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Diffstat (limited to 'src/field.rs')
| -rw-r--r-- | src/field.rs | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/src/field.rs b/src/field.rs new file mode 100644 index 0000000..b3f9fbd --- /dev/null +++ b/src/field.rs @@ -0,0 +1,170 @@ +//! `Span` and `Event` key-value data. +//! +//! Spans and events may be annotated with key-value data, referred to as known +//! as _fields_. These fields consist of a mapping from a key (corresponding to +//! a `&str` but represented internally as an array index) to a [`Value`]. +//! +//! # `Value`s and `Subscriber`s +//! +//! `Subscriber`s consume `Value`s as fields attached to [span]s or [`Event`]s. +//! The set of field keys on a given span or is defined on its [`Metadata`]. +//! When a span is created, it provides [`Attributes`] to the `Subscriber`'s +//! [`new_span`] method, containing any fields whose values were provided when +//! the span was created; and may call the `Subscriber`'s [`record`] method +//! with additional [`Record`]s if values are added for more of its fields. +//! Similarly, the [`Event`] type passed to the subscriber's [`event`] method +//! will contain any fields attached to each event. +//! +//! `tracing` represents values as either one of a set of Rust primitives +//! (`i64`, `u64`, `f64`, `bool`, and `&str`) or using a `fmt::Display` or +//! `fmt::Debug` implementation. `Subscriber`s are provided these primitive +//! value types as `dyn Value` trait objects. +//! +//! These trait objects can be formatted using `fmt::Debug`, but may also be +//! recorded as typed data by calling the [`Value::record`] method on these +//! trait objects with a _visitor_ implementing the [`Visit`] trait. This trait +//! represents the behavior used to record values of various types. For example, +//! an implementation of `Visit` might record integers by incrementing counters +//! for their field names rather than printing them. +//! +//! +//! # Using `valuable` +//! +//! `tracing`'s [`Value`] trait is intentionally minimalist: it supports only a small +//! number of Rust primitives as typed values, and only permits recording +//! user-defined types with their [`fmt::Debug`] or [`fmt::Display`] +//! implementations. However, there are some cases where it may be useful to record +//! nested values (such as arrays, `Vec`s, or `HashMap`s containing values), or +//! user-defined `struct` and `enum` types without having to format them as +//! unstructured text. +//! +//! To address `Value`'s limitations, `tracing` offers experimental support for +//! the [`valuable`] crate, which provides object-safe inspection of structured +//! values. User-defined types can implement the [`valuable::Valuable`] trait, +//! and be recorded as a `tracing` field by calling their [`as_value`] method. +//! If the [`Subscriber`] also supports the `valuable` crate, it can +//! then visit those types fields as structured values using `valuable`. +//! +//! <pre class="ignore" style="white-space:normal;font:inherit;"> +//! <strong>Note</strong>: <code>valuable</code> support is an +//! <a href = "../index.html#unstable-features">unstable feature</a>. See +//! the documentation on unstable features for details on how to enable it. +//! </pre> +//! +//! For example: +//! ```ignore +//! // Derive `Valuable` for our types: +//! use valuable::Valuable; +//! +//! #[derive(Clone, Debug, Valuable)] +//! struct User { +//! name: String, +//! age: u32, +//! address: Address, +//! } +//! +//! #[derive(Clone, Debug, Valuable)] +//! struct Address { +//! country: String, +//! city: String, +//! street: String, +//! } +//! +//! 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(), +//! }, +//! }; +//! +//! // Recording `user` as a `valuable::Value` will allow the `tracing` subscriber +//! // to traverse its fields as a nested, typed structure: +//! tracing::info!(current_user = user.as_value()); +//! ``` +//! +//! Alternatively, the [`valuable()`] function may be used to convert a type +//! implementing [`Valuable`] into a `tracing` field value. +//! +//! When the `valuable` feature is enabled, the [`Visit`] trait will include an +//! optional [`record_value`] method. `Visit` implementations that wish to +//! record `valuable` values can implement this method with custom behavior. +//! If a visitor does not implement `record_value`, the [`valuable::Value`] will +//! be forwarded to the visitor's [`record_debug`] method. +//! +//! [`fmt::Debug`]: std::fmt::Debug +//! [`fmt::Display`]: std::fmt::Debug +//! [`valuable`]: https://crates.io/crates/valuable +//! [`valuable::Valuable`]: https://docs.rs/valuable/latest/valuable/trait.Valuable.html +//! [`as_value`]: https://docs.rs/valuable/latest/valuable/trait.Valuable.html#tymethod.as_value +//! [`valuable::Value`]: https://docs.rs/valuable/latest/valuable/enum.Value.html +//! [`Subscriber`]: crate::Subscriber +//! [`record_value`]: Visit::record_value +//! [`record_debug`]: Visit::record_debug +//! [span]: mod@crate::span +//! [`Event`]: crate::event::Event +//! [`Metadata`]: crate::Metadata +//! [`Attributes`]: crate::span::Attributes +//! [`Record`]: crate::span::Record +//! [`new_span`]: crate::Subscriber::new_span +//! [`record`]: crate::Subscriber::record +//! [`event`]: crate::Subscriber::event +pub use tracing_core::field::*; + +use crate::Metadata; + +/// Trait implemented to allow a type to be used as a field key. +/// +/// <pre class="ignore" style="white-space:normal;font:inherit;"> +/// <strong>Note</strong>: Although this is implemented for both the +/// <a href="./struct.Field.html"><code>Field</code></a> type <em>and</em> any +/// type that can be borrowed as an <code>&str</code>, only <code>Field</code> +/// allows <em>O</em>(1) access. +/// Indexing a field with a string results in an iterative search that performs +/// string comparisons. Thus, if possible, once the key for a field is known, it +/// should be used whenever possible. +/// </pre> +pub trait AsField: crate::sealed::Sealed { + /// Attempts to convert `&self` into a `Field` with the specified `metadata`. + /// + /// If `metadata` defines this field, then the field is returned. Otherwise, + /// this returns `None`. + fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field>; +} + +// ===== impl AsField ===== + +impl AsField for Field { + #[inline] + fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> { + if self.callsite() == metadata.callsite() { + Some(self.clone()) + } else { + None + } + } +} + +impl<'a> AsField for &'a Field { + #[inline] + fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> { + if self.callsite() == metadata.callsite() { + Some((*self).clone()) + } else { + None + } + } +} + +impl AsField for str { + #[inline] + fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> { + metadata.fields().field(&self) + } +} + +impl crate::sealed::Sealed for Field {} +impl<'a> crate::sealed::Sealed for &'a Field {} +impl crate::sealed::Sealed for str {} |