github.com/valyala/fasthttp

Fasthttp delivers on its promise of speed, but this comes at the cost of a significantly different API from net/http. The object pooling pattern requires careful understanding of when RequestCtx objects are reused, which can lead to subtle bugs if you hold references beyond handler scope. The documentation exists but assumes you'll read it thoroughly—skimming leads to production issues.

The API design feels lower-level than standard library alternatives. Simple tasks like reading JSON bodies or handling middleware require more boilerplate. Error messages when you misuse pooled objects are cryptic, often manifesting as race conditions or unexpected nil values. IDE support is adequate but autocompletion doesn't save you from the conceptual differences.

Migration from net/http isn't straightforward—you'll rewrite request handlers completely. The library shines in high-throughput scenarios where every allocation matters, but for typical web services, the complexity overhead often isn't justified. Third-party middleware ecosystem is limited compared to standard library options, so expect to write more plumbing yourself.

fasthttp delivers on its promise of speed but at the cost of a significantly different API from Go's standard net/http. The core concepts like RequestCtx feel foreign at first, and you'll need to unlearn net/http patterns. The zero-allocation design means working with byte slices everywhere instead of strings, which is performant but verbose.

The documentation exists but lacks the depth needed for non-trivial use cases. You'll find yourself reading source code frequently to understand behavior. Error messages are terse and not particularly helpful when debugging issues. Type safety is fine since it's Go, but the API design doesn't guide you toward correct usage - it's easy to make mistakes with request/response lifecycle management.

The ecosystem is smaller than net/http, so middleware and integrations often don't exist or require custom adapters. Migration from net/http requires a complete rewrite, not just swapping imports. For high-throughput services where performance justifies the tradeoffs, it works well, but be prepared for higher maintenance burden.

fasthttp delivers impressive performance gains over net/http through aggressive object pooling and zero-copy optimizations. In production, I've seen 2-3x throughput improvements with lower memory allocation rates. However, this comes with strict API requirements that bite you if ignored: request/response objects are pooled and reused, so copying data before returning from handlers is mandatory. Forgetting this causes subtle bugs that are painful to debug.

Connection pooling is excellent once configured properly. The default client pool settings are aggressive (no timeout limits initially), so you must set ReadTimeout, WriteTimeout, and MaxConnsPerHost explicitly. The Server type handles backpressure well under load, but error messages when limits are hit could be more descriptive. Observability requires manual instrumentation - there are no built-in metrics hooks.

The API diverges significantly from net/http, making it harder to swap implementations or use middleware ecosystems. Documentation covers basics well but advanced patterns like streaming responses or proper connection reuse require digging through issues. Breaking changes between minor versions have caught me before, so pin versions carefully.