Field conventions
Event fields map onto Cloud Logging’s structured LogEntry fields as follows.
Anything else is written verbatim into the JSON payload.
| Event field | Log entry field | Format |
|---|---|---|
severity | severity | One of DEFAULT DEBUG INFO NOTICE WARNING ERROR CRITICAL ALERT EMERGENCY, matched case-insensitively. Overrides the level mapping: TRACE and DEBUG are DEBUG, INFO is INFO, WARN is WARNING, ERROR is ERROR; the level maps when the field is absent or not a name |
http_request.request_method, .request_url, .user_agent, .remote_ip, .server_ip, .referer, .protocol | httpRequest.*, camel-cased | strings |
http_request.status | httpRequest.status | integer |
http_request.request_size, .response_size, .cache_fill_bytes | httpRequest.* | integers |
http_request.latency | httpRequest.latency | a duration string such as "250ms" or "1.5s", or a number of seconds |
http_request.cache_lookup, .cache_hit, .cache_validated_with_origin_server | httpRequest.* | booleans |
labels.<name> | logging.googleapis.com/labels.<name> | value stringified |
operation.id, .producer | logging.googleapis.com/operation.{id,producer} | strings |
operation.first, .last | logging.googleapis.com/operation.{first,last} | booleans |
insert_id | logging.googleapis.com/insertId | string |
| source location | logging.googleapis.com/sourceLocation | file and line; on by default, disable with with_source_location(false) |
The field names are not valid Rust identifiers, so they are written as string literals in the macros:
info!(
"labels.tenant" = "acme",
"http_request.request_method" = "GET",
"http_request.request_url" = "https://example.test/orders",
"http_request.status" = 200,
"Serving a request."
);Only the httpRequest.* keys are camel-cased, matching Google’s own field names; every other field name is written as given.
On the Cloud Logging API and OTLP sinks, a value that does not fit the typed field it is destined for, such as a malformed latency, stays in the payload instead of being dropped.
Errors
An event field passed as &dyn Error keeps its whole source() chain, one Caused by: line per source:
tracing::error!(error = &failure as &dyn std::error::Error, "checkout failed");error = %err and error = ?err record only the text they format.
See Error Reporting for how an error event is grouped.