Why is advertising with ADV_DATA producing Invalid Parameters

I'm trying to write some BlueZ code using the Management API but I can't seem to get BlueZ to advertise arbitrary data on the advertisement system

I have 2 tests one in C++ and one using the btmgmt tool that BlueZ has released

When I run this command it fails this way

btmgmt add-adv -d 8C33 1
Add Advertising failed with status 0x0d (Invalid Parameters)

The equivalent C++ code also fails identically

#include <iostream>

extern "C" {
  #include "external/bluetooth/lib/bluetooth.h"
  #include "external/bluetooth/lib/mgmt.h"
  #include "external/bluetooth/lib/hci.h"
  #include "external/bluetooth/lib/hci_lib.h"
  #include "external/bluetooth/src/shared/mgmt.h"
}

static void setup_dv(uint8_t status, uint16_t length,
                     const void *param, void *user_data)
{
  std::cout << "good" << std::endl;
}

struct CPadvertising {
        uint8_t  instance;
        uint32_t flags;
        uint16_t duration;
        uint16_t timeout;
        uint8_t  adv_data_len;
        uint8_t  scan_rsp_len;
        uint8_t  data[4];
} __packed;


int main()
{
  mgmt* sock =  mgmt_new_default();


  CPadvertising* data = new CPadvertising();

  data->instance = 1;
  data->duration = 2;
  data->timeout = 100;
  data->adv_data_len = 4;
  data->scan_rsp_len = 0;
  data->flags = 0;
  data->data[0] = 8;
  data->data[1] = 12;
  data->data[2] = 3;
  data->data[3] = 3;

  mgmt_send(sock, MGMT_OP_ADD_ADVERTISING, index, 
  sizeof(CPadvertising), data, setup_dv, nullptr, nullptr);
  auto  loop = g_main_loop_new(nullptr, FALSE);
  g_main_loop_run(loop);

}

has this output in btmon

@ MGMT Command: Add Advertising (0x003e) plen 13                               {0x0003} [hci0] 98.205359
        Instance: 1
        Flags: 0x00000000
        Duration: 2
        Timeout: 100
        Advertising data length: 4
        8 c 3 3                                            .3              
        Scan response length: 0
@ MGMT Event: Command Status (0x0002) plen 3                                   {0x0003} [hci0] 98.205376
      Add Advertising (0x003e)
        Status: Invalid Parameters (0x0d)

Referring to these docs, I should not get invalid parameter for any of this but I do

https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/mgmt-api.txt

However, I know certain types of data does indeed work

btmgmt add-adv -d 080954657374204C45

works even in an even weirder way prompting this output on btmon

@ MGMT Command: Add Advertising (0x003e) plen 20                              {0x0002} [hci0] 143.671485
        Instance: 1
        Flags: 0x00000000
        Duration: 0
        Timeout: 0
        Advertising data length: 9
        Name (complete): Test LL <--- What is this
        Scan response length: 0

Looking at the source for btmgmt, these are the options available:

static void add_adv_usage(void)
{
    bt_shell_usage();
    print("Options:\n"
        "\t -u, --uuid <uuid>         Service UUID\n"
        "\t -d, --adv-data <data>     Advertising Data bytes\n"
        "\t -s, --scan-rsp <data>     Scan Response Data bytes\n"
        "\t -t, --timeout <timeout>   Timeout in seconds\n"
        "\t -D, --duration <duration> Duration in seconds\n"
        "\t -P, --phy <phy>           Phy type, Specify 1M/2M/CODED\n"
        "\t -c, --connectable         \"connectable\" flag\n"
        "\t -g, --general-discov      \"general-discoverable\" flag\n"
        "\t -l, --limited-discov      \"limited-discoverable\" flag\n"
        "\t -n, --scan-rsp-local-name \"local-name\" flag\n"
        "\t -a, --scan-rsp-appearance \"appearance\" flag\n"
        "\t -m, --managed-flags       \"managed-flags\" flag\n"
        "\t -p, --tx-power            \"tx-power\" flag\n"
        "e.g.:\n"
        "\tadd-adv -u 180d -u 180f -d 080954657374204C45 1");
}

Looking at the advert that worked, the first number is the length of the data, the second is the data_type, and the rest is the local name string. So:

0x08 = Length of datatype is 8
0x09 = Data type is <Complete Local Name>
0x54 = T
0x65 = e
0x73 = s
0x74 = t
0x20 = ' ' 
0x4C = L
0x45 = E

Not sure why that has turned up as Test LL in the btmon output. I'll assume it was a slightly different run that you recorded.

Looking at your data of 8c33; the 8c does not represent the length and 33 is not a valid data type.

I suspect what you want to do is send manufacturer data. Assuming you don't have a company identifier, then you can use 0xffff for testing purposes.

This would be a command of:

btmgmt add-adv -d 05ffffff8C33 -g 1

Which gave the following in btmon

@ MGMT Command: Add Adver.. (0x003e) plen 17  {0x0002} [hci0] 341.378134
        Instance: 1
        Flags: 0x00000002
          Advertise as Discoverable
        Duration: 0
        Timeout: 0
        Advertising data length: 6
        Company: internal use (65535)
          Data: 8c33
        Scan response length: 0