github.com/gorilla/websocket

The gorilla/websocket package is the de facto standard for WebSocket implementations in Go, and for good reason. The API is straightforward with clear separation between the Upgrader (HTTP->WebSocket transition) and Conn (message handling). Origin checking is enabled by default via CheckOrigin, which is excellent from a security standpoint, though you need to explicitly override it if you want different behavior - this secure-by-default approach prevents CSRF attacks.

Input validation requires manual attention. The library provides ReadMessage size limits via ReadLimit() which you must set yourself - there's no default, so forgetting this can expose you to memory exhaustion attacks. The library handles framing validation internally, but you're responsible for validating message content. TLS support is solid since it leverages Go's net/http, inheriting those crypto defaults.

Error handling is generally clean with explicit error returns, though connection errors don't always clearly distinguish between network issues and protocol violations. The WriteControl and message sending methods can expose timing information if you're not careful with goroutine patterns. Overall, it's a well-maintained library that requires security-conscious configuration.

After running gorilla/websocket in production handling millions of connections, it's proven to be exceptionally reliable. The API gives you fine-grained control over connection lifecycles, message framing, and resource management. The Upgrader type with customizable CheckOrigin, buffer sizes, and compression settings lets you tune performance exactly how you need it. Memory usage is predictable and connection pooling integrates cleanly with standard patterns.

Error handling is transparent - you get clear distinctions between normal closures, protocol errors, and network failures. The IsCloseError and IsUnexpectedCloseError helpers are invaluable for production logging. Timeouts are manual (SetReadDeadline/SetWriteDeadline) which initially feels low-level but gives precise control for implementing heartbeats and detecting stale connections.

One gotcha: concurrent writes panic by design, forcing you to add your own write mutex. This seems restrictive but prevents subtle race conditions. The PreparedMessage type helps optimize broadcasts. Documentation includes practical examples for common patterns like chat servers and proper cleanup sequences.

After using gorilla/websocket in production for several projects, I'm consistently impressed by how straightforward it is. The Upgrader pattern for HTTP-to-WebSocket transitions is intuitive, and the API closely mirrors Go's standard net package conventions, making it feel natural. The examples in the repository (chat server, echo server) are minimal but complete - I've literally copy-pasted and adapted them dozens of times as starting points.

Error handling is where this package really shines. When connections drop or messages are malformed, you get clear, actionable errors. The distinction between CloseError types helps you handle graceful shutdowns versus network failures appropriately. Debugging is straightforward because the connection lifecycle is explicit - you control reading, writing, and closing without hidden goroutines doing magic behind the scenes.

The learning curve is gentle if you understand basic Go concurrency. Common pitfalls (concurrent writes, not reading messages promptly) are well-documented in the package docs. Community support is strong - most Stack Overflow questions already have detailed answers. The maintainers are responsive on GitHub, though the package is so stable that issues are rare.