Module bt: Bluetooth Communication

This module provides access to Bluetooth® wireless communication with other Bluetooth equipped devices. The supported functions are:

• Obtaining the own bluetooth address and name, and modifying the latter.
• Getting and setting the Bluetooth visibility flag.
• Scanning for visible devices and obtaining the address, name and class, also interactively.
• Creation of services (passive connections), either directly using a channel number, or by registering with an UUID for service discovery.
• Connecting to services (active connections), either directly using a channel number, or by looking an UUID up via service discovery.

• Terminology
• Connections Are Streams
• Simple Example
• bt.accept
• bt.adr
• bt.chan
• bt.conn
• bt.name
• bt.scan
• bt.select
• bt.start
• bt.stop
• bt.timeout
• bt.uuid
• bt.visible

Terminology

• Device Address: Each Bluetooth device is identified by a unique 48 bit address. In this module, an address is a string of six hexadecimal bytes, separated by colons, e.g. "00:E0:03:5E:AF:CD", or "0:e0:3:5e:af:cd".
• Device Name: Each Bluetooth device can have a freely assignable name. A well chosen name helps in distinguishing visible devices, but is of little use when trying to automatically identify or find a device.
• Device Class: Each Bluetooth device has a class defining its type and capabilities. The device class is a 24 bit integer, encoded as follows:

  Bits	Value	Contents
  0-1		Always zero
  2-7		Minor device class:
  		interpretation depends on Major device class
  8-12		Major device class:
  	0	Miscellaneous
  	1	Computer
  	2	Phone
  	3	LAN/Network access point
  	4	Audio/Video
  	5	Peripheral (mouse, joystick, keyboard)
  	6	Imaging (printer, display, scanner, camera)
  	7	Wearable
  	31	Uncategorized
  13-23		Service class:
  16	1	Positioning (GPS)
  17	1	Networking (LAN)
  18	1	Rendering (Video and Audio)
  19	1	Capturing (Video and Audio)
  20	1	Object Transfer (vCal, vCard)
  21	1	Audio
  22	1	Telephony
  23	1	Information (WWW/WAP-Servers)

• SDP (Service Discovery Protocol): A mechanism to advertise services (e.g. data synchronization, printing, scanning, or own services), and discover them. Services are identified by UUIDs.
• UUID (Universally Unique Identifier): This is a 128 bit (16 byte) quantity. In Bluetooth, each service has one or more UUIDs assigned: when creating a service, a UUID should be assigned to it (see bt.start).

  In this module, a UUID is represented as an array of four nonnegative numbers, starting with bits 127 to 96, and ending with bits 31 to 0. See also bt.uuid.

  In Bluetooth, often only 32 bits of the UUID are specified. Such an UUID maps to a 128 bit UUID by adding fixed values for the lower 96 bits:

  u=bt.uuid(12345); print u → [12345,4096,2147483776,1604007163] for v in u do print hexstr(v) end → 3039 1000 80000080 5f9b34fb

  A few of the standard 32 bit UUIDs are:

  Hex	Decimal	Service Class
  3	3	RFCOMM
  100	256	L2CAP
  1101	4353	Serial Port
  1103	4355	Dialup Networking
  1105	4357	Obex (Object Exchange)
  1111	4369	Fax
  1204	4612	Generic Telephony

• RFCOMM (Radio Frequency Communications): Provides reliable communication between two Bluetooth devices. This corresponds to the TCP layer in the Internet world.
• Channel: An integer identifying an RFCOMM communication stream. This corresponds to a port number in the Internet world. A service can be reached by a device address and a channel number.

Connections Are Streams

• io.read, io.readln, and io.readm receive data,
• io.write, io.writeln, io.writem, io.print, and io.println send data,
• io.avail gets the number of bytes which can be read without blocking,
• io.wait waits for data which can be read without blocking,
• io.close closes the connection.
• io.ces gets and sets the character encoding scheme. As with files, the default is io.raw.
• io.timeout sets the timeout for send and receive operations.
• io.flush sets the auto flush state. If auto flushing is disabled, io.flush must be called to make sure all data is sent.

