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core: add initial support for
valuable
field values (#1608)
This branch adds initial support for using the [`valuable`] crate as an opt-in `Value` type in `tracing`. `valuable` provides a mechanism for defining custom ways to record user-implemented types, as well as structured recording of standard library data structures such as maps, arrays, and sets. For more details, see the tracking issue #1570. In `tracing` v0.2, the intent is for `valuable` to replace the existing `tracing_core::field::Value` trait. However, in v0.1.x, `valuable` support must be added in a backwards-compatible way, so recording types that implement `valuable::Valueable` currently requires opting in using a `field::valuable` wrapper function. Since this is the first release of `valuable` and the API is still stabilizing, we don't want to tie `tracing-core`'s stability to `valuable`'s. Therefore, the valuable dependency is feature-flagged *and* also requires `RUSTFLAGS="--cfg tracing_unstable"`. [`valuable`]: https://github.com/tokio-rs/valuable Co-authored-by: Daniel McKenna <daniel@emotech.co> Co-authored-by: David Barsky <me@davidbarsky.com> Co-authored-by: Eliza Weisman <eliza@buoyant.io>
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#![allow(dead_code)] | ||
//! This example shows how a field value may be recorded using the `valuable` | ||
//! crate (https://crates.io/crates/valuable). | ||
//! | ||
//! `valuable` provides a lightweight but flexible way to record structured data, allowing | ||
//! visitors to extract individual fields or elements of structs, maps, arrays, and other | ||
//! nested structures. | ||
//! | ||
//! `tracing`'s support for `valuable` is currently feature flagged. Additionally, `valuable` | ||
//! support is considered an *unstable feature*: in order to use `valuable` with `tracing`, | ||
//! the project must be built with `RUSTFLAGS="--cfg tracing_unstable`. | ||
//! | ||
//! Therefore, when `valuable` support is not enabled, this example falls back to using | ||
//! `fmt::Debug` to record fields that implement `valuable::Valuable`. | ||
#[cfg(tracing_unstable)] | ||
use tracing::field::valuable; | ||
use tracing::{info, info_span}; | ||
use valuable::Valuable; | ||
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#[derive(Clone, Debug, Valuable)] | ||
struct User { | ||
name: String, | ||
age: u32, | ||
address: Address, | ||
} | ||
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#[derive(Clone, Debug, Valuable)] | ||
struct Address { | ||
country: String, | ||
city: String, | ||
street: String, | ||
} | ||
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fn main() { | ||
tracing_subscriber::fmt() | ||
.with_max_level(tracing::Level::TRACE) | ||
.init(); | ||
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let user = User { | ||
name: "Arwen Undomiel".to_string(), | ||
age: 3000, | ||
address: Address { | ||
country: "Middle Earth".to_string(), | ||
city: "Rivendell".to_string(), | ||
street: "leafy lane".to_string(), | ||
}, | ||
}; | ||
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// If the `valuable` feature is enabled, record `user` using its' | ||
// `valuable::Valuable` implementation: | ||
#[cfg(tracing_unstable)] | ||
let span = info_span!("Processing", user = valuable(&user)); | ||
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// Otherwise, record `user` using its `fmt::Debug` implementation: | ||
#[cfg(not(tracing_unstable))] | ||
let span = info_span!("Processing", user = ?user); | ||
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let _handle = span.enter(); | ||
info!("Nothing to do"); | ||
} |
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#[cfg(tracing_unstable)] | ||
mod app { | ||
use std::collections::HashMap; | ||
use tracing::field::valuable; | ||
use tracing::{info, info_span, instrument}; | ||
use valuable::Valuable; | ||
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#[derive(Valuable)] | ||
struct Headers<'a> { | ||
headers: HashMap<&'a str, &'a str>, | ||
} | ||
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// Current there's no way to automatically apply valuable to a type, so we need to make use of | ||
// the fields argument for instrument | ||
#[instrument(fields(headers=valuable(&headers)))] | ||
fn process(headers: Headers) { | ||
info!("Handle request") | ||
} | ||
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pub fn run() { | ||
let headers = [ | ||
("content-type", "application/json"), | ||
("content-length", "568"), | ||
("server", "github.com"), | ||
] | ||
.iter() | ||
.cloned() | ||
.collect::<HashMap<_, _>>(); | ||
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let http_headers = Headers { headers }; | ||
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process(http_headers); | ||
} | ||
} | ||
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fn main() { | ||
tracing_subscriber::fmt() | ||
.with_max_level(tracing::Level::TRACE) | ||
.init(); | ||
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#[cfg(tracing_unstable)] | ||
app::run(); | ||
#[cfg(not(tracing_unstable))] | ||
println!("Nothing to do, this example needs --cfg=tracing_unstable to run"); | ||
} |
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