log: fix crash on removing log dir

Fix double closing the chanel on log dirs removing.

cli/cmd/log.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 	"os/signal"
+	"sync"
 
 	"github.com/spf13/cobra"
 	"github.com/tarantool/tt/cli/cmd/internal"
@@ -74,10 +75,12 @@ func follow(instances []running.InstanceCtx, n int) error {
 	const logLinesChannelCapacity = 64
 	logLines := make(chan string, logLinesChannelCapacity)
 	tailRoutinesStarted := 0
+	// Wait group to wait for completion of all log reading routines to close the channel once.
+	var wg sync.WaitGroup
 	for _, inst := range instances {
 		if err := tail.Follow(ctx, logLines,
 			tail.NewLogFormatter(running.GetAppInstanceName(inst)+": ", color),
-			inst.Log, n); err != nil {
+			inst.Log, n, &wg); err != nil {
 			if errors.Is(err, os.ErrNotExist) {
 				continue
 			}
@@ -89,6 +92,10 @@ func follow(instances []running.InstanceCtx, n int) error {
 	}
 
 	if tailRoutinesStarted > 0 {
+		go func() {
+			wg.Wait()
+			close(logLines)
+		}()
 		return printLines(ctx, logLines)
 	}
 	return nil

cli/tail/tail.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"os"
 	"strings"
+	"sync"
 
 	"github.com/apex/log"
 	"github.com/fatih/color"
@@ -131,7 +132,7 @@ func TailN(ctx context.Context, logFormatter LogFormatter, fileName string,
 
 // Follow sends to the channel each new line from the file as it grows.
 func Follow(ctx context.Context, out chan<- string, logFormatter LogFormatter, fileName string,
-	n int) error {
+	n int, wg *sync.WaitGroup) error {
 	file, err := os.Open(fileName)
 	if err != nil {
 		return fmt.Errorf("cannot open %q: %w", fileName, err)
@@ -157,7 +158,9 @@ func Follow(ctx context.Context, out chan<- string, logFormatter LogFormatter, f
 		return err
 	}
 
+	wg.Add(1)
 	go func() {
+		defer wg.Done()
 		for {
 			select {
 			case <-ctx.Done():
@@ -172,7 +175,6 @@ func Follow(ctx context.Context, out chan<- string, logFormatter LogFormatter, f
 					} else {
 						log.Errorf("The log file %q is unavailable for reading. Exiting.")
 					}
-					close(out)
 					return
 				}
 				out <- logFormatter(line.Text)

cli/tail/tail_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"os"
+	"sync"
 	"testing"
 	"time"
 
@@ -299,7 +300,8 @@ func TestFollow(t *testing.T) {
 			defer stop()
 			in := make(chan string)
 			err = Follow(ctx, in,
-				func(str string) string { return str }, outFile.Name(), tt.nLines)
+				func(str string) string { return str }, outFile.Name(), tt.nLines,
+				&sync.WaitGroup{})
 			require.NoError(t, err)
 
 			if tt.nLines > 0 && len(tt.expectedLastLines) > 0 {

test/integration/log/test_log.py

@@ -256,7 +256,7 @@ def test_log_output_default_follow_want_zero_last(tt_cmd, mock_env_dir):
     assert 'app1:inst0' not in output
 
 
-def test_log__dir_removed_after_follow(tt_cmd, mock_env_dir):
+def test_log_dir_removed_after_follow(tt_cmd, mock_env_dir):
     cmd = [tt_cmd, 'log', '-f']
     process = subprocess.Popen(
         cmd,
@@ -270,7 +270,40 @@ def test_log__dir_removed_after_follow(tt_cmd, mock_env_dir):
                              ['app0:inst0: line 19', 'app1:inst2: line 19',
                               'app0:inst1: line 19', 'app1:inst1: line 19'])
 
-    var_dir = os.path.join(mock_env_dir, 'ie', 'app0', 'var')
+    var_dir = os.path.join(mock_env_dir, 'ie')
+    assert os.path.exists(var_dir)
+    shutil.rmtree(var_dir)
+
+    assert process.wait(2) == 0
+    assert "Failed to detect creation of" in process.stdout.read()
+
+
+# There are two apps in this test: app0 and app1. After removing app0 dirs,
+# tt log -f is still able to monitor the app1 log files, so there should be no issue.
+def test_log_dir_partially_removed_after_follow(tt_cmd, mock_env_dir):
+    cmd = [tt_cmd, 'log', '-f']
+    process = subprocess.Popen(
+        cmd,
+        cwd=mock_env_dir,
+        stderr=subprocess.STDOUT,
+        stdout=subprocess.PIPE,
+        text=True,
+    )
+
+    wait_for_lines_in_output(process.stdout,
+                             ['app0:inst0: line 19', 'app1:inst2: line 19',
+                              'app0:inst1: line 19', 'app1:inst1: line 19'])
+
+    # Remove one app log dir.
+    var_dir = os.path.join(mock_env_dir, 'ie', 'app0', 'var', 'log')
+    assert os.path.exists(var_dir)
+    shutil.rmtree(var_dir)
+
+    wait_for_lines_in_output(process.stdout, ['Failed to detect creation of'])
+    assert process.poll() is None  # Still running.
+
+    # Remove app1 log dir.
+    var_dir = os.path.join(mock_env_dir, 'ie', 'app1')
     assert os.path.exists(var_dir)
     shutil.rmtree(var_dir)