Add firewall task.

firewall/README.md

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+## firewall
+
+В этой задаче нужно написать примитивный файрвол.
+
+Файрвол - это прокси сервер, пропускающий через себя все запросы,
+и отвергающий некоторые из них по заданному набору правил.
+
+Пример правил можно посмотреть в [example.yaml](./configs/example.yaml).
+Все правила можно разделить на 2 группы: те, что приминяются к запросу и те, что приминяются к ответу.
+
+На все заблокированные запросы нужно отвечать статусом 403 и строкой `Forbidden`.
+
+## Примеры:
+В [http service](./cmd/service/main.go) находится примитивный сервис, который мы хотим защитить.
+```
+go run ./firewall/cmd/service/main.go -port 8080
+```
+```
+curl -i http://localhost:8080/list -d '"loooooooooooooooooooooooooooooong-line"'
+HTTP/1.1 200 OK
+Date: Thu, 02 Apr 2020 19:14:36 GMT
+Content-Length: 40
+Content-Type: text/plain; charset=utf-8
+
+"loooooooooooooooooooooooooooooong-line"
+```
+Стартуем firewall:
+```
+go run ./firewall/cmd/firewall/main.go -service-addr http://localhost:8080 -addr localhost:8081 -conf ./firewall/configs/example.yaml
+```
+Делем тот же запрос через него:
+```
+curl -i http://localhost:8081/list -d '"loooooooooooooooooooooooooooooong-line"'
+HTTP/1.1 403 Forbidden
+Date: Thu, 02 Apr 2020 19:14:40 GMT
+Content-Length: 9
+Content-Type: text/plain; charset=utf-8
+
+Forbidden
+```
+Сработало правило на максимальную длину запроса.
+
+
+## Resources
+
+* project layout: https://github.com/golang-standards/project-layout
+* yaml: https://gopkg.in/yaml.v2

firewall/cmd/firewall/main.go

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+// +build !solution
+
+package main
+
+func main() {
+
+}

