Challenge 2 - Microservice

Write a service with HTTP API + database + Docker.

Challenge: a robust service

You will combine three pieces that make an HTTP service production-ready: middleware that adds a request ID, recover middleware that turns panics into 500, and a mux serving only the GET /urunler/{id} route. An unknown id returns 404.

chain: recoverMW → istekID → mux
GET /urunler/1  → 200 "Kalem"
GET /urunler/9  → 404

Plan

1) urunler := map[string]string{"1": "Kalem"}. 2) Look up with r.PathValue("id") inside mux.HandleFunc("GET /urunler/{id}", ...). 3) h := recoverMW(istekID(mux)). 4) Send two requests with httptest and print the codes. Write the middleware as in earlier groups; order matters: recover outermost.

Exercise Build the service

Implement the plan above. Print the status codes of GET /urunler/1 and GET /urunler/9 on one line.

Show example solution

package main

import (
    "fmt"
    "net/http"
    "net/http/httptest"
)

func recoverMW(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        defer func() {
            if v := recover(); v != nil {
                http.Error(w, "sunucu hatası", 500)
            }
        }()
        next.ServeHTTP(w, r)
    })
}

func istekID(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("X-Request-ID", "r1")
        next.ServeHTTP(w, r)
    })
}

func main() {
    urunler := map[string]string{"1": "Kalem"}
    mux := http.NewServeMux()
    mux.HandleFunc("GET /urunler/{id}", func(w http.ResponseWriter, r *http.Request) {
        ad, ok := urunler[r.PathValue("id")]
        if !ok {
            http.NotFound(w, r)
            return
        }
        fmt.Fprint(w, ad)
    })
    h := recoverMW(istekID(mux))
    kod := func(yol string) int {
        rec := httptest.NewRecorder()
        h.ServeHTTP(rec, httptest.NewRequest("GET", yol, nil))
        return rec.Code
    }
    fmt.Println(kod("/urunler/1"), kod("/urunler/9"))
}

Test yourself

If you read the route id and don't find it in the map, what do you do?
- Return 200 with an empty body
- Shut the server down
- Return 404 with http.NotFound(w, r)
- Call panic
Show answer

Return 404 with http.NotFound(w, r) — A missing resource is an expected case; it is reported with 404, not a panic.

Path variable

ad, ok := urunler[r.____("id")]

Show answer

ad, ok := urunler[r.PathValue("id")]

Piece and role

recoverMW

Panic → 500
istekID

X-Request-ID
mux

Routing
http.NotFound

404 response

Next lesson: Challenge 3 - Performance

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