zephyr-net-socket

name

zephyr-net-socket

description

Expert guidance for BSD sockets, TLS/DTLS secure sockets, and DNS resolution in Zephyr OS. Covers TCP/UDP socket programming, secure socket creation with mbedTLS, TLS credential management, hostname resolution with getaddrinfo/dns_resolve, mDNS/LLMNR support, and socket offloading. Use when implementing network clients/servers, adding TLS security to connections, resolving hostnames, or configuring socket-based networking.

Zephyr Network Sockets

Quick Start

1. Enable Sockets: CONFIG_NET_SOCKETS=y in prj.conf
2. Choose Protocol: TCP (CONFIG_NET_TCP=y) or UDP (CONFIG_NET_UDP=y)
3. Optional TLS: CONFIG_NET_SOCKETS_SOCKOPT_TLS=y for secure sockets
4. Optional DNS: CONFIG_DNS_RESOLVER=y for hostname resolution
5. Create Socket: socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)

Core TCP Client Pattern

#include <zephyr/net/socket.h>

int tcp_client_example(void)
{
    struct sockaddr_in addr = {
        .sin_family = AF_INET,
        .sin_port = htons(8080),
    };
    inet_pton(AF_INET, "192.168.1.100", &addr.sin_addr);

    int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock < 0) {
        return -errno;
    }

    int ret = connect(sock, (struct sockaddr *)&addr, sizeof(addr));
    if (ret < 0) {
        close(sock);
        return -errno;
    }

    /* Send/receive data */
    send(sock, "Hello", 5, 0);

    char buf[128];
    int len = recv(sock, buf, sizeof(buf), 0);

    close(sock);
    return 0;
}

Core TCP Server Pattern

int tcp_server_example(void)
{
    struct sockaddr_in addr = {
        .sin_family = AF_INET,
        .sin_port = htons(8080),
        .sin_addr.s_addr = INADDR_ANY,
    };

    int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock < 0) {
        return -errno;
    }

    int ret = bind(sock, (struct sockaddr *)&addr, sizeof(addr));
    if (ret < 0) {
        close(sock);
        return -errno;
    }

    ret = listen(sock, 5);  /* Backlog of 5 */
    if (ret < 0) {
        close(sock);
        return -errno;
    }

    while (1) {
        struct sockaddr_in client_addr;
        socklen_t client_len = sizeof(client_addr);
        int client = accept(sock, (struct sockaddr *)&client_addr, &client_len);
        if (client < 0) {
            continue;
        }

        /* Handle client connection */
        char buf[128];
        int len = recv(client, buf, sizeof(buf), 0);
        if (len > 0) {
            send(client, buf, len, 0);  /* Echo back */
        }

        close(client);
    }
}

Socket Types

Family	Type	Protocol	Description	Kconfig
AF_INET/AF_INET6	SOCK_STREAM	IPPROTO_TCP	TCP stream	CONFIG_NET_TCP
AF_INET/AF_INET6	SOCK_STREAM	IPPROTO_TLS_1_2	TLS over TCP	CONFIG_NET_SOCKETS_SOCKOPT_TLS
AF_INET/AF_INET6	SOCK_DGRAM	IPPROTO_UDP	UDP datagram	CONFIG_NET_UDP
AF_INET/AF_INET6	SOCK_DGRAM	IPPROTO_DTLS_1_2	DTLS over UDP	CONFIG_NET_SOCKETS_ENABLE_DTLS
AF_INET/AF_INET6	SOCK_RAW	IPPROTO_IP	Raw IP packets	CONFIG_NET_SOCKETS_INET_RAW
AF_PACKET	SOCK_RAW	ETH_P_ALL	Raw L2 packets	CONFIG_NET_SOCKETS_PACKET
AF_CAN	SOCK_RAW	CAN_RAW	CAN bus	CONFIG_NET_SOCKETS_CAN

Detailed References

• BSD Sockets API: references/sockets.md
• TLS/DTLS Secure Sockets: references/tls.md
• DNS Resolution: references/dns.md
• Kconfig Options: references/kconfig.md
• File Locations: references/locations.md

TLS Quick Start

#include <zephyr/net/socket.h>
#include <zephyr/net/tls_credentials.h>

#define CA_CERT_TAG 1

static const unsigned char ca_cert[] = { /* DER-encoded CA cert */ };

int tls_client_example(void)
{
    /* 1. Register credentials */
    tls_credential_add(CA_CERT_TAG, TLS_CREDENTIAL_CA_CERTIFICATE,
                       ca_cert, sizeof(ca_cert));

