FastSync/src/shared/delay_updates.c

#include "delay_updates.h"

#include "config.h"
#include "file.h"
#include "log.h"
#include "utils.h"
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <unistd.h>

DelayUpdatesContext* delay_updates_context_create(const char* root_directory) {
  if (!root_directory)
    return NULL;
  DelayUpdatesContext* context = calloc(1, sizeof(DelayUpdatesContext));
  if (!context)
    return NULL;
  context->root_directory = str_dup(root_directory);
  if (!context->root_directory) {
    free(context);
    return NULL;
  }
  context->staging_root = path_cat(root_directory, DELAY_UPDATES_STAGING_DIR);
  if (!context->staging_root) {
    free(context->root_directory);
    free(context);
    return NULL;
  }
  context->entries = NULL;
  context->count = 0;
  context->capacity = 0;
  context->prepared = false;
  context->lock_fd = -1;
  if (mtx_init(&context->mutex, mtx_plain) != thrd_success) {
    free(context->staging_root);
    free(context->root_directory);
    free(context);
    return NULL;
  }
  return context;
}

void delay_updates_context_destroy(DelayUpdatesContext* context) {
  if (!context)
    return;
  mtx_destroy(&context->mutex);
  if (context->lock_fd >= 0)
    close(context->lock_fd);
  context->lock_fd = -1;
  free(context->staging_root);
  free(context->root_directory);
  for (size_t i = 0; i < context->count; i++) {
    free(context->entries[i].staged_path);
    free(context->entries[i].final_path);
    free(context->entries[i].file_path);
  }
  free(context->entries);
  free(context);
}

bool delay_updates_staging_name_conflict(const char* dir) {
  if (!dir || !*dir)
    return false;
  size_t length = strlen(dir);
  while (length > 0 && dir[length - 1] == '/')
    length--;
  size_t reserved_length = strlen(DELAY_UPDATES_STAGING_DIR);
  if (length != reserved_length)
    return false;
  return strncmp(dir, DELAY_UPDATES_STAGING_DIR, length) == 0;
}

/* Recursively delete every entry inside an open directory (never following
   symlinks).  The directory itself is left in place.  Mirrors the fd-relative
   walk used by the delete code so a symlink planted inside the staging tree
   can never redirect removal outside of it. */
static bool delay_wipe_dir_fd(int dirfd) {
  int scanfd = dup(dirfd);
  if (scanfd < 0)
    return false;
  DIR* dir = fdopendir(scanfd);
  if (!dir) {
    close(scanfd);
    return false;
  }
  bool operation_ok = true;
  const struct dirent* entry;
  while ((entry = readdir(dir)) != NULL) {
    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
      continue;
    struct stat st;
    if (fstatat(dirfd, entry->d_name, &st, AT_SYMLINK_NOFOLLOW) != 0) {
      if (errno != ENOENT)
        operation_ok = false;
      continue;
    }
    if (S_ISDIR(st.st_mode)) {
      int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
      bool child_removed = false;
      if (childfd >= 0) {
        child_removed = delay_wipe_dir_fd(childfd);
        close(childfd);
      } else if (errno != ENOENT) {
        operation_ok = false;
      }
      if (child_removed && unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0 && errno != ENOENT)
        operation_ok = false;
    } else {
      if (unlinkat(dirfd, entry->d_name, 0) != 0 && errno != ENOENT)
        operation_ok = false;
    }
  }
  closedir(dir);
  return operation_ok;
}

bool delay_updates_prepare(DelayUpdatesContext* context) {
  if (!context)
    return false;
  if (context->prepared)
    return true;
  int fd = file_open_private_dir(context->staging_root);
  if (fd < 0) {
    int saved_errno = errno;
    char* escaped = output_escape(context->staging_root, false);
    log_message(LOG_LEVEL_ERROR, "could not create --delay-updates staging directory '%s': %s",
                escaped ? escaped : "<allocation failed>", strerror(saved_errno));
    free(escaped);
    return false;
  }
  /* Hold an exclusive advisory lock on the staging directory for the whole
     transfer.  The staging directory name is fixed, so two simultaneous
     delayed transfers to the same destination root would otherwise share it
     and destroy each other's staged files.  The lock makes the second session
     fail cleanly instead of corrupting the first.  The lock is released when
     the context (and its file descriptor) is destroyed. */
  if (flock(fd, LOCK_EX | LOCK_NB) != 0) {
    int saved_errno = errno;
    close(fd);
    if (saved_errno == EWOULDBLOCK || saved_errno == EAGAIN) {
      char* escaped = output_escape(context->staging_root, false);
      log_message(LOG_LEVEL_ERROR,
                  "another --delay-updates transfer to '%s' is already in progress; refusing to "
                  "share the staging directory",
                  escaped ? escaped : "<allocation failed>");
      free(escaped);
    } else {
      log_message(LOG_LEVEL_ERROR, "could not lock --delay-updates staging directory '%s': %s",
                  context->staging_root, strerror(saved_errno));
    }
    return false;
  }
  context->lock_fd = fd;
  /* Only now, with exclusive ownership, wipe leftovers from an interrupted
     earlier transfer; this can never race with a live session. */
  bool ok = delay_wipe_dir_fd(fd);
  if (!ok) {
    log_message(LOG_LEVEL_ERROR, "could not clear stale --delay-updates staging files under '%s'",
                context->staging_root);
    close(context->lock_fd);
    context->lock_fd = -1;
    return false;
  }
  context->prepared = true;
  return true;
}

