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//! # OpenTelemetry Propagator interface
//! Cross-cutting concerns send their state to the next process using Propagators, which are defined
//! as objects used to read and write context data to and from messages exchanged by the applications.
//!
//! `Propagator`s leverage the [`Context`] to inject and extract data for each cross-cutting concern,
//! such as `TraceContext` and [`Baggage`].
//!
//! The Propagators API is expected to be leveraged by users writing instrumentation libraries.
//!
//! Currently, the following `Propagator` types are supported:
//! - [`TextMapPropagator`], inject values into and extracts values from carriers as string key/value pairs
//!
//! A binary Propagator type will be added in
//! the future, See [tracking issues](https://github.com/open-telemetry/opentelemetry-specification/issues/437)).
//!
//! `Propagator`s uses [`Injector`] and [`Extractor`] to read and write context data to and from messages.
//! Each specific Propagator type defines its expected carrier type, such as a string map or a byte array.
//!
//! [`Baggage`]: crate::baggage::Baggage
//! [`Context`]: crate::Context
use std::collections::HashMap;
use thiserror::Error;
pub mod composite;
pub mod text_map_propagator;
pub use composite::TextMapCompositePropagator;
pub use text_map_propagator::TextMapPropagator;
/// Injector provides an interface for adding fields from an underlying struct like `HashMap`
pub trait Injector {
/// Add a key and value to the underlying data.
fn set(&mut self, key: &str, value: String);
}
/// Extractor provides an interface for removing fields from an underlying struct like `HashMap`
pub trait Extractor {
/// Get a value from a key from the underlying data.
fn get(&self, key: &str) -> Option<&str>;
/// Collect all the keys from the underlying data.
fn keys(&self) -> Vec<&str>;
}
impl<S: std::hash::BuildHasher> Injector for HashMap<String, String, S> {
/// Set a key and value in the HashMap.
fn set(&mut self, key: &str, value: String) {
self.insert(key.to_lowercase(), value);
}
}
impl<S: std::hash::BuildHasher> Extractor for HashMap<String, String, S> {
/// Get a value for a key from the HashMap.
fn get(&self, key: &str) -> Option<&str> {
self.get(&key.to_lowercase()).map(|v| v.as_str())
}
/// Collect all the keys from the HashMap.
fn keys(&self) -> Vec<&str> {
self.keys().map(|k| k.as_str()).collect::<Vec<_>>()
}
}
/// Error when extracting or injecting context data(i.e propagating) across application boundaries.
#[derive(Error, Debug)]
#[error("Cannot {} from {}, {}", ops, message, propagator_name)]
pub struct PropagationError {
message: &'static str,
// which propagator does this error comes from
propagator_name: &'static str,
// are we extracting or injecting information across application boundaries
ops: &'static str,
}
impl PropagationError {
/// Error happens when extracting information
pub fn extract(message: &'static str, propagator_name: &'static str) -> Self {
PropagationError {
message,
propagator_name,
ops: "extract",
}
}
/// Error happens when extracting information
pub fn inject(message: &'static str, propagator_name: &'static str) -> Self {
PropagationError {
message,
propagator_name,
ops: "inject",
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn hash_map_get() {
let mut carrier = HashMap::new();
carrier.set("headerName", "value".to_string());
assert_eq!(
Extractor::get(&carrier, "HEADERNAME"),
Some("value"),
"case insensitive extraction"
);
}
#[test]
fn hash_map_keys() {
let mut carrier = HashMap::new();
carrier.set("headerName1", "value1".to_string());
carrier.set("headerName2", "value2".to_string());
let got = Extractor::keys(&carrier);
assert_eq!(got.len(), 2);
assert!(got.contains(&"headername1"));
assert!(got.contains(&"headername2"));
}
}