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Report BON8 input that ends after a UTF-8 lead byte as truncated (#5677)

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A lead byte (0xC2..0xF7) inside a string begins either another character
(if a continuation byte follows) or an integer (otherwise). When the input
ended right after the lead byte, the reader took the missing byte as "not
a continuation byte", ended the string before the lead byte, and treated
the lead byte as the start of the next value. With strict=false, a message
cut off there was therefore read as a shorter value: the 11 bytes of
"😀😀é" cut after 9 bytes gave "😀😀", and ["aé"] cut after 3 of its 5
bytes gave ["a"]. With strict=true, the input was rejected with a
misleading message ("expected end of input"), or, for a key, with
parse_error.112 instead of 110.

Either reading of the lead byte leaves the message incomplete: a string at
the end of a message must be terminated by 0xFF, so the lead byte cannot
belong to a following message. Report parse_error.110 (unexpected end of
input) for strings and keys, as the comment on get_bon8_string() already
requires and as the reference decoder (HikoGUI) does.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-10-02 07:47:50 +02:00
committed by GitHub
parent 11e75a5428
commit 6aec1a085f
3 changed files with 63 additions and 0 deletions
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include/nlohmann/detail/input/binary_reader.hpp
+11
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@@ -3688,6 +3688,11 @@ class binary_reader
if (0xC2 <= byte && byte <= 0xF7)
{
const auto second = get_bon8();
if (second == char_traits<char_type>::eof())
{
// the input ends inside a character or an integer
return unexpect_eof(input_format_t::bon8, "key");
}
unget_bon8(second);
if (is_bon8_continuation(second))
{
@@ -3786,6 +3791,12 @@ class binary_reader
// a lead byte ends the string if no continuation byte follows: it
// is then the first byte of an integer
const auto second = get_bon8();
if (second == char_traits<char_type>::eof())
{
// the input ends inside a character or an integer: either
// way, the message is incomplete
return unexpect_eof(input_format_t::bon8, "string");
}
if (!is_bon8_continuation(second))
{
unget_bon8(second);