nicklan commented on code in PR #7721:
URL: https://github.com/apache/arrow-rs/pull/7721#discussion_r2159686914
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arrow-json/src/reader/tape.rs:
##########
@@ -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}"
+ ))),
+ }
Review Comment:
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 that the simple range check.
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