NAME |SYNOPSIS |DESCRIPTION |EXAMPLES |RETURN VALUE |NOTES |HISTORY |SEE ALSO |NOTES |COLOPHON | |
SD_BUS_ADD_OBJECT(3) sd_bus_add_objectSD_BUS_ADD_OBJECT(3)sd_bus_add_object, sd_bus_add_fallback, sd_bus_add_object_vtable, sd_bus_add_fallback_vtable, sd_bus_add_filter, SD_BUS_VTABLE_CAPABILITY, SD_BUS_VTABLE_START, SD_BUS_VTABLE_END, SD_BUS_METHOD_WITH_NAMES_OFFSET, SD_BUS_METHOD_WITH_NAMES, SD_BUS_METHOD_WITH_OFFSET, SD_BUS_METHOD, SD_BUS_SIGNAL_WITH_NAMES, SD_BUS_SIGNAL, SD_BUS_WRITABLE_PROPERTY, SD_BUS_PROPERTY, SD_BUS_PARAM - Declare properties and methods for a D-Bus path
#include <systemd/sd-bus-vtable.h>typedef int (*sd_bus_message_handler_t)(sd_bus_message *m,void *userdata,sd_bus_error *ret_error);typedef int (*sd_bus_property_get_t)(sd_bus *bus,const char *path,const char *interface,const char *property,sd_bus_message *reply,void *userdata,sd_bus_error *ret_error);typedef int (*sd_bus_property_set_t)(sd_bus *bus,const char *path,const char *interface,const char *property,sd_bus_message *value,void *userdata,sd_bus_error *ret_error);typedef int (*sd_bus_object_find_t)(const char *path,const char *interface,void *userdata,void **ret_found,sd_bus_error *ret_error);int sd_bus_add_object(sd_bus *bus, sd_bus_slot **slot,const char *path,sd_bus_message_handler_tcallback,void *userdata);int sd_bus_add_fallback(sd_bus *bus, sd_bus_slot **slot,const char *path,sd_bus_message_handler_tcallback,void *userdata);int sd_bus_add_object_vtable(sd_bus *bus, sd_bus_slot **slot,const char *path,const char *interface,const sd_bus_vtable *vtable,void *userdata);int sd_bus_add_fallback_vtable(sd_bus *bus, sd_bus_slot **slot,const char *prefix,const char *interface,const sd_bus_vtable *vtable,sd_bus_object_find_tfind,void *userdata);int sd_bus_add_filter(sd_bus *bus, sd_bus_slot **slot,sd_bus_message_handler_tcallback,void *userdata);SD_BUS_VTABLE_CAPABILITY(capability)SD_BUS_VTABLE_START(flags)SD_BUS_VTABLE_ENDSD_BUS_METHOD_WITH_ARGS_OFFSET(member,args,result,handler,offset,flags)SD_BUS_METHOD_WITH_ARGS(member,args,result,handler,flags)SD_BUS_METHOD_WITH_NAMES_OFFSET(member,signature,in_names,result,out_names,handler,offset,flags)SD_BUS_METHOD_WITH_NAMES(member,signature,in_names,result,out_names,handler,flags)SD_BUS_METHOD_WITH_OFFSET(member,signature,result,handler,offset,flags)SD_BUS_METHOD(member,signature,result,handler,flags)SD_BUS_SIGNAL_WITH_ARGS(member,args,flags)SD_BUS_SIGNAL_WITH_NAMES(member,signature,names,flags)SD_BUS_SIGNAL(member,signature,flags)SD_BUS_WRITABLE_PROPERTY(member,signature,get,set,offset,flags)SD_BUS_PROPERTY(member,signature,get,offset,flags)SD_BUS_PARAM(name)SD_BUS_ARGS(...)SD_BUS_RESULT(...)SD_BUS_NO_ARGSSD_BUS_NO_RESULT
sd_bus_add_object_vtable()is used to declare attributes for the object pathpath connected to the bus connectionbus under the interfaceinterface. The tablevtable may contain property declarations usingSD_BUS_PROPERTY()orSD_BUS_WRITABLE_PROPERTY(), method declarations usingSD_BUS_METHOD(),SD_BUS_METHOD_WITH_NAMES(),SD_BUS_METHOD_WITH_OFFSET(), orSD_BUS_METHOD_WITH_NAMES_OFFSET(), and signal declarations usingSD_BUS_SIGNAL_WITH_NAMES()orSD_BUS_SIGNAL(), see below. Theuserdata parameter contains a pointer that will be passed to various callback functions. It may be specified asNULLif no value is necessary. An interface can have any number of vtables attached to it.sd_bus_add_fallback_vtable()is similar tosd_bus_add_object_vtable(), but is used to register "fallback" attributes. When looking for an attribute declaration, bus object paths registered withsd_bus_add_object_vtable()are checked first. If no match is found, the fallback vtables are checked for each prefix of the bus object path, i.e. with the last slash-separated components successively removed. This allows the vtable to be used for an arbitrary number of dynamically created objects. Parameterfind is a function which is used to locate the target object based on the bus object pathpath. It must return1and set theret_found output parameter if the object is found, return0if the object was not found, and return a negative errno-style error code or initialize the error structureret_error on