metrics-helper-macros

Proc-macros for idiomatic Prometheus metrics instrumentation in Rust.

Features

• #[instrument] - Attribute macro for automatic function instrumentation
• Counters - Count function invocations
• Histograms - Measure function duration
• Error counters - Track errors for functions returning Result
• Labels - Attach static or dynamic labels from function parameters

Installation

[dependencies]
metrics-helper-macros = "0.1"
metrics = "0.24"

Usage

Basic Example

use metrics_helper_macros::instrument;

#[instrument(
    counter = "db_queries_total",
    histogram = "db_query_duration_seconds",
    error_counter = "db_query_errors_total",
)]
async fn query_database() -> Result<Data, DbError> {
    // Your code here...
}

With Labels

Labels can be static (fixed values) or dynamic (captured from function parameters):

#[instrument(
    counter = "http_requests_total",
    histogram = "http_request_duration_seconds",
    labels(
        service = "api",      // static label
        method,               // dynamic: captured from function param
        endpoint,             // dynamic: captured from function param
    ),
)]
async fn handle_request(method: &str, endpoint: &str, body: Bytes) -> Response {
    // method and endpoint values are captured as label values
}

This produces metrics like:

http_requests_total{service="api", method="GET", endpoint="/users"} 1
http_request_duration_seconds{service="api", method="GET", endpoint="/users"} 0.023

Attributes

Label Syntax

• Static: key = "value" - Fixed string value
• Dynamic: key - Captures the value of a function parameter with the same name (must implement Display)

Requirements

• Functions using dynamic labels must have parameters that implement Display
• The metrics crate must be available in your dependency tree
• For error_counter to work, the function must return a Result type

License

MIT