Hey folks,
I am looking to add grpc support to mobile networking stack at my
workplace and was wondering if we can simplify the clientInterceptor
interface. I do understand the reasons for it being a little complicated,
but we could come up with a simpler one. I am by no means an expert in
grpc, but wanted to see if we can simplify efforts required by the devs.
This is not a breaking change, my proposal is to introduce a simpler
abstract class which devs can choose to extend rather than implementing
ClientInterceptor. I come from java land and so the proposal is in java,
but should be generalizable.
public abstract class SimpleClientInterceptor<ReqT, RespT> {
/**
* Invoked with outgoing request headers.
* @param requestHeaders request headers that are sent as part of the
request.
*/
protected abstract void onRequestHeaders(Metadata requestHeaders);
/**
* Invoked when a message is sent out from client to server.
* @param message message being sent out.
*/
protected abstract void onRequestMessage(ReqT message);
/**
* Invoked with response headers.
* @param responseHeaders response headers that are received from the server.
*/
protected abstract void onResponseHeaders(Metadata responseHeaders);
/**
* Invoked with message received from the server.
* @param msg message being received.
*/
protected abstract void onResponseMessage(RespT msg);
/**
* Invoked when the call is closed.
* @param status
* @param trailers
*/
protected void onClose(Status status, Metadata trailers) {}
}
Here is the impl draft
<https://gist.github.com/nsivabalan/a60789c97e7d67bb743a64ea3396a163> on
how we could achieve this. Basic idea is to add a ClientCallHandler/wrapper
and call into the interceptor impl where ever required.
As of today, an interceptor which just processes headers looks complicated
as below.
public class HeaderClientInterceptor extends InterceptorChannel {
public HeaderClientInterceptor(InterceptorChannel next){
super(next);
}
@Override
public <ReqT, RespT> ClientCall<ReqT, RespT>
interceptCall(MethodDescriptor<ReqT,
RespT> method,
CallOptions callOptions) {
return new SimpleForwardingClientCall<ReqT,
RespT>(next.newCall(method, callOptions)) {
@Override
public void start(Listener<RespT> responseListener, Metadata
headers) {
// process request headers. add/edit/remove headers.
super.start(new
SimpleForwardingClientCallListener<RespT>(responseListener) {
@Override
public void onHeaders(Metadata headers) {
super.onHeaders(headers);
}
}, headers);
}
};
}
@Override
public String authority() {
return next.authority();
}
}
Definitely, this looks complicated just to process/edit request headers and
demands a learning curve for someone who is looking to implement an
interceptor.
With the new proposal, an interceptor which accesses some headers would be
like below.
public class HeaderInterceptor<ReqT, RespT> extends SimpleClientInterceptor<
ReqT, RespT> {
public HeaderInterceptor(InterceptorChannel next) {
super(next);
}
@Override
protected void onRequestHeaders(Metadata requestHeaders) {
// process request headers. add/ edit / remove headers
}
@Override
protected void onRequestMessage(ReqT message) { }
@Override
protected void onResponseHeaders(Metadata responseHeaders) {
// process response headers. add/edit/remove
}
@Override
protected void onResponseMessage(RespT msg) { }
}
Implementors don't need to worry about calling next entity in the chain as
its taken care by the CallHandler/wrapper. More details can be checked out
here <https://gist.github.com/nsivabalan/a60789c97e7d67bb743a64ea3396a163> on
how to get this done.
Just a reminder, that this is not a breaking change, just that a new
abstract class will be introduced which devs can use if they want to,
instead of the ClientInterceptor interface directly.
Would love to hear your thoughts.
--
Regards,
-Sivabalan
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