queue: Implement persistency

This patch makes the queue read and write items to disk.

It uses protobuf for serialization. We serialize to text format to make
manual troubleshooting easier, as the performance difference is not very
relevant for us.

internal/queue/queue_test.go

@@ -2,6 +2,7 @@ package queue
 
 import (
 	"bytes"
+	"fmt"
 	"sync"
 	"testing"
 	"time"
@@ -57,7 +58,9 @@ func newTestCourier() *TestCourier {
 func TestBasic(t *testing.T) {
 	localC := newTestCourier()
 	remoteC := newTestCourier()
-	q := New(localC, remoteC, set.NewString("loco"))
+	q := New("/tmp/queue_test", set.NewString("loco"))
+	q.localC = localC
+	q.remoteC = remoteC
 
 	localC.wg.Add(2)
 	remoteC.wg.Add(1)
@@ -96,35 +99,39 @@ func TestBasic(t *testing.T) {
 }
 
 func TestFullQueue(t *testing.T) {
-	localC := newChanCourier()
-	remoteC := newChanCourier()
-	q := New(localC, remoteC, set.NewString())
+	q := New("/tmp/queue_test", set.NewString())
 
 	// Force-insert maxQueueSize items in the queue.
 	oneID := ""
 	for i := 0; i < maxQueueSize; i++ {
 		item := &Item{
-			ID:      <-newID,
-			From:    "from",
-			To:      []string{"to"},
-			Data:    []byte("data"),
-			Created: time.Now(),
-			Results: map[string]error{},
+			Message: Message{
+				ID:   <-newID,
+				From: fmt.Sprintf("from-%d", i),
+				Rcpt: []*Recipient{{"to", Recipient_EMAIL, Recipient_PENDING}},
+				Data: []byte("data"),
+			},
+			CreatedAt: time.Now(),
 		}
 		q.q[item.ID] = item
 		oneID = item.ID
 	}
 
 	// This one should fail due to the queue being too big.
-	id, err := q.Put("from", []string{"to"}, []byte("data"))
+	id, err := q.Put("from", []string{"to"}, []byte("data-qf"))
 	if err != errQueueFull {
 		t.Errorf("Not failed as expected: %v - %v", id, err)
 	}
 
 	// Remove one, and try again: it should succeed.
+	// Write it first so we don't get complaints about the file not existing
+	// (as we did not all the items properly).
+	q.q[oneID].WriteTo(q.path)
 	q.Remove(oneID)
-	_, err = q.Put("from", []string{"to"}, []byte("data"))
+
+	id, err = q.Put("from", []string{"to"}, []byte("data"))
 	if err != nil {
 		t.Errorf("Put: %v", err)
 	}
+	q.Remove(id)
 }