[protobuf_cpp] Updated to Protobuf 3.5.1 + fixed protoc issue

Protobuf has been updated to 3.5.1, it's not the last version (3.6.1)
because last version cause trouble during compilation and needs more
work.

This patch also fixes the issue with hardcoded local path for protoc which
could not work. Protobuf needs a version of "protoc" (its compiler, used
to produce .py file from .proto files) compiled for the host platform.
Official binaries for protoc are available, the recipe will download the
one suitable for host and use it.
If the platform is not supported, building may still work if the right "protoc"
is available in search path.

Author: goffi-contrib

ci/constants.py

@@ -44,6 +44,9 @@ class TargetPython(Enum):
     'm2crypto',
     'netifaces',
     'Pillow',
+    # requires autoconf system dependency on host
+    # https://api.travis-ci.org/v3/job/450538715/log.txt
+    'protobuf_cpp',
     # https://github.com/kivy/python-for-android/issues/1405
     'psycopg2',
     'pygame',

pythonforandroid/recipes/protobuf_cpp/__init__.py

@@ -1,21 +1,60 @@
 from pythonforandroid.recipe import PythonRecipe
-from pythonforandroid.logger import shprint
+from pythonforandroid.logger import shprint, info_notify
 from pythonforandroid.util import current_directory, shutil
 from os.path import exists, join, dirname
 import sh
 from multiprocessing import cpu_count
-
-
 from pythonforandroid.toolchain import info
+import sys
+import os
 
 
 class ProtobufCppRecipe(PythonRecipe):
     name = 'protobuf_cpp'
-    version = '3.1.0'
+    version = '3.5.1'
     url = 'https://github.com/google/protobuf/releases/download/v{version}/protobuf-python-{version}.tar.gz'
     call_hostpython_via_targetpython = False
     depends = ['cffi', 'setuptools']
     site_packages_name = 'google/protobuf/pyext'
+    protoc_dir = None
+
+    def prebuild_arch(self, arch):
+        super(ProtobufCppRecipe, self).prebuild_arch(arch)
+        # During building, host needs to transpile .proto files to .py
+        # ideally with the same version as protobuf runtime, or with an older one.
+        # Because protoc is compiled for target (i.e. Android), we need an other binary
+        # which can be run by host.
+        # To make it easier, we download prebuild protoc binary adapted to the platform
+
+        info_notify("Downloading protoc compiler for your platform")
+        url_prefix = "https://github.com/protocolbuffers/protobuf/releases/download/v{version}".format(version=self.version)
+        if sys.platform.startswith('linux'):
+            info_notify("GNU/Linux detected")
+            filename = "protoc-{version}-linux-x86_64.zip".format(version=self.version)
+        elif sys.platform.startswith('darwin'):
+            info_notify("Mac OS X detected")
+            filename = "protoc-{version}-osx-x86_64.zip".format(version=self.version)
+        else:
+            info_notify("Your platform is not supported, but recipe can still "
+                        "be built if you have a valid protoc (<={version}) in "
+                        "your path".format(version=self.version))
+            return
+
+        protoc_url = join(url_prefix, filename)
+        self.protoc_dir = join(self.ctx.build_dir, "tools", "protoc")
+        if os.path.exists(join(self.protoc_dir, "bin", "protoc")):
+            info_notify("protoc found, no download needed")
+            return
+        try:
+            os.makedirs(self.protoc_dir)
+        except OSError as e:
+            # if dir already exists (errno 17), we ignore the error
+            if e.errno != 17:
+                raise e
+        info_notify("Will download into {dest_dir}".format(dest_dir=self.protoc_dir))
+        self.download_file(protoc_url, join(self.protoc_dir, filename))
+        with current_directory(self.protoc_dir):
+            shprint(sh.unzip, join(self.protoc_dir, filename))
 
     def build_arch(self, arch):
         env = self.get_recipe_env(arch)
@@ -85,7 +124,9 @@ def install_python_package(self, arch):
 
     def get_recipe_env(self, arch):
         env = super(ProtobufCppRecipe, self).get_recipe_env(arch)
-        env['PROTOC'] = '/home/fipo/soft/protobuf-3.1.0/src/protoc'
+        if self.protoc_dir is not None:
+            # we need protoc with binary for host platform
+            env['PROTOC'] = join(self.protoc_dir, 'bin', 'protoc')
         env['PYTHON_ROOT'] = self.ctx.get_python_install_dir()
         env['TARGET_OS'] = 'OS_ANDROID_CROSSCOMPILE'
         env['CFLAGS'] += (
@@ -103,7 +144,7 @@ def get_recipe_env(self, arch):
         env['LDFLAGS'] += (
             ' -L' + self.ctx.ndk_dir +
             '/sources/cxx-stl/gnu-libstdc++/' + self.ctx.toolchain_version +
-            '/libs/' + arch.arch + ' -lgnustl_shared -lpython2.7')
+            '/libs/' + arch.arch + ' -lgnustl_shared -lpython2.7 -landroid -llog')
 
         env['LDSHARED'] = env['CC'] + ' -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions'
         return env