buffer.for('teststring') do |buffer| 
  buffer.pread(File.open('/dev/urandom', 'rb'), 0, 2, 3)
  p buffer.get_string 
end
```
...is expected to read **2** chars from `/dev/urandom`, starting from **0**th char, and write it to buffer starting from its **3**rd byte.
Actual output:
```
"F\x94ststring"
```
E.g. two first chars of the buffer are replaced.

Am I missing something, or is it a legitimate bug?..

UPD: Seems the same for `pwrite`:
```ruby
IO::Buffer.for('1234567').pwrite(File.open('tmp/buf.txt', 'wb'), 0, 2, 3) # expected to write "45" to file
`cat tmp/buf.txt`
# => "12"
```



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