1//! Structured logging.
2//!
3//! Add the `kv` feature to your `Cargo.toml` to enable
4//! this module:
5//!
6//! ```toml
7//! [dependencies.log]
8//! features = ["kv"]
9//! ```
10//!
11//! # Structured logging in `log`
12//!
13//! Structured logging enhances traditional text-based log records with user-defined
14//! attributes. Structured logs can be analyzed using a variety of data processing
15//! techniques, without needing to find and parse attributes from unstructured text first.
16//!
17//! In `log`, user-defined attributes are part of a [`Source`] on the log record.
18//! Each attribute is a key-value; a pair of [`Key`] and [`Value`]. Keys are strings
19//! and values are a datum of any type that can be formatted or serialized. Simple types
20//! like strings, booleans, and numbers are supported, as well as arbitrarily complex
21//! structures involving nested objects and sequences.
22//!
23//! ## Adding key-values to log records
24//!
25//! Key-values appear before the message format in the `log!` macros:
26//!
27//! ```
28//! # use log::info;
29//! info!(a = 1; "Something of interest");
30//! ```
31//!
32//! Key-values support the same shorthand identifier syntax as `format_args`:
33//!
34//! ```
35//! # use log::info;
36//! let a = 1;
37//!
38//! info!(a; "Something of interest");
39//! ```
40//!
41//! Values are capturing using the [`ToValue`] trait by default. To capture a value
42//! using a different trait implementation, use a modifier after its key. Here's how
43//! the same example can capture `a` using its `Debug` implementation instead:
44//!
45//! ```
46//! # use log::info;
47//! info!(a:? = 1; "Something of interest");
48//! ```
49//!
50//! The following capturing modifiers are supported:
51//!
52//! - `:?` will capture the value using `Debug`.
53//! - `:debug` will capture the value using `Debug`.
54//! - `:%` will capture the value using `Display`.
55//! - `:display` will capture the value using `Display`.
56//! - `:err` will capture the value using `std::error::Error` (requires the `kv_std` feature).
57//! - `:sval` will capture the value using `sval::Value` (requires the `kv_sval` feature).
58//! - `:serde` will capture the value using `serde::Serialize` (requires the `kv_serde` feature).
59//!
60//! ## Working with key-values on log records
61//!
62//! Use the [`Record::key_values`](../struct.Record.html#method.key_values) method to access key-values.
63//!
64//! Individual values can be pulled from the source by their key:
65//!
66//! ```
67//! # fn main() -> Result<(), log::kv::Error> {
68//! use log::kv::{Source, Key, Value};
69//! # let record = log::Record::builder().key_values(&[("a", 1)]).build();
70//!
71//! // info!(a = 1; "Something of interest");
72//!
73//! let a: Value = record.key_values().get(Key::from("a")).unwrap();
74//! assert_eq!(1, a.to_i64().unwrap());
75//! # Ok(())
76//! # }
77//! ```
78//!
79//! All key-values can also be enumerated using a [`VisitSource`]:
80//!
81//! ```
82//! # fn main() -> Result<(), log::kv::Error> {
83//! use std::collections::BTreeMap;
84//!
85//! use log::kv::{self, Source, Key, Value, VisitSource};
86//!
87//! struct Collect<'kvs>(BTreeMap<Key<'kvs>, Value<'kvs>>);
88//!
89//! impl<'kvs> VisitSource<'kvs> for Collect<'kvs> {
90//! fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), kv::Error> {
91//! self.0.insert(key, value);
92//!
93//! Ok(())
94//! }
95//! }
96//!
97//! let mut visitor = Collect(BTreeMap::new());
98//!
99//! # let record = log::Record::builder().key_values(&[("a", 1), ("b", 2), ("c", 3)]).build();
100//! // info!(a = 1, b = 2, c = 3; "Something of interest");
101//!
102//! record.key_values().visit(&mut visitor)?;
103//!
104//! let collected = visitor.0;
105//!
106//! assert_eq!(
107//! vec!["a", "b", "c"],
108//! collected
109//! .keys()
110//! .map(|k| k.as_str())
111//! .collect::<Vec<_>>(),
112//! );
113//! # Ok(())
114//! # }
115//! ```
116//!
117//! [`Value`]s have methods for conversions to common types:
118//!
119//! ```
120//! # fn main() -> Result<(), log::kv::Error> {
121//! use log::kv::{Source, Key};
122//! # let record = log::Record::builder().key_values(&[("a", 1)]).build();
123//!
124//! // info!(a = 1; "Something of interest");
125//!
126//! let a = record.key_values().get(Key::from("a")).unwrap();
127//!
