refactor(server): decompose handler into phases

src/server/server.c

@@ -705,69 +705,85 @@ static const char* server_module_gate(const Config* config, void* context) {
   return module_gate_install_root(config, module);
 }
 
-void handler(int file_descriptor) {
-  SSL* ssl = io_get_ssl();
+/* Per-connection state threaded through the handler phase helpers below.  The
+ * fields are a faithful split of the former handler() locals: the protocol
+ * session, the config-frame gate context, the accepted config, the optional
+ * multithreaded pipeline context and the teardown bookkeeping all live here so
+ * the single `done` epilogue in handler() can release them exactly as before. */
+typedef struct ServerSession {
+  int fd;
+  SSL* ssl;
   ProtocolSession session;
-  protocol_session_init(&session, file_descriptor, file_descriptor);
-  protocol_session_set_ssl(&session, ssl);
-  protocol_session_bind(&session);
   ModuleGateContext gate_ctx;
-  gate_ctx.ssl = ssl;
-  gate_ctx.fd = file_descriptor;
-  gate_ctx.super_mode_override = -1;
-  gate_ctx.has_peer_ip = false;
-  gate_ctx.peer_ip[0] = '\0';
-  gate_ctx.is_local = false;
-  /* All teardown state starts empty so the single `done` epilogue is safe to
-   * reach from any error path (including before the config frame arrives). */
-  Config* config = NULL;
-  PipelineContextReceiver* context = NULL;
-  char* joined_destination = NULL;
-  bool charset_ready = false;
-  config = config_receive_with_validate(file_descriptor, server_module_gate, &gate_ctx);
-  if (config == NULL) {
+  Config* config;
+  PipelineContextReceiver* context;
+  char* joined_destination;
+  bool charset_ready;
+} ServerSession;
+
+/* Phase 1 -- config receipt + validation.  Receives the client config frame
+ * through the module gate, applies the super-mode override the gate recorded
+ * exactly once, and installs the per-connection protocol/compression state.
+ * Returns false when the config frame was refused (the gate has already
+ * answered the client); the caller jumps to the shared `done` epilogue. */
+static bool server_accept_config(ServerSession* state) {
+  state->config = config_receive_with_validate(state->fd, server_module_gate, &state->gate_ctx);
+  if (state->config == NULL) {
     log_message(LOG_LEVEL_ERROR, "Failed to receive config");
-    goto done;
+    return false;
   }
   /* Apply the super-mode veto the gate decided on (operator --no-super, or a
    * daemon module without the `client owner = yes` opt-in) exactly once, so
    * every downstream gate (identity_apply_ownership via privilege_super_permitted,
    * device-node creation) sees SUPER_MODE_OFF.  The gate never mutated the
    * received config. */
-  if (gate_ctx.super_mode_override != -1)
-    config->super_mode = (SuperMode)gate_ctx.super_mode_override;
+  if (state->gate_ctx.super_mode_override != -1)
+    state->config->super_mode = (SuperMode)state->gate_ctx.super_mode_override;
   /* Install the codec this connection negotiated before the receiver/writer
    * threads start (the server forks per connection, so the process-global
    * codec is private to this session). */
-  compression_set_algo((CompressionAlgo)config->compression_algo);
+  compression_set_algo((CompressionAlgo)state->config->compression_algo);
   /* If the client requested ownership but the effective super mode forbids it
    * (operator --no-super, a privileged standalone receiver's secure default, or
    * a daemon module without `client owner = yes`), say so ONCE per connection so
    * a successful -a/-o/-g transfer is not mistaken for preserved ownership. */
-  if (config->super_mode == SUPER_MODE_OFF && identity_ownership_requested(config))
+  if (state->config->super_mode == SUPER_MODE_OFF && identity_ownership_requested(state->config))
     log_message(LOG_LEVEL_WARNING,
                 "requested ownership will NOT be applied: super-user activities are disabled "
                 "for this connection (operator veto, or module without `client owner = yes`)");
-  protocol_set_8_bit_output(config->eight_bit_output);
+  protocol_set_8_bit_output(state->config->eight_bit_output);
   /* Server-side per-message protocol deadline for every frame from here on.
