Merge fix/receiver-correctness into dev

fixes #251 #252 #253 #255 #256 #257 (remove-source-files skips, backup NULL-empty,
partial-dir install, lazy STATUS_CHECK, delta *failed, >64MiB files)

README.md

@@ -484,10 +484,11 @@ defaults to the current directory. |
 
 ## Protocol and Security
 
-FastSync protocol version `2.4.0` is shared by the client and server. The
+FastSync protocol version `2.5.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
 including the maximum allocation limit, incremental checks, checksums,
-manifests, keep-alives, abort handling, and FastSync-native delta messages.
+manifests, keep-alives, abort handling, per-file remove-source results, and
+FastSync-native delta messages.
 Client and server versions must currently match exactly.
 
 TLS provides encrypted TCP transport. Supplying `--ca` enables certificate

src/client/client_cli.c

@@ -12,6 +12,7 @@
 #include "utils.h"
 #include <errno.h>
 #include <limits.h>
+#include <signal.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
@@ -903,6 +904,10 @@ static int read_patterns_from_file(const char* filepath, char*** patterns, int*
 
 #ifndef FASTSYNC_TEST_BUILD
 int main(int argc, char* argv[]) {
+  /* The server may close a connection mid-stream (e.g. when it rejects an
+     oversized delta).  Ignore SIGPIPE so that a broken TCP connection
+     surfaces as a clean write error instead of killing the client. */
+  signal(SIGPIPE, SIG_IGN);
   const char* env_source = NULL;
   const char* env_dest = NULL;
   bool save_to_disk = false;

src/client/client_send.c

@@ -109,16 +109,13 @@ static bool add_chunk_to_manifest(ArrayList* manifest, const Chunk* chunk) {
   return true;
 }
 
-static bool finalize_transfer(Client* client) {
-  Status status;
-  return send_status(client->file_descriptor, STATUS_FINISHED) &&
-         receive_status(client->file_descriptor, &status) && status == STATUS_OK;
-}
+/* (finalize_transfer is defined after the SourceFile helpers below.) */
 
-typedef struct {
+typedef struct SourceFile {
   char* path;
   dev_t device;
   ino_t inode;
+  bool skipped; /* receiver reported the file was not written */
 } SourceFile;
 
 static void source_file_destroy(void* item) {
@@ -135,6 +132,8 @@ static void remove_transferred_sources(const Config* config, ArrayList* paths) {
     return;
   for (int i = 0; i < paths->size; i++) {
     SourceFile* source = paths->items[i];
+    if (source->skipped)
+      continue;
     const char* slash = strrchr(source->path, '/');
     const char* leaf = slash ? slash + 1 : source->path;
     char parent[PATH_MAX];
@@ -177,6 +176,7 @@ static SourceFile* source_file_create(const File* file) {
   source->path = str_dup(file->path);
   source->device = st.st_dev;
   source->inode = st.st_ino;
+  source->skipped = false;
   if (!source->path) {
     source_file_destroy(source);
     return NULL;
@@ -203,6 +203,33 @@ static void mark_sender_done(PipelineContextSender* context) {
   mtx_unlock(&context->mutex_progress);
 }
 
+/* Send the final STATUS_FINISHED frame and await the receiver's verdict.
+   When --remove-source-files is active the receiver acknowledges each data
+   file it processed, in send order: STATUS_NEXT means the file was written,
+   STATUS_OK means the file was skipped/unchanged.  Skipped sources are marked
+   so the later removal pass keeps them. */
+static bool finalize_transfer(Client* client, const Config* config, ArrayList* remove_sources) {
+  if (!send_status(client->file_descriptor, STATUS_FINISHED))
+    return false;
+  if (config->remove_source_files && remove_sources) {
+    for (int i = 0; i < remove_sources->size; i++) {
+      Status per_file;
+      if (!receive_status(client->file_descriptor, &per_file))
+        return false;
+      if (per_file == STATUS_ERROR)
+        return false;
+      if (per_file == STATUS_OK) {
+        ((SourceFile*)remove_sources->items[i])->skipped = true;
+      } else if (per_file != STATUS_NEXT) {
+        log_message(LOG_LEVEL_ERROR, "Unexpected per-file status from receiver");
+        return false;
+      }
+    }
+  }
+  Status status;
+  return receive_status(client->file_descriptor, &status) && status == STATUS_OK;
+}
+
 static void pipeline_cancel(PipelineContextSender* context) {
   mtx_lock(&context->mutex_scanner);
   mtx_lock(&context->mutex_loader);
@@ -575,7 +602,7 @@ static int send_chunks_multithreaded(void* pipeline_context) {
         if (send_delete_manifest(client->file_descriptor, context->manifest) != 0)
           goto send_fail;
       }
-      bool ok = finalize_transfer(client);
+      bool ok = finalize_transfer(client, context->config, context->remove_source_files);
       if (ok)
         remove_transferred_sources(context->config, context->remove_source_files);
       mtx_lock(&context->mutex_progress);
@@ -866,7 +893,7 @@ int send_files(Config* config) {
     array_list_delete(manifest);
     manifest = NULL;
   }
-  bool ok = finalize_transfer(client);
+  bool ok = finalize_transfer(client, config, remove_sources);
   if (ok)
     remove_transferred_sources(config, remove_sources);
   if (config->show_progress && !config->quiet)

src/server/receiver.c

@@ -1,6 +1,7 @@
 #include "receiver.h"
 
 #include "chunk.h"
+#include "file_receive.h"
 #include "log.h"
 #include "metadata.h"
 #include "protocol.h"
@@ -8,6 +9,48 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 
+bool receiver_outcomes_append(ReceiverOutcomes* outcomes, unsigned char code) {
+  if (!outcomes)
+    return false;
+  if (outcomes->count == outcomes->capacity) {
+    size_t new_capacity = outcomes->capacity == 0 ? 64 : outcomes->capacity * 2;
+    if (new_capacity < outcomes->capacity)
+      return false;
+    unsigned char* grown = realloc(outcomes->entries, new_capacity);
+    if (!grown)
+      return false;
+    outcomes->entries = grown;
+    outcomes->capacity = new_capacity;
+  }
+  outcomes->entries[outcomes->count++] = code;
+  return true;
+}
+
+void receiver_outcomes_destroy(ReceiverOutcomes* outcomes) {
+  if (!outcomes)
+    return;
+  free(outcomes->entries);
+  outcomes->entries = NULL;
+  outcomes->count = 0;
+  outcomes->capacity = 0;
+}
+
+/* End-of-transfer success frame.  When --remove-source-files was negotiated
+   each processed data file is acknowledged first (STATUS_NEXT = written,
+   STATUS_OK = skipped) so the sender never removes a source the receiver did
+   not actually store.  The frame always ends with a plain STATUS_OK. */
+bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes) {
+  if (!config->remove_source_files)
+    return send_status(fd, STATUS_OK);
+  size_t count = outcomes ? outcomes->count : 0;
+  for (size_t i = 0; i < count; i++) {
+    Status per_file = outcomes->entries[i] == FILE_SAVE_WRITTEN ? STATUS_NEXT : STATUS_OK;
+    if (!send_status(fd, per_file))
+      return false;
+  }
+  return send_status(fd, STATUS_OK);
+}
+
 static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
   if (!chunk || !sink || !sink->store_file)
     return false;
@@ -52,7 +95,7 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
       send_status(file_descriptor, STATUS_ERROR);
       return false;
     }
-    if (check_size > MAX_RECEIVE_FILE_SIZE) {
+    if (check_size > MAX_RECEIVE_WHOLE_FILE_SIZE) {
       free(check_path);
       send_status(file_descriptor, STATUS_ERROR);
       return false;
@@ -130,8 +173,14 @@ int receiver_process(Config* config, int file_descriptor, const ReceiverSink* si
     log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
     goto receive_error;
   }
-  if (sink->send_success && !send_status(file_descriptor, STATUS_OK))
-    return -1;
+  if (sink->send_success) {
+    if (sink->send_success_frame) {
+      if (!sink->send_success_frame(file_descriptor, sink->context))
+        return -1;
+    } else if (!send_status(file_descriptor, STATUS_OK)) {
+      return -1;
+    }
+  }
   return 0;
 
