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fix JSON decoder error checking for UTF16 / surrogate parsing panic #7721

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Merged
merged 2 commits into from
Jun 22, 2025
Merged

fix JSON decoder error checking for UTF16 / surrogate parsing panic #7721

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4c756d0
fix surrogate parsing panic
nicklan Jun 20, 2025
30170ce
fmt
nicklan Jun 20, 2025
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24 changes: 21 additions & 3 deletions arrow-json/src/reader/tape.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -705,9 +705,16 @@ fn err(b: u8, ctx: &str) -> ArrowError {

/// Creates a character from an UTF-16 surrogate pair
fn char_from_surrogate_pair(low: u16, high: u16) -> Result<char, ArrowError> {
let n = (((high - 0xD800) as u32) << 10) | ((low - 0xDC00) as u32 + 0x1_0000);
char::from_u32(n)
.ok_or_else(|| ArrowError::JsonError(format!("Invalid UTF-16 surrogate pair {n}")))
match (low, high) {
(0xDC00..=0xDFFF, 0xD800..=0xDBFF) => {
let n = (((high - 0xD800) as u32) << 10) | ((low - 0xDC00) as u32 + 0x1_0000);
char::from_u32(n)
.ok_or_else(|| ArrowError::JsonError(format!("Invalid UTF-16 surrogate pair {n}")))
}
_ => Err(ArrowError::JsonError(format!(
"Invalid UTF-16 surrogate pair. High: {high:#02X}, Low: {low:#02X}"
))),
}
Comment on lines +708 to +717
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@scovich scovich Jun 20, 2025

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Would a pair of checked_sub work?

Suggested change
match (low, high) {
(0xDC00..=0xDFFF, 0xD800..=0xDBFF) => {
let n = (((high - 0xD800) as u32) << 10) | ((low - 0xDC00) as u32 + 0x1_0000);
char::from_u32(n)
.ok_or_else(|| ArrowError::JsonError(format!("Invalid UTF-16 surrogate pair {n}")))
}
_ => Err(ArrowError::JsonError(format!(
"Invalid UTF-16 surrogate pair. High: {high:#02X}, Low: {low:#02X}"
))),
}
char_from_surrogate_pair_opt(low, high).ok_or_else(|| {
ArrowError::JsonError(format!("Invalid UTF-16 surrogate pair: {lo:#02X}, {high:#02X}"))
})
}
fn char_from_surrogate_pair_opt(low: u16, high: u16) -> Option<char> {
let high = high.checked_sub(0xD800)? as u32;
let low = low.checked_sub(0xDC00)? as u32;
char::from_u32((high << 10) | (low + 0x1_0000))

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@nicklan nicklan Jun 20, 2025 •
edited
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I did consider this, and it does have the benefit of being more succinct. I opted for the range check because if one of the arguments was too high the checked sub would not catch it and I wasn't able to convince myself that only valid inputs would allow char::from_u32 to succeed.

I could dig more into the calling layers to check if that's prevented there, but it still felt like more of a foot-gun than the simple range check.

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@alamb alamb Jun 21, 2025

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For what it is worth, I think the current way this is encoded is quite understandable and will generate clear error messages. I double checked and it conforms to my reading of UTF-16 on https://en.wikipedia.org/wiki/UTF-16

}

/// Writes `c` as UTF-8 to `out`
Expand Down Expand Up @@ -951,4 +958,15 @@ mod tests {
let err = decoder.finish().unwrap_err().to_string();
assert_eq!(err, "Json error: Encountered truncated UTF-8 sequence");
}

#[test]
fn test_invalid_surrogates() {
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@alamb alamb Jun 21, 2025

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I verified this test panic's on main:

attempt to subtract with overflow
thread 'reader::tape::tests::test_invalid_surrogates' panicked at arrow-json/src/reader/tape.rs:708:49:
attempt to subtract with overflow

And the test actually fails to detect an error in release mode


---- reader::tape::tests::test_invalid_surrogates stdout ----

thread 'reader::tape::tests::test_invalid_surrogates' panicked at arrow-json/src/reader/tape.rs:959:9:
assertion failed: res.is_err()
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

let mut decoder = TapeDecoder::new(16, 2);
let res = decoder.decode(b"{\"test\": \"\\ud800\\ud801\"}");
assert!(res.is_err());

let mut decoder = TapeDecoder::new(16, 2);
let res = decoder.decode(b"{\"test\": \"\\udc00\\udc01\"}");
assert!(res.is_err());
}
}
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