Metadata
Structure of the gRPC call looks like this:
> :path /package/Method/
> ...
> ... request metadata
> data (request)
< :status 200
< ...
< ... initial metadata
< data (reply)
< grpc-status 0
< ...
< ... trailing metadata
The same as regular HTTP request but with trailers. So client can send request metadata and server can return initial and trailing metadata.
Metadata sent as regular HTTP headers. It may contain printable ascii text with spaces:
auth-token: 0d16ad85-6ce4-4773-a1be-9f62b2e886a3
Or it may contain binary data:
auth-token-bin: DRathWzkR3Ohvp9isuiGow
Binary metadata keys should contain -bin suffix and values should be encoded
using base64 encoding without padding.
Keys with grpc- prefix are reserved for gRPC protocol. You can read more
additional details here: gRPC Wire Format.
grpclib encodes and decodes binary metadata automatically. In Python you
will receive text metadata as str type:
{"auth-token": "0d16ad85-6ce4-4773-a1be-9f62b2e886a3"}
Binary metadata you will receive as bytes type:
{"auth-token-bin": b"\r\x16\xad\x85l\xe4Gs\xa1\xbe\x9fb\xb2\xe8\x86\xa3"}
Client-Side
Sending metadata:
reply = await stub.Method(Request(), metadata={'auth-token': auth_token})
Sending and receiving metadata:
async with stub.Method.open(metadata={'auth-token': auth_token}) as stream:
await stream.recv_initial_metadata()
print(stream.initial_metadata)
await stream.send_message(Request())
reply = await stream.recv_message()
await stream.recv_trailing_metadata()
print(stream.trailing_metadata)
See reference docs for more details: Client.
Server-Side
Receiving and sending metadata:
class Service(ServiceBase):
async def Method(self, stream):
print(stream.metadata) # request metadata
await stream.send_initial_metadata(metadata={
'begin-time': current_time(),
})
request = await stream.recv_message()
...
await stream.send_message(Reply())
await stream.send_trailing_metadata(metadata={
'end-time': current_time(),
})
See reference docs for more details: Server.