error. The pointer passed inret_found will be used as theuserdata parameter for the callback functions (offset by theoffset offsets as specified in the vtable entries).sd_bus_add_object()attaches a callback directly to the object pathpath. An object path can have any number of callbacks attached to it. Each callback is prepended to the list of callbacks which are always called in order.sd_bus_add_fallback() is similar tosd_bus_add_object()but applies to fallback paths instead.sd_bus_add_filter()installs a callback that is invoked for each incoming D-Bus message. Filters can be used to handle logic common to all messages received by a service (e.g. authentication or authorization). When a request is received, any associated callbacks are called sequentially until a callback returns a non-zero integer. Return zero from a callback to give other callbacks the chance to process the request. Callbacks are called in the following order: first, global callbacks installed withsd_bus_add_filter()are called. Second, callbacks attached directly to the request object path are called, followed by any D-Bus method callbacks attached to the request object path, interface and member. Finally, the property callbacks attached to the request object path, interface and member are called. If the final callback returns zero, an error reply is sent back to the caller indicating no matching object for the request was found. Note that you can return a positive integer from amethod callback without immediately sending a reply. This informs sd-bus this callback will take responsibility for replying to the request without forcing the callback to produce a reply immediately. This allows a callback to perform any number of asynchronous operations required to construct a reply. However, if producing a reply takes too long, the method call will time out at the caller. This is only available to methods and not properties. If a callback was invoked to handle a request that expects a reply and the callback returns a negative value, the value is interpreted as a negative errno-style error code and sent back to the caller as a D-Bus error as ifsd_bus_reply_method_errno(3) was called. Additionally, all callbacks take a sd_bus_error output parameter that can be used to provide more detailed error information. Ifret_error is set when the callback finishes, the corresponding D-Bus error is sent back to the caller as ifsd_bus_reply_method_error(3) was called. Any error stored inret_error takes priority over any negative values returned by the same callback when determining which error to send back to the caller. Usesd_bus_error_set(3) or one of its variants to setret_error and return a negative integer from a callback with a single function call. To send an error reply after a callback has already finished, usesd_bus_reply_method_errno(3) or one of its variants. For all functions, a match slot is created internally. If the output parameterslot isNULL, a "floating" slot object is created, seesd_bus_slot_set_floating(3). Otherwise, a pointer to the slot object is returned. In that case, the reference to the slot object should be dropped when the vtable is not needed anymore, seesd_bus_slot_unref(3).The sd_bus_vtable array The array consists of the structures of type sd_bus_vtable, but it should never be filled in manually, but through one of the following macros:SD_BUS_VTABLE_START(flags),SD_BUS_VTABLE_END Those must always be the first and last element. Theflags parameter can be used to set attributes that apply to the whole array; see the "Flags" section below.SD_BUS_METHOD_WITH_ARGS_OFFSET(),SD_BUS_METHOD_WITH_ARGS() Declare a D-Bus method with the namemember, argumentsargs and resultresult.args expects a sequence of argument type/name pairs wrapped in theSD_BUS_ARGS()macro. The elements at even indices in this list describe the types of the method's arguments. The method's parameter signature is the concatenation of all the string literals at even indices inargs. If a method has no parameters, passSD_BUS_NO_ARGStoargs. The elements at uneven indices describe the names of the method's arguments.result expects a sequence of