 receive_error:
@@ -140,15 +189,41 @@ receive_error:
   return -1;
 }
 
-static bool receiver_save_file(File* file, void* context) {
-  Config* config = context;
-  bool success =
-      !config->save_to_disk || file_save_to_disk(config->receive_root_directory, file, config);
+/* ---- Single-threaded sink (used by receiver_receive_files) ---- */
+
+typedef struct {
+  Config* config;
+  ReceiverOutcomes outcomes;
+} ReceiverSaveContext;
+
+static bool receiver_save_file(File* file, void* context_pointer) {
+  ReceiverSaveContext* context = context_pointer;
+  FileSaveResult result = FILE_SAVE_ERROR;
+  if (!context->config->save_to_disk) {
+    /* Nothing is stored; report the file as not-written so a
+       --remove-source-files sender keeps its source. */
+    result = FILE_SAVE_SKIPPED;
+  } else {
+    result = file_save_to_disk_full(context->config->receive_root_directory, file, context->config);
+  }
+  if (result != FILE_SAVE_ERROR && context->config->remove_source_files &&
+      !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
+    file_destroy(file);
+    return false;
+  }
   file_destroy(file);
-  return success;
+  return result != FILE_SAVE_ERROR;
+}
+
+static bool receiver_send_success_frame(int fd, void* context_pointer) {
+  ReceiverSaveContext* context = context_pointer;
+  return receiver_send_final_success(fd, context->config, &context->outcomes);
 }
 
 int receiver_receive_files(Config* config, int file_descriptor) {
-  ReceiverSink sink = {receiver_save_file, config, true, true};
-  return receiver_process(config, file_descriptor, &sink);
+  ReceiverSaveContext context = {.config = config, .outcomes = {0}};
+  ReceiverSink sink = {receiver_save_file, &context, true, true, receiver_send_success_frame};
+  int ret = receiver_process(config, file_descriptor, &sink);
+  receiver_outcomes_destroy(&context.outcomes);
+  return ret;
 }

src/server/receiver.h

@@ -3,16 +3,37 @@
 
 #include "config.h"
 #include "file.h"
+#include "file_receive.h"
 
 typedef bool (*ReceiverFileSink)(File* file, void* context);
 
+/* Ordered per-file save outcomes for one connection.  One entry is appended
+   for every data-bearing file the receiver processes (in the order the files
+   were sent) so the sender of a --remove-source-files transfer can be told
+   which sources were actually written versus skipped on the receiver. */
+typedef struct {
+  unsigned char* entries; /* FILE_SAVE_WRITTEN or FILE_SAVE_SKIPPED */
+  size_t count;
+  size_t capacity;
+} ReceiverOutcomes;
+
+typedef bool (*ReceiverSuccessFrame)(int fd, void* context);
+
 typedef struct {
   ReceiverFileSink store_file;
   void* context;
   bool send_error;
   bool send_success;
+  /* Emits the end-of-transfer success frame.  When the sender requested
+     --remove-source-files this includes one per-file status per processed
+     data file followed by the final STATUS_OK; otherwise just STATUS_OK. */
+  ReceiverSuccessFrame send_success_frame;
 } ReceiverSink;
 
+bool receiver_outcomes_append(ReceiverOutcomes* outcomes, unsigned char code);
+void receiver_outcomes_destroy(ReceiverOutcomes* outcomes);
+bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes);
+
 int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink);
 int receiver_receive_files(Config* config, int file_descriptor);
 

src/server/server.c

@@ -342,9 +342,15 @@ void handler(int file_descriptor) {
     int writer_result;
     thrd_join(receiver, &receiver_result);
     thrd_join(writer, &writer_result);
-    send_status(file_descriptor, receiver_result == thrd_success && writer_result == thrd_success
-                                     ? STATUS_OK
-                                     : STATUS_ERROR);
+    bool transfer_ok = receiver_result == thrd_success && writer_result == thrd_success;
+    if (transfer_ok) {
+      if (!receiver_send_final_success(file_descriptor, config, &context->outcomes))
+        transfer_ok = false;
+    } else {
+      send_status(file_descriptor, STATUS_ERROR);
+    }
+    if (!transfer_ok)
+      log_message(LOG_LEVEL_ERROR, "Transfer failed");
     pipeline_context_receiver_destroy(context);
   } else {
     if (receiver_receive_files(config, file_descriptor) != 0)

src/shared/config.c

@@ -139,8 +139,9 @@ static bool validate_received_config(const Config* config) {
          valid_wire_bool(config->use_delete) && valid_wire_bool(config->use_incremental) &&
          valid_wire_bool(config->size_only) && valid_wire_bool(config->ignore_times) &&
          valid_wire_bool(config->use_delta) && valid_wire_bool(config->backup) &&
-         valid_wire_bool(config->follow_symlinks) && valid_wire_bool(config->copy_links) &&
-         valid_wire_bool(config->safe_links) && valid_wire_bool(config->copy_unsafe_links) &&
+         valid_wire_bool(config->remove_source_files) && valid_wire_bool(config->follow_symlinks) &&
+         valid_wire_bool(config->copy_links) && valid_wire_bool(config->safe_links) &&
+         valid_wire_bool(config->copy_unsafe_links) &&
          valid_wire_bool(config->preserve_hard_links) && valid_wire_bool(config->preserve_acls) &&
          valid_wire_bool(config->preserve_xattrs) && valid_wire_bool(config->preserve_devices) &&
          valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->ignore_existing) &&
@@ -274,11 +275,11 @@ static bool send_delta_fields(int fd, const Config* c) {
 
 static bool send_file_options(int fd, const Config* c) {
   return send_int(fd, c->backup) && send_str(fd, c->backup_dir ? c->backup_dir : "") &&
-         send_int(fd, c->follow_symlinks) && send_int(fd, c->copy_links) &&
-         send_int(fd, c->safe_links) && send_int(fd, c->copy_unsafe_links) &&
-         send_int(fd, c->preserve_hard_links) && send_int(fd, c->preserve_acls) &&
-         send_int(fd, c->preserve_xattrs) && send_int(fd, c->preserve_devices) &&
-         send_int(fd, c->preserve_sparse);
+         send_int(fd, c->remove_source_files) && send_int(fd, c->follow_symlinks) &&
+         send_int(fd, c->copy_links) && send_int(fd, c->safe_links) &&
+         send_int(fd, c->copy_unsafe_links) && send_int(fd, c->preserve_hard_links) &&
+         send_int(fd, c->preserve_acls) && send_int(fd, c->preserve_xattrs) &&
+         send_int(fd, c->preserve_devices) && send_int(fd, c->preserve_sparse);
 }
 
 static bool send_selection_options(int fd, const Config* c) {
@@ -355,8 +356,17 @@ static bool receive_delta_fields(int fd, Config* c) {
 static bool receive_file_options(int fd, Config* c) {
   if (!receive_wire_bool(fd, &c->backup))
     return false;
-  c->backup_dir = receive_str(fd);
-  if (!c->backup_dir)
+  char* backup_dir = receive_str(fd);
+  if (!backup_dir)
+    return false;
+  if (*backup_dir != '\0') {
+    c->backup_dir = backup_dir;
+  } else {
+    /* The sender serializes an unset (NULL) string as "", so canonicalize the
+       empty wire value back to NULL to preserve NULL-vs-empty semantics. */
+    free(backup_dir);
+  }
+  if (!receive_wire_bool(fd, &c->remove_source_files))
     return false;
   bool* flags[] = {&c->follow_symlinks,   &c->copy_links,          &c->safe_links,
                    &c->copy_unsafe_links, &c->preserve_hard_links, &c->preserve_acls,
@@ -386,12 +396,37 @@ static bool receive_selection_options(int fd, Config* c) {
 }
 
