fix: #251 #252 #253 #255 #256 #257 receiver & remove-source correctness

#251 --remove-source-files deletes sources that were skipped receiver-side
     (--existing/--ignore-existing/--update). The receiver now reports a
     per-file outcome for every processed data file when the sender requests
     removal; the client only unlinks sources the receiver actually wrote.
     add remove_source_files to the wire config and bump the protocol to 2.5.0.
#252 --backup/--suffix/--backup-dir broken by NULL-vs-empty wire loss. Receivers
     canonicalize the empty wire string back to NULL for backup_dir, temp_dir,
     partial_dir and suffix, and --suffix is received unconditionally.
#253 --partial --partial-dir never installed completed files. file_save_to_disk
     now renames a fully written partial-dir file into the real destination.
#255 STATUS_CHECK read the entire old file before the size/mtime quick check.
     Old contents are only read when a checksum compare or delta needs them.
#256 receive_delta_file failure paths did not set *failed, so the caller sent
     STATUS_NEXT and waited for a body that never came. Every NULL return now
     marks the transfer failed.
#257 files >64 MiB could not transfer. Whole-file receive caps raised to the
     256 MiB connection/allocation ceiling (chunk caps stay 64 MiB) and the
     client ignores SIGPIPE so a server-side close surfaces as a clean error.

Unit tests added: config NULL-vs-empty round trip, incremental quick-check
skip/NEXT paths, delta oversize failure, partial-dir install, save-result
skip reporting.

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();
   }
 }