type/name pairs wrapped in theSD_BUS_RESULT()macro in the same format asSD_BUS_ARGS(). The method's result signature is the concatenation of all the string literals at even indices inresult. If a method has no result, passSD_BUS_NO_RESULTtoresult. Note that argument types are expected to be quoted string literals and argument names are expected to be unquoted string literals. See below for a complete example. The handler functionhandler must be of typesd_bus_message_handler_t. It will be called to handle the incoming messages that call this method. It receives a pointer that is theuserdata parameter passed to the registration function offset byoffset bytes. This may be used to pass pointers to different fields in the same data structure to different methods in the same vtable. To send a reply fromhandler, callsd_bus_reply_method_return(3) with the message the callback was invoked with. Parameterflags is a combination of flags, see below.SD_BUS_METHOD_WITH_ARGS()is a shorthand for callingSD_BUS_METHOD_WITH_ARGS_OFFSET()with an offset of zero.SD_BUS_METHOD_WITH_NAMES_OFFSET(),SD_BUS_METHOD_WITH_NAMES(),SD_BUS_METHOD_WITH_OFFSET(),SD_BUS_METHOD() Declare a D-Bus method with the namemember, parameter signaturesignature, result signatureresult. Parametersin_names andout_names specify the argument names of the input and output arguments in the function signature.in_names andout_names should be created using theSD_BUS_PARAM()macro, see below. In all other regards, this macro behaves exactly the same asSD_BUS_METHOD_WITH_ARGS_OFFSET().SD_BUS_METHOD_WITH_NAMES(),SD_BUS_METHOD_WITH_OFFSET(), andSD_BUS_METHOD()are variants which specify zero offset (userdata parameter is passed with no change), leave the names unset (i.e. no parameter names), or both. Prefer usingSD_BUS_METHOD_WITH_ARGS_OFFSET()andSD_BUS_METHOD_WITH_ARGS()over these macros as they allow specifying argument types and names next to each other which is less error-prone than first specifying all argument types followed by specifying all argument names.SD_BUS_SIGNAL_WITH_ARGS() Declare a D-Bus signal with the namemember and argumentsargs.args expects a sequence of argument type/name pairs wrapped in theSD_BUS_ARGS()macro. The elements at even indices in this list describe the types of the signal's arguments. The signal's parameter signature is the concatenation of all the string literals at even indices inargs. If a signal has no parameters, passSD_BUS_NO_ARGStoargs. The elements at uneven indices describe the names of the signal's arguments. Parameterflags is a combination of flags. See below for a complete example.SD_BUS_SIGNAL_WITH_NAMES(),SD_BUS_SIGNAL() Declare a D-Bus signal with the namemember, parameter signaturesignature, and argument namesnames.names should be created using theSD_BUS_PARAM()macro, see below. Parameterflags is a combination of flags, see below.SD_BUS_SIGNAL()is equivalent toSD_BUS_SIGNAL_WITH_NAMES() with thenames parameter unset (i.e. no parameter names). Prefer usingSD_BUS_SIGNAL_WITH_ARGS()over these macros as it allows specifying argument types and names next to each other which is less error-prone than first specifying all argument types followed by specifying all argument names.SD_BUS_WRITABLE_PROPERTY(),SD_BUS_PROPERTY() Declare a D-Bus property with the namemember and value signaturesignature. Parametersget andset are the getter and setter methods. They are called with a pointer that is theuserdata parameter passed to the registration function offset byoffset bytes. This may be used pass pointers to different fields in the same data structure to different setters and getters in the same vtable. Parameterflags is a combination of flags, see below. The setter and getter methods may be omitted (specified asNULL), if the property is one of the basic types or "as" in case of read-only properties. In those cases, theuserdata andoffset parameters must together point to a valid variable of the corresponding type. A default setter and getter will be provided, which simply copy the argument between this variable and the message.SD_BUS_PROPERTY()is used to define a read-only property.SD_BUS_PARAM() Parameter