Understanding about pairing options mentioned in the URL are perfect, but BlueZ doesn't work in the same way. To simply the discussion here, please consider the explanation from Bluetooth Pairing blog from Bluetooth SIG.
To simplify, the below image is copied from the above mentioned blog.
So input can be three forms "No Input", "Yes/No" and "Keyboard". Output can be "No Output" and "Numeric Output".
In your case, Android is the initiator where you want to enter the passkey which is displayed in responder. So Android device's input is "Keyboard" and responder is "Numeric Output" capable.
To achieve your case, you need to specify "DisplayOnly" in responder (you are already correct) and "KeyboardOnly" or "KeyboardDisplay" in input Android device.
But BlueZ by default doesn't treat "KeyboardDisplay" as a separate option, instead it converts/considers it as "DisplayYesNO", see here in mgmt.txt API for more details. So your android input device acts as "DisplayYesNo" and results in confusion.
So you need to use "DisplayOnly" at responder and "KeyboardOnly" at initiator end. To experiment this use case with custom agent (not using bluetoothctl's agent), use the below sample example (Note: Not fully implemented, fscanf from stdin is bad :-(, etc.,)
/*
* gcc `pkg-config --cflags glib-2.0 gio-2.0` -Wall -Wextra -o ./bin/agent ./agent.c `pkg-config --libs glib-2.0 gio-2.0`
*/
#include <glib.h>
#include <gio/gio.h>
#include <stdio.h>
GMainLoop *loop;
GDBusConnection *con;
#define AGENT_PATH "/org/bluez/AutoPinAgent"
static void bluez_agent_method_call(GDBusConnection *conn,
const gchar *sender,
const gchar *path,
const gchar *interface,
const gchar *method,
GVariant *params,
GDBusMethodInvocation *invocation,
void *userdata)
{
int pass;
int entered;
char *opath;
GVariant *p= g_dbus_method_invocation_get_parameters(invocation);
g_print("Agent method call: %s.%s()\n", interface, method);
if(!strcmp(method, "RequestPinCode")) {
;
}
else if(!strcmp(method, "DisplayPinCode")) {
;
}
else if(!strcmp(method, "RequestPasskey")) {
g_print("Getting the Pin from user: ");
fscanf(stdin, "%d", &pass);
g_print("\n");
g_dbus_method_invocation_return_value(invocation, g_variant_new("(u)", pass));
}
else if(!strcmp(method, "DisplayPasskey")) {
g_variant_get(params, "(ouq)", &opath, &pass, &entered);
g_print("Path: %s Pass: %d Entered: %d\n", opath, pass, entered);
g_dbus_method_invocation_return_value(invocation, NULL);
}
else if(!strcmp(method, "RequestConfirmation")) {
g_variant_get(params, "(ou)", &opath, &pass);
g_print("Path: %s Pass: %d\n", opath, pass);
g_dbus_method_invocation_return_value(invocation, NULL);
}
else if(!strcmp(method, "RequestAuthorization")) {
;
}
else if(!strcmp(method, "AuthorizeService")) {
;
}
else if(!strcmp(method, "Cancel")) {
;
}
else
g_print("We should not come here, unknown method\n");
}
static const GDBusInterfaceVTable agent_method_table = {
.method_call = bluez_agent_method_call,
};
int bluez_register_agent(GDBusConnection *con)
{
GError *error = NULL;
guint id = 0;
GDBusNodeInfo *info = NULL;
static const gchar bluez_agent_introspection_xml[] =
"<node name='/org/bluez/SampleAgent'>"
" <interface name='org.bluez.Agent1'>"
" <method name='Release'>"
" </method>"
" <method name='RequestPinCode'>"
" <arg type='o' name='device' direction='in' />"
" <arg type='s' name='pincode' direction='out' />"
" </method>"
" <method name='DisplayPinCode'>"
" <arg type='o' name='device' direction='in' />"
" <arg type='s' name='pincode' direction='in' />"
" </method>"
" <method name='RequestPasskey'>"
" <arg type='o' name='device' direction='in' />"
" <arg type='u' name='passkey' direction='out' />"
" </method>"
" <method name='DisplayPasskey'>"
" <arg type='o' name='device' direction='in' />"
" <arg type='u' name='passkey' direction='in' />"
" <arg type='q' name='entered' direction='in' />"
" </method>"
" <method name='RequestConfirmation'>"
" <arg type='o' name='device' direction='in' />"
" <arg type='u' name='passkey' direction='in' />"
" </method>"
" <method name='RequestAuthorization'>"
" <arg type='o' name='device' direction='in' />"
" </method>"
" <method name='AuthorizeService'>"
" <arg type='o' name='device' direction='in' />"
" <arg type='s' name='uuid' direction='in' />"
" </method>"
" <method name='Cancel'>"
" </method>"
" </interface>"
"</node>";
info = g_dbus_node_info_new_for_xml(bluez_agent_introspection_xml, &error);
if(error) {
g_printerr("Unable to create node: %s\n", error->message);
g_clear_error(&error);
return 0;
}
id = g_dbus_connection_register_object(con,
AGENT_PATH,
info->interfaces[0],
&agent_method_table,
NULL, NULL, &error);
g_dbus_node_info_unref(info);
//g_dbus_connection_unregister_object(con, id);
/* call register method in AgentManager1 interface */
return id;
}
static int bluez_agent_call_method(const gchar *method, GVariant *param)
{
GVariant *result;
GError *error = NULL;
result = g_dbus_connection_call_sync(con,
"org.bluez",
"/org/bluez",
"org.bluez.AgentManager1",
method,
param,
NULL,
G_DBUS_CALL_FLAGS_NONE,
-1,
NULL,
&error);
if(error != NULL) {
g_print("Register %s: %s\n", AGENT_PATH, error->message);
return 1;
}
g_variant_unref(result);
return 0;
}
static int bluez_register_autopair_agent(const char *cap)
{
int rc;
rc = bluez_agent_call_method("RegisterAgent", g_variant_new("(os)", AGENT_PATH, cap));
if(rc)
return 1;
rc = bluez_agent_call_method("RequestDefaultAgent", g_variant_new("(o)", AGENT_PATH));
if(rc) {
bluez_agent_call_method("UnregisterAgent", g_variant_new("(o)", AGENT_PATH));
return 1;
}
return 0;
}
static void cleanup_handler(int signo)
{
if (signo == SIGINT) {
g_print("received SIGINT\n");
g_main_loop_quit(loop);
}
}
int main(int argc, char **argv)
{
int id;
int rc;
if(argc < 2)
return 1;
if(signal(SIGINT, cleanup_handler) == SIG_ERR)
g_print("can't catch SIGINT\n");
con = g_bus_get_sync(G_BUS_TYPE_SYSTEM, NULL, NULL);
if(con == NULL) {
g_print("Not able to get connection to system bus\n");
return 1;
}
loop = g_main_loop_new(NULL, FALSE);
id = bluez_register_agent(con);
if(id == 0)
goto fail;
rc = bluez_register_autopair_agent(argv[1]);
if(rc) {
g_print("Not able to register default autopair agent\n");
goto fail;
}
g_main_loop_run(loop);
fail:
g_dbus_connection_unregister_object(con, id);
g_object_unref(con);
return 0;
}
To experiment this, you must disable agent in bluetoothctl "agent off" and turn on the agent as,
Responder: ./bin/agent "DisplayOnly"
Initiator: ./bin/agent "KeyboardOnly"
When you try to pair from initiator, DisplayPasskey will be called in responder and displays 6 digit PIN and initiator will call RequestPasskey and takes the input PIN from stdin.
