feat: add rsync modify-window option

src/shared/config.c

@@ -35,6 +35,7 @@ static void config_set_defaults(Config* config) {
   config->min_size = 0;
   config->use_incremental = false;
   config->use_delta = false;
+  config->modify_window = 0;
   config->delta_block_size = DELTA_BLOCK_SIZE_DEFAULT;
   config->delta_max_file_size = DELTA_MAX_FILE_SIZE;
   config->use_tls = false;
@@ -134,7 +135,8 @@ static bool validate_received_config(const Config* config) {
          config->chunk_size > 0 && config->chunk_size <= MAX_CHUNK_SIZE &&
          config->delta_block_size >= DELTA_BLOCK_SIZE_MIN &&
          config->delta_block_size <= DELTA_BLOCK_SIZE_MAX &&
-         config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->max_delete >= 0;
+         config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->modify_window >= 0 &&
+         config->max_delete >= 0;
 }
 
 Config* config_create(void) {
@@ -253,7 +255,8 @@ static bool send_resume_options(int fd, const Config* c) {
   return send_str(fd, c->temp_dir ? c->temp_dir : "") && send_int(fd, c->partial) &&
          send_str(fd, c->partial_dir ? c->partial_dir : "") &&
          send_str(fd, c->suffix ? c->suffix : "") && send_int(fd, c->delete_before) &&
-         send_int(fd, c->checksum) && send_str(fd, c->compress_choice ? c->compress_choice : "");
+         send_int(fd, c->checksum) && send_int(fd, c->modify_window) &&
+         send_str(fd, c->compress_choice ? c->compress_choice : "");
 }
 
 static bool receive_core_fields(int fd, Config* c) {
@@ -329,6 +332,8 @@ static bool receive_resume_options(int fd, Config* c) {
     return false;
   if (!receive_wire_bool(fd, &c->checksum))
     return false;
+  if (!receive_n_data(fd, &c->modify_window, sizeof(c->modify_window)))
+    return false;
   c->compress_choice = receive_str(fd);
   return c->compress_choice != NULL;
 }

src/shared/config.h

@@ -35,6 +35,7 @@ typedef struct Config {
   unsigned long long min_size;
   bool use_incremental;
   bool use_delta;
+  int modify_window;
   uint32_t delta_block_size;
   unsigned long long delta_max_file_size;
   bool use_tls;
@@ -128,7 +129,7 @@ typedef struct Config {
   char* compress_choice;
 } Config;
 
-#define PROTOCOL_VERSION "2.2.0"
+#define PROTOCOL_VERSION "2.3.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 
 Config* config_create(void);

src/shared/file_receive.c

@@ -314,12 +314,19 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
 
   unsigned long long check_size;
   long long check_mtime;
+  long long check_mtime_nsec;
   uint64_t check_checksum = 0;
   if (!receive_n_data(fd, &check_size, sizeof(check_size)) ||
       !receive_n_data(fd, &check_mtime, sizeof(check_mtime))) {
     free(check_path);
     return NULL;
   }
+  if (!receive_n_data(fd, &check_mtime_nsec, sizeof(check_mtime_nsec)) || check_mtime_nsec < 0 ||
+      check_mtime_nsec >= 1000000000LL) {
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
   if (config->checksum && !receive_n_data(fd, &check_checksum, sizeof(check_checksum))) {
     free(check_path);
     return NULL;
@@ -384,7 +391,12 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     free(old_data);
     old_data = NULL;
   } else if (match) {
-    match = (long long)st.st_mtime == check_mtime;
+    long long old_mtime_nsec = 0;
+#ifdef __linux__
+    old_mtime_nsec = st.st_mtim.tv_nsec;
+#endif
+    match = metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
+                                   (long)check_mtime_nsec, config->modify_window);
   }
 
   if (match) {

src/shared/metadata.c

@@ -24,6 +24,23 @@ typedef char static_assert_mode_t_fits[(sizeof(mode_t) <= sizeof(int32_t)) ? 1 :
 typedef char static_assert_uid_t_fits[(sizeof(uid_t) <= sizeof(int32_t)) ? 1 : -1];
 typedef char static_assert_gid_t_fits[(sizeof(gid_t) <= sizeof(int32_t)) ? 1 : -1];
 
+bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, long right_nsec,
+                            int modify_window) {
+  int64_t left = (int64_t)left_sec;
+  int64_t right = (int64_t)right_sec;
+  int64_t seconds;
+  int64_t nanoseconds;
+
+  if (left > right || (left == right && left_nsec >= right_nsec)) {
+    seconds = left - right;
+    nanoseconds = (int64_t)left_nsec - (int64_t)right_nsec;
+  } else {
+    seconds = right - left;
+    nanoseconds = (int64_t)right_nsec - (int64_t)left_nsec;
+  }
+  return seconds < modify_window || (seconds == modify_window && nanoseconds == 0);
+}
+
 void metadata_to_buf(char** buf, const FileMetadata* m) {
   int32_t present = (m != NULL) ? 1 : 0;
   memcpy(*buf, &present, sizeof(present));

src/shared/metadata.h

@@ -5,6 +5,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <sys/stat.h>
+#include <time.h>
 
 /*
  * Wire format (introduced in protocol version 2.0.0):
@@ -32,4 +33,8 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok);
 void file_restore_metadata(const char* path, const FileMetadata* metadata);
 bool file_restore_metadata_fd(int fd, const FileMetadata* metadata);
 
+/* Compare timestamps using rsync's whole-second modification window. */
+bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, long right_nsec,
+                            int modify_window);
+
 #endif