 static bool receive_resume_options(int fd, Config* c) {
-  c->temp_dir = receive_str(fd);
-  if (!c->temp_dir || !receive_wire_bool(fd, &c->partial))
+  char* temp_dir = receive_str(fd);
+  if (!temp_dir)
     return false;
-  c->partial_dir = receive_str(fd);
-  c->suffix = c->partial_dir ? receive_str(fd) : NULL;
-  if (!c->partial_dir || !c->suffix || !receive_wire_bool(fd, &c->delete_before))
+  if (*temp_dir != '\0') {
+    c->temp_dir = temp_dir;
+  } else {
+    free(temp_dir);
+  }
+  if (!receive_wire_bool(fd, &c->partial))
+    return false;
+  /* These options have NULL client defaults, so the sender transmits an empty
+     string for "unset".  Canonicalize the empty wire value back to NULL so
+     receivers observe exactly what the client configured (plain --backup, for
+     example, must not look like --backup-dir ""). */
+  char* partial_dir = receive_str(fd);
+  if (!partial_dir)
+    return false;
+  if (*partial_dir != '\0') {
+    c->partial_dir = partial_dir;
+  } else {
+    free(partial_dir);
+  }
+  char* suffix = receive_str(fd);
+  if (!suffix)
+    return false;
+  if (*suffix != '\0') {
+    c->suffix = suffix;
+  } else {
+    free(suffix);
+  }
+  if (!receive_wire_bool(fd, &c->delete_before))
     return false;
   if (!receive_wire_bool(fd, &c->checksum))
     return false;

src/shared/config.h

@@ -147,7 +147,7 @@ typedef struct Config {
   bool skip_compress_set;
 } Config;
 
-#define PROTOCOL_VERSION "2.4.0"
+#define PROTOCOL_VERSION "2.5.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 
 Config* config_create(void);

src/shared/file_receive.c

@@ -20,9 +20,14 @@
 #include "utils.h"
 
 #define MAX_SERVER_DELETE_COUNT 100000U
-#define MAX_FILE_DATA_SIZE MAX_RECEIVE_FILE_SIZE
+#define MAX_FILE_DATA_SIZE MAX_RECEIVE_WHOLE_FILE_SIZE
 
 bool file_save_to_disk(const char* root_directory, const File* file, const Config* config) {
+  return file_save_to_disk_full(root_directory, file, config) != FILE_SAVE_ERROR;
+}
+
+FileSaveResult file_save_to_disk_full(const char* root_directory, const File* file,
+                                      const Config* config) {
   /* 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;
@@ -32,6 +37,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
   const char* backup_suffix = (config && config->suffix) ? config->suffix : "~";
   const char* backup_dir = (config && config->backup_dir) ? config->backup_dir : NULL;
   const char* partial_dir = (config && config->partial_dir) ? config->partial_dir : NULL;
+  bool use_partial_root = partial_dir && config && config->partial;
   char *confined_backup = NULL, *confined_partial = NULL, *disk_path = NULL;
   char* destination_path = NULL;
   char *backup_path = NULL, *parent_copy = NULL;
@@ -42,23 +48,22 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
        (!backup_suffix || backup_suffix[0] == '\0' || strchr(backup_suffix, '/') != NULL ||
         strcmp(backup_suffix, ".") == 0 || strcmp(backup_suffix, "..") == 0))) {
     log_message(LOG_LEVEL_ERROR, "Invalid file or path received");
-    return false;
+    return FILE_SAVE_ERROR;
   }
 
   /* These options arrive from the client.  They are names below the server
      root, never independent filesystem roots. */
   if ((backup_dir && (backup_dir[0] == '/' || has_path_traversal(backup_dir))) ||
       (partial_dir && (partial_dir[0] == '/' || has_path_traversal(partial_dir))))
-    return false;
+    return FILE_SAVE_ERROR;
   if (backup_dir && !(confined_backup = path_cat(root_directory, backup_dir)))
-    return false;
+    return FILE_SAVE_ERROR;
   if (partial_dir && !(confined_partial = path_cat(root_directory, partial_dir))) {
     free(confined_backup);
-    return false;
+    return FILE_SAVE_ERROR;
   }
 
-  const char* actual_root =
-      (partial_dir && config && config->partial) ? confined_partial : root_directory;
+  const char* actual_root = use_partial_root ? confined_partial : root_directory;
   destination_path = path_cat(root_directory, file->path);
   disk_path = path_cat(actual_root, file->path);
   if (destination_path == NULL || disk_path == NULL) {
@@ -66,7 +71,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
     free(confined_partial);
     free(destination_path);
     free(disk_path);
-    return false;
+    return FILE_SAVE_ERROR;
   }
 
   /* --existing checks the final destination, not a temporary partial path. */
@@ -75,7 +80,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
     free(confined_partial);
     free(destination_path);
     free(disk_path);
-    return true;
+    return FILE_SAVE_SKIPPED;
   }
 
   /* --ignore-existing checks the final destination before partial files or
@@ -87,34 +92,40 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
       free(confined_partial);
       free(destination_path);
       free(disk_path);
-      return true;
+      return FILE_SAVE_SKIPPED;
     }
   }
-  free(destination_path);
-  destination_path = NULL;
 
   /* --update is receiver-side policy: never replace a newer destination.
-     The secure stat does not require read permission on the destination. */
-  if (config && config->update && file_destination_is_newer_secure(disk_path, file->metadata)) {
+     In partial-dir mode the entry that would be replaced is the real
+     destination, not the temporary partial file.  The secure stat does not
+     require read permission on the destination. */
+  const char* update_target = use_partial_root ? destination_path : disk_path;
+  if (config && config->update && file_destination_is_newer_secure(update_target, file->metadata)) {
     free(confined_backup);
     free(confined_partial);
+    free(destination_path);
     free(disk_path);
-    return true;
+    return FILE_SAVE_SKIPPED;
   }
 
   if (backup_enabled) {
+    /* Back up the entry that the incoming write will replace.  When writing
+       through a partial dir the pre-existing destination file is the one to
+       preserve; any stale partial file is overwritten without a backup. */
+    const char* replace_target = use_partial_root ? destination_path : disk_path;
     struct stat backup_stat;
-    if (file_stat_secure(disk_path, &backup_stat)) {
+    if (file_stat_secure(replace_target, &backup_stat)) {
       if (backup_dir) {
         backup_path = path_cat(confined_backup, file->path);
       } else {
-        size_t path_len = strlen(disk_path);
+        size_t path_len = strlen(replace_target);
         size_t suffix_len = strlen(backup_suffix);
         if (path_len > SIZE_MAX - suffix_len - 1)
           goto fail;
         backup_path = malloc(path_len + suffix_len + 1);
         if (backup_path) {
-          memcpy(backup_path, disk_path, path_len);
+          memcpy(backup_path, replace_target, path_len);
           memcpy(backup_path + path_len, backup_suffix, suffix_len + 1);
         }
       }
@@ -125,7 +136,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
         goto fail;
       free(parent_copy);
       parent_copy = NULL;
-      if (!file_rename_secure(disk_path, backup_path))
+      if (!file_rename_secure(replace_target, backup_path))
         goto fail;
       free(backup_path);
       backup_path = NULL;
@@ -149,13 +160,25 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
                 : file_to_disk_secure_with_fsync(disk_path, file->data->data, file->data->size,
                                                  inplace, sparse, metadata, preserve_executability,
                                                  config && config->use_fsync);
+  if (!ok)
+    goto fail;
+
+  /* --partial --partial-dir writes the complete file under the partial dir so
+     interrupted transfers leave a resumable copy there.  Once the file is
+     fully written it must be atomically installed at the real destination;
+     otherwise completed transfers would linger under the partial dir. */
+  if (use_partial_root) {
+    if (!file_rename_secure(disk_path, destination_path))
+      goto fail;
+  }
+
   free(parent_copy);
   free(backup_path);
   free(confined_backup);
   free(confined_partial);
   free(destination_path);
   free(disk_path);
-  return ok;
+  return FILE_SAVE_WRITTEN;
 
 fail:
   free(parent_copy);
@@ -164,13 +187,15 @@ fail:
   free(confined_partial);
   free(destination_path);
   free(disk_path);
-  return false;
+  return FILE_SAVE_ERROR;
 }
 
 static File* receive_delta_file(int fd, const Config* config, const char* check_path,
                                 void* old_data, unsigned long long old_size, bool* failed) {
-  if (!old_data)
+  if (!old_data) {
+    *failed = true;
     return NULL;
+  }
 
