C API, wrong uuid value from vector

[barsdeveloper]

TLDR: When reading a uuid it will have the first bit swapped so that for example initial 80 becomes 00, 11 becomes 91

Hello, I am trying to read a uuid from a vector

let data = *(data as *const duckdb_hugeint).add(row);
println!("upper: {:#x}, lower: {:#x}", data.upper, data.lower);
let uuid = Uuid::from_u64_pair(data.upper as u64, data.lower);
println!("uuid: {}", uuid);

Data is:

let chunk = duckdb_stream_fetch_chunk(*result);
let vector = duckdb_data_chunk_get_vector(*chunk, i);
let data = duckdb_vector_get_data(vector);

You get the idea and I think the way I get it is not the problem. I insert a UUID column with value 550e8400-e29b-41d4-a716-446655440000 and I verify (using duckdb -ui) that my order_id is actually 550e8400-e29b-41d4-a716-446655440000.

The problem is that the first snippet of code prints

upper: 0xd50e8400e29b41d4, lower: 0xa716446655440000
uuid: d50e8400-e29b-41d4-a716-446655440000

If we compare, the value received is one bit off (D = 1101, 5 = 0101)

Read:     d50e8400-e29b-41d4-a716-446655440000
Expected: 550e8400-e29b-41d4-a716-446655440000

I don't understand why would that be the case. I also tried reading duckdb_uhugeint instead of duckdb_hugeint (this is what the documentation says to be the storage type: https://duckdb.org/docs/stable/sql/data_types/numeric.html#universally-unique-identifiers-uuids, also why? A uuid should use unsigned integer). Reading unsigned produces the same problem.

[mlafeldt]

Hey @barsdeveloper,

I think this problem was fixed by @Mytherin in duckdb/duckdb#17612, which shipped as part of duckdb-rs 1.3.1 last week.

I still wonder though whether

• FromUHugeint() should apply the bit flip after conversion
• ToUHugeint() should undo the bit flip before conversion

https://github.com/duckdb/duckdb/blob/v1.3.1/src/common/types/uuid.cpp#L104-L124

🤔