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update Bluetooth LE beacon support: set choice of TCP port

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F. Duncanh
2025-09-26 21:14:17 -04:00
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README.md
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@@ -4,8 +4,8 @@
- **NEW on github**: Support for **service discovery using a Bluetooth LE "beacon"** (as an alternative to Bonjour/Rendezvous DNS-SD
service discovery). The user must set up a Bluetooth LE "beacon", (a USB 4.0 or later "dongle" can be used). See instructions
below. The beacon runs independently of UxPlay and regularly broadcasts a Bluetooth LE ("Low Energy") 44 byte packet informing nearby iOS/macOS devices of
the local IPv4 network address of the UxPlay server, which they can use to contact it on TCP port 7000.
below. The beacon runs independently of UxPlay and regularly broadcasts a Bluetooth LE ("Low Energy") 46 byte packet informing nearby iOS/macOS devices of
the local IPv4 network address of the UxPlay server, and which TCP port to contact UxPlay on.
Instructions for manually setting up such a beacon in Linux are [given below](#bluetooth-le-beacon-setup).
__It is hoped that users will submit Pull Requests contributing scripts for automating beacon setup on all platforms.
(Python may be an appropriate language choice)__
@@ -1471,24 +1471,28 @@ GStreamer inner workings.
To allow UxPlay to work with Bluetooth Low Energy (LE) Service Discovery, as an alternative to DNS-SD (Bonjour/Rendezvous)
service discovery, start it with the option "`-ble <path-to-writeable-file>`", which at startup writes a data file containing
the uxplay process ID and process name, and is deleted when uxplay terminates normally. **This file
the uxplay TCP port for receiving replies to the advertisement, plus the uxplay process ID and process name, and is deleted when uxplay terminates normally. **This file
is not used in the simple manual method for creating a beacon described below**.
Bluetooth LE Service discovery uses a "beacon" broadcasting a simple 12-byte
advertisement "`0B FF 4C 00 09 06 03 30 XX XX XX XX`" where XX XX XX XX is an IPv4 internet
address of the UxPlay host translated into hexadecimal octets: For
example, "`XX XX XX XX`" = "``C0 A8 01 FD``" means 192.168.2.253. UxPlay
must be able to receive messages on TCP port 7000 at this
address. The uxplay option "`-p`" sets up uxplay to listen on port 7000 for these messages.
Bluetooth LE Service discovery uses a "beacon" broadcasting a simple 14-byte
advertisement "`0D FF 4C 00 09 08 13 30 XX XX XX XX YY YY`" where XX XX XX XX is an IPv4 internet
address (and port YY YY) of the UxPlay host translated into hexadecimal octets. For
example, "`XX XX XX XX YY YY`" = "``C0 A8 01 FD 1B 58``" means 192.168.2.253 port 0x1b58 (decimal value 7000). UxPlay
must be able to receive messages on this TCP port at this
address. The uxplay option "`-p`" sets up uxplay to listen on the default port 7000 for these messages, as used in the
example above. Otherwise the port in the beacon message should
be the first (`<n>`) of the 3 open TCP ports specified with uxplay option ``-p <n>``. If
the `-p` option is not used (which is only possible if there is no active firewall) the TCP port is selected at random, and its value
must be taken from the beginning of the file written with the `-ble` option.
The full translation of this message is that it has length 0B = 0x0b = 11 octets, and is a single "Advertising Protocol Data Unit" (PDU) of type "`FF`",
The full translation of this message is that it has length 0D = 0x0d = 13 octets, and is a single "Advertising Protocol Data Unit" (PDU) of type "`FF`",
called "Manufacturer-Specific Data", with "manufacturer code" "`4C 00`" = 0x004c = Apple (note the reversal of octet order when
two octets are combined to make a two-byte unsigned short integer), and "`09 06 03 30 XX XX XX XX`" is the Apple-specific data.
two octets are combined to make a two-byte unsigned short integer), and "`09 08 13 30 XX XX XX XX YY YY`" is the Apple-specific data.
The Apple-specific data contains a single Apple Data Unit with Apple type = 09 (Airplay), Apple Data length 06 (0x06 = 6 octets) and
Apple Data "`03 30 XX XX XX XX`" where 03 = 0000 0011 is Apple Flags, 30 is a seed (which will be ignored), and XX XX XX XX
is the IPv4 internet address. This is smaller than the "iBeacon" Apple Data Unit, which has Apple type 02 and Apple length 15 (0x15 = 21 octets).
