Struct Json

pub struct Json { /* private fields */ }

Available on crate features fmt and std and json only.

Marker for Format that indicates that the newline-delimited JSON log format should be used.

This formatter is intended for production use with systems where structured logs are consumed as JSON by analysis and viewing tools. The JSON output is not optimized for human readability; instead, it should be pretty-printed using external JSON tools such as jq, or using a JSON log viewer.

Example Output

:; cargo run --example fmt-json
    Finished dev [unoptimized + debuginfo] target(s) in 0.08s
     Running `target/debug/examples/fmt-json`
{"timestamp":"2022-02-15T18:47:10.821315Z","level":"INFO","fields":{"message":"preparing to shave yaks","number_of_yaks":3},"target":"fmt_json"}
{"timestamp":"2022-02-15T18:47:10.821422Z","level":"INFO","fields":{"message":"shaving yaks"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.821495Z","level":"TRACE","fields":{"message":"hello! I'm gonna shave a yak","excitement":"yay!"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"},{"yak":1,"name":"shave"}]}
{"timestamp":"2022-02-15T18:47:10.821546Z","level":"TRACE","fields":{"message":"yak shaved successfully"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"},{"yak":1,"name":"shave"}]}
{"timestamp":"2022-02-15T18:47:10.821598Z","level":"DEBUG","fields":{"yak":1,"shaved":true},"target":"yak_events","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.821637Z","level":"TRACE","fields":{"yaks_shaved":1},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.821684Z","level":"TRACE","fields":{"message":"hello! I'm gonna shave a yak","excitement":"yay!"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"},{"yak":2,"name":"shave"}]}
{"timestamp":"2022-02-15T18:47:10.821727Z","level":"TRACE","fields":{"message":"yak shaved successfully"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"},{"yak":2,"name":"shave"}]}
{"timestamp":"2022-02-15T18:47:10.821773Z","level":"DEBUG","fields":{"yak":2,"shaved":true},"target":"yak_events","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.821806Z","level":"TRACE","fields":{"yaks_shaved":2},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.821909Z","level":"TRACE","fields":{"message":"hello! I'm gonna shave a yak","excitement":"yay!"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"},{"yak":3,"name":"shave"}]}
{"timestamp":"2022-02-15T18:47:10.821956Z","level":"WARN","fields":{"message":"could not locate yak"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"},{"yak":3,"name":"shave"}]}
{"timestamp":"2022-02-15T18:47:10.822006Z","level":"DEBUG","fields":{"yak":3,"shaved":false},"target":"yak_events","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.822041Z","level":"ERROR","fields":{"message":"failed to shave yak","yak":3,"error":"missing yak"},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.822079Z","level":"TRACE","fields":{"yaks_shaved":2},"target":"fmt_json::yak_shave","spans":[{"yaks":3,"name":"shaving_yaks"}]}
{"timestamp":"2022-02-15T18:47:10.822117Z","level":"INFO","fields":{"message":"yak shaving completed","all_yaks_shaved":false},"target":"fmt_json"}

Options

This formatter exposes additional options to configure the structure of the output JSON objects:

• Json::flatten_event can be used to enable flattening event fields into the root
• Json::with_current_span can be used to control logging of the current span
• Json::with_span_list can be used to control logging of the span list object.

By default, event fields are not flattened, and both current span and span list are logged.

Valuable Support

Experimental support is available for using the valuable crate to record user-defined values as structured JSON. When the “valuable” unstable feature is enabled, types implementing valuable::Valuable will be recorded as structured JSON, rather than using their std::fmt::Debug implementations.

Note: This is an experimental feature. Unstable features must be enabled in order to use valuable support.

Implementations

impl Json

pub fn flatten_event(&mut self, flatten_event: bool)

If set to true event metadata will be flattened into the root object.

pub fn with_current_span(&mut self, display_current_span: bool)

If set to false, formatted events won’t contain a field for the current span.

pub fn with_span_list(&mut self, display_span_list: bool)

If set to false, formatted events won’t contain a list of all currently entered spans. Spans are logged in a list from root to leaf.

Trait Implementations

impl Clone for Json

fn clone(&self) -> Json

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Json

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Json

fn default() -> Json

Returns the “default value” for a type.

impl PartialEq for Json

fn eq(&self, other: &Json) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Json

impl Eq for Json

impl StructuralPartialEq for Json