    /* 2. Create TLS socket */
    int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TLS_1_2);

    /* 3. Configure TLS options */
    sec_tag_t tags[] = { CA_CERT_TAG };
    setsockopt(sock, SOL_TLS, TLS_SEC_TAG_LIST, tags, sizeof(tags));

    char hostname[] = "example.com";
    setsockopt(sock, SOL_TLS, TLS_HOSTNAME, hostname, sizeof(hostname));

    /* 4. Connect and use like regular socket */
    struct sockaddr_in addr = { /* ... */ };
    connect(sock, (struct sockaddr *)&addr, sizeof(addr));

    send(sock, "GET / HTTP/1.1\r\n\r\n", 18, 0);

    close(sock);
    return 0;
}

DNS Quick Start (getaddrinfo)

#include <zephyr/net/socket.h>

int dns_lookup_example(void)
{
    struct addrinfo hints = {
        .ai_family = AF_INET,      /* or AF_UNSPEC for IPv4/IPv6 */
        .ai_socktype = SOCK_STREAM,
    };
    struct addrinfo *res;

    int ret = getaddrinfo("example.com", "443", &hints, &res);
    if (ret != 0) {
        printk("DNS lookup failed: %d\n", ret);
        return -1;
    }

    /* Use resolved address */
    int sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
    connect(sock, res->ai_addr, res->ai_addrlen);

    freeaddrinfo(res);  /* Free when done */
    return 0;
}

Minimum Kconfig

Basic Sockets

CONFIG_NETWORKING=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_TCP=y
CONFIG_NET_UDP=y
CONFIG_NET_IPV4=y
CONFIG_NET_IPV6=y

With TLS

CONFIG_NET_SOCKETS_SOCKOPT_TLS=y
CONFIG_MBEDTLS=y
CONFIG_MBEDTLS_BUILTIN=y
CONFIG_MBEDTLS_ENABLE_HEAP=y
CONFIG_MBEDTLS_HEAP_SIZE=60000

With DNS

CONFIG_DNS_RESOLVER=y
CONFIG_DNS_SERVER_IP_ADDRESSES=y
CONFIG_DNS_SERVER1="8.8.8.8"

Common Socket Options

Level	Option	Description
SOL_SOCKET	SO_REUSEADDR	Reuse local address
SOL_SOCKET	SO_RCVTIMEO	Receive timeout
SOL_SOCKET	SO_SNDTIMEO	Send timeout
SOL_SOCKET	SO_BINDTODEVICE	Bind to specific interface
SOL_TLS	TLS_SEC_TAG_LIST	TLS credential tags
SOL_TLS	TLS_HOSTNAME	Server hostname for SNI
SOL_TLS	TLS_PEER_VERIFY	Peer verification level
SOL_TLS	TLS_CIPHERSUITE_LIST	Allowed ciphersuites

Non-Blocking Sockets

/* Set non-blocking mode */
int flags = fcntl(sock, F_GETFL, 0);
fcntl(sock, F_SETFL, flags | O_NONBLOCK);

/* Or use MSG_DONTWAIT per-call */
recv(sock, buf, sizeof(buf), MSG_DONTWAIT);

poll() for Multiple Sockets

#include <zephyr/net/socket.h>

struct zsock_pollfd fds[2];
fds[0].fd = sock1;
fds[0].events = ZSOCK_POLLIN;
fds[1].fd = sock2;
fds[1].events = ZSOCK_POLLIN;

int ret = zsock_poll(fds, 2, 5000);  /* 5 second timeout */
if (ret > 0) {
    if (fds[0].revents & ZSOCK_POLLIN) {
        /* sock1 has data */
    }
    if (fds[1].revents & ZSOCK_POLLIN) {
        /* sock2 has data */
    }
}

POSIX API Mode

Enable CONFIG_POSIX_API=y to use standard function names without zsock_ prefix:

/* With CONFIG_POSIX_API=y */
socket();   /* Instead of zsock_socket() */
connect();  /* Instead of zsock_connect() */
send();     /* Instead of zsock_send() */
recv();     /* Instead of zsock_recv() */
close();    /* Instead of zsock_close() */

Related Skills

• zephyr-wifi: WiFi connectivity before socket operations
• zephyr-kconfig: Configure CONFIG_NET_* options
• zephyr-shell-commands: Network shell for debugging (CONFIG_NET_SHELL=y)
• zephyr-cbor: Binary serialization for CoAP/UDP payloads