lib/model: Properly schedule pull on reconnect (fixes #4504)

We need to reset prevSeq so that we force a full check when someone
reconnects - the sequence number may not have changed due to the
reconnect. (This is a regression; we did this before f6ea2a7.)

Also add an optimization: we schedule a pull after scanning, but there
is no need to do so if no changes were detected. This matters now
because the scheduled pull actually traverses the database which is
expensive.

This, however, makes the pull not happen on initial scan if there were
no changes during the initial scan. Compensate by always scheduling a
pull after initial scan in the rwfolder itself.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4508
LGTM: imsodin, AudriusButkevicius

3 files changed, 29 insertions, 63 deletions

diff --git a/test/reconnect_test.go b/test/reconnect_test.go
index 12f3afd91..25f499f38 100644
--- a/test/reconnect_test.go
+++ b/test/reconnect_test.go
@@ -10,27 +10,19 @@ package integration
 
 import (
 	"log"
-	"sync"
 	"testing"
 	"time"
 )
 
 func TestReconnectReceiverDuringTransfer(t *testing.T) {
-	testReconnectDuringTransfer(t, false, true, 0, 0)
+	testReconnectDuringTransfer(t, false, true)
 }
 
 func TestReconnectSenderDuringTransfer(t *testing.T) {
-	testReconnectDuringTransfer(t, true, false, 0, 0)
+	testReconnectDuringTransfer(t, true, false)
 }
 
-func TestReconnectSenderAndReceiverDuringTransfer(t *testing.T) {
-	// Give the receiver some time to rot with needed files but
-	// without any peer. This triggers
-	// https://github.com/syncthing/syncthing/issues/463
-	testReconnectDuringTransfer(t, true, true, 10*time.Second, 0)
-}
-
-func testReconnectDuringTransfer(t *testing.T, ReconnectSender, ReconnectReceiver bool, senderDelay, receiverDelay time.Duration) {
+func testReconnectDuringTransfer(t *testing.T, restartSender, restartReceiver bool) {
 	log.Println("Cleaning...")
 	err := removeAll("s1", "s2", "h1/index*", "h2/index*")
 	if err != nil {
@@ -38,7 +30,7 @@ func testReconnectDuringTransfer(t *testing.T, ReconnectSender, ReconnectReceive
 	}
 
 	log.Println("Generating files...")
-	err = generateFiles("s1", 2500, 20, "../LICENSE")
+	err = generateFiles("s1", 250, 20, "../LICENSE")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -63,8 +55,9 @@ func testReconnectDuringTransfer(t *testing.T, ReconnectSender, ReconnectReceive
 	if err != nil {
 		t.Fatal(err)
 	}
-	cfg.Options.MaxRecvKbps = 100
-	cfg.Options.MaxSendKbps = 100
+	cfg.Options.MaxRecvKbps = 750
+	cfg.Options.MaxSendKbps = 750
+	cfg.Options.LimitBandwidthInLan = true
 	if err := receiver.PostConfig(cfg); err != nil {
 		t.Fatal(err)
 	}
@@ -86,42 +79,22 @@ func testReconnectDuringTransfer(t *testing.T, ReconnectSender, ReconnectReceive
 			// Receiver has made progress
 			prevBytes = recv.InSyncBytes
 
-			if ReconnectReceiver {
-				log.Printf("Pausing receiver...")
-				receiver.PauseAll()
-			}
-
-			if ReconnectSender {
-				log.Printf("Pausing sender...")
-				sender.PauseAll()
+			if restartReceiver {
+				log.Printf("Stopping receiver...")
+				receiver.Stop()
+				receiver = startInstance(t, 2)
+				receiver.ResumeAll()
 			}
 
-			var wg sync.WaitGroup
-
-			if ReconnectReceiver {
-				wg.Add(1)
-				go func() {
-					time.Sleep(receiverDelay)
-					log.Printf("Resuming receiver...")
-					receiver.ResumeAll()
-					wg.Done()
-				}()
-			}
-
-			if ReconnectSender {
-				wg.Add(1)
-				go func() {
-					time.Sleep(senderDelay)
-					log.Printf("Resuming sender...")
-					sender.ResumeAll()
-					wg.Done()
-				}()
+			if restartSender {
+				log.Printf("Stopping sender...")
+				sender.Stop()
+				sender = startInstance(t, 1)
+				sender.ResumeAll()
 			}
-
-			wg.Wait()
 		}
 
-		time.Sleep(time.Second)
+		time.Sleep(250 * time.Millisecond)
 	}
 
 	// Reset rate limits
@@ -131,6 +104,7 @@ func testReconnectDuringTransfer(t *testing.T, ReconnectSender, ReconnectReceive
 	}
 	cfg.Options.MaxRecvKbps = 0
 	cfg.Options.MaxSendKbps = 0
+	cfg.Options.LimitBandwidthInLan = false
 	if err := receiver.PostConfig(cfg); err != nil {
 		t.Fatal(err)
 	}
diff --git a/test/reset_test.go b/test/reset_test.go
index e0b1c2029..bb9711fe4 100644
--- a/test/reset_test.go
+++ b/test/reset_test.go
@@ -10,7 +10,9 @@ package integration
 
 import (
 	"bytes"
+	"fmt"
 	"io"
+	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -128,25 +130,15 @@ func TestReset(t *testing.T) {
 }
 
 func createFiles(t *testing.T) int {
-	// Create eight empty files and directories
-	files := []string{"f1", "f2", "f3", "f4", "f11", "f12", "f13", "f14"}
-	dirs := []string{"d1", "d2", "d3", "d4", "d11", "d12", "d13", "d14"}
-	all := append(files, dirs...)
-
-	for _, file := range files {
-		fd, err := os.Create(filepath.Join("s1", file))
-		if err != nil {
-			t.Fatal(err)
-		}
-		fd.Close()
-	}
+	// Create a few files
 
-	for _, dir := range dirs {
-		err := os.Mkdir(filepath.Join("s1", dir), 0755)
-		if err != nil {
+	const n = 8
+	for i := 0; i < n; i++ {
+		file := fmt.Sprintf("f%d", i)
+		if err := ioutil.WriteFile(filepath.Join("s1", file), []byte("data"), 0644); err != nil {
 			t.Fatal(err)
 		}
 	}
 
-	return len(all)
+	return n
 }
diff --git a/test/sync_test.go b/test/sync_test.go
index 600dcd3c1..ad5d1388c 100644
--- a/test/sync_test.go
+++ b/test/sync_test.go
@@ -20,8 +20,8 @@ import (
 )
 
 const (
-	longTimeLimit  = 5 * time.Minute
-	shortTimeLimit = 45 * time.Second
+	longTimeLimit  = 1 * time.Minute
+	shortTimeLimit = 25 * time.Second
 	s12Folder      = `¯\_(ツ)_/¯ Räksmörgås 动作 Адрес` // This was renamed to ensure arbitrary folder IDs are fine.
 )