All spans and events have the following metadata:
- A name, represented as a static string.
- A target, a string that categorizes part of the system where the span
or event occurred. The
tracingmacros default to using the module path where the span or event originated as the target, but it may be overridden.
- A verbosity level. This determines how verbose a given span or event
is, and allows enabling or disabling more verbose diagnostics
situationally. See the documentation for the
Leveltype for details.
- The names of the fields defined by the span or event.
- Whether the metadata corresponds to a span or event.
In addition, the following optional metadata describing the source code location where the span or event originated may be provided:
Metadata is used by
Subscribers when filtering spans and events, and it
may also be used as part of their data payload.
When created by the
span! macro, the metadata describing a
particular event or span is constructed statically and exists as a single
static instance. Thus, the overhead of creating the metadata is
significantly lower than that of creating the actual span. Therefore,
filtering is based on metadata, rather than on the constructed span.
Note: Although instances of
Metadatacannot be compared directly, they provide a method
id, returning an opaque callsite identifierwhich uniquely identifies the callsite where the metadata originated. This can be used to determine if two
Metadatacorrespond to the same callsite.
name: &'static str
The name of the span described by this metadata.
target: &'a str
The part of the system that the span that this metadata describes occurred in.
The level of verbosity of the described span.
module_path: Option<&'a str>
The name of the Rust module where the span occurred, or
None if this
could not be determined.
file: Option<&'a str>
The name of the source code file where the span occurred, or
this could not be determined.
The line number in the source code file where the span occurred, or
None if this could not be determined.
The names of the key-value fields attached to the described span or event.
The kind of the callsite.
Construct new metadata for a span or event, with a name, target, level, field names, and optional source code location.
Returns the names of the fields on the described span or event.
Returns the level of verbosity of the described span or event.
Returns the name of the span.
Returns a string describing the part of the system where the span or event that this metadata describes occurred.
Typically, this is the module path, but alternate targets may be set when spans or events are constructed.
Returns the path to the Rust module where the span occurred, or
None if the module path is unknown.
Returns the name of the source code file where the span
None if the file is unknown
Returns the line number in the source code file where the span
None if the line number is unknown.
Returns an opaque
Identifier that uniquely identifies the callsite
Metadata originated from.
Returns true if the callsite kind is
Return true if the callsite kind is
Returns the argument unchanged.