Unable to initialize GDBusConnection with cellular modem on linux - linux

Question

I am currently trying to access cellular modem data from within a C application on Linux using mmlib-glib.
When trying to establish a GDBusConnection on a GFileIOStream created from a GFile from path /dev/cdc-wdm0, the call to g_dbus_connection_new_sync() hangs infinitely and gives the following error _g_dbus_worker_do_read_cb: error determining bytes needed: Unable to determine message blob length - given blob is malformed. Also, after this the modem will either become no longer available, or be kicked to a different modem number (i.e. org/freedesktop/ModemManager/Modem/2 will change to 3) I am constructing a GFile with the path /dev/cdc-wdm0, and from that initialize a GDBusConnection.
I have also tried initializing a new GIOStream and passing that to the mm_manager_scan_devices_sync() following instructions from this post but this results in the following errors :
g_dbus_connection_signal_subscribe: assertion 'sender == NULL || (g_dbus_is_name (sender) && (connection->flags & G_DBUS_CONNECTION_FLAGS_MESSAGE_BUS_CONNECTION))' failed
I have placed code below followed by mmcli output with modem information
#include <libmm-glib.h>
#include <gio/gio.h>
//#include <gtk/gtk.h>
#include <stdio.h>
#include <stdbool.h>
GDBusConnection *pConnection;
int main (void)
{
printf("begin\n");
GFile * pFile = g_file_new_for_path("/dev/cdc-wdm0");
GFileIOStream *pStream = g_file_open_readwrite(pFile, NULL, NULL);
pConnection= g_dbus_connection_new_sync(pStream,
guid, // for server auth.
G_DBUS_CONNECTION_FLAGS_MESSAGE_BUS_CONNECTION,
NULL, // observer
NULL, // cancellable,
NULL);
pManager = mm_manager_new_sync(pConnection,
G_DBUS_CONNECTION_FLAGS_MESSAGE_BUS_CONNECTION,
NULL,
NULL);
mm_manager_scan_devices_sync(pManager,
cancellable,
NULL);
printf("end\n");
return(0);
}
Below is the output from modemmanager mmcli --modem=0
----------------------------------
General | path: /org/freedesktop/ModemManager1/Modem/0
| device id:
----------------------------------
Hardware | manufacturer: Telit
| model: LE910C4-NF
| firmware revision: 25.21.660 1 [Mar 04 2021 12:00:00]
| carrier config: default
| h/w revision: 1.30
| supported: gsm-umts, lte
| current: gsm-umts, lte
| equipment id: 0
----------------------------------
System | device: /sys/devices/platform/soc#0/32c00000.bus/32e50000.usb/ci_hdrc.1/usb1/1-1/1-1.2
| drivers: qmi_wwan, option
| plugin: telit
| primary port: cdc-wdm0
| ports: cdc-wdm0 (qmi), ttyUSB0 (ignored), ttyUSB1 (gps),
| ttyUSB4 (ignored), wwan0 (net)
----------------------------------
Status | lock: sim-pin2
| unlock retries: sim-pin (3), sim-puk (10), sim-pin2 (10), sim-puk2 (10)
| state: connected
| power state: on
| access tech: lte
| signal quality: 75% (cached)
----------------------------------
Modes | supported: allowed: 3g; preferred: none
| allowed: 4g; preferred: none
| allowed: 3g, 4g; preferred: 4g
| allowed: 3g, 4g; preferred: 3g
| current: allowed: 3g, 4g; preferred: 4g
----------------------------------
Bands | supported: utran-4, utran-5, utran-2, eutran-2, eutran-4, eutran-5,
| eutran-12, eutran-13, eutran-14, eutran-66, eutran-71
| current: utran-4, utran-5, utran-2, eutran-2, eutran-4, eutran-5,
| eutran-12, eutran-13, eutran-14, eutran-66, eutran-71
----------------------------------
IP | supported: ipv4, ipv6, ipv4v6
----------------------------------
3GPP | imei: 3
| enabled locks: fixed-dialing
| operator id: 311480
| operator name: VZW
| registration: home
----------------------------------
3GPP EPS | initial bearer path: /org/freedesktop/ModemManager1/Bearer/0
| initial bearer apn: super
| initial bearer ip type: ipv4
----------------------------------
SIM | primary sim path: /org/freedesktop/ModemManager1/SIM/0
| sim slot paths: slot 1: /org/freedesktop/ModemManager1/SIM/0 (active)
| slot 2: none
----------------------------------
Bearer | paths: /org/freedesktop/ModemManager1/Bearer/2
| /org/freedesktop/ModemManager1/Bearer/1