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Fix Zlib::GzipReader#gets with a limit shorter than the separator #155

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Fix Zlib::GzipReader#gets with a limit shorter than the separator #155

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4 changes: 4 additions & 0 deletions ext/zlib/zlib.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4447,6 +4447,10 @@ gzreader_gets(int argc, VALUE *argv, VALUE obj)
n = rslen;
for (;;) {
rb_len_t filled;
if (limit > 0 && limit < rslen) {

@hsbt hsbt Oct 24, 2026

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This misses the case where fewer than rslen bytes remain at EOF. The early return in the while loop above reads rslen bytes without the limit, so gets("xyz", 1) on Zlib.gzip("ab") returns "ab" while StringIO returns "a".

n = limit;
break;
}
if (n > ZSTREAM_BUF_FILLED(&gz->z)) {
if (ZSTREAM_IS_FINISHED(&gz->z)) break;
gzfile_read_more(gz, Qnil);
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8 changes: 8 additions & 0 deletions test/zlib/test_zlib.rb
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Expand Up @@ -1306,6 +1306,14 @@ def test_gets2
}
end

def test_gets_limit_shorter_than_separator
gz = Zlib::GzipReader.new(StringIO.new(Zlib.gzip("abcd")))
assert_equal("a", gz.gets("xyz", 1))
assert_equal("bc", gz.gets("xyz", 2))
assert_equal("d", gz.gets("xyz", 2))
assert_nil(gz.gets("xyz", 2))
end

def test_readline
Tempfile.create("test_zlib_gzip_reader_readline") {|t|
t.close
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