lwIP (Sockets API) setup¶

lwIP (Sockets API) platform

Wiring the adapters so a sender can resolve and address its destination. lwIP (Sockets API) covers what the pack fills and what your build must enable; the config fields are documented on the structs themselves. This page is the wiring.

What your lwipopts.h must say¶

#define NO_SYS          0
#define LWIP_SOCKET     1
#define LWIP_NETCONN    1
#define LWIP_DNS        1

Turning the sockets layer on grows the upstream build as well as the configuration: lwIP compiles api/sockets.c, api/api_lib.c, api/api_msg.c, api/netbuf.c and api/netdb.c, which cost on the order of 12 KB of flash on a Cortex-M3. Budget for it before choosing this tier.

Drawing the pieces¶

#include "SolidSyslogLwipSocketAddress.h"
#include "SolidSyslogLwipSocketResolver.h"

struct SolidSyslogAddress*  address  = SolidSyslogLwipSocketAddress_Create();
struct SolidSyslogResolver* resolver = SolidSyslogLwipSocketResolver_Create();

Neither takes a configuration, because neither has anything only you can decide. One address and one resolver serve one sender. The pool sizes that bound how many you may draw are in Adding it to your build; drawing past them hands back a Null object and reports CRITICAL, so a sender wired from an exhausted pool delivers nothing rather than misbehaving.

Resolving by name¶

The resolver takes the destination host as given and asks lwIP for an IPv4 address, applying your port to the answer. A numeric literal resolves without touching the network; a name needs a DNS server your stack can reach.

Where there is no DNS server, DNS_LOCAL_HOSTLIST maps names statically and resolves entirely on-device:

#define LWIP_DNS                1
#define DNS_LOCAL_HOSTLIST      1
#define DNS_LOCAL_HOSTLIST_INIT \
    { DNS_LOCAL_HOSTLIST_ELEM("collector", IPADDR4_INIT_BYTES(10, 0, 2, 2)) }

The one thing that will catch you out¶

A resolve blocks the calling task, and it must not be the tcpip thread. The call hands the lookup to that thread and waits for it, so asking from inside a callback lwIP invoked waits for a thread that is waiting for you.

Call SolidSyslog_Service from an ordinary task, and the resolve that happens inside it is safe.

Which build this pack suits¶

One where lwIP is built with NO_SYS=0 and a task can afford to block while the stack answers. That is what buys the absence of a marshal seam and of any per-call hop. Where your build cannot host the sockets layer, the platform x capability matrix is the place to choose from.