lwIP

Provide core TCP/IP features within a small memory budget

The README targets embedded systems with tens of kilobytes of free RAM and roughly 40 kilobytes of ROM. Its selectable features include IPv4, IPv6, ICMP, TCP, UDP, DHCP, DNS, PPP, and 6LoWPAN, plus applications such as an HTTP server, MQTT client, and SNTP.

Sources: [1]

Choose APIs and OS integration for the runtime

lwIP offers a callback-based raw API for low overhead, sequential APIs for calls from other threads, and a BSD-like socket compatibility API. No-OS mainloop mode and OS mode with a TCPIP thread have different available APIs and call-context rules.

Sources: [2]

Fits network ports for RTOS and bare-metal devices

lwIP fits sensors, controllers, and IoT devices that cannot simply use a general-purpose operating system's network stack. It is suitable when a team will implement the network interface, timing, locking, and memory hooks for its hardware and enable only the protocols it needs.

Sources: [1][2]

Design the port and execution contexts for each device

lwIP is not a complete standalone network application. A port needs device drivers, OS abstractions, timers, and an lwipopts.h configuration adapted from the supplied examples. GitHub reports NOASSERTION for SPDX metadata, while the pinned README states that lwIP is available under a BSD license.

Raw APIs execute in the lwIP core context and callbacks must not block. The official documentation identifies calls from interrupt context as a common pitfall and requires OS-mode raw API calls to run in the TCPIP thread or under the correct core lock.

Sources: [1][2]