Lectures

We break down the updated routing in Go’s standard library: how http.ServeMux in Go 1.22+ can match routes by method and path ( "GET /tasks", "POST /tasks"), supports wildcard segments ( {id}, {path...}), and helps remove manual if checks and URL-string parsing from handlers.

We break down why a resource identifier belongs in the path (for example, /api/v1/tasks/42), how net/http.ServeMux (starting with Go 1.22) matches a segment like { id }, and how to safely extract the value via r . PathValue ( "id" ). We also compare path parameters and query parameters, show an example with multiple parameters, and go over common mistakes.

We break down the semantic difference between 404 and 405 in HTTP, where exactly they are “born” in Go via net/http and ServeMux, how to distinguish a “routing 404” from a “data 404”, when Allow is useful, and how to quickly check behavior with curl. Examples are shown using a training API and handlers ( handler).

We break down how to extract parsing of the id parameter from handlers into a parseID helper with a single contract ( string → int, error), how to return a typed ValidationError with per-field details in Fields, and how, in a handler, to use errors.As to turn this into a unified JSON error envelope with fields.

We break down a practical “Go way” to clean HTTP handlers: we move the routine (statuses, headers, JSON encoding, a single error format) into a shared adapter, and leave the handlers focused “on the meaning”. We build an error contract via ValidationError and HTTPError, write single response points writeJSON/ writeError (with errors.As), and wire everything up through a function type with a ServeHTTP method.