    * `timeout` is not serialized, so this is the server's own config (the server
    * has no --timeout CLI and defaults it to 0).  A client's --timeout tightens
    * only that client's own protocol I/O; the server floors its own deadline at
    * SERVER_IO_TIMEOUT_SEC so a silent peer can never hold a session slot
    * forever (the socket layer gets the same floor at startup). */
-  protocol_session_set_io_timeout(&session, protocol_server_io_timeout_sec(config->timeout));
+  protocol_session_set_io_timeout(&state->session,
+                                  protocol_server_io_timeout_sec(state->config->timeout));
+  return true;
+}
+
+/* Phase 2 -- security gates.  The ORDER here is load-bearing and must not be
+ * merged or reordered: transport/authentication (plaintext refusal, TLS
+ * client-CN verification), then daemon-root confinement (absolute-destination
+ * rejection, traversal + within-authorized-root), then delete/force
+ * authorization -- exactly the sequence the former handler() used.  Returns
+ * false after logging the matching rejection; the caller jumps to the shared
+ * `done` epilogue. */
+static bool server_apply_security_gates(ServerSession* state) {
+  Config* config = state->config;
   const char* authorized_root = utils_get_authorized_root_path();
   if (!authorized_root) {
     log_message(LOG_LEVEL_ERROR, "No server-side destination root configured");
-    goto done;
+    return false;
   }
-  if (!allow_unauthenticated && ssl == NULL) {
+  if (!allow_unauthenticated && state->ssl == NULL) {
     log_message(LOG_LEVEL_ERROR, "Rejected unauthenticated plaintext connection");
-    goto done;
+    return false;
   }
-  if (ssl && required_client_cn && !tls_client_identity_allowed(ssl)) {
+  if (state->ssl && required_client_cn && !tls_client_identity_allowed(state->ssl)) {
     log_message(LOG_LEVEL_ERROR, "Rejected TLS client with unauthorized identity");
-    goto done;
+    return false;
   }
   /* Daemon mode: the module's root is the authorized root (installed by
      server_module_gate), and the client's destination is a MODULE-RELATIVE
@@ -777,27 +793,27 @@ void handler(int file_descriptor) {
   if (g_daemon_conf && config->receive_root_directory && config->receive_root_directory[0] == '/') {
     log_message(LOG_LEVEL_ERROR, "Rejected absolute daemon destination (must be relative to the "
                                  "selected module root)");
-    goto done;
+    return false;
   }
   char* destination = config->receive_root_directory;
   if (destination && destination[0] != '/')
-    joined_destination = path_cat(authorized_root, destination);
-  if (joined_destination)
-    destination = joined_destination;
+    state->joined_destination = path_cat(authorized_root, destination);
+  if (state->joined_destination)
+    destination = state->joined_destination;
   if (!destination || has_path_traversal(destination) ||
       !path_is_within_root(authorized_root, destination)) {
     log_message(LOG_LEVEL_ERROR, "Rejected destination outside authorized root");
-    free(joined_destination);
-    joined_destination = NULL;
-    goto done;
+    free(state->joined_destination);
+    state->joined_destination = NULL;
+    return false;
   }
-  if (joined_destination) {
+  if (state->joined_destination) {
     free(config->receive_root_directory);
-    config->receive_root_directory = joined_destination;
-    joined_destination = NULL;
+    config->receive_root_directory = state->joined_destination;
+    state->joined_destination = NULL;
   }
   if (!config->receive_root_directory) {
-    goto done;
+    return false;
   }
   config->use_delete = config->use_delete && allow_delete;
   /* --force (receiver-side) is deletion authority too: it lets an incoming
@@ -807,6 +823,18 @@ void handler(int file_descriptor) {
    * --delete-missing-args, so a client cannot use --force to bypass the delete
    * policy. */
   config->force_delete = config->force_delete && allow_delete;
+  return true;
+}
+
+/* Phase 3 -- session preparation.  Installs the negotiated conversion, applies
+ * the remaining deletion policy, materializes the destination root (--mkpath),
+ * creates the --delay-updates staging tree, snapshots the identity policy, and
+ * publishes the --keep-dirlinks/--trust-sender globals and the daemon MOTD.
