From the standard library to a running service — HTTP servers and the 1.22 router, JSON, requests and middleware, the http.Client, files and io, time, CLIs, database/sql, and testing in depth (table-driven, httptest, benchmarks, fuzzing) — every program built and run against Go 1.26.
Building a real HTTP server with only the standard library: the Handler interface, ResponseWriter and Request, why writing a body auto-sends a 200, and the WriteHeader ordering rule that silently drops your headers. Compiled and run against Go 1.26.5.
The modern http.ServeMux with method and wildcard patterns, r.PathValue, the automatic 405 with an Allow header, precedence rules, the {$} end-anchor, and the {rest...} trailing wildcard. Why this removed most reasons to reach for a third-party router. Compiled and run against Go 1.26.5.
Pulling data out of an *http.Request: query params with r.URL.Query, forms with FormValue and the ParseForm it hides, headers, reading the raw body with io.ReadAll and why you close it, and bounding it with http.MaxBytesReader. Compiled and run against Go 1.26.5.
encoding/json end to end — Marshal and Unmarshal, struct tags and omitempty, why only exported fields survive, streaming with Encoder and Decoder, and the three silent gotchas: ignored unknown fields, DisallowUnknownFields, and numbers that decode to float64. Compiled and run against Go 1.26.5.
The func(next http.Handler) http.Handler pattern — building logging and auth middleware, chaining them, capturing the status code with a ResponseWriter wrapper, and passing request-scoped values through context with typed unexported keys. Compiled and run against Go 1.26.5.
Making outbound requests with net/http — http.Get versus a configured http.Client, the default client's missing timeout that hangs you forever, closing the body, checking StatusCode, decoding JSON, reusing one client, and per-request deadlines with NewRequestWithContext. Compiled and run against Go 1.26.5.
Reading and writing files with os, the two tiny interfaces io.Reader and io.Writer that unify every stream in Go, io.Copy, buffered scanning and its 64KB line trap, and why io.EOF is a value you expect. Compiled and run against Go 1.26.5.
The time package: instants and durations, the arithmetic on both, and the famous reference-date layout string that is an example time rather than a set of format codes, plus tickers, timers, and the monotonic clock. Compiled and run against Go 1.26.5.
Building a real CLI with flag and os: parsing flags and positional args, the auto-generated usage, exit codes with os.Exit and the deferred-function trap it springs, writing errors to stderr, and subcommands with flag.NewFlagSet. Compiled and run against Go 1.26.5.
How Go talks to a SQL database through the database/sql package: opening a pool, querying rows and scanning them, the sql.ErrNoRows and NULL traps that bite everyone once, placeholders that stop injection, prepared statements, and context for cancellation. Compiled and run against Go 1.26.5 with a real SQLite database.
Go's testing is built into the toolchain: table-driven tests, t.Run subtests, t.Helper, t.Cleanup, t.Parallel, comparing composites with slices.Equal and reflect.DeepEqual, and exercising HTTP handlers with httptest — a recorder for the fast path and a real server for the honest one. Compiled and run against Go 1.26.5.
Measuring code with go test -bench and the modern b.Loop, reading a real ns/op B/op allocs/op line, then handing a naive string reverse to the fuzzer and watching it corrupt UTF-8 and write the failing input to disk. Coverage as a number, not a goal. Compiled and run against Go 1.26.5.
Generating HTML with the standard library's html/template: parsing and executing templates, passing structs and ranging over slices, composing pages with define/template/block — and the headline feature, contextual auto-escaping, that turns a <script> payload into harmless text in every context. Plus the one import line separating html/template from text/template that decides whether your site is safe. Compiled and run against Go 1.26.5.
Building and running a small JSON REST service on the 1.22 ServeMux — GET/POST/GET-by-id/DELETE, an in-memory store behind an RWMutex, logging and panic-recovery middleware, request-scoped context, and go:embed serving a static page. Table-driven httptest tests, run. Compiled and run against Go 1.26.5.