Function extract_field

nodedb-query/src/msgpack_scan/field.rs:24–53

Locate the value for `field` in a MessagePack map starting at `offset`. Returns the byte range `(value_start, value_end)` of the matched value. Scans map keys sequentially — O(n) in number of keys. For documents with many fields queried repeatedly, see structural indexing (Phase 8). # Returns - `Some((start, end))` — the value's byte range (use offset `start` with readers) - `None` — field not f

(buf: &[u8], offset: usize, field: &str)

/// - `Some((start, end))` — the value's byte range (use offset `start` with readers)
/// - `None` — field not found, or buffer is not a valid map
pub fn extract_field(buf: &[u8], offset: usize, field: &str) -> Option<FieldRange> {
    let (count, mut pos) = map_header(buf, offset)?;
    let field_bytes = field.as_bytes();

    for _ in 0..count {
        // Read key string bounds
        let key_match = match str_bounds(buf, pos) {
            Some((start, len)) => buf
                .get(start..start + len)
                .map(|kb| kb == field_bytes)
                .unwrap_or(false),
            None => false,
        };

        // Skip past the key
        pos = skip_value(buf, pos)?;

        if key_match {
            // Found — return the value's byte range
            let value_start = pos;
            let value_end = skip_value(buf, pos)?;
            return Some((value_start, value_end));
        }

        // Skip the value
        pos = skip_value(buf, pos)?;
    }

    None
}

/// Extract a value at a nested path (e.g., `["address", "city"]`).
/// Each segment must be a string key in a nested map.