You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tracing.rs
    path of file: ./repos/salvo/crates/otel/src
    
    the code of the file until where you have to start completion: use headers03::{HeaderMap, HeaderName, HeaderValue};
use opentelemetry::trace::{FutureExt, Span, SpanKind, TraceContextExt, Tracer};
use opentelemetry::{global, Context, KeyValue};
use opentelemetry_http::HeaderExtractor;
use opentelemetry_semantic_conventions::{resource, trace};
use salvo_core::http::headers::{self, HeaderMapExt};
use salvo_core::prelude::*;

/// Middleware for tracing with OpenTelemetry.
pub struct Tracing<T> {
    tracer: T,
}

impl<T> Tracing<T> {
    /// Create `Tracing` middleware with `tracer`.
    pub fn new(tracer: T) -> Self {
        Self { tracer }
    }
}

#[async_trait]
impl<T> Handler for Tracing<T>
where
    T: Tracer + Sync + Send + 'static,
    T::Span: Send + Sync + 'static
    
    async fn handle(&self, req: &mut Request, depot: &mut Depot, res: &mut Response, ctrl: &mut FlowCtrl) {
        let remote_addr = req.remote_addr().to_string();

        //TODO: Will remove after opentelemetry_http updated
        let mut headers = HeaderMap::with_capacity(req.headers().len());
        headers.extend(req.headers().into_iter().map(|(name, value)| {
            let name = HeaderName::from_bytes(name.as_ref()).expect("Invalid header name");
            let value = HeaderValue::from_bytes(value.as_ref()).expect("Invalid header value");
            (name, value)
        }));

        let parent_cx = global::get_text_map_propagator(|propagator| propagator.extract(&HeaderExtractor(&headers)));

        let mut attributes = Vec::new();
        attributes.push(KeyValue::new(resource::TELEMETRY_SDK_NAME, env!("CARGO_CRATE_NAME")));
        attributes.push(KeyValue::new(
            resource::TELEMETRY_SDK_VERSION,
            env!("CARGO_PKG_VERSION"),
        ));
        attributes.push(KeyValue::new(resource::TELEMETRY_SDK_LANGUAGE, "rust"));
        attributes.push(KeyValue::new(trace::HTTP_REQUEST_METHOD, req.method().to_string()));
        attributes.push(KeyValue::new(trace::URL_FULL, req.uri().to_string()));
        attributes.push(KeyValue::new(trace::CLIENT_ADDRESS, remote_addr));
        attributes.push(KeyValue::new(
            trace::NETWORK_PROTOCOL_VERSION,
            format!("{:?}", req.version()),
        ));
        let mut span = self
            .tracer
            .span_builder(format!("{} {}", req.method(), req.uri()))
            .with_kind(SpanKind::Server)
            .with_attributes(attributes)
            .start_with_context(&self.tracer, &parent_cx);

        span.add_event("request.started".to_string(), vec![]);

        async move {
            ctrl.call_next(req, depot, res).await;
            let cx = Context::current();
            let span = cx.span();

            let status = res.status_code.unwrap_or(StatusCode::NOT_FOUND);
            let event = if status.is_client_error() || status.is_server_error() {
                "request.failure"
            } else {
                "request.success"
            };
            span.add_event(event.to_string(), vec![]);
            span.set_attribute(KeyValue::new(trace::HTTP_RESPONSE_STATUS_CODE, status.as_u16() as i64));
            if let Some(content_length) = res.headers().typed_get::<headers::ContentLength>() {
                span.set_attribute(KeyValue::new(trace::HTTP_RESPONSE_BODY_SIZE, content_length.0 as i64));
            }
        }
        .with_context(Context::current_with_span(span))
        .await
    }