+ * All of it must happen before any receiver/writer thread is spawned.  Returns
+ * false after logging the matching failure; the caller jumps to the shared
+ * `done` epilogue. */
+static bool server_prepare_session(ServerSession* state) {
+  Config* config = state->config;
   /* --iconv (protocol 2.16.0): install the receiver-side wire->local conversion
      now that the client's full CONVERT_SPEC has been received and validated,
      before any received file name is decoded.  The server's own --iconv (if
@@ -817,14 +845,14 @@ void handler(int file_descriptor) {
     if (!charset_wire_init_receiver(config->iconv_spec, server_iconv_spec)) {
       log_message(LOG_LEVEL_ERROR,
                   "--iconv: unsupported charset conversion requested (LOCAL[,REMOTE])");
-      goto done;
+      return false;
     }
-    charset_ready = true;
+    state->charset_ready = true;
   }
   /* --delete-missing-args deletes destination mirrors receiver-side, so it is
-     deletion and stays gated by the same --allow-delete server policy.  When
-     the server policy is off the flag is inert (the missing entries are still
-     skipped via its implied --ignore-missing-args, but nothing is deleted). */
+   * deletion and stays gated by the same --allow-delete server policy.  When
+   * the server policy is off the flag is inert (the missing entries are still
+   * skipped via its implied --ignore-missing-args, but nothing is deleted). */
   config->delete_missing_args = config->delete_missing_args && allow_delete;
   /* --mkpath: create the destination root (and its missing leading components)
    * before anything else; without it the root must pre-exist.  The precondition
@@ -839,7 +867,7 @@ void handler(int file_descriptor) {
     log_message(LOG_LEVEL_ERROR, "destination root is not available: %s",
                 escaped_root ? escaped_root : "<allocation failed>");
     free(escaped_root);
-    goto done;
+    return false;
   }
   /* A --delay-updates transfer stages under a private 0700 directory inside
      the receive root.  Create it up front (wiping leftovers of any previously
@@ -849,7 +877,7 @@ void handler(int file_descriptor) {
     config->delay_context = delay_updates_context_create(config->receive_root_directory);
     if (!config->delay_context || !delay_updates_prepare(config->delay_context)) {
       log_message(LOG_LEVEL_ERROR, "Failed to initialize --delay-updates staging area");
-      goto done;
+      return false;
     }
   }
   /* Preserve the negotiated identity policy for the fd-relative ownership
@@ -859,7 +887,7 @@ void handler(int file_descriptor) {
      rather than silently applying the wrong ownership policy. */
   if (!identity_set_active(config)) {
     log_message(LOG_LEVEL_ERROR, "Failed to activate identity policy");
-    goto done;
+    return false;
   }
   /* Persist the negotiated --keep-dirlinks policy once, here at config-accept,
      before any multithreaded receiver/writer threads are spawned, so the
@@ -887,61 +915,72 @@ void handler(int file_descriptor) {
      Wave C note in config.h). */
   if (g_daemon_conf) {
     char* motd = motd_read_file(g_daemon_conf->global.motd_file);
-    if (!motd_send(file_descriptor, motd ? motd : "")) {
+    if (!motd_send(state->fd, motd ? motd : "")) {
       free(motd);
       log_message(LOG_LEVEL_ERROR, "Failed to send daemon MOTD");
-      goto done;
+      return false;
     }
     free(motd);
   }
-  if (config->use_multithreading) {
+  return true;
+}
+
+/* Phase 4a -- transfer via the multithreaded receiver.  Spawns the receive/write
+ * thread pair, joins them, then commits the late deletion, --delay-updates
+ * publication and directory times before emitting the terminal stats/success
+ * frame.  On any failure the helper just returns; the caller's `done` epilogue
+ * releases the pipeline context (which owns the config and queue) exactly as the
