It may be normal in the gRPC world, but I'll note that a beginner was unexpectedly addicted to writing a gRPC client in Python.
Work based on Python Quick Start. First, download the sample code. Now use the slightly older v1.19.0 instead of the latest v1.25.0. The reason will be described later.
git clone -b v1.19.0 https://github.com/grpc/grpc
Let's change the taste from the document and create a Python project in a different directory. Again, we'll use v1.19.0.
mkdir python-grpc
cd python-grpc
pipenv --python 3.7
pipenv install grpcio~=1.19.0
pipenv install --dev grpcio-tools
pipenv shell
mkdir pb
Create a py from the proto file using the grpc_tools.protoc command and write it to the pb directory.
python -m grpc_tools.protoc \
-I../grpc/examples/protos/ \
--python_out=pb \
--grpc_python_out=pb \
../grpc/examples/protos/helloworld.proto
-I: In addition to include in proto, the location of the proto file processed by this command must also be specified with -I.--python_out: xxx_pb2.py Specifies the directory to output the file.--grpc_python_out: xxx_pb2_grpc.py Specifies the directory to output the file.First, the -I option is required. Without it, you will get the error File does not reside within any path specified using --proto_path (or -I) .. It is unreasonable why I can not find it because I have specified the position of proto properly.
Also, the -I option has a trick: if you specify a higher directory, for example -I ../grpc/examples/, the file will be generated in pb / protos instead of pb. If you don't know, you'll be at a loss as to where the file went.
Also, the description of the --help option does not mention the difference between --python_out and --grpc_python_out. Although there are differences as described above, it is unreasonable to have another option because it is not enough to just fail to import if you put it in another directory.
When I try to read the created one from python, I get an error.
$ python
>>> import pb.helloworld_pb2_grpc
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/tyamamiya/tmp/python-grpc/pb/helloworld_pb2_grpc.py", line 4, in <module>
import helloworld_pb2 as helloworld__pb2
ModuleNotFoundError: No module named 'helloworld_pb2'
The relative path of the generated code is wrong (it seems to be Python2 style). It can't be helped, so add pb / __ init__.py according to python: use relative imports in generated modules.
import sys
from pathlib import Path
sys.path.append(str(Path(__file__).parent))
If it doesn't work because there are no errors, it is better to set environment variables and execute. Now start the server and client and check the operation.
$ python ../grpc/examples/python/helloworld/greeter_server.py &
$ export GRPC_TRACE=all
$ export GRPC_VERBOSITY=DEBUG
$ python ../grpc/examples/python/helloworld/greeter_client.py
...A lot of things come out.
Greeter client received: Hello, you!
$ unset GRPC_TRACE
$ unset GRPC_VERBOSITY
Good.
Occasionally there is a proto file that includes google.api. The proto file itself is located at https://github.com/googleapis/googleapis/tree/master/google/api, so you can download it and specify it with -I, but I included it in the converted code. The contents of proto are not included. I felt that it would be imported with the option --include_imports, but that is not the case, and I need to install the converted one separately.
pipenv install googleapis-common-protos
Well, if you know this, it doesn't matter.
missing selected ALPN property.When connecting to an existing gRPC server over TLS with the latest Python grpcio library, you may get missing selected ALPN property..
D1125 19:20:57.313482000 4619453888 security_handshaker.cc:186] Security handshake failed: {"created":"@1574677257.313465000","description":"Cannot check peer: missing selected ALPN property.","file":"src/core/lib/security/security_connector/ssl_utils.cc","file_line":118}
I1125 19:20:57.313703000 4619453888 subchannel.cc:1000] Connect failed: {"created":"@1574677257.313465000","description":"Cannot check peer: missing selected ALPN property.","file":"src/core/lib/security/security_connector/ssl_utils.cc","file_line":118}
Searching with this keyword reveals a lot of interesting facts, but from https://github.com/grpc/grpc/issues/18710, it seems that you can't access a server that doesn't support the ALPN check feature.
It can't be helped, so use the old version v1.19.0 to make the tea muddy. https://stackoverflow.com/questions/57397723/grpc-client-failing-to-connect-to-server-with-tls-certificates
The combination of Python and gRPC feels unfamiliar.
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