Function parse_batch_header 

pub fn parse_batch_header(header: &str) -> Result<(String, usize), String>

What: One successful batch header: the object ID and its byte length. Why: parseBatchHeader: <oid> blob <size>, exactly three space-separated fields, a blob, and a canonical decimal size.

In TS you’d write (pseudocode):

function parseBatchHeader({ header }): { oid: string; size: number };