names should be wrapped in this macro, see the example below.Flags Theflags parameter is used to specify a combination ofD-Busannotations[1].SD_BUS_VTABLE_DEPRECATED Mark this vtable entry as deprecated using theorg.freedesktop.DBus.Deprecatedannotation in introspection data. If specified forSD_BUS_VTABLE_START(), the annotation is applied to the enclosing interface.SD_BUS_VTABLE_HIDDEN Make this vtable entry hidden. It will not be shown in introspection data. If specified forSD_BUS_VTABLE_START(), all entries in the array are hidden.SD_BUS_VTABLE_METHOD_NO_REPLY Mark this vtable entry as a method that will not return a reply using theorg.freedesktop.DBus.Method.NoReplyannotation in introspection data.SD_BUS_VTABLE_PROPERTY_CONST,SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE,SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION Those three flags correspond to different values of theorg.freedesktop.DBus.Property.EmitsChangedSignalannotation, which specifies whether theorg.freedesktop.DBus.Properties.PropertiesChangedsignal is emitted whenever the property changes.SD_BUS_VTABLE_PROPERTY_CONSTcorresponds toconstand means that the property never changes during the lifetime of the object it belongs to, so no signal needs to be emitted.SD_BUS_VTABLE_PROPERTY_EMITS_CHANGEcorresponds totrueand means that the signal is emitted.SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATIONcorresponds toinvalidatesand means that the signal is emitted, but the value is not included in the signal.SD_BUS_VTABLE_PROPERTY_EXPLICIT Mark this vtable property entry as requiring explicit request to for the value to be shown (generally because the value is large or slow to calculate). This entry cannot be combined withSD_BUS_VTABLE_PROPERTY_EMITS_CHANGE, and will not be shown in property listings by default (e.g.busctlintrospect). This corresponds to theorg.freedesktop.systemd1.Explicitannotation in introspection data.SD_BUS_VTABLE_SENSITIVE Mark this vtable method entry as processing sensitive data. When set, incoming method call messages and their outgoing reply messages are marked as sensitive usingsd_bus_message_sensitive(3), so that they are erased from memory when freed.SD_BUS_VTABLE_ABSOLUTE_OFFSET Mark this vtable method or property entry so that the user data pointer passed to its associated handler functions is determined slightly differently: instead of adding the offset parameter of the entry to the user data pointer specified during vtable registration, the offset is passed directly, converted to a pointer, without taking the user data pointer specified during vtable registration into account.SD_BUS_VTABLE_CAPABILITY(capability) Access to this vtable entry will be allowed if the calling process has the capabilitycapability, as described insd_bus_query_sender_privilege(3). If used forSD_BUS_VTABLE_START(), provides a default for all entries in the array. If not specified, either for an individual entry or the whole array,CAP_SYS_ADMINis checked by default. Seecapabilities(7) for information about capabilities. Note that vtable entries may be marked as unprivileged and the whole bus may be marked as trusted, see the discussion ofSD_BUS_VTABLE_UNPRIVILEGEDbelow.SD_BUS_VTABLE_UNPRIVILEGED Mark this vtable entry as unprivileged. Access to privileged entries is limited to users with appropriate capabilities as described above. In practice many vtable entries are marked as unprivileged, and either are open to everyone, or the decision whether to allow access is taken later, e.g. by delegating topolkit[2]. The whole bus may be marked as trusted, in which case annotations at the entry level are ignored, seesd_bus_set_trusted(3). Whennot specified, theorg.freedesktop.systemd1.Privileged annotation with value "true" will be shown in introspection data.SD_BUS_VTABLE_UNPRIVILEGEDmay not be applied to read-only properties, but read access (to both read-only and writable properties) is always unrestricted. Note that this page describes checks implemented in the D-Bus client. The D-Bus server has an additional policy that may permit or deny connections, see "CONFIGURATION FILE" indbus-daemon(1).