   DeltaSignature* sig = delta_signature_create(old_data, old_size, config->delta_block_size);
   if (!sig) {
@@ -206,7 +231,7 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
   }
 
   if (resp == STATUS_DELTA_DATA) {
-    Data* delta_data = receive_data_limited(fd, MAX_RECEIVE_FILE_SIZE);
+    Data* delta_data = receive_data_limited(fd, MAX_RECEIVE_WHOLE_FILE_SIZE);
     if (!delta_data) {
       delta_signature_destroy(sig);
       free(old_data);
@@ -219,7 +244,7 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
         !compression_should_skip_with_suffixes(
             check_path, config->skip_compress_suffixes,
             config->skip_compress_set ? config->skip_compress_count : -1)) {
-      raw_delta = data_decompress_limited(delta_data, MAX_RECEIVE_FILE_SIZE);
+      raw_delta = data_decompress_limited(delta_data, MAX_RECEIVE_WHOLE_FILE_SIZE);
       data_destroy(delta_data);
       if (!raw_delta) {
         free(old_data);
@@ -239,11 +264,12 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
     }
 
     uint64_t new_size = delta->new_file_size;
-    if (new_size > MAX_RECEIVE_FILE_SIZE || new_size > SIZE_MAX) {
+    if (new_size > MAX_RECEIVE_WHOLE_FILE_SIZE || new_size > SIZE_MAX) {
       delta_destroy(delta);
       free(old_data);
       delta_signature_destroy(sig);
       send_status(fd, STATUS_ERROR);
+      *failed = true;
       return NULL;
     }
     void* new_data = delta_apply(old_data, old_size, delta, config->delta_block_size);
@@ -284,6 +310,7 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
       free(old_data);
       delta_signature_destroy(sig);
       send_status(fd, STATUS_ERROR);
+      *failed = true;
       return NULL;
     }
     data_destroy(file->data);
@@ -314,7 +341,7 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
       }
     }
 
-    Data* file_data = receive_data_limited(fd, MAX_RECEIVE_FILE_SIZE);
+    Data* file_data = receive_data_limited(fd, MAX_RECEIVE_WHOLE_FILE_SIZE);
     if (file_data == NULL) {
       file_destroy(file);
       *failed = true;
@@ -325,7 +352,7 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
         !compression_should_skip_with_suffixes(
             file->path, config->skip_compress_suffixes,
             config->skip_compress_set ? config->skip_compress_count : -1)) {
-      Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
+      Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_WHOLE_FILE_SIZE);
       data_destroy(file_data);
       if (uncompressed == NULL) {
         file_destroy(file);
@@ -384,7 +411,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     return NULL;
   }
 
-  if (check_size > MAX_RECEIVE_FILE_SIZE) {
+  if (check_size > MAX_RECEIVE_WHOLE_FILE_SIZE) {
     free(check_path);
     send_status(fd, STATUS_ERROR);
     return NULL;
@@ -405,6 +432,9 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     send_status(fd, STATUS_ERROR);
     return NULL;
   }
+
+  /* Open the existing destination entry (if any) once and keep the descriptor
+     until the quick-check below decides whether the old contents are needed. */
   struct stat st;
   bool has_old_file = false;
   int old_fd = -1;
@@ -416,9 +446,34 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     close(parent_fd);
     has_old_file = old_fd >= 0 && fstat(old_fd, &st) == 0 && S_ISREG(st.st_mode);
   }
+  if (!has_old_file && old_fd >= 0) {
+    close(old_fd);
+    old_fd = -1;
+  }
   unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;
+
+  /* Decide from metadata alone whether the receiver already holds the file
+     the sender is offering.  The old contents are only read into memory when
+     a checksum comparison or a delta transfer actually requires them. */
+  bool size_equal = has_old_file && old_size == check_size;
+  bool match_by_metadata = false;
+  if (size_equal && !config->ignore_times && !config->size_only) {
+    long long old_mtime_nsec = 0;
+#ifdef __linux__
+    old_mtime_nsec = st.st_mtim.tv_nsec;
+#endif
+    match_by_metadata = metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
+                                               (long)check_mtime_nsec, config->modify_window);
+  }
+
+  bool try_delta = config->use_delta && !config->whole_file && has_old_file &&
+                   delta_should_attempt(old_size, check_size, config->delta_max_file_size);
+  bool checksum_needs_read = size_equal && !config->ignore_times && config->checksum;
+  bool need_old_data = checksum_needs_read || try_delta;
+
   void* old_data = NULL;
-  if (has_old_file && old_size > 0 && old_size <= MAX_RECEIVE_FILE_SIZE && old_size <= SIZE_MAX) {
+  if (need_old_data && has_old_file && old_size > 0 && old_size <= MAX_RECEIVE_WHOLE_FILE_SIZE &&
+      old_size <= SIZE_MAX) {
     old_data = protocol_alloc((size_t)old_size);
     if (old_data) {
       size_t got = 0;
@@ -433,73 +488,63 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
       }
     }
   }
-  if (old_fd >= 0) {
-    close(old_fd);
-  }
 
-  bool match =
-      !config->ignore_times && has_old_file && (unsigned long long)st.st_size == check_size;
-  if (match && config->checksum) {
-    uint64_t old_checksum = old_size == 0 ? delta_xxhash64("", 0) : 0;
-    if (old_data)
-      old_checksum = delta_xxhash64(old_data, (size_t)old_size);
-    match = (old_size == 0 || old_data) && old_checksum == check_checksum;
-    free(old_data);
-    old_data = NULL;
-  } else if (match && !config->size_only) {
-    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);
+  /* Quick-skip decision.  If no content comparison is required this is final
+     and the old file was never read; if the read failed the file is not
+     skipped and the transfer proceeds with the full new contents. */
+  bool match = false;
+  if (checksum_needs_read) {
+    if (old_size == 0)
+      match = delta_xxhash64("", 0) == check_checksum;
+    else
+      match = old_data != NULL && delta_xxhash64(old_data, (size_t)old_size) == check_checksum;
+  } else if (size_equal && !config->ignore_times) {
+    match = config->size_only || match_by_metadata;
   }
 
   if (match) {
     free(old_data);
     if (!send_status(fd, STATUS_OK)) {
+      close(old_fd);
       free(full_path);
       free(check_path);
       return NULL;
     }
+    close(old_fd);
     free(full_path);
     free(check_path);
     *skipped = true;
     return NULL;
   }
 
-  bool try_delta = config->use_delta && !config->whole_file && has_old_file && old_data != NULL &&
-                   delta_should_attempt(old_size, check_size, config->delta_max_file_size);
-
-  if (try_delta) {
+  if (try_delta && old_data != NULL) {
     bool delta_failed = false;
     File* delta_file =
         receive_delta_file(fd, config, check_path, old_data, old_size, &delta_failed);
     old_data = NULL; /* receive_delta_file consumes the snapshot on every path */
     if (delta_file) {
+      close(old_fd);
       free(full_path);
       free(check_path);
       return delta_file;
     }
     if (delta_failed) {
+      close(old_fd);
       free(full_path);
       free(check_path);
       return NULL;
     }
-    free(old_data);
-    old_data = NULL;
-    try_delta = false;
   }
+  free(old_data);
+  old_data = NULL;
 
-  if (!try_delta) {
-    free(old_data);
-    old_data = NULL;
-    if (!send_status(fd, STATUS_NEXT)) {
-      free(full_path);
-      free(check_path);
-      return NULL;
-    }
+  if (!send_status(fd, STATUS_NEXT)) {
+    close(old_fd);
+    free(full_path);
+    free(check_path);
+    return NULL;
   }
+  close(old_fd);
 
