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mruby-sprintf: reject a %c argument with no UTF-8 encoding #7113

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Merged
matz merged 1 commit into from
Aug 12, 2026
Merged

mruby-sprintf: reject a %c argument with no UTF-8 encoding #7113

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7 changes: 6 additions & 1 deletion mrbgems/mruby-sprintf/src/sprintf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -536,8 +536,13 @@ mrb_str_format(mrb_state *mrb, mrb_int argc, const mrb_value *argv, mrb_value fm
/* Integer: encode directly to stack buffer (no allocation) */
mrb_int code = mrb_integer(val);
#ifdef MRB_UTF8_STRING
/* mrb_utf8_to_buf() writes nothing for a value it cannot encode,
and takes a uint32_t, which wraps a value outside the Unicode
range into a codepoint. Either way there is no byte to write. */
if (code < 0 || 0x10FFFF < code) {
mrb_raise(mrb, E_ARGUMENT_ERROR, "invalid character");
}
clen = (int)mrb_utf8_to_buf(cbuf, (uint32_t)code);
if (clen == 0) clen = 1; /* invalid codepoint: write single byte */
#else
cbuf[0] = (char)(code & 0xff);
clen = 1;
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15 changes: 15 additions & 0 deletions mrbgems/mruby-sprintf/test/sprintf.rb
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Expand Up @@ -130,3 +130,18 @@ def mutator.to_s
assert_equal "ok", result[0, 2]
assert_equal "B" * 200, result[2..]
end

assert('sprintf("%c") with an integer that has no UTF-8 encoding') do
skip unless __ENCODING__ == "UTF-8"
# Nothing was written to the encoder's buffer for these, and %c used to emit
# whatever byte the stack happened to hold there.
assert_raise(ArgumentError) { sprintf("%c", 0x110000) }
assert_raise(ArgumentError) { sprintf("%c", -1) }
# The encoder takes a uint32_t, so a value that wraps into the Unicode range
# must not come out as the character it wraps to. The shift is computed at
# run time because the constant folder would reject the literal on a build
# with a 32-bit mrb_int and no bigint, where there is nothing to test.
shift = 32
wrapping = ((1 << shift) + 0x41) rescue nil
assert_raise(ArgumentError) { sprintf("%c", wrapping) } if wrapping.is_a?(Integer)
end
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