+ * former inline code did. */
+static void server_run_mt_receiver(ServerSession* state) {
+  Config* config = state->config;
   Queue* q = queue_create(100, file_destroy);
   if (q == NULL)
-      goto done;
-    context = pipeline_context_receiver_create(config, q, file_descriptor, ssl);
-    if (context == NULL) {
+    return;
+  state->context = pipeline_context_receiver_create(config, q, state->fd, state->ssl);
+  if (state->context == NULL) {
     queue_destroy(q);
-      goto done;
+    return;
   }
-    protocol_session_set_max_alloc(&context->session, config->max_alloc);
-    protocol_session_set_io_timeout(&context->session,
+  protocol_session_set_max_alloc(&state->context->session, config->max_alloc);
+  protocol_session_set_io_timeout(&state->context->session,
                                   protocol_server_io_timeout_sec(config->timeout));
-    atomic_store(&context->session.total_allocated_bytes,
-                 atomic_load(&session.total_allocated_bytes));
-    pipeline_context_receiver_set_queue_byte_limit(context, RECEIVER_QUEUE_MAX_BYTES);
+  atomic_store(&state->context->session.total_allocated_bytes,
+               atomic_load(&state->session.total_allocated_bytes));
+  pipeline_context_receiver_set_queue_byte_limit(state->context, RECEIVER_QUEUE_MAX_BYTES);
   thrd_t receiver = {0};
   thrd_t writer = {0};
-    bool receiver_created = thrd_create(&receiver, receive_thread, context) == thrd_success;
+  bool receiver_created = thrd_create(&receiver, receive_thread, state->context) == thrd_success;
   bool writer_created = false;
   if (receiver_created)
-      writer_created = thrd_create(&writer, write_thread, context) == thrd_success;
+    writer_created = thrd_create(&writer, write_thread, state->context) == thrd_success;
   if (!receiver_created || !writer_created) {
     log_perror("Error creating Threads");
     if (receiver_created) {
-        mtx_lock(&context->mutex);
-        atomic_store(&context->cancelled, true);
-        cnd_broadcast(&context->condition_not_full);
-        cnd_broadcast(&context->condition_not_empty);
-        mtx_unlock(&context->mutex);
+      mtx_lock(&state->context->mutex);
+      atomic_store(&state->context->cancelled, true);
+      cnd_broadcast(&state->context->condition_not_full);
+      cnd_broadcast(&state->context->condition_not_empty);
+      mtx_unlock(&state->context->mutex);
       /* Unblock a worker parked in socket I/O without closing the fd (the
        * child owns the single close).  shutdown() only affects sockets; for
        * the --stdio pipe the receiver's per-message poll timeout still
        * bounds the join, so do nothing there rather than close a descriptor
        * another thread may still be using. */
       struct stat fd_stat;
-        if (fstat(file_descriptor, &fd_stat) == 0 && S_ISSOCK(fd_stat.st_mode))
-          shutdown(file_descriptor, SHUT_RDWR);
+      if (fstat(state->fd, &fd_stat) == 0 && S_ISSOCK(fd_stat.st_mode))
+        shutdown(state->fd, SHUT_RDWR);
       thrd_join(receiver, NULL);
     }
     if (writer_created)
       thrd_join(writer, NULL);
-      goto done;
+    return;
   }
   int receiver_result;
   int writer_result;
   thrd_join(receiver, &receiver_result);
   thrd_join(writer, &writer_result);
   bool transfer_ok = receiver_result == thrd_success && writer_result == thrd_success;
+  PipelineContextReceiver* context = state->context;
   if (transfer_ok && !config->dry_run) {
     /* Commit-style (late) deletion: receive_thread handed the keep-set
        manifest here instead of deleting while write_thread might still be
@@ -1008,20 +1047,64 @@ void handler(int file_descriptor) {
     Status final_status = context->delete_limit_reached ? STATUS_DELETE_LIMIT : STATUS_OK;
     /* Emit the optional wire-stats record first (protocol 2.25.0), then the
        success/outcome frame, exactly like the single-threaded receiver. */
