diff --git a/digitalclock/README.md b/digitalclock/README.md
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--- /dev/null
+++ b/digitalclock/README.md
@@ -0,0 +1,114 @@
+## digitalclock
+
+В этой задаче нужно написать http server,
+который по запросу `/?time=hh:mm:ss` вернет PNG с данным временем.
+
+Сервер должен слушать порт, переданный через аргумент `--port`.
+
+### Примеры
+
+Запуск:
+```
+$ digitalclock -port 6029
+```
+
+После запуска можно открыть в браузере `http://localhost:6029/?time=15:04:05` и получить png наподобие этой:
+
+![Image description](assets/150405.png)
+
+Если параметр `time` не задан (или равен ""), сервен должен вернуть текущее время.
+В этом случае при обновлении страницы картинка должна меняться.
+
+В запросе также нужно поддержать параметр 1 <=`k` <= 30,
+который отвечает за увеличение картинки в `k` раз:
+
+http://localhost:6029/?time=15:04:05?k=15
+
+![Image description](assets/150405_15.png)
+
+На невалидных `time` и `k` сервер должен возврщать произвольное сообщение об ошибке и http status 400 (Bad Request):
+
+```
+$ curl -i "http://localhost:6029/?k=100" 
+HTTP/1.1 400 Bad Request
+Content-Type: text/plain; charset=utf-8
+X-Content-Type-Options: nosniff
+Date: Fri, 14 Feb 2020 02:02:41 GMT
+Content-Length: 10
+
+invalid k
+```
+
+В случае успеха приложение должно возвращать http status 200 (OK),
+а также проставлять http header `Content-Type: image/png`:
+
+```
+$ curl -i "http://localhost:6029/"                   
+HTTP/1.1 200 OK
+Content-Type: image/png
+Date: Fri, 14 Feb 2020 02:08:19 GMT
+Content-Length: 193
+...
+```
+
+### Формат
+
+`hh:mm:ss`
+
+В [./symbols.go](./symbols.go) определены строковые константы, кодирующие цифры и двоеточие.
+Один символ константы (отличный от '\n') - 1 пиксель.
+'.' должны кодироваться в белый цвет, '1' - в бирюзовый (переменная **Cyan** в [./symbols.go](./symbols.go)).
+Все константы имеют одинаковую высоту `h`, все цифры имеют одинаковую ширину `w`.
+
+`k` отличный от 1 (default) превращает каждый пиксель `p` картинки в блок `k x k` пикселей `p`.
+Высота результирующей картинки - `h * k`, ширина - `(6 * w + 2 * w_colon) * k`,
+где `w_colon` ширина константы, соответствующей ':'.
+
+### Проверка решения
+
+Для запуска тестов нужно выполнить следующую команду:
+
+```
+go test -v ./digitalclock/...
+```
+
+### Запуск программы
+
+```
+go run -v ./digitalclock/...
+```
+
+### Компиляция
+
+```
+go install ./digitalclock/...
+```
+
+После выполнения в `$GOPATH/bin` появится исполняемый файл с именем `digitalclock`.
+
+### Walkthrough
+
+1. парсинг аргументов командной строки https://gobyexample.com/command-line-flags
+2. http server: https://p.go.manytask.org/00-intro/lecture.slide#23
+3. url params: https://golang.org/pkg/net/url/#URL.Query
+3. форматирование времени: https://gobyexample.com/time-formatting-parsing
+4. работа с картинками: https://golang.org/pkg/image/
+
+Пример, создания простой png размера 5x5:
+```go
+package main
+
+import (
+        "image"
+        "image/color"
+        "image/png"
+        "os"
+)
+
+func main() {
+        img := image.NewRGBA(image.Rect(0, 0, 5, 5))
+        img.Set(2, 2, color.RGBA{255, 0, 0, 255})
+        f, _ := os.Create("/tmp/img.png")
+        png.Encode(f, img)
+}
+```
diff --git a/digitalclock/assets/150405.png b/digitalclock/assets/150405.png
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diff --git a/digitalclock/main.go b/digitalclock/main.go
new file mode 100644
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--- /dev/null
+++ b/digitalclock/main.go
@@ -0,0 +1,7 @@
+// +build !solution
+
+package main
+
+func main() {
+
+}