   File* file = file_create(check_path);
   free(check_path);
@@ -517,7 +562,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     }
   }
 
-  Data* file_data = receive_data_limited(fd, MAX_RECEIVE_FILE_SIZE);
+  Data* file_data = receive_data_limited(fd, MAX_RECEIVE_WHOLE_FILE_SIZE);
   if (file_data == NULL) {
     file_destroy(file);
     return NULL;
@@ -527,7 +572,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
       !compression_should_skip_with_suffixes(file->path, config->skip_compress_suffixes,
                                              config->skip_compress_set ? config->skip_compress_count
                                                                        : -1)) {
-    Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
+    Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_WHOLE_FILE_SIZE);
     data_destroy(file_data);
     if (uncompressed == NULL) {
       file_destroy(file);
@@ -571,7 +616,7 @@ File* file_receive(const Config* config, int file_descriptor) {
       return NULL;
     }
   }
-  Data* file_data = receive_data_limited(file_descriptor, MAX_RECEIVE_FILE_SIZE);
+  Data* file_data = receive_data_limited(file_descriptor, MAX_RECEIVE_WHOLE_FILE_SIZE);
   if (file_data == NULL) {
     file_destroy(file);
     return NULL;
@@ -580,7 +625,7 @@ File* file_receive(const Config* config, int file_descriptor) {
       !compression_should_skip_with_suffixes(file->path, config->skip_compress_suffixes,
                                              config->skip_compress_set ? config->skip_compress_count
                                                                        : -1)) {
-    Data* file_data_uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
+    Data* file_data_uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_WHOLE_FILE_SIZE);
     data_destroy(file_data);
     if (file_data_uncompressed == NULL) {
       file_destroy(file);

src/shared/file_receive.h

@@ -10,6 +10,14 @@
 File* file_receive(const Config* config, int file_descriptor);
 File* receive_incremental_check(int fd, const Config* config, bool* skipped);
 int receive_manifest(int fd, const Config* config, int* next_status);
+
+/* Outcome of a single file_save_to_disk operation.  The receiver needs to
+   distinguish "written" from "skipped" so --remove-source-files can be told
+   which sources were actually stored. */
+typedef enum { FILE_SAVE_ERROR = 0, FILE_SAVE_WRITTEN = 1, FILE_SAVE_SKIPPED = 2 } FileSaveResult;
+
+FileSaveResult file_save_to_disk_full(const char* root_directory, const File* file,
+                                      const Config* config);
 bool file_save_to_disk(const char* root_directory, const File* file, const Config* config);
 
 #endif

src/shared/multiprocessing.c

@@ -105,6 +105,9 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
   context->queue = queue;
   context->file_descriptor = file_descriptor;
   context->ssl = ssl;
+  context->outcomes.entries = NULL;
+  context->outcomes.count = 0;
+  context->outcomes.capacity = 0;
   protocol_session_init(&context->session, file_descriptor, file_descriptor);
   protocol_session_set_ssl(&context->session, ssl);
   context->receiver_done = false;
@@ -137,6 +140,7 @@ fail:
 void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
   config_delete(context->config);
   queue_destroy(context->queue);
+  receiver_outcomes_destroy(&context->outcomes);
   mtx_destroy(&context->mutex);
   cnd_destroy(&context->condition_not_full);
   cnd_destroy(&context->condition_not_empty);
@@ -170,7 +174,7 @@ int receive_thread(void* pipeline_context) {
   const Config* config = context->config;
   mtx_unlock(&context->mutex);
 
-  ReceiverSink sink = {receiver_enqueue_file, context, false, false};
+  ReceiverSink sink = {receiver_enqueue_file, context, false, false, NULL};
   if (receiver_process((Config*)config, file_descriptor, &sink) != 0) {
     receiver_thread_fail(context);
     protocol_session_unbind();
@@ -211,7 +215,26 @@ int write_thread(void* pipeline_context) {
       protocol_session_unbind();
       return thrd_success;
     }
-    if (save_to_disk && !file_save_to_disk(root_directory, file, context->config)) {
+    FileSaveResult result = FILE_SAVE_SKIPPED;
+    if (save_to_disk) {
+      result = file_save_to_disk_full(root_directory, file, context->config);
+      if (result == FILE_SAVE_ERROR) {
+        file_destroy(file);
+        mtx_lock(&context->mutex);
+        atomic_store(&context->cancelled, true);
+        context->receiver_done = true;
+        cnd_broadcast(&context->condition_not_full);
+        cnd_broadcast(&context->condition_not_empty);
+        mtx_unlock(&context->mutex);
+        free(root_directory);
+        protocol_session_unbind();
+        return thrd_error;
+      }
+    }
+    /* Record the per-file outcome so a --remove-source-files sender learns
+       which sources were actually written versus skipped on the receiver. */
+    if (context->config->remove_source_files &&
+        !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
       file_destroy(file);
       mtx_lock(&context->mutex);
       atomic_store(&context->cancelled, true);

src/shared/multiprocessing.h

@@ -9,6 +9,7 @@
 #include "file.h"
 #include "protocol.h"
 #include "queue.h"
+#include "receiver.h"
 #include <openssl/ssl.h>
 
 typedef struct {
@@ -40,6 +41,7 @@ typedef struct PipelineContextReceiver {
   int file_descriptor;
   SSL* ssl;
   ProtocolSession session;
+  ReceiverOutcomes outcomes;
   mtx_t mutex;
   cnd_t condition_not_full;
   cnd_t condition_not_empty;

src/shared/protocol.h

@@ -9,10 +9,16 @@
 /* Maximum allowed string size for receive_str (64 KB) */
 #define MAX_STRING_SIZE (64 * 1024)
 
-/* Maximum allowed data payload size for receive_data (100 MB) */
-#define MAX_DATA_PAYLOAD_SIZE (100ULL * 1024 * 1024)
-/* Maximum uncompressed file payload accepted by the receiver. */
-#define MAX_RECEIVE_FILE_SIZE (64ULL * 1024 * 1024)
+/* Maximum uncompressed file payload accepted by the receiver's whole-file
+ * paths.  A single whole file is charged against the per-connection memory
+ * reservation (MAX_CONNECTION_MEMORY) and against the server allocation
+ * ceiling (MAX_SERVER_ALLOC), so this mirrors those 256 MB bounds rather than
+ * the older 64 MB chunk-era cap.  Chunk-serialized payloads keep their own
+ * 64 MB cap (MAX_CHUNK_SIZE). */
+#define MAX_RECEIVE_WHOLE_FILE_SIZE (256ULL * 1024 * 1024)
+
+/* Maximum allowed data payload size for receive_data (whole-file bound) */
+#define MAX_DATA_PAYLOAD_SIZE MAX_RECEIVE_WHOLE_FILE_SIZE
 
 /* Maximum chunk size (64 MB) — prevents unbounded allocation from the wire */
 #define MAX_CHUNK_SIZE (64ULL * 1024 * 1024)

