Add end-to-end 'git clone' test

.gitignore

 gitlab-git-http-server
+test/data
+test/scratch

Makefile

@@ -6,3 +6,13 @@ gitlab-git-http-server: main.go
 
 install: gitlab-git-http-server
 	install gitlab-git-http-server ${PREFIX}/bin/
+
+.PHONY: test
+test: test/data/test.git
+	go test
+
+test/data/test.git: test/data
+	git clone --bare https://gitlab.com/gitlab-org/gitlab-test.git test/data/test.git
+
+test/data:
+	mkdir -p test/data

main_test.go

+package main
+
+import (
+	"fmt"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path"
+	"syscall"
+	"testing"
+	"time"
+)
+
+const servAddr = "127.0.0.1:8181"
+const servWaitListen = 10000 // milliseconds to wait for server to start listening
+const servWaitSleep = 100    // milliseconds sleep interval
+const scratchDir = "test/scratch"
+const testRepoRoot = "test/data"
+
+func TestAllowedClone(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, `{"GL_ID":"user-123"}`)
+	}))
+	defer ts.Close()
+	defer cleanUpProcessGroup(startServer(t, ts))
+	if err := os.RemoveAll(scratchDir); err != nil {
+		t.Fatal(err)
+	}
+	cloneCmd := exec.Command("git", "clone", fmt.Sprintf("http://%s/test.git", servAddr), path.Join(scratchDir, "test"))
+	if out, err := cloneCmd.CombinedOutput(); err != nil {
+		t.Logf("%s", out)
+		t.Fatal(err)
+	}
+}
+
+func startServer(t *testing.T, ts *httptest.Server) (cmd *exec.Cmd) {
+	var conn net.Conn
+	var err error
+	cmd = exec.Command("go", "run", "main.go", fmt.Sprintf("-authBackend=%s", ts.URL), fmt.Sprintf("-listenAddr=%s", servAddr), testRepoRoot)
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < servWaitListen/servWaitSleep; i++ {
+		conn, err = net.Dial("tcp", servAddr)
+		if err == nil {
+			conn.Close()
+			break
+		}
+		time.Sleep(servWaitSleep * time.Millisecond)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+	return
+}