diff --git a/digitalclock/main_test.go b/digitalclock/main_test.go
new file mode 100644
index 0000000..20e8bff
--- /dev/null
+++ b/digitalclock/main_test.go
@@ -0,0 +1,249 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"image"
+	"image/png"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"os"
+	"os/exec"
+	"path"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"gitlab.com/slon/shad-go/tools/testtool"
+)
+
+const importPath = "gitlab.com/slon/shad-go/digitalclock"
+
+var binCache testtool.BinCache
+
+func TestMain(m *testing.M) {
+	os.Exit(func() int {
+		var teardown testtool.CloseFunc
+		binCache, teardown = testtool.NewBinCache()
+		defer teardown()
+
+		return m.Run()
+	}())
+}
+
+func startServer(t *testing.T) (port string, stop func()) {
+	binary, err := binCache.GetBinary(importPath)
+	require.NoError(t, err)
+
+	port, err = testtool.GetFreePort()
+	require.NoError(t, err, "unable to get free port")
+
+	cmd := exec.Command(binary, "-port", port)
+	cmd.Stdout = nil
+	cmd.Stderr = os.Stderr
+
+	require.NoError(t, cmd.Start())
+
+	done := make(chan error)
+	go func() {
+		done <- cmd.Wait()
+	}()
+
+	stop = func() {
+		_ = cmd.Process.Kill()
+		<-done
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*30)
+	defer cancel()
+
+	testtool.WaitForPort(ctx, port)
+	if ctx.Err() != nil {
+		err = ctx.Err()
+		stop()
+	}
+
+	require.NoError(t, err)
+	return
+}
+
+func readImage(fname string) (image.Image, error) {
+	f, err := os.Open(fname)
+	if err != nil {
+		return nil, fmt.Errorf("unable to open %s: %w", fname, err)
+	}
+	defer func() { _ = f.Close() }()
+
+	img, _, err := image.Decode(f)
+	if err != nil {
+		return nil, fmt.Errorf("unable to decode %s: %w", fname, err)
+	}
+
+	return img, nil
+}
+
+func abs(a, b uint32) int64 {
+	if a > b {
+		return int64(a - b)
+	}
+	return int64(b - a)
+}
+
+func calcImgDiff(i1, i2 image.Image) float64 {
+	w, h := i1.Bounds().Dx(), i1.Bounds().Dy()
+
+	var sum int64
+	for x := 0; x < w; x++ {
+		for y := 0; y < h; y++ {
+			r1, g1, b1, _ := i1.At(x, y).RGBA()
+			r2, g2, b2, _ := i2.At(x, y).RGBA()
+			sum += abs(r1, r2)
+			sum += abs(g1, g2)
+			sum += abs(b1, b2)
+		}
+	}
+
+	return float64(sum) / (float64(w*h) * 0xffff * 3) * 100.0
+}
+
+func queryImage(t *testing.T, c *http.Client, url string) image.Image {
+	t.Logf("querying: %s", url)
+
+	resp, err := c.Get(url)
+	require.NoError(t, err)
+	defer func() { _ = resp.Body.Close() }()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+	require.Equal(t, "image/png", resp.Header.Get("Content-Type"))
+
+	img, err := png.Decode(resp.Body)
+	require.Nil(t, err)
+
+	return img
+}
+
+func TestDigitalClock_valid(t *testing.T) {
+	port, stop := startServer(t)
+	defer stop()
+
+	files, err := ioutil.ReadDir("./testdata")
+	require.Nil(t, err)
+
+	c := &http.Client{Timeout: time.Second * 10}
+
+	for _, f := range files {
+		t.Run(f.Name(), func(t *testing.T) {
+			parts := strings.SplitN(strings.TrimSuffix(f.Name(), ".png"), "_", 2)
+
+			v := url.Values{}
+			v.Add("time", parts[0])
+			v.Add("k", parts[1])
+
+			u := fmt.Sprintf("http://localhost:%s/?%s", port, v.Encode())
+			img := queryImage(t, c, u)
+
+			expected, err := readImage(path.Join("testdata", f.Name()))
+			require.NoError(t, err)
+
+			w, h := img.Bounds().Dx(), img.Bounds().Dy()
+			ew, eh := expected.Bounds().Dx(), expected.Bounds().Dy()
+			if w != ew || h != eh {
+				t.Errorf("expected size %d x %d got %d x %d", ew, eh, w, h)
+			}
+
+			diff := calcImgDiff(img, expected)
+			t.Logf("image diff: %.2f %%", diff)
+			require.True(t, diff < 1.0,
+				fmt.Sprintf("%s images are too different (%.2f %%)", f.Name(), diff))
