Issue #20416 has been updated by nobu (Nobuyoshi Nakada). The subject should be "IO#read doesn't change buffer encoding unless `maxlen = nil`"? Since `IO#read` with `maxlen` is byte-oriented operation, there is not an encoding to be set from that `IO`. ---------------------------------------- Bug #20416: IO#read doesn't preserve buffer encoding if `maxlen = nil` https://bugs.ruby-lang.org/issues/20416#change-108604 * Author: andrykonchin (Andrew Konchin) * Status: Open * ruby -v: 3.3.0 * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- `IO#read(nil, buffer)` doesn't change buffer's encoding, but it does when `maxlen` parameter is specified: ```ruby buffer = "".encode(Encoding::ISO_8859_1) p File.open("test.rb").read(1000, buffer).encoding # => #<Encoding:ISO-8859-1> buffer = "".encode(Encoding::ISO_8859_1) p File.open("test.rb").read(nil, buffer).encoding # => #<Encoding:UTF-8> ``` I would expect changing buffer encoding in all the cases. -- https://bugs.ruby-lang.org/