tests/integration/test_features.py

@@ -1,4 +1,5 @@
 """Feature tests: incremental sync, bandwidth limiting, dry run, metadata, filters."""
+import filecmp
 import os
 import shutil
 import sys
@@ -813,3 +814,186 @@ class TestBandwidthLimit:
         mismatches, missing = verify_transfer(SOURCE_DIR, received)
         assert not missing, f"Missing: {missing}"
         assert not mismatches, f"Mismatch: {mismatches}"
+
+
+def _read_file(path):
+    with open(path, "rb") as fh:
+        return fh.read()
+
+
+class TestRemoveSourceFilesSkips:
+    """--remove-source-files must not delete sources the receiver skipped
+    (rsync reference behavior)."""
+
+    def test_existing_first_sync_keeps_new_source(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "remove_rsf_existing_src")
+        dest = os.path.join(TEST_DATA_DIR, "remove_rsf_existing_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        with open(os.path.join(source, "only.txt"), "wb") as f:
+            f.write(b"keep me")
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files", "--existing"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Sync failed: {result.stderr[:200]}"
+        # The file exists only on the source side, so --existing makes the
+        # receiver skip it; the source must therefore not be removed.
+        assert os.path.isfile(os.path.join(source, "only.txt"))
+        received = get_dest_received_dir(dest, source)
+        assert not os.path.exists(os.path.join(received, "only.txt"))
+
+    def test_ignore_existing_keeps_skipped_source(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "remove_rsf_ignore_src")
+        dest = os.path.join(TEST_DATA_DIR, "remove_rsf_ignore_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "file.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"payload")
+
+        result, _ = run_client(source, dest, port=shared_server.port)
+        assert result.returncode == 0
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files", "--ignore-existing"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Sync failed: {result.stderr[:200]}"
+        # Destination already has the file, so the second run is a receiver
+        # skip; the source file must survive.
+        assert os.path.isfile(source_file)
+        received = get_dest_received_dir(dest, source)
+        assert _read_file(os.path.join(received, "file.txt")) == b"payload"
+
+    def test_update_newer_destination_keeps_source(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "remove_rsf_update_src")
+        dest = os.path.join(TEST_DATA_DIR, "remove_rsf_update_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "file.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"source payload")
+
+        result, _ = run_client(source, dest, port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(dest, source)
+        received_file = os.path.join(received, "file.txt")
+        with open(received_file, "wb") as f:
+            f.write(b"newer destination payload")
+        os.utime(received_file, ns=(time.time_ns() + 10**9, time.time_ns() + 10**9))
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files", "--update"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Sync failed: {result.stderr[:200]}"
+        # --update skips a destination that is newer than the source, so the
+        # source must not be removed.
+        assert os.path.isfile(source_file)
+        assert _read_file(received_file) == b"newer destination payload"
+
+
+class TestBackup:
+    def _sync(self, source, dest, flags, port):
+        return run_client(source, dest, flags=flags, port=port)
+
+    def test_plain_backup_keeps_previous_version(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "backup_src")
+        dest = os.path.join(TEST_DATA_DIR, "backup_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "f.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"AAAA")
+
+        result, _ = self._sync(source, dest, ["--backup"], shared_server.port)
+        assert result.returncode == 0, f"Backup sync failed: {result.stderr[:200]}"
+
+        with open(source_file, "wb") as f:
+            f.write(b"BBBB")
+        result, _ = self._sync(source, dest, ["--backup"], shared_server.port)
+        assert result.returncode == 0, f"Backup sync failed: {result.stderr[:200]}"
+
+        received = get_dest_received_dir(dest, source)
+        assert _read_file(os.path.join(received, "f.txt")) == b"BBBB"
+        # rsync default suffix "~" keeps the overwritten version.
+        assert _read_file(os.path.join(received, "f.txt~")) == b"AAAA"
+
+    def test_backup_custom_suffix(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "backup_suffix_src")
+        dest = os.path.join(TEST_DATA_DIR, "backup_suffix_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "f.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"AAAA")
+
+        flags = ["--backup", "--suffix", ".bak"]
+        result, _ = self._sync(source, dest, flags, shared_server.port)
+        assert result.returncode == 0, f"Backup sync failed: {result.stderr[:200]}"
+        with open(source_file, "wb") as f:
+            f.write(b"BBBB")
+        result, _ = self._sync(source, dest, flags, shared_server.port)
+        assert result.returncode == 0, f"Backup sync failed: {result.stderr[:200]}"
+
+        received = get_dest_received_dir(dest, source)
+        assert _read_file(os.path.join(received, "f.txt")) == b"BBBB"
+        assert _read_file(os.path.join(received, "f.txt.bak")) == b"AAAA"
+
+    def test_backup_dir_stores_backups_separately(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "backup_dir_src")
+        dest = os.path.join(TEST_DATA_DIR, "backup_dir_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "f.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"AAAA")
+
+        flags = ["--backup", "--backup-dir", "backups"]
+        result, _ = self._sync(source, dest, flags, shared_server.port)
+        assert result.returncode == 0, f"Backup sync failed: {result.stderr[:200]}"
+        with open(source_file, "wb") as f:
+            f.write(b"BBBB")
+        result, _ = self._sync(source, dest, flags, shared_server.port)
+        assert result.returncode == 0, f"Backup sync failed: {result.stderr[:200]}"
+
+        received = get_dest_received_dir(dest, source)
+        assert _read_file(os.path.join(received, "f.txt")) == b"BBBB"
+        backup = os.path.join(dest, "backups", os.path.relpath(source_file, os.path.sep))
+        assert _read_file(backup) == b"AAAA"
+
+
+class TestPartialDir:
+    def test_completed_transfer_installed_in_destination(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "partial_src")
+        dest = os.path.join(TEST_DATA_DIR, "partial_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "f.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"partial payload")
+
+        result, _ = run_client(source, dest, flags=["--partial", "--partial-dir", ".partial"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Partial sync failed: {result.stderr[:200]}"
+
+        received = get_dest_received_dir(dest, source)
+        assert _read_file(os.path.join(received, "f.txt")) == b"partial payload"
+        # A completed transfer must not remain under the partial directory.
+        partial = os.path.join(dest, ".partial", os.path.relpath(source_file, os.path.sep))
+        assert not os.path.exists(partial)
+
+
+class TestLargeFile:
+    def test_transfer_100mb_file(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "large_src")
+        dest = os.path.join(TEST_DATA_DIR, "large_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "big.bin")
+        chunk = os.urandom(1024 * 1024)
+        with open(source_file, "wb") as f:
+            for _ in range(100):
+                f.write(chunk)
+
+        result, _ = run_client(source, dest, port=shared_server.port)
+        assert result.returncode == 0, f"Large-file sync failed: {result.stderr[:200]}"
+        received = get_dest_received_dir(dest, source)
+        assert filecmp.cmp(source_file, os.path.join(received, "big.bin"), shallow=False)

tests/test_config.c

@@ -282,6 +282,105 @@ static void test_config_receive_truncated() {
   close(p[1]);
 }
 
