Go Development

Project Structure

myproject/ ├── cmd/ │ └── server/ │ └── main.go ├── internal/ │ ├── handler/ │ ├── service/ │ └── repository/ ├── pkg/ │ └── shared/ ├── go.mod └── go.sum

Error Handling

// Custom error types type NotFoundError struct { Resource string ID string }

func (e *NotFoundError) Error() string { return fmt.Sprintf("%s not found: %s", e.Resource, e.ID) }

// Error wrapping func GetUser(id string) (*User, error) { user, err := db.FindUser(id) if err != nil { return nil, fmt.Errorf("GetUser(%s): %w", id, err) } return user, nil }

// Error checking if errors.Is(err, sql.ErrNoRows) { return nil, &NotFoundError{Resource: "user", ID: id} }

Concurrency

// Goroutines with errgroup func fetchAll(ctx context.Context, urls []string) ([]Response, error) { g, ctx := errgroup.WithContext(ctx) results := make([]Response, len(urls))

for i, url := range urls {
    i, url := i, url // capture loop variables
    g.Go(func() error {
        resp, err := fetch(ctx, url)
        if err != nil {
            return err
        }
        results[i] = resp
        return nil
    })
}

if err := g.Wait(); err != nil {
    return nil, err
}
return results, nil

}

// Channels func producer(ch chan<- int) { for i := 0; i < 10; i++ { ch <- i } close(ch) }

func consumer(ch <-chan int) { for v := range ch { fmt.Println(v) } }

HTTP Handler

func (h *Handler) GetUser(w http.ResponseWriter, r *http.Request) { ctx := r.Context() id := chi.URLParam(r, "id")

user, err := h.service.GetUser(ctx, id)
if err != nil {
    var notFound *NotFoundError
    if errors.As(err, &notFound) {
        http.Error(w, err.Error(), http.StatusNotFound)
        return
    }
    http.Error(w, "Internal error", http.StatusInternalServerError)
    return
}

w.Header().Set("Content-Type", "application/json")
json.NewEncoder(w).Encode(user)

}

Testing

func TestGetUser(t *testing.T) { t.Parallel()

tests := []struct {
    name    string
    id      string
    want    *User
    wantErr bool
}{
    {
        name: "existing user",
        id:   "123",
        want: &User{ID: "123", Email: "test@example.com"},
    },
    {
        name:    "non-existent user",
        id:      "999",
        wantErr: true,
    },
}

for _, tt := range tests {
    t.Run(tt.name, func(t *testing.T) {
        got, err := service.GetUser(context.Background(), tt.id)
        if (err != nil) != tt.wantErr {
            t.Errorf("error = %v, wantErr %v", err, tt.wantErr)
        }
        if !reflect.DeepEqual(got, tt.want) {
            t.Errorf("got = %v, want %v", got, tt.want)
        }
    })
}

}

Tooling

Format

gofmt -w . goimports -w .

Lint

golangci-lint run

Test

go test -v -race -cover ./...