fix: complete ignore-existing destination protection

README.md

@@ -465,7 +465,7 @@ defaults to the current directory. |
 
 ## Protocol and Security
 
-FastSync protocol version `2.2.0` is shared by the client and server. The
+FastSync protocol version `2.3.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
 incremental checks, checksums, manifests, keep-alives, abort handling, and
 FastSync-native delta messages. Client and server versions must currently

src/shared/file_receive.c

@@ -22,7 +22,9 @@
 #define MAX_FILE_DATA_SIZE MAX_RECEIVE_FILE_SIZE
 
 bool file_save_to_disk(const char* root_directory, const File* file, const Config* config) {
-  bool backup_enabled = config && config->backup;
+  /* Backups are incompatible with ignore-existing: moving the entry first
+     would make a concurrent no-replace commit overwrite its old name. */
+  bool backup_enabled = config && config->backup && !config->ignore_existing;
   bool inplace = config && config->inplace;
   bool sparse = config && config->preserve_sparse;
   const char* backup_suffix = (config && config->suffix) ? config->suffix : "~";
@@ -64,9 +66,8 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
   /* --ignore-existing checks the final destination before partial files or
      overwrite policies can modify it. */
   if (config && config->ignore_existing) {
-    struct stat destination_stat;
     char* final_path = path_cat(root_directory, file->path);
-    bool exists = final_path && file_stat_secure(final_path, &destination_stat);
+    bool exists = final_path && file_path_exists_secure(final_path);
     free(final_path);
     if (exists) {
       free(confined_backup);

tests/test_file.c

@@ -120,6 +120,67 @@ static void test_file_save_to_disk_ignore_existing() {
   rmdir("test_ignore_existing_tmp");
 }
 
+static void test_file_save_to_disk_ignore_existing_entry_types() {
+  const char* root = "test_ignore_existing_entries_tmp";
+  const char* directory = "test_ignore_existing_entries_tmp/directory";
+  const char* link = "test_ignore_existing_entries_tmp/link";
+  const char* target = "test_ignore_existing_entries_tmp/target";
+  const char* backup = "test_ignore_existing_entries_tmp/backup.txt~";
+  const char* backup_file = "test_ignore_existing_entries_tmp/backup.txt";
+  Config* config = config_create();
+  File* file = file_create("unused");
+
+  unlink(link);
+  unlink(target);
+  unlink(backup);
+  unlink(backup_file);
+  rmdir(directory);
+  rmdir(root);
+  EXPECT_NOT_NULL(config);
+  EXPECT_NOT_NULL(file);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (!config || !file)
+    return;
+  config->ignore_existing = true;
+  config->backup = true;
+  file->data->data = malloc(3);
+  EXPECT_NOT_NULL(file->data->data);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (!file->data->data) {
+    file_destroy(file);
+    config_delete(config);
+    return;
+  }
+  memcpy(file->data->data, "new", 3);
+  file->data->size = 3;
+
+  EXPECT_EQ_INT(mkdir(root, 0755), 0);
+  EXPECT_EQ_INT(mkdir(directory, 0755), 0);
+  EXPECT_TRUE(file_write_to_disk(target, "old", 3, false, false));
+  EXPECT_EQ_INT(symlink("target", link), 0);
+  free(file->path);
+  file->path = str_dup("directory");
+  EXPECT_TRUE(file_save_to_disk(root, file, config));
+  free(file->path);
+  file->path = str_dup("link");
+  EXPECT_TRUE(file_save_to_disk(root, file, config));
+
+  free(file->path);
+  file->path = str_dup("backup.txt");
+  EXPECT_TRUE(file_write_to_disk(backup_file, "old", 3, false, false));
+  EXPECT_TRUE(file_save_to_disk(root, file, config));
+  EXPECT_TRUE(file_path_exists_secure(backup_file));
+  EXPECT_FALSE(file_path_exists_secure(backup));
+
+  file_destroy(file);
+  config_delete(config);
+  unlink(link);
+  unlink(target);
+  unlink(backup_file);
+  rmdir(directory);
+  rmdir(root);
+}
+
 static void test_file_write_to_disk_basic() {
   const char* content = "Basic file_write_to_disk test";
   EXPECT_TRUE(file_write_to_disk("test_file_write_to_disk_basic.txt", content, strlen(content),
@@ -491,6 +552,7 @@ void test_file() {
   test_file_load_data_missing_file();
   test_file_save_to_disk();
   test_file_save_to_disk_ignore_existing();
+  test_file_save_to_disk_ignore_existing_entry_types();
   test_file_write_to_disk_basic();
   test_file_write_to_disk_creates_dirs();
   test_file_write_to_disk_does_not_follow_symlink();