Simple Example

To illustrate use of the m Bluetooth module, a trivial client-server example is presented. The server reverses each line of input it receives.

Client code:

use bt, io // have the user select a device dev=bt.select(); // connect to server s=bt.conn(dev["adr"], "Reverser"); // write a line io.writeln(s, "Hello world!"); // read the result print io.readln(s) → !dlrow olleH // and again io.writeln(s, "Bye server"); print io.readln(s) → revres eyB io.close(s)

Server code:

// a function which reverses a string function reverse(s)   c=code(s);   i=0; j=len(c)-1;   while i<j do     h=c[i]; c[i]=c[j]; c[j]=h; i++; j--   end;   return char(c) end use bt, io // create and advertise a service called "Reverser" service=bt.start("Reverser"); while true do // loop forever   // wait for a client   io.print(io.stdout, "Waiting...");   s=bt.accept(service);   print bt.adr(s),"ok.";   // read each line, writing it back reversed   line=io.readln(s);   while line#null do     io.writeln(s, reverse(line));     line=io.readln(s)   end;   io.close(s) end → Waiting...00:0E:07:C9:EE:88 ok. Waiting...

bt.accept

Marks service available, then waits for a device connecting to service. When a device connects successfully, marks service as unavailable, and returns the connection stream.

See bt.start for an example.

bt.adr

With one argument, returns the Bluetooth address of the device stream is connected to.

Without arguments, returns the local (own) Bluetooth address.

s=bt.accept(service); // who connected? print bt.adr(s) → 00:0E:07:C9:EE:88 // our own bluetooth address print bt.adr() → 00:E0:03:5E:AF:CD

bt.chan

With one argument, returns the channel number of service, in an array with the service name as key.

With two arguments, queries the service discovery database of the device with address adr for all services with the service class UUID defined by uuid, and returns their channel numbers in an array with the service names as keys. See bt.uuid for the values allowed for uuid.

// create a service on a fixed channel s=bt.start("Sample", 18); // obtain the channel of the service c=bt.chan(s); print c, keys(c) → [18] [Sample] // query a device for all Obex services c=bt.chan("00:0E:07:C9:EE:88", 4357); print c, keys(c) → [9] [OBEX Object Push] // query a device for all services using RFCOMM c=bt.chan("00:0E:07:C9:EE:88", 3); print c, keys(c) → [1,2,10,9,15,11,12,3] [Hands-Free Audio Gateway, Headset Audio Gateway,OBEX File Transfer,OBEX Object Push, Imaging,SyncMLClient,...<8>]

bt.conn

If uuidOrChannel is an array or a string, queries the service discovery database of the device with address adr for the first service with the service class UUID defined by uuidOrChannel, then connects to the service's channel.

If uuidOrChannel is a number, connects directly to channel uuidOrChannel of the device with address adr, without querying the database.

// connect to the Obex service on a device dev="00:0E:07:C9:EE:88"; s=bt.conn(dev, [4357]); io.close(s) // connect to channel 18 on the same device s=bt.conn(dev, 18); io.close(s)

bt.name

Without an argument, returns the local (own) device name. With a single argument, set the local device name to newname and returns the old name.

// change the name, returning the old one print bt.name("Test Device #1") → Nokia 6670 // get the current name print bt.name() → Test Device #1

bt.scan

With a single argument, scans for other visible bluetooth devices in the neighborhood, and returns the first device found, or null if there is no visible device.
If limited=false, the scan is performed with general unlimited inquiry access code (IAC), returning all devices.
If limited=true, the scan is performed with the faster limited IAC, but only returning devices which are scanning with limited IAC.

Without an argument, continues scanning, and returns the next device found, or null if there are no more devices.

Making an SDP request (bt.chan, bt.conn) ends the current scan, i.e. the next call to bt.scan will always start a new scan.

