*(dnsforward): added QLogFile struct

This struct is supposed to use an easier algorithm for scanning query
log files. The end goal is allow us scanning multiple query log files.

querylog/qlog_file_test.go

@@ -0,0 +1,59 @@
+package querylog
+
+import (
+	"io"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Check adding and loading (with filtering) entries from disk and memory
+func TestQLogFile(t *testing.T) {
+	conf := Config{
+		Enabled:  true,
+		Interval: 1,
+		MemSize:  100,
+	}
+	conf.BaseDir = prepareTestDir()
+	defer func() { _ = os.RemoveAll(conf.BaseDir) }()
+	l := newQueryLog(conf)
+
+	// add disk entries
+	addEntry(l, "example.org", "1.2.3.4", "0.1.2.4")
+	addEntry(l, "example.org", "1.2.3.4", "0.1.2.5")
+
+	// write to disk
+	_ = l.flushLogBuffer(true)
+
+	// create the new QLogFile instance
+	q, err := NewQLogFile(l.logFile)
+	assert.Nil(t, err)
+	assert.NotNil(t, q)
+
+	// seek to the start
+	pos, err := q.SeekStart()
+	assert.Nil(t, err)
+	assert.True(t, pos > 0)
+
+	// read first line
+	line, err := q.ReadNext()
+	assert.Nil(t, err)
+	assert.True(t, strings.Contains(line, "0.1.2.5"), line)
+	assert.True(t, strings.HasPrefix(line, "{"), line)
+	assert.True(t, strings.HasSuffix(line, "}"), line)
+
+	// read second line
+	line, err = q.ReadNext()
+	assert.Nil(t, err)
+	assert.Equal(t, int64(0), q.position)
+	assert.True(t, strings.Contains(line, "0.1.2.4"), line)
+	assert.True(t, strings.HasPrefix(line, "{"), line)
+	assert.True(t, strings.HasSuffix(line, "}"), line)
+
+	// try reading again (there's nothing to read anymore)
+	line, err = q.ReadNext()
+	assert.Equal(t, io.EOF, err)
+	assert.Equal(t, "", line)
+}