The Apple-specific data contains a single Apple Data Unit with Apple type = 09 (Airplay), Apple Data length 08 (0x08 = 8 octets) and
Apple Data "`13 30 XX XX XX XX YY YY`" where 13 = 0001 0011 is Apple Flags, 30 is a seed (which will be ignored), XX XX XX XX
is the IPv4 internet address and YY YY is the port. This is smaller than the "iBeacon" Apple Data Unit, which has Apple type 02 and Apple length 15 (0x15 = 21 octets).
In addition to creating the message, we need to set the "Advertising type" (ADV_NONCONN_IND) and "Advertising interval" range [AdvMin, AdvMax],
where 0x00a0 = 100 msec <= AdvMin <= AdvMax <= 0x4000 = 10.24 sec
@@ -1555,14 +1559,14 @@ advertising channels.
An Apple TV (Gen 3) seems to use AdvMin = AdvMax = 180 msec = 0x0120 ("`0x20 0x01`").
**Step 2.** Set the advertising message with HCI LE command 0x0008. For this command, hcitool requires a 32 octet message after
`sudo hcitool -i hci0 cmd 0x08 0x0008`: The first octet is the length 0C = 0x0c = 12 of the "significant part" of the following 31 octets,
followed by the 12 octets of the advertisement, then padded with 19 zeroes to a total length of 32 octets. The example below sends an
IPv4 address 192.168.1.253 as "`0xc0 0xa8 0x01 0xfd`":
`sudo hcitool -i hci0 cmd 0x08 0x0008`: The first octet is the length 0E = 0x0e = 14 of the "significant part" of the following 31 octets,
followed by the 14 octets of the advertisement, then padded with 17 zeroes to a total length of 32 octets. The example below sends an
IPv4 address 192.168.1.253 as "`0xc0 0xa8 0x01 0xfd`" and the TCP port as 0x1b 0x58 (port 7000 = 0x1b58):
```
$ sudo hcitool -i hci0 cmd 0x08 0x0008 0x0c 0x0b 0xff 0x4c 0x00 0x09 0x06 0x03 0x30 0xc0 0xa8 0x01 0xfd 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
$ sudo hcitool -i hci0 cmd 0x08 0x0008 0x0e 0x0d 0xff 0x4c 0x00 0x09 0x08 0x13 0x30 0xc0 0xa8 0x01 0xfd 0x1b 0x58 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
< HCI Command: ogf 0x08, ocf 0x0008, plen 32
0C 0B FF 4C 00 09 06 03 30 C0 A8 01 FD 00 00 00 00 00 00 00
0E 0D FF 4C 00 09 08 13 30 C0 A8 01 FD 1B 58 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
> HCI Event: 0x0e plen 4
01 08 20 00
@@ -1577,7 +1581,7 @@ $ sudo hcitool -i hci0 cmd 0x08 0x000a 0x01
> HCI Event: 0x0e plen 4
02 0A 20 00
```
The full length of the broadcasted beacon message is 43 bytes.
The full length of the broadcasted beacon message is 46 bytes.
To stop the beacon, use this command to send the 1-byte message "`0x00`" = "off".
@@ -1594,9 +1598,13 @@ $ sudo systemctl stop avahi-daemon
An automated procedure for creating the beacon would presumably want to switch it on when uxplay starts, and off when it
stops. The 20-byte file created when uxplay starts (and deleted when it stops) contains the PID as a uint32_t unsigned integer in the first 4 bytes,
stops. The 22-byte file created when uxplay starts (and deleted when it stops) contains the RAOP port as a uint16_t unsigned short,
in the first 2 bytes, followed by
the uxplay PID as a uint32_t unsigned integer in the next 4 bytes, then
followed by up to the first
11 characters of the process name (usually "uxplay") as a null-terminated string, padded with zeroes to 16 bytes. This data can be used to test
11 characters of the process name (usually "uxplay") as a null-terminated string, padded with zeroes to 16 bytes. The port data
identifies the port on the Host that uxplay listens on, which should be included along with the Host IPv4 address
in the advertisement broadcast by the beacon. The remaining data can be used to check
whether uxplay is actually running, including cases where it has segfaulted and not deleted the file.