gateway_runtime/layers/
metadata.rs

1//! # Metadata Extraction Layer
2//!
3//! This layer orchestrates the extraction of gRPC metadata from incoming HTTP requests.
4//!
5//! It executes registered [MetadataAnnotator] functions to pull context (e.g., Request IDs,
6//! Auth Tokens) into a `MetadataMap`. The resulting metadata is stored in the request
7//! extensions, where it can be later retrieved by the generated code to populate the
8//! `tonic::Request`.
9//!
10//! It also injects the [MetadataForwardingConfig] into the extensions, ensuring downstream
11//! components respect the configured security rules.
12
13use crate::alloc::boxed::Box;
14use crate::alloc::vec::Vec;
15use crate::gateway::MetadataAnnotator;
16use crate::metadata::MetadataForwardingConfig;
17use crate::GatewayRequest;
18use core::task::{Context, Poll};
19use std::future::Future;
20use std::pin::Pin;
21use tower::Service;
22
23/// A Tower middleware that executes metadata annotators.
24#[derive(Clone)]
25pub struct MetadataLayer<S> {
26    inner: S,
27    annotators: Vec<MetadataAnnotator>,
28    config: MetadataForwardingConfig,
29}
30
31impl<S> MetadataLayer<S> {
32    /// Creates a new `MetadataLayer`.
33    ///
34    /// # Parameters
35    /// *   `inner`: The inner service.
36    /// *   `annotators`: A list of functions that extract metadata from the request.
37    /// *   `config`: Security configuration for metadata forwarding.
38    pub fn new(
39        inner: S,
40        annotators: Vec<MetadataAnnotator>,
41        config: MetadataForwardingConfig,
42    ) -> Self {
43        Self {
44            inner,
45            annotators,
46            config,
47        }
48    }
49}
50
51impl<S> Service<GatewayRequest> for MetadataLayer<S>
52where
53    S: Service<GatewayRequest>,
54    S::Future: Send + 'static,
55{
56    type Response = S::Response;
57    type Error = S::Error;
58    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
59
60    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
61        self.inner.poll_ready(cx)
62    }
63
64    fn call(&mut self, mut req: GatewayRequest) -> Self::Future {
65        // Execute all registered annotators
66        for annotator in &self.annotators {
67            let metadata = annotator(&req);
68            if !metadata.is_empty() {
69                // Merge new metadata into existing extensions
70                if let Some(existing) = req
71                    .extensions_mut()
72                    .get_mut::<tonic::metadata::MetadataMap>()
73                {
74                    for item in metadata.iter() {
75                        match item {
76                            tonic::metadata::KeyAndValueRef::Ascii(key, val) => {
77                                existing.insert(key.clone(), val.clone());
78                            }
79                            tonic::metadata::KeyAndValueRef::Binary(key, val) => {
80                                existing.insert_bin(key.clone(), val.clone());
81                            }
82                        }
83                    }
84                } else {
85                    // Initialize if missing
86                    req.extensions_mut().insert(metadata);
87                }
88            }
89        }
90
91        // Inject the forwarding configuration for use by `forward_metadata`
92        req.extensions_mut().insert(self.config.clone());
93
94        let fut = self.inner.call(req);
95        Box::pin(async move { fut.await })
96    }
97}
gateway_runtime/layers/metadata.rs

gateway_runtime/layers/
metadata.rs
