taildrop: implement asynchronous file deletion (#9844)

File resumption requires keeping partial files around for some time,
but we must still eventually delete them if never resumed.
Thus, we implement asynchronous file deletion, which could
spawn a background goroutine to delete the files.

We also use the same mechanism for deleting files on Windows,
where a file can't be deleted if there is still an open file handle.
We can enqueue those with the asynchronous file deleter as well.

Updates tailscale/corp#14772

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

taildrop/taildrop_test.go

@@ -4,153 +4,37 @@
 package taildrop
 
 import (
-	"errors"
-	"fmt"
-	"io/fs"
-	"os"
 	"path/filepath"
-	"runtime"
+	"strings"
 	"testing"
 )
 
-// Tests "foo.jpg.deleted" marks (for Windows).
-func TestDeletedMarkers(t *testing.T) {
+func TestJoinDir(t *testing.T) {
 	dir := t.TempDir()
-	h := &Manager{Dir: dir}
-
-	nothingWaiting := func() {
-		t.Helper()
-		h.knownEmpty.Store(false)
-		if h.HasFilesWaiting() {
-			t.Fatal("unexpected files waiting")
-		}
-	}
-	touch := func(base string) {
-		t.Helper()
-		if err := touchFile(filepath.Join(dir, base)); err != nil {
-			t.Fatal(err)
-		}
-	}
-	wantEmptyTempDir := func() {
-		t.Helper()
-		if fis, err := os.ReadDir(dir); err != nil {
-			t.Fatal(err)
-		} else if len(fis) > 0 && runtime.GOOS != "windows" {
-			for _, fi := range fis {
-				t.Errorf("unexpected file in tempdir: %q", fi.Name())
-			}
-		}
-	}
-
-	nothingWaiting()
-	wantEmptyTempDir()
-
-	touch("foo.jpg.deleted")
-	nothingWaiting()
-	wantEmptyTempDir()
-
-	touch("foo.jpg.deleted")
-	touch("foo.jpg")
-	nothingWaiting()
-	wantEmptyTempDir()
-
-	touch("foo.jpg.deleted")
-	touch("foo.jpg")
-	wf, err := h.WaitingFiles()
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(wf) != 0 {
-		t.Fatalf("WaitingFiles = %d; want 0", len(wf))
-	}
-	wantEmptyTempDir()
-
-	touch("foo.jpg.deleted")
-	touch("foo.jpg")
-	if rc, _, err := h.OpenFile("foo.jpg"); err == nil {
-		rc.Close()
-		t.Fatal("unexpected foo.jpg open")
-	}
-	wantEmptyTempDir()
-
-	// And verify basics still work in non-deleted cases.
-	touch("foo.jpg")
-	touch("bar.jpg.deleted")
-	if wf, err := h.WaitingFiles(); err != nil {
-		t.Error(err)
-	} else if len(wf) != 1 {
-		t.Errorf("WaitingFiles = %d; want 1", len(wf))
-	} else if wf[0].Name != "foo.jpg" {
-		t.Errorf("unexpected waiting file %+v", wf[0])
-	}
-	if rc, _, err := h.OpenFile("foo.jpg"); err != nil {
-		t.Fatal(err)
-	} else {
-		rc.Close()
-	}
-}
-
-func TestRedactErr(t *testing.T) {
-	testCases := []struct {
-		name string
-		err  func() error
-		want string
+	tests := []struct {
+		in     string
+		want   string // just relative to m.Dir
+		wantOk bool
 	}{
-		{
-			name: "PathError",
-			err: func() error {
-				return &os.PathError{
-					Op:   "open",
-					Path: "/tmp/sensitive.txt",
-					Err:  fs.ErrNotExist,
-				}
-			},
-			want: `open redacted.41360718: file does not exist`,
-		},
-		{
-			name: "LinkError",
-			err: func() error {
-				return &os.LinkError{
-					Op:  "symlink",
-					Old: "/tmp/sensitive.txt",
-					New: "/tmp/othersensitive.txt",
-					Err: fs.ErrNotExist,
-				}
-			},
-			want: `symlink redacted.41360718 redacted.6bcf093a: file does not exist`,
-		},
-		{
-			name: "something else",
-			err:  func() error { return errors.New("i am another error type") },
-			want: `i am another error type`,
-		},
+		{"", "", false},
+		{"foo", "foo", true},
+		{"./foo", "", false},
+		{"../foo", "", false},
+		{"foo/bar", "", false},
+		{"😋", "😋", true},
+		{"\xde\xad\xbe\xef", "", false},
+		{"foo.partial", "", false},
+		{"foo.deleted", "", false},
+		{strings.Repeat("a", 1024), "", false},
+		{"foo:bar", "", false},
 	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			// For debugging
-			var i int
-			for err := tc.err(); err != nil; err = errors.Unwrap(err) {
-				t.Logf("%d: %T @ %p", i, err, err)
-				i++
-			}
-
-			t.Run("Root", func(t *testing.T) {
-				got := redactErr(tc.err()).Error()
-				if got != tc.want {
-					t.Errorf("err = %q; want %q", got, tc.want)
-				}
-			})
-			t.Run("Wrapped", func(t *testing.T) {
-				wrapped := fmt.Errorf("wrapped error: %w", tc.err())
-				want := "wrapped error: " + tc.want
-
-				got := redactErr(wrapped).Error()
-				if got != want {
-					t.Errorf("err = %q; want %q", got, want)
-				}
-			})
-		})
+	for _, tt := range tests {
+		got, gotErr := joinDir(dir, tt.in)
+		got, _ = filepath.Rel(dir, got)
+		gotOk := gotErr == nil
+		if got != tt.want || gotOk != tt.wantOk {
+			t.Errorf("joinDir(%q) = (%v, %v), want (%v, %v)", tt.in, got, gotOk, tt.want, tt.wantOk)
+		}
 	}
 }