[build] fix when openssl is static build fail

[lilinxiong]

In actual usage, I experienced a problem where I set(OpenSSL_DIR /path/lib/cmake/OpenSSL) and then integrated the SRT project into my own by using add_subdirectory. The first CMake configuration would succeed, but the second configuration attempt would fail.

The details are as follows:

set(OpenSSL_DIR ${THIRD_PARTY_DIR}/binaries/openssl-android/${ANDROID_ABI}/lib/cmake/OpenSSL)
message("OpenSSL_DIR:${OpenSSL_DIR}")
find_package(OpenSSL REQUIRED CONFIG)

if (OpenSSL_FOUND)
    message("OpenSSL_FOUND = ${OpenSSL_FOUND}")
    message("OPENSSL_INCLUDE_DIR = ${OPENSSL_INCLUDE_DIR}")
    message("OPENSSL_LIBRARY_DIR = ${OPENSSL_LIBRARY_DIR}")
    message("OPENSSL_LIBRARIES = ${OPENSSL_LIBRARIES}")
endif ()

message("add_subdirectory: srt:${SRT_DIR} ......")
set(ENABLE_APPS OFF)
set(ENABLE_SHARED OFF)
set(USE_OPENSSL_PC OFF)
set(OPENSSL_USE_STATIC_LIBS ON)
add_subdirectory(${SRT_DIR} ./srt-bin)

message("add_subdirectory: srt:${SRT_DIR} done!")

It seems to be ok, but when I do the first cmake config, and the second cmake config with caching, I get different results.

In the above message, OPENSSL_INCLUDE_DIR has a value the first time, and is empty the second time.

After cmake config and troubleshooting again and again, I finally found that: CMakeLists.txt#L175-OPENSSL_USE_STATIC_LIBS will cause cmake config to fail.

The reason is that there will be the same variables in OpenSSLConfig.cmake.

....
if(OPENSSL_USE_STATIC_LIBS)
  set(_ossl_use_static_libs True)
elseif(DEFINED OPENSSL_USE_STATIC_LIBS)
  # We know OPENSSL_USE_STATIC_LIBS is defined and False
  if(_ossl_use_static_libs)
    # OPENSSL_USE_STATIC_LIBS is explicitly false, indicating that shared libraries are
    # required.  However, _ossl_use_static_libs indicates that no shared libraries are
    # available.  The best course of action is to simply return and leave it to CMake to
    # use another OpenSSL config.
    unset(_ossl_use_static_libs)
    unset(CMAKE_IMPORT_FILE_VERSION)
    return()
  endif()
endif()
....

Because there is no cache when cmake config is run for the first time, it works fine, but the second time, there is a cache, which causes failure.

We should not define the same variables as those in config.cmake generated by make install, we should name them differently.

[ethouris]

Ok, let me ask directly: the OPENSSL_ prefix of the variable is the cause of the problem?

[lilinxiong]

Ok, let me ask directly: the OPENSSL_ prefix of the variable is the cause of the problem?

Yes!

[maxsharabayko]

Given the build option is being renamed anyway, might be worth considering #2914 for it then.
I am also not yet sure if this change can go to a patch version v1.5.5 instead of v1.6.0. The API/ABI is not being changed, but the build option name is... Might provide some inconvenience.
Maybe makes sense to keep the old name as an alias and mark it duplicated for 1.5.5, and then remove in 1.6.0?

[lilinxiong]

Given the build option is being renamed anyway, might be worth considering #2914 for it then. I am also not yet sure if this change can go to a patch version v1.5.5 instead of v1.6.0. The API/ABI is not being changed, but the build option name is... Might provide some inconvenience. Maybe makes sense to keep the old name as an alias and mark it duplicated for 1.5.5, and then remove in 1.6.0?

Hmm, it is indeed a good idea, I totally agree. If other developers encounter the same problem as me during this period, they can make temporary modifications so that it can be compiled.

[ethouris]

You can simply check if OPENSSL_USE_STATIC_LIBS is defined as 1 and if so, forcefully set this option to TRUE.