Example 1. Create a simple listener on the bus /* SPDX-License-Identifier: MIT-0 */ #define _GNU_SOURCE 1 #include <errno.h> #include <stdbool.h> #include <stddef.h> #include <stdlib.h> #include <stdio.h> #include <systemd/sd-bus.h> #define _cleanup_(f) __attribute__((cleanup(f))) typedef struct object { char *name; uint32_t number; } object; static int method(sd_bus_message *m, void *userdata, sd_bus_error *error) { int r; printf("Got called with userdata=%p\n", userdata); if (sd_bus_message_is_method_call(m, "org.freedesktop.systemd.VtableExample", "Method4")) return 1; const char *string; r = sd_bus_message_read(m, "s", &string); if (r < 0) { fprintf(stderr, "sd_bus_message_read() failed: %s\n", strerror(-r)); return 0; } r = sd_bus_reply_method_return(m, "s", string); if (r < 0) { fprintf(stderr, "sd_bus_reply_method_return() failed: %s\n", strerror(-r)); return 0; } return 1; } static const sd_bus_vtable vtable[] = { SD_BUS_VTABLE_START(0), SD_BUS_METHOD( "Method1", "s", "s", method, 0), SD_BUS_METHOD_WITH_NAMES_OFFSET( "Method2", "so", SD_BUS_PARAM(string) SD_BUS_PARAM(path), "s", SD_BUS_PARAM(returnstring), method, offsetof(object, number), SD_BUS_VTABLE_DEPRECATED), SD_BUS_METHOD_WITH_ARGS_OFFSET( "Method3", SD_BUS_ARGS("s", string, "o", path), SD_BUS_RESULT("s", returnstring), method, offsetof(object, number), SD_BUS_VTABLE_UNPRIVILEGED), SD_BUS_METHOD_WITH_ARGS( "Method4", SD_BUS_NO_ARGS, SD_BUS_NO_RESULT, method, SD_BUS_VTABLE_UNPRIVILEGED), SD_BUS_SIGNAL( "Signal1", "so", 0), SD_BUS_SIGNAL_WITH_NAMES( "Signal2", "so", SD_BUS_PARAM(string) SD_BUS_PARAM(path), 0), SD_BUS_SIGNAL_WITH_ARGS( "Signal3", SD_BUS_ARGS("s", string, "o", path), 0), SD_BUS_WRITABLE_PROPERTY( "AutomaticStringProperty", "s", NULL, NULL, offsetof(object, name), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE), SD_BUS_WRITABLE_PROPERTY( "AutomaticIntegerProperty", "u", NULL, NULL, offsetof(object, number), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION), SD_BUS_VTABLE_END }; int main(int argc, char **argv) { _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL; int r; sd_bus_default(&bus); object object = { .number = 666 }; object.name = strdup("name"); if (!object.name) { fprintf(stderr, "OOM\n"); return EXIT_FAILURE; } r = sd_bus_add_object_vtable(bus, NULL, "/org/freedesktop/systemd/VtableExample", "org.freedesktop.systemd.VtableExample", vtable, &object); if (r < 0) { fprintf(stderr, "sd_bus_add_object_vtable() failed: %s\n", strerror(-r)); return EXIT_FAILURE; } r = sd_bus_request_name(bus, "org.freedesktop.systemd.VtableExample", 0); if (r < 0) { fprintf(stderr, "sd_bus_request_name() failed: %s\n", strerror(-r)); return EXIT_FAILURE; } for (;;) { r = sd_bus_wait(bus, UINT64_MAX); if (r < 0) { fprintf(stderr, "sd_bus_wait() failed: %s\n", strerror(-r)); return EXIT_FAILURE; } r = sd_bus_process(bus, NULL); if (r < 0) { fprintf(stderr, "sd_bus_process() failed: %s\n", strerror(-r)); return EXIT_FAILURE; } } r = sd_bus_release_name(bus, "org.freedesktop.systemd.VtableExample"); if (r < 0) { fprintf(stderr, "sd_bus_release_name() failed: %s\n", strerror(-r)); return EXIT_FAILURE; } free(object.name); return 0; } This creates a simple client on the bus (the user bus, when run as normal user). We may use the D-Busorg.freedesktop.DBus.Introspectable.Introspectcall to acquire the XML description of the interface: <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN" "https://www.freedesktop.org/standards/dbus/1.0/introspect.