Set version upper bound for protobuf; installs grpcio-tools instead

requirements.bazel.txt

@@ -2,7 +2,7 @@
 coverage>=4.0
 cython>=0.29.8
 enum34>=1.0.4
-protobuf>=3.5.0.post1
+protobuf>=3.5.0.post1, < 4.0dev
 six>=1.10
 wheel>=0.29
 futures>=2.2.0

requirements.txt

@@ -2,7 +2,7 @@
 coverage>=4.0
 cython>=0.29.8
 enum34>=1.0.4
-protobuf>=3.5.0.post1
+protobuf>=3.5.0.post1, < 4.0dev
 six>=1.10
 wheel>=0.29
 # rsa 4.3 is the last version support Python 2

setup.py

@@ -356,7 +356,7 @@ INSTALL_REQUIRES = (
     "enum34>=1.0.4; python_version<'3.4'",
 )
 EXTRAS_REQUIRES = {
-    "protobuf": "protobuf>=3.5.0.post1",
+    'grpcio-tools>={version}'.format(version=grpc_version.VERSION),
 }
 
 SETUP_REQUIRES = INSTALL_REQUIRES + (

tools/distrib/python/grpcio_tools/setup.py

@@ -219,7 +219,7 @@ setuptools.setup(
     ext_modules=extension_modules(),
     packages=setuptools.find_packages('.'),
     install_requires=[
-        'protobuf>=3.5.0.post1',
+        'protobuf>=3.5.0.post1, < 4.0dev',
         'grpcio>={version}'.format(version=grpc_version.VERSION),
     ],
     package_data=package_data(),