add O_TRUNC when the first open() for a file

src/file.c

@@ -367,6 +367,7 @@ static int file_dst_prepare(struct file *f, sftp_session sftp)
 
 	pr_debug("prepare for %s\n", path);
 
+	/* mkdir -p */
 	for (p = strchr(path + 1, '/'); p; p = strchr(p + 1, '/')) {
 		*p = '\0';
 
@@ -398,6 +399,30 @@ static int file_dst_prepare(struct file *f, sftp_session sftp)
 		*p = '/';
 	}
 
+	/* open file with O_TRUNC to set file size 0 */
+	mode = O_WRONLY|O_CREAT|O_TRUNC;
+	if (sftp) {
+		sftp_file sf;
+		if ((sf = sftp_open(sftp, f->dst_path, mode, S_IRUSR|S_IWUSR)) == NULL) {
+			pr_err("sftp_open: %s\n", sftp_get_ssh_error(sftp));
+			return -1;
+		}
+		if (sftp_close(sf) < 0) {
+			pr_err("sftp_close: %s\n", sftp_get_ssh_error(sftp));
+			return -1;
+		}
+	} else {
+		int fd;
+		if ((fd = open(f->dst_path, mode, S_IRUSR|S_IWUSR)) < 0) {
+			pr_err("open: %s\n", strerrno());
+			return -1;
+		}
+		if (close(fd) < 0) {
+			pr_err("close: %s\n", strerrno());
+			return -1;
+		}
+	}
+
 	return 0;
 }
 
@@ -824,7 +849,7 @@ static int chunk_copy_local_to_remote(struct chunk *c, sftp_session sftp,
 		goto out;
 	}
 
-	flags = O_WRONLY|O_CREAT;
+	flags = O_WRONLY;
 	mode = S_IRUSR|S_IWUSR;
 	if (!(sf = chunk_open_remote(f->dst_path, flags, mode, c->off, sftp))) {
 		ret = -1;
@@ -866,7 +891,7 @@ static int chunk_copy_remote_to_local(struct chunk *c, sftp_session sftp,
 	int fd = 0;
 	int ret = 0;
 
-	flags = O_WRONLY|O_CREAT;
+	flags = O_WRONLY;
 	mode = S_IRUSR|S_IWUSR;
 	if ((fd = chunk_open_local(f->dst_path, flags, mode, c->off)) < 0) {
 		ret = -1;

src/file.h

@@ -37,7 +37,8 @@ struct file {
  * if the file state of the chunk is INIT:
  *     acquire the file lock
  * *         if file state is INIT:
- *             create destination file and directory if necessary
+ *             create directory if necessary
+ *             open file with O_TRUNC and close.
  *             set file state OPENED.
  *             // only the first thread in the lock open the destination file
  *     release the file lock

test/test_e2e.py

@@ -174,3 +174,11 @@ def test_transfer_zero_bytes(mscp, src_prefix, dst_prefix):
     src.cleanup()
     dst.cleanup()
 
+@pytest.mark.parametrize("src_prefix, dst_prefix", param_remote_prefix)
+def test_override_dst_having_larger_size(mscp, src_prefix, dst_prefix):
+    src = File("src", size = 1024 * 1024).make()
+    dst = File("dst", size = 1024 * 1024 * 2).make()
+    run2ok([mscp, "-H", src_prefix + src.path, dst_prefix + "dst"])
+    assert check_same_md5sum(src, dst)
+    src.cleanup()
+    dst.cleanup()