128//! assert_eq!(1, a.to_i64().unwrap());
129//! # Ok(())
130//! # }
131//! ```
132//!
133//! Values also have their own [`VisitValue`] type. Value visitors are a lightweight
134//! API for working with primitives types:
135//!
136//! ```
137//! # fn main() -> Result<(), log::kv::Error> {
138//! use log::kv::{self, Source, Key, VisitValue};
139//! # let record = log::Record::builder().key_values(&[("a", 1)]).build();
140//!
141//! struct IsNumeric(bool);
142//!
143//! impl<'kvs> VisitValue<'kvs> for IsNumeric {
144//! fn visit_any(&mut self, _value: kv::Value) -> Result<(), kv::Error> {
145//! self.0 = false;
146//! Ok(())
147//! }
148//!
149//! fn visit_u64(&mut self, _value: u64) -> Result<(), kv::Error> {
150//! self.0 = true;
151//! Ok(())
152//! }
153//!
154//! fn visit_i64(&mut self, _value: i64) -> Result<(), kv::Error> {
155//! self.0 = true;
156//! Ok(())
157//! }
158//!
159//! fn visit_u128(&mut self, _value: u128) -> Result<(), kv::Error> {
160//! self.0 = true;
161//! Ok(())
162//! }
163//!
164//! fn visit_i128(&mut self, _value: i128) -> Result<(), kv::Error> {
165//! self.0 = true;
166//! Ok(())
167//! }
168//!
169//! fn visit_f64(&mut self, _value: f64) -> Result<(), kv::Error> {
170//! self.0 = true;
171//! Ok(())
172//! }
173//! }
174//!
175//! // info!(a = 1; "Something of interest");
176//!
177//! let a = record.key_values().get(Key::from("a")).unwrap();
178//!
179//! let mut visitor = IsNumeric(false);
180//!
181//! a.visit(&mut visitor)?;
182//!
183//! let is_numeric = visitor.0;
184//!
185//! assert!(is_numeric);
186//! # Ok(())
187//! # }
188//! ```
189//!
190//! To serialize a value to a format like JSON, you can also use either `serde` or `sval`:
191//!
192//! ```
193//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
194//! # #[cfg(feature = "serde")]
195//! # {
196//! # use log::kv::Key;
197//! #[derive(serde::Serialize)]
198//! struct Data {
199//! a: i32, b: bool,
200//! c: &'static str,
201//! }
202//!
203//! let data = Data { a: 1, b: true, c: "Some data" };
204//!
205//! # let source = [("a", log::kv::Value::from_serde(&data))];
206//! # let record = log::Record::builder().key_values(&source).build();
207//! // info!(a = data; "Something of interest");
208//!
209//! let a = record.key_values().get(Key::from("a")).unwrap();
210//!
211//! assert_eq!("{\"a\":1,\"b\":true,\"c\":\"Some data\"}", serde_json::to_string(&a)?);
212//! # }
213//! # Ok(())
214//! # }
215//! ```
216//!
217//! The choice of serialization framework depends on the needs of the consumer.
218//! If you're in a no-std environment, you can use `sval`. In other cases, you can use `serde`.
219//! Log producers and log consumers don't need to agree on the serialization framework.
220//! A value can be captured using its `serde::Serialize` implementation and still be serialized
221//! through `sval` without losing any structure or data.
222//!
223//! Values can also always be formatted using the standard `Debug` and `Display`
224//! traits:
225//!
226//! ```
227//! # use log::kv::Key;
228//! # #[derive(Debug)]
229//! struct Data {
230//! a: i32,
231//! b: bool,
232//! c: &'static str,
233//! }
234//!
235//! let data = Data { a: 1, b: true, c: "Some data" };
236//!
237//! # let source = [("a", log::kv::Value::from_debug(&data))];
238//! # let record = log::Record::builder().key_values(&source).build();
239//! // info!(a = data; "Something of interest");
240//!
241//! let a = record.key_values().get(Key::from("a")).unwrap();
242//!
243//! assert_eq!("Data { a: 1, b: true, c: \"Some data\" }", format!("{a:?}"));
244//! ```
245
246mod error;
247mod key;
248
249#[cfg(not(feature = "kv_unstable"))]
250mod source;
251#[cfg(not(feature = "kv_unstable"))]
252mod value;
253
254pub use self::error::Error;
255pub use self::key::{Key, ToKey};
256pub use self::source::{Source, VisitSource};
257pub use self::value::{ToValue, Value, VisitValue};
258
259#[cfg(feature = "kv_unstable")]
260pub mod source;
261#[cfg(feature = "kv_unstable")]
262pub mod value;
263
264#[cfg(feature = "kv_unstable")]
265pub use self::source::Visitor;
266