I found an odd situation, when using IO.copy_stream with a File writer quack class, where the data passed to #write somehow ends overwritten, despite the instance being duped.
class ProcIO
def initialize(block)
@block = block
end
# Implementation the IO write protocol, which yield the given chunk to +@block+.
def write(data)
@block.call(data.dup)
data.bytesize
end
end
rng = Random.new(42)
body = Tempfile.new("ruby-bug", binmode: true)
body.write(rng.bytes(16_385))
body.rewind
payload = []
block = ->(data){ payload << data.dup }
IO.copy_stream(body, ProcIO.new(block))
body.rewind
if payload.join != body.read
puts "it's a bug"
end
if you use the debugger, you'll see that the first yielded chunk has the correct bytes when yielded the first time, but when the second 1 byte chunk is yielded (IO.copy_stream reads in chunks of 16384 bytes), the first chunk string value suddenly changes. This should not happen, as the first yielded chunk was a string duped from the string yielded by IO.copy_stream (which is expected to be a buffer).
Backport changed from 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.1: REQUIRED, 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED
Thank you for the report. This is definitely a bug. My testing shows it affects all versions of Ruby, at least back to 1.9.3. I submitted a PR to fix this issue: https://github.com/ruby/ruby/pull/12771
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Updated by jeremyevans (Jeremy Evans) 
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