+		})
+	}
+}
+
+func TestDigitalClock_invalid(t *testing.T) {
+	port, stop := startServer(t)
+	defer stop()
+
+	c := &http.Client{Timeout: time.Second * 10}
+
+	type TestCase struct {
+		Time string `json:"time"`
+		K    string `json:"k"`
+	}
+
+	testName := func(tc *TestCase) string {
+		data, err := json.Marshal(tc)
+		require.Nil(t, err)
+		return string(data)
+	}
+
+	for _, tc := range []*TestCase{
+		{K: "0"},
+		{K: "31"},
+		{K: "2.5"},
+		{K: "f"},
+		{Time: "15:04"},
+		{Time: "15:04:0"},
+		{Time: "3:04:05"},
+		{Time: "15:4:05"},
+		{Time: "24:00:00"},
+		{Time: "00:00:60"},
+		{Time: "f"},
+	} {
+		t.Run(testName(tc), func(t *testing.T) {
+			v := url.Values{}
+			if tc.Time != "" {
+				v.Add("time", tc.Time)
+			}
+			if tc.K != "" {
+				v.Add("k", tc.K)
+			}
+
+			u := fmt.Sprintf("http://localhost:%s/?%s", port, v.Encode())
+			t.Logf("querying: %s", u)
+
+			resp, err := c.Get(u)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+
+			require.Equal(t, http.StatusBadRequest, resp.StatusCode)
+		})
+	}
+}
+
+func TestDigitalClock_now(t *testing.T) {
+	port, stop := startServer(t)
+	defer stop()
+
+	c := &http.Client{Timeout: time.Second * 10}
+
+	for _, k := range []int{1, 10, 29} {
+		k := k
+		t.Run(fmt.Sprintf("k=%d", k), func(t *testing.T) {
+			v := url.Values{"k": []string{strconv.Itoa(k)}}
+			u := fmt.Sprintf("http://localhost:%s/?%s", port, v.Encode())
+			img := queryImage(t, c, u)
+
+			w, h := img.Bounds().Dx(), img.Bounds().Dy()
+			ew, eh := getExpectedWidth(k), getExpectedHeight(k)
+			if w != ew || h != eh {
+				t.Errorf("expected size %d x %d got %d x %d", ew, eh, w, h)
+			}
+		})
+	}
+}
+
+func getSymbolWidth(s string) int {
+	return len(strings.SplitN(s, "\n", 2)[0])
+}
+
+func getExpectedWidth(k int) int {
+	return (getSymbolWidth(Zero)*6 + getSymbolWidth(Colon)*2) * k
+}
+
+func getExpectedHeight(k int) int {
+	return len(strings.Split(Zero, "\n")) * k
+}
diff --git a/digitalclock/symbols.go b/digitalclock/symbols.go
new file mode 100644
index 0000000..8578102
--- /dev/null
+++ b/digitalclock/symbols.go
@@ -0,0 +1,152 @@
+// +build !change
+
+package main
+
+import "image/color"
+
+var Cyan = color.RGBA{R: 100, G: 200, B: 200, A: 0xff}
+
+const (
+	Zero = `........
+.111111.
+.111111.
+.11..11.
+.11..11.
+.11..11.
+.11..11.
+.11..11.
+.11..11.
+.111111.
+.111111.
+........`
+
+	One = `........
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+........`
+
+	Two = `........
+.111111.
+.111111.
+.....11.
+.....11.
+.111111.
+.111111.
+.11.....
+.11.....
+.111111.
+.111111.
+........`
+
+	Three = `........
+.111111.
+.111111.
+.....11.
+.....11.
+.111111.
+.111111.
+.....11.
+.....11.
+.111111.
+.111111.
+........`
+
+	Four = `........
+.11..11.
+.11..11.
+.11..11.
+.11..11.
+.111111.
+.111111.
+.....11.
+.....11.
+.....11.
+.....11.
+........`
+
+	Five = `........
+.111111.
+.111111.
+.11.....
+.11.....
+.111111.
+.111111.
+.....11.
+.....11.
+.111111.
+.111111.
+........`
+
+	Six = `........
+.111111.
+.111111.
+.11.....
+.11.....
+.111111.
+.111111.
+.11..11.
+.11..11.
+.111111.
+.111111.
+........`
+
+	Seven = `........
+.111111.
+.111111.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+.....11.
+........`
+
+	Eight = `........
+.111111.
+.111111.
+.11..11.
+.11..11.
+.111111.
+.111111.
+.11..11.
+.11..11.
+.111111.
+.111111.
+........`
+
+	Nine = `........
+.111111.
+.111111.
+.11..11.
+.11..11.
+.111111.
+.111111.
+.....11.
+.....11.
+.....11.
+.....11.
+........`
+
+	Colon = `....
+....
+....
+....
+.11.
+.11.
+....
+.11.
+.11.
+....
+....
+....`
+)
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