move "link or copy" functionality to moxio

and add a bit more logging for unexpected failures when closing files.
and make tests pass with a TMPDIR on a different filesystem than the testdata directory.

store/account.go

@@ -693,13 +693,11 @@ func (a *Account) DeliverMessage(log *mlog.Log, tx *bstore.Tx, m *Message, msgFi
 
 	if consumeFile {
 		if err := os.Rename(msgFile.Name(), msgPath); err != nil {
+			// Could be due to cross-filesystem rename. Users shouldn't configure their systems that way.
 			return fmt.Errorf("moving msg file to destination directory: %w", err)
 		}
-	} else if err := os.Link(msgFile.Name(), msgPath); err != nil {
-		// Assume file system does not support hardlinks. Copy it instead.
-		if err := writeFile(msgPath, &moxio.AtReader{R: msgFile}); err != nil {
-			return fmt.Errorf("copying message to new file: %w", err)
-		}
+	} else if err := moxio.LinkOrCopy(log, msgPath, msgFile.Name(), &moxio.AtReader{R: msgFile}, true); err != nil {
+		return fmt.Errorf("linking/copying message to new file: %w", err)
 	}
 
 	if sync {
@@ -719,28 +717,6 @@ func (a *Account) DeliverMessage(log *mlog.Log, tx *bstore.Tx, m *Message, msgFi
 	return nil
 }
 
-// write contents of r to new file dst, for delivering a message.
-func writeFile(dst string, r io.Reader) error {
-	df, err := os.OpenFile(dst, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0660)
-	if err != nil {
-		return fmt.Errorf("create: %w", err)
-	}
-	defer func() {
-		if df != nil {
-			df.Close()
-		}
-	}()
-	if _, err := io.Copy(df, r); err != nil {
-		return fmt.Errorf("copy: %s", err)
-	} else if err := df.Sync(); err != nil {
-		return fmt.Errorf("sync: %s", err)
-	} else if err := df.Close(); err != nil {
-		return fmt.Errorf("close: %s", err)
-	}
-	df = nil
-	return nil
-}
-
 // SetPassword saves a new password for this account. This password is used for
 // IMAP, SMTP (submission) sessions and the HTTP account web page.
 func (a *Account) SetPassword(password string) error {

store/account_test.go

@@ -231,20 +231,6 @@ func TestMailbox(t *testing.T) {
 	}
 }
 
-func TestWriteFile(t *testing.T) {
-	name := "../testdata/account.test"
-	os.Remove(name)
-	defer os.Remove(name)
-	err := writeFile(name, strings.NewReader("test"))
-	if err != nil {
-		t.Fatalf("writeFile, unexpected error %v", err)
-	}
-	buf, err := os.ReadFile(name)
-	if err != nil || string(buf) != "test" {
-		t.Fatalf("writeFile, read file, got err %v, data %q", err, buf)
-	}
-}
-
 func TestMessageRuleset(t *testing.T) {
 	f, err := os.Open("/dev/null")
 	tcheck(t, err, "open")

store/export_test.go

@@ -30,7 +30,7 @@ func TestExport(t *testing.T) {
 
 	log := mlog.New("export")
 
-	msgFile, err := os.CreateTemp("", "mox-test-export")
+	msgFile, err := CreateMessageTemp("mox-test-export")
 	tcheck(t, err, "create temp")
 	defer os.Remove(msgFile.Name()) // To be sure.
 	const msg = "test: test\r\n\r\ntest\r\n"

store/tmp.go

@@ -6,10 +6,12 @@ import (
 	"github.com/mjl-/mox/mox-"
 )
 
-// CreateMessageTemp creates a temporary file for a message to be delivered.
-// Caller is responsible for removing the temporary file on error, and for closing the file.
-// Caller should ensure the contents of the file are synced to disk before
-// attempting to deliver the message.
+// CreateMessageTemp creates a temporary file, e.g. for delivery. The is created in
+// subdirectory tmp of the data directory, so the file is on the same file system
+// as the accounts directory, so renaming files can succeed. The caller is
+// responsible for closing and possibly removing the file. The caller should ensure
+// the contents of the file are synced to disk before attempting to deliver the
+// message.
 func CreateMessageTemp(pattern string) (*os.File, error) {
 	dir := mox.DataDirPath("tmp")
 	os.MkdirAll(dir, 0770)