Building lwIP
=============

lwIP uses a CMake based build system.

The CMake files in this project are designed to
be included into your own CMake files. They are
mainly variable definitions containing a list of
source files and predefined static libraries to
be linked against application code.

1) lwIP sources:
   src/Filelists.cmake provides file lists containing
   the lwIP core library.
   The file also contains two static libraries, lwipcore
   and lwipallapps, where you can link your app against.
   This is the file that is useful to all lwIP users.

2) Example applications:
   contrib/Filelists.cmake provides several file lists
   containing the example applications.
   The file also contains several static libraries
   for these example apps.
   This file is only useful for you, if you can use one
   of the examples in your application, which is normally
   not the case.

3) OS/platform port:
   Usually the OS port needs to be provided by the user.
   If a port to Linux, Windows or MacOS is useful for
   you, you can use
   contrib/ports/{win32, unix}/Filelists.cmake
   that contains file lists and libraries for
   these operating systems.

VARIABLES
=========
In all cases, you need to provide two variables.

"LWIP_DIR" pointing to the lwIP directory
Example:
set(LWIP_DIR ${CMAKE_CURRENT_SOURCE_DIR}/externals/lwip)

"LWIP_INCLUDE_DIRS" that contains the include base paths
- for lwIP itself (${LWIP_DIR}/src/include)
- for lwIP contrib if you use it (${LWIP_DIR}/contrib)
- to a directory containing an OS port
- to a directory containing lwipopts.h

Example:
set (LWIP_INCLUDE_DIRS
    "${LWIP_DIR}/src/include"
    "${LWIP_DIR}/contrib"
    "${LWIP_DIR}/contrib/ports/unix/port/include"
    "${LWIP_DIR}/contrib/examples/example_app"
)

Putting it all together
=======================
To get a working application, your CMake system
needs to provide the variables described above, e.g.
set (LWIP_DIR <path to lwip sources>)
set (LWIP_INCLUDE_DIRS
    "${LWIP_DIR}/src/include"
    "${LWIP_DIR}/contrib"
    "<path to my port>/include"
    "<path to lwipopts.h>"
)

You may add some defines:
set (LWIP_DEFINITIONS LWIP_DEBUG=1)

Then include the filelists you need:
include(${LWIP_DIR}/src/Filelists.cmake)
include(${LWIP_DIR}/contrib/Filelists.cmake)

Then, declare you executable:
add_executable(my_app <my source files> <my lwip port files>)

Add lwIP include dirs to your app:
target_include_directories(my_app PRIVATE ${LWIP_INCLUDE_DIRS})

Link your app against the lwIP libs from the filelists you need:
target_link_libraries(my_app lwipcontribapps lwipallapps lwipcore)

Working example
===============
Working build examples can be found in the
contrib/ports/{win32, unix}/example_app
subdirectory.
To use them, create a build directory and call cmake with
the lwIP root dir:

- mkdir build
- cd build
- cmake ..
- cmake --build .

The CMakeLists.txt will autoselect the correct port
for your system (supported: Linux, Windows, Darwin).

Makefile based build system
===========================
lwIP also maintains file lists for Makefile-based
build systems. Look for Filelists.mk files
in the source tree. We try to maintain them,
but lwIP's mainly focused build system is CMake.
