io.grpc.NameResolver Maven / Gradle / Ivy
/*
* Copyright 2015 The gRPC Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.grpc;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.net.URI;
import java.util.List;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;
/**
* A pluggable component that resolves a target {@link URI} and return addresses to the caller.
*
* A {@code NameResolver} uses the URI's scheme to determine whether it can resolve it, and uses
* the components after the scheme for actual resolution.
*
*
The addresses and attributes of a target may be changed over time, thus the caller registers a
* {@link Listener} to receive continuous updates.
*
*
A {@code NameResolver} does not need to automatically re-resolve on failure. Instead, the
* {@link Listener} is responsible for eventually (after an appropriate backoff period) invoking
* {@link #refresh()}.
*
* @since 1.0.0
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1770")
@ThreadSafe
public abstract class NameResolver {
/**
* Returns the authority used to authenticate connections to servers. It must be
* from a trusted source, because if the authority is tampered with, RPCs may be sent to the
* attackers which may leak sensitive user data.
*
*
An implementation must generate it without blocking, typically in line, and
* must keep it unchanged. {@code NameResolver}s created from the same factory
* with the same argument must return the same authority.
*
* @since 1.0.0
*/
public abstract String getServiceAuthority();
/**
* Starts the resolution.
*
* @param listener used to receive updates on the target
* @since 1.0.0
*/
public abstract void start(Listener listener);
/**
* Stops the resolution. Updates to the Listener will stop.
*
* @since 1.0.0
*/
public abstract void shutdown();
/**
* Re-resolve the name.
*
*
Can only be called after {@link #start} has been called.
*
*
This is only a hint. Implementation takes it as a signal but may not start resolution
* immediately. It should never throw.
*
*
The default implementation is no-op.
*
* @since 1.0.0
*/
public void refresh() {}
/**
* Factory that creates {@link NameResolver} instances.
*
* @since 1.0.0
*/
public abstract static class Factory {
/**
* The port number used in case the target or the underlying naming system doesn't provide a
* port number.
*
* @deprecated this will be deleted along with {@link #newNameResolver(URI, Attributes)} in
* a future release.
*
* @since 1.0.0
*/
@Deprecated
public static final Attributes.Key PARAMS_DEFAULT_PORT =
Attributes.Key.create("params-default-port");
/**
* If the NameResolver wants to support proxy, it should inquire this {@link ProxyDetector}.
* See documentation on {@link ProxyDetector} about how proxies work in gRPC.
*
* @deprecated this will be deleted along with {@link #newNameResolver(URI, Attributes)} in
* a future release
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/5113")
@Deprecated
public static final Attributes.Key PARAMS_PROXY_DETECTOR =
Attributes.Key.create("params-proxy-detector");
/**
* Creates a {@link NameResolver} for the given target URI, or {@code null} if the given URI
* cannot be resolved by this factory. The decision should be solely based on the scheme of the
* URI.
*
* @param targetUri the target URI to be resolved, whose scheme must not be {@code null}
* @param params optional parameters. Canonical keys are defined as {@code PARAMS_*} fields in
* {@link Factory}.
*
* @deprecated Implement {@link #newNameResolver(URI, NameResolver.Helper)} instead. This is
* going to be deleted in a future release.
*
* @since 1.0.0
*/
@Nullable
@Deprecated
public NameResolver newNameResolver(URI targetUri, Attributes params) {
throw new UnsupportedOperationException("This method is going to be deleted");
}
/**
* Creates a {@link NameResolver} for the given target URI, or {@code null} if the given URI
* cannot be resolved by this factory. The decision should be solely based on the scheme of the
* URI.
*
* @param targetUri the target URI to be resolved, whose scheme must not be {@code null}
* @param helper utility that may be used by the NameResolver implementation
*
* @since 1.19.0
*/
// TODO(zhangkun83): make this abstract when the other override is deleted
@Nullable
public NameResolver newNameResolver(URI targetUri, Helper helper) {
return newNameResolver(
targetUri,
Attributes.newBuilder()
.set(PARAMS_DEFAULT_PORT, helper.getDefaultPort())
.set(PARAMS_PROXY_DETECTOR, helper.getProxyDetector())
.build());
}
/**
* Returns the default scheme, which will be used to construct a URI when {@link
* ManagedChannelBuilder#forTarget(String)} is given an authority string instead of a compliant
* URI.
*
* @since 1.0.0
*/
public abstract String getDefaultScheme();
}
/**
* Receives address updates.
*
* All methods are expected to return quickly.
*
* @since 1.0.0
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1770")
@ThreadSafe
public interface Listener {
/**
* Handles updates on resolved addresses and attributes.
*
*
Implementations will not modify the given {@code servers}.
*
* @param servers the resolved server addresses. An empty list will trigger {@link #onError}
* @param attributes extra information from naming system.
* @since 1.3.0
*/
void onAddresses(
List servers, @ResolutionResultAttr Attributes attributes);
/**
* Handles an error from the resolver. The listener is responsible for eventually invoking
* {@link #refresh()} to re-attempt resolution.
*
* @param error a non-OK status
* @since 1.0.0
*/
void onError(Status error);
}
/**
* Annotation for name resolution result attributes. It follows the annotation semantics defined
* by {@link Attributes}.
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/4972")
@Retention(RetentionPolicy.SOURCE)
@Documented
public @interface ResolutionResultAttr {}
/**
* A utility object passed to {@link Factory#newNameResolver(URI, NameResolver.Helper)}.
*
* @since 1.19.0
*/
public abstract static class Helper {
/**
* The port number used in case the target or the underlying naming system doesn't provide a
* port number.
*
* @since 1.19.0
*/
public abstract int getDefaultPort();
/**
* If the NameResolver wants to support proxy, it should inquire this {@link ProxyDetector}.
* See documentation on {@link ProxyDetector} about how proxies work in gRPC.
*
* @since 1.19.0
*/
public abstract ProxyDetector getProxyDetector();
}
}