Function build_segment 

fn build_segment(
    span: &SpanContext,
    service: &str,
    instance: &str,
    method: &str,
    path: &str,
    status: u16,
    end_ms: u64,
) -> Value

Builds the SkyWalking trace segment JSON for a finished span (pure; does no I/O). A single Entry/Http span mirroring the OAP HTTP segment protocol.