1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123

//! # 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"));
    }
}