firewall/cmd/firewall/main_test.go

@@ -0,0 +1,282 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path"
+	"testing"
+	"time"
+
+	"github.com/go-resty/resty/v2"
+	"github.com/stretchr/testify/require"
+
+	"gitlab.com/slon/shad-go/tools/testtool"
+)
+
+const importPath = "gitlab.com/slon/shad-go/firewall/cmd/firewall"
+
+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 storeConfig(t *testing.T, conf string) (filename string, cleanup func()) {
+	t.Helper()
+
+	filename = path.Join(os.TempDir(), testtool.RandomName()+".yaml")
+	err := ioutil.WriteFile(filename, []byte(conf), 0777)
+	require.NoError(t, err)
+
+	cleanup = func() { _ = os.Remove(filename) }
+	return
+}
+
+func startServer(t *testing.T, serviceURL string, conf string) (port string, stop func()) {
+	binary, err := binCache.GetBinary(importPath)
+	require.NoError(t, err)
+
+	confPath, removeConf := storeConfig(t, conf)
+	defer removeConf()
+
+	port, err = testtool.GetFreePort()
+	require.NoError(t, err, "unable to get free port")
+
+	addr := fmt.Sprintf("localhost:%s", port)
+
+	cmd := exec.Command(binary, "-service-addr", serviceURL, "-addr", addr, "-conf", confPath)
+	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
+	}
+
+	if err = testtool.WaitForPort(t, time.Second*5, port); err != nil {
+		stop()
+	}
+
+	require.NoError(t, err)
+	return
+}
+
+func TestFirewall(t *testing.T) {
+	echoService := func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.Copy(w, r.Body)
+		defer func() { _ = r.Body.Close() }()
+		w.Header().Set("Content-Length", fmt.Sprintf("%d", r.ContentLength))
+	}
+
+	c := resty.New()
+
+	type result struct {
+		code int
+		body string
+	}
+
+	for _, tc := range []struct {
+		name        string
+		conf        string
+		service     http.HandlerFunc
+		makeRequest func() *resty.Request
+		expected    result
+	}{
+		{
+			name:    "empty",
+			conf:    ``,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello")
+			},
+			expected: result{code: http.StatusOK, body: "hello"},
+		},
+		{
+			name: "simple",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_user_agents:
+      - 'python-requests.*'
+    forbidden_headers:
+      - 'Content-Type: text/html'
+    required_headers:
+      - "Content-Type"
+    max_request_length_bytes: 50
+    max_response_length_bytes: 50
+    forbidden_response_codes: [201]
+    forbidden_request_re:
+      - '.*(\.\./){3,}.*'
+    forbidden_response_re:
+      - '.*admin.*'
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().
+					SetBody(`{"user_id": 123, "path": "../../user"}`).
+					SetHeaders(map[string]string{
+						"User-Agent":   "Mozilla/5.0",
+						"Content-Type": "application/json",
+					})
+			},
+			expected: result{code: http.StatusOK, body: `{"user_id": 123, "path": "../../user"}`},
+		},
+		{
+			name: "bad-user-agent",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_user_agents:
+      - 'python-requests.*'
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello").SetHeader("User-Agent", "python-requests/2.22.0")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "forbidden-header",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_headers:
+      - 'Content-Type: text/html'
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello").SetHeader("Content-Type", "text/html")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "missing-required-header",
+			conf: `
+rules:
+  - endpoint: "/"
+    required_headers:
+      - "Content-Type"
+      - "Content-Length"
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello").SetHeader("Content-Length", "5")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "max-request-length-exceeded",
+			conf: `
+rules:
+  - endpoint: "/"
+    max_request_length_bytes: 4
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "max-response-length-exceeded",
+			conf: `
+rules:
+  - endpoint: "/"
+    max_response_length_bytes: 4
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "bad-status-code",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_response_codes: [20]
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "bad-status-code",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_response_codes: [20]
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody("hello")
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "bad-response",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_request_re:
+      - '.*(\.\./){3,}.*'
+`,
+			service: func(w http.ResponseWriter, r *http.Request) {},
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody(`{"path": "../../../../etc.passwd"}`)
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+		{
+			name: "bad-response",
+			conf: `
+rules:
+  - endpoint: "/"
+    forbidden_response_re:
+      - '.*admin.*'
+`,
+			service: echoService,
+			makeRequest: func() *resty.Request {
+				return c.R().SetBody(`{"user": "admin", "password": "1234"}`)
+			},
+			expected: result{code: http.StatusForbidden, body: "Forbidden"},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			service := httptest.NewServer(tc.service)
+			defer service.Close()
+
+			port, cleanup := startServer(t, service.URL, tc.conf)
+			defer cleanup()
+
+			u := fmt.Sprintf("http://localhost:%s", port)
+
+			resp, err := tc.makeRequest().Post(u)
+			require.NoError(t, err)
+
+			require.Equal(t, tc.expected.code, resp.StatusCode())
+			require.Equal(t, tc.expected.body, resp.String())
+		})
+	}
+}

firewall/cmd/service/main.go

@@ -0,0 +1,24 @@
+// +build !change
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+)
+
+func main() {
+	port := flag.String("port", "", "port to listen")
+	flag.Parse()
+
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.Copy(w, r.Body)
+		defer func() { _ = r.Body.Close() }()
+		w.Header().Set("Content-Length", fmt.Sprintf("%d", r.ContentLength))
+	})
+
+	log.Fatal(http.ListenAndServe(":"+*port, nil))
+}

firewall/configs/example.yaml

@@ -0,0 +1,29 @@
+rules:
+  - endpoint: "/list"
+
+    # Regular expressions that forbid specific user agents.
+    forbidden_user_agents:
+      - 'python-requests.*'
+
+    # Regular expressions that forbid specific header values.
+    forbidden_headers:
+      - 'Content-Type: text/html'
+
+    required_headers:
+      - "Content-Type"
+      - "Content-Length"
+
+    max_request_length_bytes: 20
+    max_response_length_bytes: 50
+
+    forbidden_response_codes: [201]
+
+  - endpoint: "/login"
+
+    # Regular expressions that ban specific requests.
+    forbidden_request_re:
+      - '.*(\.\./){3,}.*'
+
+    # Regular expressions that ban specific responses.
+    forbidden_response_re:
+      - '.*admin.*'