AdafruitUDP makes it easy to work with raw UDP sockets. It includes a convenient callback for incoming data, and a number of helper functions to read and write data over a UDP socket.
You're free to 'poll' for incoming data and connection status, but the 'data received' callback fires whenever incoming data is available, which can then be read via the .read() and related commands. Callbacks aren't mandatory, but help keep your code easy to understand and more maintainable as your project grows in complexity.
// UDP API virtual uint8_t begin (uint16_t port); virtual void stop (void); virtual int beginPacket (IPAddress ip, uint16_t port); virtual int beginPacket (const char *host, uint16_t port); virtual int endPacket (void); virtual int parsePacket (void); virtual IPAddress remoteIP (void); virtual uint16_t remotePort (void); // Stream API virtual int read (void); virtual int read (unsigned char* buffer, size_t len); virtual int read (char* buffer, size_t len); virtual int peek (void); virtual int available (void); virtual void flush (void); virtual size_t write (uint8_t byte); virtual size_t write (const uint8_t *buffer, size_t size); // Callback void setReceivedCallback (udpcallback_t fp);
UDP API
The following functions are primarilly based on the Arduino EthernetUDP class and enable you to work with UDP connections and packets.
uint8_t begin (uint16_t port)
Initialises the AdafruitUDP class for the specified local port.
Parameters:
- port: The local port number to listen on (0..65535)
Returns: 1 if successful, 0 if there are no sockets available to be used.
void stop (void)
Disconnects from the UDP server, and releases any resources used during the UDP session.
Parameters: None
Returns: Nothing
int beginPacket (IPAddress ip, uint16_t port)
Starts a UDP connection to write data to the specified remote IP address and port.
Parameters:
- ip: The remote IPAddress where the UDP server is located
- port: The remote port number to connect to (0..65535)
Returns: '1' if successful, '0' if there was a problem connecting to the specified IP address or port.
int beginPacket (const char *host, uint16_t port)
Starts a UDP connection to write data to the specified domain name and remote port.
Parameters:
- host: A string containing the domain name to connect to
- port: The port number to connect to (0..65536)
Returns: '1' if the connection was successfully established, otherwise '0'.
int endPacket (void)
This function must be called after writing UDP data to the remote server.
Parameters: None
Returns: '1' if the packet was sent successfully, otherwise '0'.
int parsePacket (void)
Checks whether a UDP packet is available, and returns the size of the UDP packet as a return value.
Parameters: None
Returns: The number of bytes available in the buffered UDP packet.
Parameters: None
Returns: The IPAddress of the remote UDP server/connection.
Returns the port for the remote UDP server.
Parameters: None
Returns: The port of the remote UDP server/connection.
Stream API
The following functions are based on the Stream class that Arduino EthernetUDP implements.
Parameters: None
Returns: The first character available in the UDP buffer, or 'EOF' if no data is available.
int read (unsigned char* buffer, size_t len)
int read (char* buffer, size_t len)
These two identical functions (other than the type used for the 'buffer') will read up to 'len' bytes from the UDP response data, copying them into the buffer provided in the first argument of this function.
Parameters:
- buffer: A pointer to the buffer where the UDP data will be copied
- len: The maximum number of bytes to read
Returns:
- The actual number of bytes read from the UDP data and copied into 'buffer'
- '0' if no data was read or available
- '-1' if an error occured
int peek (void)
Reads a single byte from the UDP response buffer without advancing to the next position in the buffer.
Parameters: None
Returns: The first byte available in the UDP buffer, or '-1' if no data is available.
Parameters: None
Returns: The number of bytes available to be read in the UDP buffer, otherwise '0' if the read buffer is empty.
void flush (void)
This function will flush the buffer of any outgoing data, and return when the buffered data has been sent and the buffer is empty.
Parameters: None
Returns: Nothing
size_t write (uint8_t byte)
Writes a single byte to the remote UDP server. This function must be placed after AdafruitUDP.beginPacket() and before AdafruitUDP.endPacket(). The packet will not be sent until .endPacket is called!
Parameters:
- byte: The single byte to write to the transmit buffer
Returns: The number of bytes written.
size_t write (const uint8_t *buffer, size_t size)
Writes the specified 'buffer' to the remote UDP server. This function must be placed after AdafruitUDP.beginPacket() and before AdafruitUDP.endPacket(). The packet will not be sent until .endPacket is called!
Parameters:
- buffer: The buffer where the data to transmit is stored
- size: The number of bytes contained in 'buffer'
Returns: The number of bytes written.
Callback Handlers
AdafruitUDP supports a 'read' callback that will fire every time incoming UDP data is recieved over the open socket connection.
The callback function has the following signature (although you are free to choose a different name if you wish to):
void received_callback(void);
Before you can use the callback function, you need to register your callback handler (using the function signature in the paragraph above).
You register the callback with the following function:
void setReceivedCallback (udpcallback_t fp)
Registers the function used to process 'data received' callbacks.
Parameters:
- fp: The name of the function where callback events should be redirected to
Returns: Nothing
Examples
The examples below illustration some basic UDP concepts to help you understand the class described above.
UDP Echo Server
The following example will listen on port 8888 for any incoming UDP requests, and then echo them back to the requesting device via the 'received' callback handler:
#include <adafruit_feather.h>
#define WLAN_SSID "yourSSID"
#define WLAN_PASS "yourPass"
#define LOCAL_PORT 8888
AdafruitUDP udp;
char packetBuffer[255];
bool connectAP(void)
{
// Attempt to connect to an AP
Serial.print("Attempting to connect to: ");
Serial.println(WLAN_SSID);
if ( Feather.connect(WLAN_SSID, WLAN_PASS) )
{
Serial.println("Connected!");
}
else
{
Serial.printf("Failed! %s (%d)", Feather.errstr(), Feather.errno());
Serial.println();
}
Serial.println();
return Feather.connected();
}
void setup()
{
Serial.begin(115200);
// wait for Serial port to connect. Needed for native USB port only
while (!Serial) delay(1);
Serial.println("UDP Echo Callback Example");
Serial.println();
while( !connectAP() )
{
delay(500);
}
// Tell the UDP client to auto print error codes and halt on errors
udp.err_actions(true, true);
udp.setReceivedCallback(received_callback);
Serial.printf("Openning UDP at port %d ... ", LOCAL_PORT);
udp.begin(LOCAL_PORT);
Serial.println("OK");
Serial.println("Please use your PC/mobile and send any text to ");
Serial.print( IPAddress(Feather.localIP()) );
Serial.print(" UDP port ");
Serial.println(LOCAL_PORT);
}
void loop()
{
}
/**************************************************************************/
/*!
@brief Received something from the UDP port
*/
/**************************************************************************/
void received_callback(void)
{
int packetSize = udp.parsePacket();
if ( packetSize )
{
// Print out the contents with remote information
Serial.printf("Received %d bytes from ", packetSize);
Serial.print( IPAddress(udp.remoteIP()) );
Serial.print( " : ");
Serial.println( udp.remotePort() );
udp.read(packetBuffer, sizeof(packetBuffer));
Serial.print("Contents: ");
Serial.write(packetBuffer, packetSize);
Serial.println();
// Echo back contents
udp.beginPacket(udp.remoteIP(), udp.remotePort());
udp.write(packetBuffer, packetSize);
udp.endPacket();
}
}
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