fix: address modify-window review findings

src/server/receiver.c

@@ -66,9 +66,11 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
     struct stat st;
     bool has_old = file_stat_secure(full_path, &st);
     long long old_mtime_nsec = 0;
+    if (has_old) {
 #ifdef __linux__
-    old_mtime_nsec = st.st_mtim.tv_nsec;
+      old_mtime_nsec = st.st_mtim.tv_nsec;
 #endif
+    }
     bool match = has_old && (unsigned long long)st.st_size == check_size &&
                  metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
                                         (long)check_mtime_nsec, config->modify_window);

src/server/server.c

@@ -183,9 +183,11 @@ int receive_files(Config* config, int fd) {
         }
         bool has_old = full_path && file_stat_secure(full_path, &st);
         long long old_mtime_nsec = 0;
+        if (has_old) {
 #ifdef __linux__
-        old_mtime_nsec = st.st_mtim.tv_nsec;
+          old_mtime_nsec = st.st_mtim.tv_nsec;
 #endif
+        }
         bool match = has_old && (unsigned long long)st.st_size == check_size &&
                      metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
                                             (long)check_mtime_nsec, config->modify_window);

src/shared/metadata.c

@@ -38,6 +38,10 @@ bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, l
     seconds = right - left;
     nanoseconds = (int64_t)right_nsec - (int64_t)left_nsec;
   }
+  if (nanoseconds < 0) {
+    seconds--;
+    nanoseconds += 1000000000LL;
+  }
   return seconds < modify_window || (seconds == modify_window && nanoseconds == 0);
 }
 

tests/test_metadata.c

@@ -126,6 +126,10 @@ static void test_metadata_mtime_window() {
   EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 101, 600000000, 2));
   EXPECT_FALSE(metadata_mtime_matches(100, 100000000, 102, 600000000, 2));
   EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 102, 100000000, 2));
+  EXPECT_TRUE(metadata_mtime_matches(100, 900000000, 102, 100000000, 2));
+  EXPECT_FALSE(metadata_mtime_matches(100, 100000000, 102, 900000000, 2));
+  EXPECT_TRUE(metadata_mtime_matches(100, 900000000, 102, 900000000, 2));
+  EXPECT_FALSE(metadata_mtime_matches(100, 900000000, 101, 100000001, 0));
   EXPECT_FALSE(metadata_mtime_matches(100, 100000000, 100, 100000001, 0));
   EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 100, 100000000, 0));
 }

tests/test_server.c

@@ -182,11 +182,40 @@ static void test_receive_manifest_rejects_traversal() {
   config_delete(cfg);
 }
 
+static void test_receive_incremental_check_rejects_invalid_nanoseconds() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  cfg->receive_root_directory = str_dup("/tmp/dst");
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[1]);
+  EXPECT_TRUE(send_str(p[1], "file.txt"));
+  unsigned long long size = 0;
+  long long mtime = 100;
+  long long mtime_nsec = 1000000000LL;
+  EXPECT_TRUE(send_n_data(p[1], &size, sizeof(size)));
+  EXPECT_TRUE(send_n_data(p[1], &mtime, sizeof(mtime)));
+  EXPECT_TRUE(send_n_data(p[1], &mtime_nsec, sizeof(mtime_nsec)));
+
+  bool skipped = false;
+  EXPECT_NULL(receive_incremental_check(p[0], cfg, &skipped));
+  Status status;
+  EXPECT_TRUE(receive_status(p[1], &status));
+  EXPECT_EQ_INT(status, STATUS_ERROR);
+  EXPECT_FALSE(skipped);
+
+  close(p[0]);
+  close(p[1]);
+  config_delete(cfg);
+}
+
 void test_server() {
   if (!is_running_under_valgrind()) {
     test_receive_files_finished();
     test_receive_files_single_file();
     test_receive_files_abort();
     test_receive_manifest_rejects_traversal();
+    test_receive_incremental_check_rejects_invalid_nanoseconds();
   }
 }