witchcraft-server 3.12.0

// Copyright 2022 Palantir Technologies, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use crate::service::{Layer, Service};
use http::header::HeaderName;
use http::{HeaderValue, Response};

#[allow(clippy::declare_interior_mutable_const)]
const TRACE_ID: HeaderName = HeaderName::from_static("x-b3-traceid");

/// A layer which adds an `X-B3-TraceId` header to responses.
///
/// It must be installed after trace propagation.
pub struct TraceIdHeaderLayer;

impl<S> Layer<S> for TraceIdHeaderLayer {
    type Service = TraceIdHeaderService<S>;

    fn layer(self, inner: S) -> Self::Service {
        TraceIdHeaderService { inner }
    }
}

pub struct TraceIdHeaderService<S> {
    inner: S,
}

impl<S, R, B> Service<R> for TraceIdHeaderService<S>
where
    S: Service<R, Response = Response<B>> + Sync,
    R: Send,
{
    type Response = S::Response;

    async fn call(&self, req: R) -> Self::Response {
        let mut response = self.inner.call(req).await;
        let context = zipkin::current().expect("zipkin trace not initialized");
        response.headers_mut().insert(
            TRACE_ID,
            HeaderValue::from_str(&context.trace_id().to_string()).unwrap(),
        );
        response
    }
}