otlp-stdout-span-exporter

A Rust span exporter that writes OpenTelemetry spans to stdout in OTLP format. Part of the serverless-otlp-forwarder project.

This exporter is particularly useful in serverless environments like AWS Lambda where writing to stdout is a common pattern for exporting telemetry data.

Features

Uses OTLP Protobuf serialization for efficient encoding
Applies GZIP compression with configurable levels
Detects service name from environment variables
Supports custom headers via environment variables
Consistent JSON output format
Zero external HTTP dependencies
Lightweight and fast

Installation

Add this to your Cargo.toml:

[dependencies]
otlp-stdout-span-exporter = "0.1.0"

Usage

The recommended way to use this exporter is with batch export, which provides better performance by buffering and exporting spans in batches:

use opentelemetry::{trace::{Tracer, TracerProvider}, KeyValue};
use opentelemetry_sdk::{trace::TracerProvider as SdkTracerProvider, Resource, runtime};
use otlp_stdout_span_exporter::OtlpStdoutSpanExporter;

#[tokio::main]
async fn main() {
    // Create a new stdout exporter
    let exporter = OtlpStdoutSpanExporter::new();

    // Create a new tracer provider with batch export
    let provider = SdkTracerProvider::builder()
        .with_batch_exporter(exporter, runtime::Tokio)
        .with_resource(Resource::new(vec![KeyValue::new("service.name", "my-service")]))
        .build();

    // Create a tracer
    let tracer = provider.tracer("my-service");

    // Create spans
    tracer.in_span("parent-operation", |_cx| {
        println!("Doing work...");
        
        // Create nested spans
        tracer.in_span("child-operation", |_cx| {
            println!("Doing more work...");
        });
    });
    
    // Shut down the provider
    let _ = provider.shutdown();
}

This setup ensures that:

Spans are batched together for efficient export
Parent-child relationships are preserved
System resources are used efficiently
Spans are properly flushed on shutdown

Environment Variables

The exporter respects the following environment variables:

OTEL_SERVICE_NAME: Service name to use in output
AWS_LAMBDA_FUNCTION_NAME: Fallback service name (if OTEL_SERVICE_NAME not set)
OTEL_EXPORTER_OTLP_HEADERS: Global headers for OTLP export
OTEL_EXPORTER_OTLP_TRACES_HEADERS: Trace-specific headers (takes precedence)

Header format examples:

# Single header
export OTEL_EXPORTER_OTLP_HEADERS="api-key=secret123"

# Multiple headers
export OTEL_EXPORTER_OTLP_HEADERS="api-key=secret123,custom-header=value"

# Headers with special characters
export OTEL_EXPORTER_OTLP_HEADERS="authorization=Basic dXNlcjpwYXNzd29yZA=="

Output Format

The exporter writes each batch of spans as a JSON object to stdout:

{
  "__otel_otlp_stdout": "0.1.0",
  "source": "my-service",
  "endpoint": "http://localhost:4318/v1/traces",
  "method": "POST",
  "content-type": "application/x-protobuf",
  "content-encoding": "gzip",
  "headers": {
    "api-key": "secret123",
    "custom-header": "value"
  },
  "payload": "<base64-encoded-gzipped-protobuf>",
  "base64": true
}

Configuration

The exporter can be configured with different GZIP compression levels:

// Create exporter with custom GZIP level (0-9)
let exporter = OtlpStdoutSpanExporter::with_gzip_level(9);

Development

Clone the repository:

git clone https://github.com/dev7a/serverless-otlp-forwarder
cd serverless-otlp-forwarder/packages/rust/otlp-stdout-span-exporter

Run tests:

cargo test

Run the example:

cargo run --example hello

License

Apache License 2.0

otlp-stdout-span-exporter 0.6.0