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> <node> <interface name="org.freedesktop.DBus.Peer"> <method name="Ping"/> <method name="GetMachineId"> <arg type="s" name="machine_uuid" direction="out"/> </method> </interface> <interface name="org.freedesktop.DBus.Introspectable"> <method name="Introspect"> <arg name="xml_data" type="s" direction="out"/> </method> </interface> <interface name="org.freedesktop.DBus.Properties"> <method name="Get"> <arg name="interface_name" direction="in" type="s"/> <arg name="property_name" direction="in" type="s"/> <arg name="value" direction="out" type="v"/> </method> <method name="GetAll"> <arg name="interface_name" direction="in" type="s"/> <arg name="props" direction="out" type="a{sv}"/> </method> <method name="Set"> <arg name="interface_name" direction="in" type="s"/> <arg name="property_name" direction="in" type="s"/> <arg name="value" direction="in" type="v"/> </method> <signal name="PropertiesChanged"> <arg type="s" name="interface_name"/> <arg type="a{sv}" name="changed_properties"/> <arg type="as" name="invalidated_properties"/> </signal> </interface> <interface name="org.freedesktop.systemd.VtableExample"> <method name="Method1"> <arg type="s" direction="in"/> <arg type="s" direction="out"/> </method> <method name="Method2"> <arg type="s" name="string" direction="in"/> <arg type="o" name="path" direction="in"/> <arg type="s" name="returnstring" direction="out"/> <annotation name="org.freedesktop.DBus.Deprecated" value="true"/> </method> <property name="AutomaticStringProperty" type="s" access="readwrite"> </property> <property name="AutomaticIntegerProperty" type="u" access="readwrite"> <annotation name="org.freedesktop.DBus.Property.EmitsChangedSignal" value="invalidates"/> </property> </interface> </node>On success,sd_bus_add_object_vtable()andsd_bus_add_fallback_vtable()return a non-negative integer. On failure, they return a negative errno-style error code.Errors Returned errors may indicate the following problems:-EINVAL One of the required parameters isNULLor invalid. A reserved D-Bus interface was passed as theinterface parameter.-ENOPKG The bus cannot be resolved.-ECHILD The bus was created in a different process, library or module instance.-ENOMEM Memory allocation failed.-EPROTOTYPEsd_bus_add_object_vtable()andsd_bus_add_fallback_vtable() have been both called for the same bus object path, which is not allowed.-EEXIST This vtable has already been registered for thisinterface andpath.
Functions described here are available as a shared library, which can be compiled against and linked to with thelibsystemd pkg-config(1) file. The code described here usesgetenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not callsetenv(3) from a parallel thread. It is recommended to only do calls tosetenv()from an early phase of the program when no other threads have been started.
sd_bus_property_get_t(),sd_bus_property_set_t(),sd_bus_object_find_t(),sd_bus_add_object(),sd_bus_add_fallback(),sd_bus_add_object_vtable(),sd_bus_add_fallback_vtable(), andsd_bus_add_filter()were added in version 221.
sd-bus(3),busctl(1),sd_bus_emit_properties_changed(3),sd_bus_emit_object_added(3)
1. D-Bus annotationshttps://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format 2. polkithttps://www.freedesktop.org/software/polkit/docs/latest/
This page is part of thesystemd (systemd system and service manager) project. Information about the project can be found at ⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug report for this manual page, see ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This page was obtained from the project's upstream Git repository ⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-08-11.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_BUS_ADD_OBJECT(3)Pages that refer to this page:sd-bus(3), sd_bus_add_node_enumerator(3), sd_bus_add_object_manager(3), sd_bus_call(3), sd_bus_process(3), sd_bus_slot_set_userdata(3), systemd.directives(7), systemd.index(7)
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