+static bool config_string_roundtrip_matches(const Config* send_cfg, Config* recv) {
+  /* The sender serializes NULL strings as "" on the wire.  Receivers must
+     canonicalize those empty values back to NULL for the options whose client
+     default is NULL (backup_dir, temp_dir, partial_dir, suffix), while a real
+     non-empty value round-trips unchanged. */
+  const char* fields[4];
+  char* const* recv_fields[4];
+  fields[0] = send_cfg->backup_dir;
+  recv_fields[0] = &recv->backup_dir;
+  fields[1] = send_cfg->temp_dir;
+  recv_fields[1] = &recv->temp_dir;
+  fields[2] = send_cfg->partial_dir;
+  recv_fields[2] = &recv->partial_dir;
+  fields[3] = send_cfg->suffix;
+  recv_fields[3] = &recv->suffix;
+  for (int i = 0; i < 4; i++) {
+    const char* sent = fields[i];
+    const char* got = *recv_fields[i];
+    if (sent == NULL || sent[0] == '\0') {
+      if (got != NULL)
+        return false;
+    } else if (got == NULL || strcmp(sent, got) != 0) {
+      return false;
+    }
+  }
+  return true;
+}
+
+static bool roundtrip_config_ok(const Config* send_cfg) {
+  int p[2];
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, p) != 0)
+    return false;
+  pid_t pid = fork();
+  if (pid == 0) {
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    Config* recv = config_receive(p[0]);
+    bool ok = recv != NULL;
+    if (ok) {
+      ok = recv->version != NULL && strcmp(recv->version, PROTOCOL_VERSION) == 0;
+      ok = ok && recv->send_directory && recv->receive_root_directory;
+      ok = ok && config_string_roundtrip_matches(send_cfg, recv);
+    }
+    config_delete(recv);
+    close(p[0]);
+    _exit(ok ? 0 : 1);
+  } else {
+    close(p[0]);
+    io_set_fds(p[1], p[1]);
+    bool sent = config_send(p[1], send_cfg);
+    int status;
+    waitpid(pid, &status, 0);
+    close(p[1]);
+    return sent && WIFEXITED(status) && WEXITSTATUS(status) == 0;
+  }
+}
+
+/* Issue #252: NULL-vs-empty must survive the wire for backup_dir, temp_dir,
+   partial_dir, and suffix.  NULL and explicitly-empty client values are both
+   serialized as "" and must be reconstructed as NULL so plain --backup (with
+   no --suffix/--backup-dir) works exactly like the client configured it. */
+static void test_config_string_null_vs_empty_roundtrip() {
+  if (is_running_under_valgrind())
+    return;
+
+  /* NULL values on the wire must come back as NULL. */
+  Config* a = config_create();
+  EXPECT_NOT_NULL(a);
+  a->send_directory = str_dup("/src");
+  a->receive_root_directory = str_dup("/dst");
+  EXPECT_TRUE(roundtrip_config_ok(a));
+  config_delete(a);
+
+  /* Explicitly empty strings (indistinguishable on the wire from NULL) must
+     be canonicalized to NULL by the receiver. */
+  Config* b = config_create();
+  EXPECT_NOT_NULL(b);
+  b->send_directory = str_dup("/src");
+  b->receive_root_directory = str_dup("/dst");
+  b->backup_dir = str_dup("");
+  b->temp_dir = str_dup("");
+  b->partial_dir = str_dup("");
+  b->suffix = str_dup("");
+  EXPECT_TRUE(roundtrip_config_ok(b));
+  config_delete(b);
+
+  /* Non-empty values must round-trip unchanged. */
+  Config* c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->backup_dir = str_dup("backups");
+  c->temp_dir = str_dup("/tmp/fast");
+  c->partial_dir = str_dup(".partial");
+  c->suffix = str_dup(".bak");
+  EXPECT_TRUE(roundtrip_config_ok(c));
+  config_delete(c);
+}
+
 static void test_config_is_remote_dest() {
   /* Valid SSH-style destinations */
   EXPECT_TRUE(config_is_remote_dest("user@host:/path"));
@@ -315,6 +414,7 @@ void test_config() {
     test_config_send_receive();
     test_config_send_receive_version_mismatch();
     test_config_receive_truncated();
+    test_config_string_null_vs_empty_roundtrip();
   }
   test_config_is_remote_dest();
 }

tests/test_file.c

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
+#include <time.h>
 #include <unistd.h>
 
 static void test_file_create() {
@@ -250,6 +251,111 @@ static void test_file_save_to_disk_ignore_existing_entry_types() {
   rmdir(root);
 }
 
+/* Issue #253: with --partial --partial-dir a completed write must be installed
+   at the real destination rather than left under the partial directory. */
+static void test_file_save_to_disk_partial_install() {
+  const char* root = "test_partial_install_tmp";
+  const char* dest_file = "test_partial_install_tmp/file.txt";
+  const char* partial_file = "test_partial_install_tmp/.partial/file.txt";
+  unlink(dest_file);
+  unlink(partial_file);
+  rmdir("test_partial_install_tmp/.partial");
+  rmdir(root);
+
+  File* f = file_create("file.txt");
+  EXPECT_NOT_NULL(f);
+  const char* content = "partial-dir content";
+  f->data->data = malloc(strlen(content));
+  EXPECT_NOT_NULL(f->data->data);
+  memcpy(f->data->data, content, strlen(content));
+  f->data->size = strlen(content);
+
+  Config* config = config_create();
+  EXPECT_NOT_NULL(config);
+  config->partial = true;
+  config->partial_dir = str_dup(".partial");
+
+  EXPECT_EQ_INT(file_save_to_disk_full(root, f, config), FILE_SAVE_WRITTEN);
+
+  FILE* fp = fopen(dest_file, "rb");
+  EXPECT_NOT_NULL(fp);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (fp) {
+    char buf[64] = {0};
+    size_t nread = fread(buf, 1, sizeof(buf) - 1, fp);
+    fclose(fp);
+    EXPECT_EQ_INT((int)nread, (int)strlen(content));
+    EXPECT_EQ_INT(memcmp(buf, content, strlen(content)), 0);
+  }
+  /* A completed transfer must not linger under the partial dir. */
+  EXPECT_EQ_INT(access(partial_file, F_OK), -1);
+
+  file_destroy(f);
+  config_delete(config);
+  unlink(dest_file);
+  rmdir(root);
+}
+
+/* Issue #251: file_save_to_disk_full must distinguish receiver-side skips
+   (--existing/--ignore-existing/--update) from real writes so the sender can
+   decide whether --remove-source-files may unlink its source. */
+static void test_file_save_to_disk_reports_skips() {
+  const char* root = "test_save_skip_tmp";
+  const char* existing_path = "test_save_skip_tmp/existing.txt";
+  unlink(existing_path);
+  rmdir(root);
+  EXPECT_TRUE(file_write_to_disk(existing_path, "old", 3, false, false));
+
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+
+  File* new_file = file_create("missing.txt");
+  EXPECT_NOT_NULL(new_file);
+  new_file->data->data = malloc(7);
+  EXPECT_NOT_NULL(new_file->data->data);
+  memcpy(new_file->data->data, "skipped", 7);
+  new_file->data->size = 7;
+
+  /* --existing: destination is missing -> skipped, not an error. */
+  cfg->existing = true;
+  EXPECT_EQ_INT(file_save_to_disk_full(root, new_file, cfg), FILE_SAVE_SKIPPED);
+  cfg->existing = false;
+
+  /* --ignore-existing: destination present -> skipped. */
+  File* present = file_create("existing.txt");
+  EXPECT_NOT_NULL(present);
+  present->data->data = malloc(3);
+  EXPECT_NOT_NULL(present->data->data);
+  memcpy(present->data->data, "new", 3);
+  present->data->size = 3;
+  cfg->ignore_existing = true;
+  EXPECT_EQ_INT(file_save_to_disk_full(root, present, cfg), FILE_SAVE_SKIPPED);
+  cfg->ignore_existing = false;
+
+  /* A normal overwrite of an existing file is a real write. */
+  EXPECT_EQ_INT(file_save_to_disk_full(root, present, cfg), FILE_SAVE_WRITTEN);
+
+  /* --update: a newer destination is skipped. */
+  struct stat st;
+  EXPECT_EQ_INT(stat(existing_path, &st), 0);
+  time_t now = time(NULL);
+  FileMetadata metadata = {.mode = st.st_mode,
+                           .uid = st.st_uid,
+                           .gid = st.st_gid,
+                           .mtime_sec = now - 100,
+                           .mtime_nsec = 0};
+  present->metadata = &metadata;
+  cfg->update = true;
+  EXPECT_EQ_INT(file_save_to_disk_full(root, present, cfg), FILE_SAVE_SKIPPED);
+  present->metadata = NULL;
+
+  file_destroy(new_file);
+  file_destroy(present);
+  config_delete(cfg);
+  unlink(existing_path);
+  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),
@@ -635,6 +741,8 @@ void test_file() {
   test_file_save_to_disk_existing();
   test_file_save_to_disk_ignore_existing();
   test_file_save_to_disk_ignore_existing_entry_types();
+  test_file_save_to_disk_partial_install();
+  test_file_save_to_disk_reports_skips();
   test_file_write_to_disk_basic();
   test_file_write_to_disk_with_fsync();
   test_file_write_to_disk_creates_dirs();

tests/test_server.c

@@ -1,14 +1,18 @@
 #include "test_server.h"
 #include "config.h"
+#include "delta.h"
 #include "file.h"
 #include "protocol.h"
 #include "test_utils.h"
 #include "utils.h"
+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/wait.h>
+#include <time.h>
 #include <unistd.h>
 
 #include "receiver.h"
@@ -210,6 +214,249 @@ static void test_receive_incremental_check_rejects_invalid_nanoseconds() {
   config_delete(cfg);
 }
 
