The BSD Socket Interface is layered on top of the transport protocols. It supports both the Nordic's IPv6 stack (UDP), as well as the LwIP stack (TCP only). Only one of them can be compiled at a time. In addition, and by default, the BSD Socket Interface automatically configures the BLE configuration options for 6LoWPAN and the entire stack is initialized upon creating the first socket. See Configuration parameters for details.

See BSD Socket interface reference for the API documentation. See the IoT examples folder for a socket TCP client example that works with the LwIP TCP Server example. The socket example is also compilable in a POSIX environment.

Blocking/Non-Blocking behavior

The BSD Socket Interface currently supports Blocking and Non-Blocking I/O. Blocking is defined as any operation that waits for resources provided by the network. Non-Blocking I/O is supported by setting O_NONBLOCK on the socket descriptor and using select. Currently, Non-Blocking I/O with select is only supported when reading data.

The following table lists the API calls and their default behavior.

API	Blocking/Non-Blocking
socket	Non-Blocking
close	Non-Blocking
connect	TCP: Blocking, UDP: Non-Blocking
send	Blocking
recv	Blocking

Note: Any of these calls can be made non-blocking by setting O_NONBLOCK using fcntl. The send and recv also allows MSG_DONTWAIT flag to be passed to use Non-Blocking I/O for a single operation.

Blocking I/O

The following is a simple socket client sending a single UDP packet.

#include <sys/socket.h>
#include <errno.h>
int main(void)
{
 int s = socket(AF_INET6, SOCK_DGRAM, 0);
 if (s < 0)
 {
 return 1;
 }
 struct sockaddr_in6 dest_addr;
 memset(&dest_addr, 0, sizeof(dest_addr));
 inet_pton(AF_INET6, "2001:db8::1", &dest_addr.sin6_addr);
 dest_addr.sin6_port = htons(1234);
 int ret = connect(s, &dest_addr, sizeof(dest_addr));
 if (ret < 0)
 {
 return 2;
 }
 const char * msg = "Hello, Server!";
 ssize_t nbytes = send(s, msg, strlen(msg));
 if (nbytes != strlen(msg))
 {
 return 3;
 }
 ret = close(s);
 if (ret < 0)
 {
 return 4;
 }
 return 0;
}

Non-Blocking I/O

The following is a simple socket client sending and receiving messages over TCP.

#include <sys/socket.h>
#include <errno.h>
int main(void)
{
 int s = socket(AF_INET6, SOCK_STREAM, 0);
 if (s < 0)
 {
 return 1;
 }
 struct sockaddr_in6 dest_addr;
 memset(&dest_addr, 0, sizeof(dest_addr));
 inet_pton(AF_INET6, "2001:db8::1", &dest_addr.sin6_addr);
 dest_addr.sin6_port = htons(1234);
 int ret = connect(s, &dest_addr, sizeof(dest_addr));
 if (ret < 0)
 {
 return 2;
 }
 const char * msg = "Hello, Server!";
 ssize_t nbytes = send(s, msg, strlen(msg));
 if (nbytes != strlen(msg))
 {
 return 3;
 }
 nbytes = 0;
 char buf[32];
 while (nbytes < 0)
 {
 nbytes = recv(s, buf, sizeof(buf), MSG_DONTWAIT);
 }
 ret = close(s);
 if (ret < 0)
 {
 return 4;
 }
 return 0;
}

Configuration parameters

Feature	Description
SOCKET_TRANSPORT_ENABLE	Set to 1 to enable transport layer support.
SOCKET_MEDIUM_ENABLE	Set to 1 to support configuration socket using medium module.
SOCKET_AUTOINIT_ENABLE	Set to 1 to automatically configure link layer.
SOCKET_LOGS_ENABLE	Set to 1 to enable logging to UART (must set NRF_LOG_ENABLED as well).
SOCKET_ENABLE_API_PARAM_CHECK	Set to 1 to enable extra sanity checks.

Table of Contents

Blocking/Non-Blocking behavior

Blocking I/O

Non-Blocking I/O

Configuration parameters

References