[build] Fix OpenSSL static linking error (#2369).

* Use OPENSSL_USE_STATIC_LIBS option to leverage `pkg-config --static` for openssl static linking.
* Removed useless 'OPENSSL_USE_STATIC_LIBS' parameter in Android build script.
* Updated docs.

CMakeLists.txt

@@ -148,6 +148,7 @@ option(ENABLE_CODE_COVERAGE "Enable code coverage reporting" OFF)
 option(ENABLE_MONOTONIC_CLOCK "Enforced clock_gettime with monotonic clock on GC CV" ${ENABLE_MONOTONIC_CLOCK_DEFAULT})
 option(ENABLE_STDCXX_SYNC "Use C++11 chrono and threads for timing instead of pthreads" ${ENABLE_STDCXX_SYNC_DEFAULT})
 option(USE_OPENSSL_PC "Use pkg-config to find OpenSSL libraries" ON)
+option(OPENSSL_USE_STATIC_LIBS "Link OpenSSL libraries statically." OFF)
 option(USE_BUSY_WAITING "Enable more accurate sending times at a cost of potentially higher CPU load" OFF)
 option(USE_GNUSTL "Get c++ library/headers from the gnustl.pc" OFF)
 option(ENABLE_SOCK_CLOEXEC "Enable setting SOCK_CLOEXEC on a socket" ON)
@@ -345,6 +346,10 @@ if (ENABLE_ENCRYPTION)
 		# fall back to find_package method otherwise
 		if (USE_OPENSSL_PC)
 			pkg_check_modules(SSL ${SSL_REQUIRED_MODULES})
+			if (OPENSSL_USE_STATIC_LIBS)
+				# use `pkg-config --static xxx` found libs
+				set(SSL_LIBRARIES ${SSL_STATIC_LIBRARIES})
+			endif()
 		endif()
 		if (SSL_FOUND)
 			# We have some cases when pkg-config is improperly configured

configure-data.tcl

@@ -57,6 +57,7 @@ set cmake_options {
     enable-thread-check "Enable #include <threadcheck.h> that implements THREAD_* macros"
     enable-stdc++-sync "Use standard C++11 chrono/threads instead of pthread wrapper (default: OFF, on Windows: ON)"
     use-openssl-pc "Use pkg-config to find OpenSSL libraries (default: ON)"
+    openssl-use-static-libs "Link OpenSSL statically (default: OFF)."
     use-busy-waiting "Enable more accurate sending times at a cost of potentially higher CPU load (default: OFF)"
     use-gnustl "Get c++ library/headers from the gnustl.pc"
     enable-sock-cloexec "Enable setting SOCK_CLOEXEC on a socket (default: ON)"

docs/build/build-options.md

@@ -61,6 +61,7 @@ Option details are given further below.
 | [`USE_ENCLIB`](#use_enclib)                                  | 1.3.3 | `STRING`  | openssl    | Encryption library to be used (`openssl`, `gnutls`, `mbedtls`).  |
 | [`USE_GNUSTL`](#use_gnustl)                                  | 1.3.4 | `BOOL`    | OFF        | Use `pkg-config` with the `gnustl` package name to extract the header and library path for the C++ standard library.  |
 | [`USE_OPENSSL_PC`](#use_openssl_pc)                          | 1.3.0 | `BOOL`    | ON         | Use `pkg-config` to find OpenSSL libraries.  |
+| [`OPENSSL_USE_STATIC_LIBS`](#openssl_use_static_libs)        | 1.5.0 | `BOOL`    | OFF        | Link OpenSSL statically.  |
 | [`USE_STATIC_LIBSTDCXX`](#use_static_libstdcxx)              | 1.2.0 | `BOOL`    | OFF        | Enforces linking the SRT library against the static libstdc++ library. |
 | [`WITH_COMPILER_PREFIX`](#with_compiler_prefix)              | 1.3.0 | `STRING`  | OFF        | Sets C/C++ toolchains as `<prefix><c-compiler>` and `<prefix><c++-compiler>`, overriding the default compiler. |
 | [`WITH_COMPILER_TYPE`](#with_compiler_type)                  | 1.3.0 | `STRING`  | OFF        | Sets the compiler type to be used (values: gcc, cc, clang, etc.). |
@@ -551,6 +552,12 @@ built-in one).
 When ON, uses `pkg-config` to find OpenSSL libraries. You can turn this OFF to 
 force `cmake` to find OpenSSL by its own preferred method.
 
+### OPENSSL_USE_STATIC_LIBS
+**`--openssl-use-static-libs`** (default: OFF)
+
+When ON, OpenSSL libraries are linked statically.
+When `pkg-config`(`-DUSE_OPENSSL_PC=ON`) is used, static OpenSSL libraries are listed in `SSL_STATIC_LIBRARIES`. See `<prefix>_STATIC` in [CMake's FindPkgConfig](https://cmake.org/cmake/help/latest/module/FindPkgConfig.html).
+On Windows additionally links `crypt32.lib`.
 
 #### USE_STATIC_LIBSTDCXX
 **`--use-static-libstdc++`** (default: OFF)

scripts/ShowProjectConfig.cmake

@@ -165,6 +165,7 @@ function(ShowProjectConfig)
       "    ENABLE_MONOTONIC_CLOCK: ${ENABLE_MONOTONIC_CLOCK}\n"
       "    ENABLE_STDCXX_SYNC: ${ENABLE_STDCXX_SYNC}\n"
       "    USE_OPENSSL_PC: ${USE_OPENSSL_PC}\n"
+      "    OPENSSL_USE_STATIC_LIBS: ${OPENSSL_USE_STATIC_LIBS}\n"
       "    USE_BUSY_WAITING: ${USE_BUSY_WAITING}\n"
       "    USE_GNUSTL: ${USE_GNUSTL}\n"
       "    ENABLE_SOCK_CLOEXEC: ${ENABLE_SOCK_CLOEXEC}\n"

scripts/build-android/mksrt

@@ -17,7 +17,7 @@ done
 
 cd $SRC_DIR
 ./configure --use-enclib=$ENC_LIB \
---use-openssl-pc=OFF --OPENSSL_USE_STATIC_LIBS=TRUE \
+--use-openssl-pc=OFF \
 --OPENSSL_INCLUDE_DIR=$INSTALL_DIR/include \
 --OPENSSL_CRYPTO_LIBRARY=$INSTALL_DIR/lib/libcrypto.a --OPENSSL_SSL_LIBRARY=$INSTALL_DIR/lib/libssl.a \
 --STATIC_MBEDTLS=FALSE \