-      if (!receiver_send_stats_frame(file_descriptor, config, &context->stats,
-                                     context->would_delete, context->deleted_paths) ||
-          !receiver_send_final_success(file_descriptor, config, &context->outcomes, final_status))
+    if (!receiver_send_stats_frame(state->fd, config, &context->stats, context->would_delete,
+                                   context->deleted_paths) ||
+        !receiver_send_final_success(state->fd, config, &context->outcomes, final_status))
       transfer_ok = false;
   } else {
-      send_error_detail(file_descriptor, "transfer failed on receiver");
+    send_error_detail(state->fd, "transfer failed on receiver");
   }
   if (!transfer_ok)
     log_message(LOG_LEVEL_ERROR, "Transfer failed");
-  } else {
-    if (receiver_receive_files(config, file_descriptor) != 0)
+}
+
+/* Phase 4b -- transfer via the single-threaded receiver.  Failure is logged
+ * exactly as before; the caller's `done` epilogue then releases the config. */
+static void server_run_st_receiver(ServerSession* state) {
+  if (receiver_receive_files(state->config, state->fd) != 0)
     log_message(LOG_LEVEL_ERROR, "Transfer failed");
 }
 
+/* Phase 4 dispatch -- choose the receiver implementation the config asks for.
+ * Both helpers own their success/failure logging; the caller falls through to
+ * the shared `done` epilogue either way. */
+static void server_run_transfer(ServerSession* state) {
+  if (state->config->use_multithreading)
+    server_run_mt_receiver(state);
+  else
+    server_run_st_receiver(state);
+}
+
+void handler(int file_descriptor) {
+  /* Single per-connection state; every phase helper below advances it and
+   * returns false on a logged failure.  All teardown state starts empty so the
+   * single `done` epilogue is safe to reach from any error path (including
+   * before the config frame arrives). */
+  ServerSession state;
+  state.fd = file_descriptor;
+  state.ssl = io_get_ssl();
+  protocol_session_init(&state.session, file_descriptor, file_descriptor);
+  protocol_session_set_ssl(&state.session, state.ssl);
+  protocol_session_bind(&state.session);
+  state.gate_ctx.ssl = state.ssl;
+  state.gate_ctx.fd = file_descriptor;
+  state.gate_ctx.super_mode_override = -1;
+  state.gate_ctx.has_peer_ip = false;
+  state.gate_ctx.peer_ip[0] = '\0';
+  state.gate_ctx.is_local = false;
+  state.config = NULL;
+  state.context = NULL;
+  state.joined_destination = NULL;
+  state.charset_ready = false;
+
+  if (!server_accept_config(&state))
+    goto done;
+  if (!server_apply_security_gates(&state))
+    goto done;
+  if (!server_prepare_session(&state))
+    goto done;
+  server_run_transfer(&state);
+
 done:
   /* Single cleanup epilogue: every error path jumps here, so the iconv
    * receiver conversion is released, the identity snapshot cleared, the
@@ -1029,22 +1112,22 @@ done:
    * connection fd is deliberately NOT closed here -- the child functions own
    * its single close (plain_child_fn / tls_child_fn), and the --stdio call
    * site must leave stdin/stdout open. */
-  if (charset_ready)
+  if (state.charset_ready)
     charset_wire_free();
   /* The delay-updates staging tree is released by config_delete (which the
      branch below always reaches), so it is cleaned exactly once. */
   identity_clear_active();
   protocol_session_unbind();
-  if (context != NULL) {
+  if (state.context != NULL) {
     /* context owns both the config and the queue it was created with. */
-    pipeline_context_receiver_destroy(context);
-    context = NULL;
-    config = NULL;
+    pipeline_context_receiver_destroy(state.context);
+    state.context = NULL;
+    state.config = NULL;
   } else {
-    config_delete(config);
-    config = NULL;
+    config_delete(state.config);
+    state.config = NULL;
   }
-  free(joined_destination);
+  free(state.joined_destination);
 }
 
 #ifndef FASTSYNC_SERVER_AS_LIB