Each device found is returned as an array with the following keys:

Key	Meaning	Type
adr	Device address	String
name	Device name	String
class	Device class	Number

dev=bt.scan(false); // print each device while dev#null do   print dev;   // get the next device   dev=bt.scan() end → [00:E0:03:5E:AF:CD,Test Device #1,5243404] → [00:0E:07:C9:EE:88,Test Device #2,5251596]

bt.select

Shows an interactive dialog scanning for Bluetooth devices and allowing the user to select one. Returns the selected device in the same format as returned by bt.scan, or null if the user cancelled the selection.

print bt.select() → [00:E0:03:5E:AF:CD,Test Device #1,5243404]

bt.start

Creates a service with name name and returns it. To accept an incoming connection on the service, use bt.accept.

If uuidOrChannel is an array or a string, bt.start finds an unused channel and creates a service with the UUID defined by uuidOrChannel. The service is advertised in the service discovery database of the device.

uuidOrChannel=null is equivalent to uuidOrChannel=name.

If uuidOrChannel is a number, listens directly on channel uuidOrChannel, without advertising the service.

The security imposed on incoming connections is defined by flags, which is a combination of the following values:

• const authenticate = 1 Connecting devices must be paired, or mutual password authentication is requested.

• const encrypt = 2 Data transfers are encrypted.

• const authorise = 4 The user is asked for authorisation whenever a device attempts to connect to the channel.

// create a service with the UUID of the Fax // service class, and asking for authorisation service1=bt.start("My Fax", [4369], bt.authorise); // wait for a connection conn=bt.accept(service1); ... // create a service listening on channel 18 service2=bt.start("Sample", 18); conn2=bt.accept(service2); ...

bt.stop

Stops service. If it has been advertised, it is removed from the service discovery database.

bt.timeout

Gets or sets the timeout used during most functions of this module. Without arguments, returns the current timeout in milliseconds. With one argument, returns the old timeout, and sets the new timeout to ms. Setting the timeout to zero (the default) or a negative value disables timeouts, i.e. Bluetooth operations can block indefinitely, or use a timeout defined by the underlying system.

Throws ExcValueOutOfRange if ms exceeds 2147483 (35 minutes and 47.483 seconds).

The timeout is used in all following calls: whenever an operation does not complete within the given number of milliseconds, it throws ErrTimedOut.

// allow 10 seconds to connect bt.timeout(10000); try   s=bt.conn("00:E0:03:5E:AF:CD", 4)   // connection successful... catch e by   if index(e, "ErrTimedOut") # 0 then throw e end;   print "Could not connect within 10 seconds" end

bt.uuid

Converts a number, string or array to a 128 bit UUID, and returns the UUID as an array of four integers.

• If uuid is a number, uuid is considered a 32 bit Bluetooth UUID.
• If uuid is an array with one element, its only element is considered a 32 bit Bluetooth UUID.
• If uuid is an array with four elements, they are considered the four 32 bit values making up the entire 128 bit UUID (from highest to lowest).
• If uuid is a string with two characters or less, the characters are considered a 16 bit Bluetooth UIID.
• If uuid is a string with three or four characters, the characters are considered a 32 bit Bluetooth UIID.
• If uuid is a string with more than four characters, its first 16 characters are considered the 16 bytes of the UUID (from highest to lowest). Missing bytes are assumed zero.

print bt.uuid(12345); → [12345,4096,2147483776,1604007163] print bt.uuid([12345]); → [12345,4096,2147483776,1604007163] print bt.uuid("Sample") → [1398893936,1818558464,0,0] print bt.uuid([1,2]) → ErrArgument thrown

bt.visible

Compatibility of function bt.visible Nokia phones before Symbian 8[12] ok Nokia phones with Symbian 8[13] ErrNotSupported Symbian 3rd/5th Edition and Sony Ericsson phones[14] ErrNotSupported

Without an argument, returns the current visibility state of this device: true if the device is detectable by others, false if it is not visible. With an argument, sets the visibility to newvisible, and returns the old visibility state.

// make the device visible bt.visible(true) // is it visible? print bt.visible() → true