Add zlib recipe

To solve the build issues of python's zlib module

Note: This library has been slightly modified in order to force the soname to include the library version and to be android's compatible (ends with `.so`, which android library mechanism needs to successfully load a shared library). This has been done this way to avoid linkage problems with android's system library `libz`

Author: opacam

pythonforandroid/recipes/zlib/__init__.py

@@ -0,0 +1,47 @@
+import sh
+import glob
+from os.path import exists, join
+from pythonforandroid.toolchain import Recipe, shprint
+from pythonforandroid.util import current_directory
+from multiprocessing import cpu_count
+
+
+class ZlibRecipe(Recipe):
+    version = '1.2.11'
+    url = 'https://zlib.net/zlib-{version}.tar.gz'
+    depends = []
+    patches = ['lib-version.patch']
+
+    @property
+    def version_link(self):
+        return self.version.replace('.', '')
+
+    def should_build(self, arch):
+        return not exists(
+            join(self.ctx.get_libs_dir(arch.arch),
+                 'libz{}.so'.format(self.version_link)))
+
+    def build_arch(self, arch):
+        super(ZlibRecipe, self).build_arch(arch)
+        build_dir = self.get_build_dir(arch.arch)
+
+        with current_directory(build_dir):
+            env = self.get_recipe_env(arch)
+
+            shprint(sh.cmake,
+                    '-DP4A_LINK_VERSION={}'.format(self.version.replace('.', '')),
+                    '-DANDROID_ABI={}'.format(arch.arch),
+                    '-DANDROID_NATIVE_API_LEVEL={}'.format(self.ctx.ndk_api),
+
+                    '-DCMAKE_TOOLCHAIN_FILE={}'.format(
+                        join(self.ctx.ndk_dir, 'build', 'cmake',
+                             'android.toolchain.cmake')),
+                    _env=env)
+            shprint(sh.make, '-j' + str(cpu_count()), _env=env)
+
+            # copy shared libs to libs collection
+            so_libs = glob.glob(join(build_dir, '*.so'))
+            self.install_libs(arch, *so_libs)
+
+
+recipe = ZlibRecipe()

pythonforandroid/recipes/zlib/lib-version.patch

@@ -0,0 +1,28 @@
+--- zlib/CMakeLists.txt.orig	2017-01-15 18:29:40.000000000 +0100
++++ zlib/CMakeLists.txt	2019-02-16 23:05:55.699949378 +0100
+@@ -186,7 +186,6 @@ endif(MINGW)
+ add_library(zlib SHARED ${ZLIB_SRCS} ${ZLIB_ASMS} ${ZLIB_DLL_SRCS} ${ZLIB_PUBLIC_HDRS} ${ZLIB_PRIVATE_HDRS})
+ add_library(zlibstatic STATIC ${ZLIB_SRCS} ${ZLIB_ASMS} ${ZLIB_PUBLIC_HDRS} ${ZLIB_PRIVATE_HDRS})
+ set_target_properties(zlib PROPERTIES DEFINE_SYMBOL ZLIB_DLL)
+-set_target_properties(zlib PROPERTIES SOVERSION 1)
+
+ if(NOT CYGWIN)
+     # This property causes shared libraries on Linux to have the full version
+@@ -196,12 +195,14 @@ if(NOT CYGWIN)
+     #
+     # This has no effect with MSVC, on that platform the version info for
+     # the DLL comes from the resource file win32/zlib1.rc
+-    set_target_properties(zlib PROPERTIES VERSION ${ZLIB_FULL_VERSION})
+ endif()
+
+ if(UNIX)
+-    # On unix-like platforms the library is almost always called libz
+-   set_target_properties(zlib zlibstatic PROPERTIES OUTPUT_NAME z)
++    # On unix-like platforms the library is almost always called libz,
++    # and in python-for-android we rename the library to avoid conflicts with
++    # with android's system libs
++   set(libzname "z${P4A_LINK_VERSION}")
++   set_target_properties(zlib zlibstatic PROPERTIES OUTPUT_NAME ${libzname})
+    if(NOT APPLE)
+      set_target_properties(zlib PROPERTIES LINK_FLAGS "-Wl,--version-script,\"${CMAKE_CURRENT_SOURCE_DIR}/zlib.map\"")
+    endif()