int receivePacket(uint8_t* buffer, size_t buf_size, system_tick_t timeout = 0)
int receivePacket(char* buffer, size_t buf_size, system_tick_t timeout = 0)

size = Udp.receivePacket(buffer, size);
// EXAMPLE USAGE - get a string without buffer copy
UDP Udp;
char message[128];
int port = 8888;
int rxError = 0;

Udp.begin (port);
int count = Udp.receivePacket((byte*)message, 127);
if (count >= 0 && count < 128) {
  message[count] = 0;
  rxError = 0;
} else if (count < -1) {
  rxError = count;
  // need to re-initialize on error
if (!rxError) {

Checks for the presence of a UDP packet and returns the size. Note that it is possible to receive a valid packet of zero bytes, this will still return the sender's address and port after the call to receivePacket().


  • buffer: the buffer to hold any received bytes (uint8_t).
  • buf_size: the size of the buffer.
  • timeout: The timeout to wait for data in milliseconds, or 0 to not block in Device OS 2.0.0 and later. Prior to 2.0.0 this function did not block.


  • int: on success the size (greater then or equal to zero) of a received UDP packet. On failure the internal error code.