The prometheus/statsd_exporter is a production-grade Go application that receives StatsD metrics over UDP, TCP, or Unix sockets and translates them into Prometheus metrics. It acts as a drop-in replacement for StatsD, supporting multiple tagging formats (DogStatsD, InfluxDB, Librato, SignalFX) and providing flexible metric mapping via glob or regex patterns. The exporter is designed to run as a sidecar alongside application instances, converting ephemeral StatsD events into persistent Prometheus time series that can be scraped by a Prometheus server. Architecturally, the application consists of several well-separated layers: network listeners (UDP, TCP, Unixgram) that receive raw lines, a line parser that converts text into typed events (counter, gauge, observer), a metric mapper that applies user-defined mapping rules using a finite state machine (FSM) for glob patterns or regular expressions, and an exporter that registers and updates Prometheus metrics via a custom registry. Events are batched through an internal queue to improve throughput. The mapper supports caching (LRU or random replacement) to accelerate repeated lookups. Key entry points include the main.go binary with CLI flags for configuring listeners, mapping files, cache size, relay targets, and tagging options. The primary data flow is: incoming StatsD line → line parser → event queue → mapper → exporter → Prometheus registry. External dependencies are limited to Prometheus client libraries, a YAML parser, and the Go standard library. The codebase is well-tested with unit tests, integration tests, and benchmarks, and follows Prometheus project conventions.