+static char* make_check_root(const char* tag) {
+  char tmpl[128];
+  snprintf(tmpl, sizeof(tmpl), "/tmp/fastsync_%s_XXXXXX", tag);
+  char* path = str_dup(tmpl);
+  if (!path)
+    return NULL;
+  if (!mkdtemp(path)) {
+    free(path);
+    return NULL;
+  }
+  return path;
+}
+
+static void write_check_file(const char* dir, const char* name, const char* content) {
+  char path[1024];
+  snprintf(path, sizeof(path), "%s/%s", dir, name);
+  int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+  if (fd >= 0) {
+    size_t len = strlen(content);
+    if (write(fd, content, len) != (ssize_t)len) {
+      /* intentionally ignored in tests */
+    }
+    close(fd);
+  }
+}
+
+/* Issue #255: a same-size/mtime match is decided from metadata alone, so the
+   receiver answers STATUS_OK (skip) and never asks for a data body. */
+static void test_incremental_check_quick_skip_by_mtime() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  char* root = make_check_root("qskip");
+  EXPECT_NOT_NULL(root);
+  cfg->receive_root_directory = str_dup(root);
+  write_check_file(root, "file.txt", "0123456789abcdef");
+
+  char path[1024];
+  snprintf(path, sizeof(path), "%s/file.txt", root);
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[1]);
+  io_set_bwlimit(0);
+
+  pid_t pid = fork();
+  if (pid == 0) {
+    alarm(30);
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    bool skipped = false;
+    File* file = receive_incremental_check(p[0], cfg, &skipped);
+    bool ok = file == NULL && skipped;
+    file_destroy(file);
+    config_delete(cfg);
+    close(p[0]);
+    _exit(ok ? 0 : 1);
+  } else {
+    close(p[0]);
+    io_set_fds(p[1], p[1]);
+    EXPECT_TRUE(send_str(p[1], "file.txt"));
+    unsigned long long size = (unsigned long long)st.st_size;
+    long long mtime = (long long)st.st_mtime;
+    long long mtime_nsec = 0;
+#ifdef __linux__
+    mtime_nsec = (long long)st.st_mtim.tv_nsec;
+#endif
+    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)));
+    Status s;
+    EXPECT_TRUE(receive_status(p[1], &s));
+    EXPECT_EQ_INT(s, STATUS_OK);
+
+    int status;
+    waitpid(pid, &status, 0);
+    close(p[1]);
+    config_delete(cfg);
+    unlink(path);
+    rmdir(root);
+    free(root);
+    EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+  }
+}
+
+/* Issue #255: a size mismatch cannot be a skip, so the receiver answers
+   STATUS_NEXT and consumes the full data body that follows. */
+static void test_incremental_check_size_mismatch_full_transfer() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  char* root = make_check_root("qnext");
+  EXPECT_NOT_NULL(root);
+  cfg->receive_root_directory = str_dup(root);
+  write_check_file(root, "file.txt", "0123456789abcdef");
+
+  char path[1024];
+  snprintf(path, sizeof(path), "%s/file.txt", root);
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[1]);
+  io_set_bwlimit(0);
+
+  pid_t pid = fork();
+  if (pid == 0) {
+    alarm(30);
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    bool skipped = false;
+    File* file = receive_incremental_check(p[0], cfg, &skipped);
+    bool ok = file != NULL && !skipped && file->path != NULL && strcmp(file->path, "file.txt") == 0;
+    file_destroy(file);
+    config_delete(cfg);
+    close(p[0]);
+    _exit(ok ? 0 : 1);
+  } else {
+    close(p[0]);
+    io_set_fds(p[1], p[1]);
+    EXPECT_TRUE(send_str(p[1], "file.txt"));
+    unsigned long long size = (unsigned long long)st.st_size + 1;
+    long long mtime = (long long)st.st_mtime;
+    long long mtime_nsec = 0;
+#ifdef __linux__
+    mtime_nsec = (long long)st.st_mtim.tv_nsec;
+#endif
+    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)));
+    Status s;
+    EXPECT_TRUE(receive_status(p[1], &s));
+    EXPECT_EQ_INT(s, STATUS_NEXT);
+
+    Data* body = data_create_reserve(8);
+    EXPECT_NOT_NULL(body);
+    body->data = malloc(8);
+    EXPECT_NOT_NULL(body->data);
+    memcpy(body->data, "replaced", 8);
+    body->size = 8;
+    EXPECT_TRUE(send_data(p[1], body));
+    data_destroy(body);
+
+    int status;
+    waitpid(pid, &status, 0);
+    close(p[1]);
+    config_delete(cfg);
+    unlink(path);
+    rmdir(root);
+    free(root);
+    EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+  }
+}
+
+/* Issue #256: when a received delta claims a result above the whole-file cap,
+   receive_delta_file must mark the operation failed so the caller aborts with
+   STATUS_ERROR instead of emitting STATUS_NEXT and waiting for a body that
+   never arrives. */
+static void test_incremental_check_delta_oversize_reports_failure() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  char* root = make_check_root("qdelta");
+  EXPECT_NOT_NULL(root);
+  cfg->receive_root_directory = str_dup(root);
+  cfg->use_delta = true;
+
+  char content[20000];
+  memset(content, 'a', sizeof(content));
+  content[sizeof(content) - 1] = '\0';
+  write_check_file(root, "file.txt", content);
+
+  char path[1024];
+  snprintf(path, sizeof(path), "%s/file.txt", root);
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+  EXPECT_EQ_INT((int)st.st_size, 19999);
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[1]);
+  io_set_bwlimit(0);
+
+  pid_t pid = fork();
+  if (pid == 0) {
+    alarm(30);
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    bool skipped = false;
+    File* file = receive_incremental_check(p[0], cfg, &skipped);
+    bool ok = file == NULL && !skipped;
+    if (ok)
+      send_status(p[0], STATUS_ERROR); /* mirror the server error path */
+    file_destroy(file);
+    config_delete(cfg);
+    close(p[0]);
+    _exit(ok ? 0 : 1);
+  } else {
+    close(p[0]);
+    io_set_fds(p[1], p[1]);
+    EXPECT_TRUE(send_str(p[1], "file.txt"));
+    unsigned long long size = (unsigned long long)st.st_size;
+    long long mtime = 1; /* different from the file mtime: force a transfer */
+    long long mtime_nsec = 0;
+    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)));
+
+    Status s;
+    EXPECT_TRUE(receive_status(p[1], &s));
+    EXPECT_EQ_INT(s, STATUS_DELTA_SIGNATURE);
+    Data* sig_data = receive_data(p[1]);
+    EXPECT_NOT_NULL(sig_data);
+    DeltaSignature* sig = delta_signature_deserialize(sig_data);
+    EXPECT_NOT_NULL(sig);
+    delta_signature_destroy(sig);
+    data_destroy(sig_data);
+
+    /* Send a delta whose claimed output size exceeds the whole-file cap. */
+    Delta delta;
+    memset(&delta, 0, sizeof(delta));
+    delta.new_file_size = MAX_RECEIVE_WHOLE_FILE_SIZE + 1;
+    Data* bogus = delta_serialize(&delta);
+    EXPECT_NOT_NULL(bogus);
+    EXPECT_TRUE(send_status(p[1], STATUS_DELTA_DATA));
+    EXPECT_TRUE(bogus != NULL && send_data(p[1], bogus));
+    data_destroy(bogus);
+
+    /* The receiver must answer with an error, never with STATUS_NEXT. */
+    EXPECT_TRUE(receive_status(p[1], &s));
+    EXPECT_EQ_INT(s, STATUS_ERROR);
+
+    int status;
+    waitpid(pid, &status, 0);
+    close(p[1]);
+    config_delete(cfg);
+    unlink(path);
+    rmdir(root);
+    free(root);
+    EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+  }
+}
+
 void test_server() {
   if (!is_running_under_valgrind()) {
     test_receive_files_finished();
@@ -217,5 +464,8 @@ void test_server() {
     test_receive_files_abort();
     test_receive_manifest_rejects_traversal();
     test_receive_incremental_check_rejects_invalid_nanoseconds();
+    test_incremental_check_quick_skip_by_mtime();
+    test_incremental_check_size_mismatch_full_transfer();
+    test_incremental_check_delta_oversize_reports_failure();
   }
 }