Weekly Review — Month 2 · Week 2 (Days 036–042)¶

Journal index · Roadmap › Month 2 Week 2

📅 The Week in One Line¶

Assembled the standard library into a service-building toolkit: encoding/json (incl. struct tags & custom marshalers), the time package, the net/http client, context deadlines/cancellation, and log/slog structured logging.

✅ What I Completed¶

Day 036 — encoding/json Marshal & Unmarshal (+ json-tags example)
Day 037 — struct tags & custom Marshaler/Unmarshaler (+ tempjson exercise)
Day 038 — time: durations, formatting, timers (+ time-timers example, humandur exercise)
Day 039 — net/http client & requests (+ http-context example)
Day 040 — context timeouts & cancellation (+ retry exercise)
Day 041 — log/slog structured logging (+ slog-structured example)
Day 042 — Review & closed-book recall
Runnable examples: 4 (json-tags, time-timers, http-context, slog-structured)
Exercises solved: 3 (tempjson, humandur, retry) — all with table-driven tests

💡 Lessons Learned¶

json only sees exported fields; Unmarshal needs a pointer; numbers into interface{} become float64.
Custom JSON: MarshalJSON can use a value receiver, but UnmarshalJSON must be a pointer receiver or it's silently ignored. Beware self-recursion inside MarshalJSON.
time.Duration is nanoseconds; format/parse with the magic reference date 2006-01-02 15:04:05; always Stop() a Ticker.
http.Get/DefaultClient have no timeout; always close resp.Body; a 404/500 is data, not a Go error.
A context only signals — blocking code must select on ctx.Done(); always defer cancel(); use errors.Is for DeadlineExceeded/Canceled.
slog: handler decides format/destination/level; prefer typed attrs over loose pairs; With builds request-scoped child loggers.

💪 Strengths (what clicked)¶

Struct tags and the Marshaler/Unmarshaler escape hatch — the custom Celsius round trip felt natural.
The context + http pairing: per-call WithTimeout bound to a request via NewRequestWithContext.
slog typed attributes and child loggers.

🧩 Weaknesses (what's still fuzzy)¶

json.RawMessage and partial/lazy decoding.
time.Timer.Reset correctness (draining the channel) and Round vs Truncate edge cases.
Tuning http.Transport (connection pool, dial timeouts) beyond Client.Timeout.
Writing a custom slog.Handler that injects a trace ID from context.

🔁 Spaced-Repetition Re-quiz (topics from earlier weeks)¶

Q: (Month 1) nil slice vs nil map — which is safe to use, which panics?
A
A nil slice is safe to append to and range; writing to a nil map panics (reads return the zero value).
Q: (Month 2 W1) Why must you Flush a bufio.Writer?
A
It buffers writes in memory; without Flush the pending bytes never reach the underlying writer.
Q: (Month 2 W1) Which fmt verb prints a value's Go-syntax form ignoring String()?
A
%#v.
Q: (This week) Why must UnmarshalJSON have a pointer receiver?
A
It must mutate the destination; json only invokes the Unmarshaler it finds on the addressable value, so a value receiver is never called and the field stays zero.
Q: (This week) Does a ctx timeout stop a running time.Sleep?
A
No — context only signals via Done(). Blocking work must select on ctx.Done() or use a context-aware API; otherwise it runs to completion.

🎯 Action Items¶

Refactor http-context fetch to decode JSON straight from the body with json.NewDecoder.
Write a tiny custom slog.Handler that pulls a request ID out of context.Context.
Re-read the time reference-layout table once more; drill three custom layouts from memory.
Add a json.RawMessage mini-experiment for deferred decoding.

🚀 Next Week Goals¶

Deep dive on testing: table-driven subtests with t.Run, testing.B benchmarks + b.ReportAllocs(), fuzzing, and coverage.
The go toolchain end to end: go test/vet/build, gofmt/goimports, modules & versioning.
Apply this week's pieces in a small CLI/service that fetches JSON over HTTP with a context timeout and structured logs.

📊 Metrics¶

Hours	Days hit	Exercises	Commits	Avg confidence
10.5	7/7	3	7	3.⅗

Suggested commit: docs(journal): month 2 week 2 review