bool delay_updates_record(DelayUpdatesContext* context, const char* staged_path,
                          const char* final_path, const char* file_path) {
  if (!context || !staged_path || !final_path || !file_path)
    return false;
  char* staged_copy = str_dup(staged_path);
  char* final_copy = str_dup(final_path);
  char* file_copy = str_dup(file_path);
  if (!staged_copy || !final_copy || !file_copy) {
    free(staged_copy);
    free(final_copy);
    free(file_copy);
    return false;
  }
  mtx_lock(&context->mutex);
  bool ok = true;
  if (context->count == context->capacity) {
    size_t new_capacity = context->capacity == 0 ? 64 : context->capacity * 2;
    if (new_capacity < context->capacity) {
      ok = false;
    } else {
      StagedFileEntry* grown = realloc(context->entries, new_capacity * sizeof(StagedFileEntry));
      if (!grown) {
        ok = false;
      } else {
        context->entries = grown;
        context->capacity = new_capacity;
      }
    }
  }
  if (ok) {
    context->entries[context->count].staged_path = staged_copy;
    context->entries[context->count].final_path = final_copy;
    context->entries[context->count].file_path = file_copy;
    context->count++;
  }
  mtx_unlock(&context->mutex);
  if (!ok) {
    free(staged_copy);
    free(final_copy);
    free(file_copy);
  }
  return ok;
}

/* Move an existing final destination file aside before the staged replacement
   is installed.  Deferred from stage time so the final destination is not
   modified until publication.  Mirrors the immediate-mode backup logic. */
static bool delay_publish_backup(const DelayUpdatesContext* context, const Config* config,
                                 const StagedFileEntry* entry) {
  bool backup_enabled = config && config->backup && !config->ignore_existing;
  if (!backup_enabled)
    return true;
  const char* backup_suffix = (config && config->suffix) ? config->suffix : "~";
  struct stat backup_stat;
  if (!file_stat_secure(entry->final_path, &backup_stat))
    return true; /* nothing to back up */

  char* backup_path = NULL;
  if (config->backup_dir) {
    char* confined_backup = path_cat(context->root_directory, config->backup_dir);
    if (!confined_backup)
      return false;
    backup_path = path_cat(confined_backup, entry->file_path);
    free(confined_backup);
  } else {
    size_t path_len = strlen(entry->final_path);
    size_t suffix_len = strlen(backup_suffix);
    if (path_len > SIZE_MAX - suffix_len - 1)
      return false;
    backup_path = malloc(path_len + suffix_len + 1);
    if (backup_path) {
      memcpy(backup_path, entry->final_path, path_len);
      memcpy(backup_path + path_len, backup_suffix, suffix_len + 1);
    }
  }
  if (!backup_path)
    return false;
  char* parent_copy = str_dup(backup_path);
  if (!parent_copy || !file_ensure_directory_secure(dirname(parent_copy))) {
    free(parent_copy);
    free(backup_path);
    return false;
  }
  free(parent_copy);
  bool ok = file_rename_secure(entry->final_path, backup_path);
  free(backup_path);
  return ok;
}

static bool delay_publish_entry(DelayUpdatesContext* context, const Config* config,
                                const StagedFileEntry* entry) {
  if (!delay_publish_backup(context, config, entry))
    return false;
  if (!file_rename_secure(entry->staged_path, entry->final_path)) {
    if (errno == EXDEV) {
      char* escaped = output_escape(entry->final_path, false);
      log_message(LOG_LEVEL_ERROR,
                  "staging directory is on a different filesystem than the destination; cannot "
                  "atomically install file (EXDEV): %s",
                  escaped ? escaped : "<allocation failed>");
      free(escaped);
    } else {
      char* escaped = output_escape(entry->final_path, false);
      log_message(LOG_LEVEL_ERROR, "could not install staged file '%s': %s",
                  escaped ? escaped : "<allocation failed>", strerror(errno));
      free(escaped);
    }
    return false;
  }
  return true;
}

/* Remove the staging tree (contents plus the directory itself).  Returns true
   when nothing is left behind (including the case where it never existed). */
static bool delay_updates_remove_staging_tree(DelayUpdatesContext* context) {
  int fd = open(context->staging_root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
  if (fd < 0)
    return errno == ENOENT;
  bool ok = delay_wipe_dir_fd(fd);
  if (close(fd) != 0)
    ok = false;
  if (ok && rmdir(context->staging_root) != 0 && errno != ENOENT)
    ok = false;
  return ok;
}

bool delay_updates_publish(DelayUpdatesContext* context, const Config* config) {
  if (!context)
    return false;
  mtx_lock(&context->mutex);
  bool ok = true;
  for (size_t i = 0; i < context->count; i++) {
    if (!delay_publish_entry(context, config, &context->entries[i])) {
      ok = false;
      break;
    }
  }
  mtx_unlock(&context->mutex);

  /* Renaming files out of the staging tree leaves the mirrored directories
     behind, and a mid-publish failure leaves the remaining staged files.
     Remove whatever is left so a later run starts from a clean staging area
     and no staged content can linger after a failed publish.  If that cleanup
     fails, tell the operator: a stale staging directory would otherwise
     silently accumulate and make the next transfer's prepare-wipe fail. */
  if (!delay_updates_remove_staging_tree(context)) {
    log_message(LOG_LEVEL_WARNING,
                "could not fully remove --delay-updates staging directory '%s' after publish; a "
                "later --delay-updates transfer to this destination will try to clear it",
                context->staging_root);
  }
  return ok;
}

void delay_updates_cleanup(DelayUpdatesContext* context) {
  if (!context)
    return;
  /* Only a context that gained exclusive ownership may touch the shared
     staging directory.  If prepare never succeeded (e.g. lock contention with
     another live session) the directory belongs to that other session and must
     be left alone. */
  if (!context->prepared)
    return;
  delay_updates_remove_staging_tree(context);
}