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/*
* 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 com.google.common.base.Preconditions;
/**
* Provider of managed channels for transport agnostic consumption.
*
* Implementations can be automatically discovered by gRPC via Java's SPI mechanism. For
* automatic discovery, the implementation must have a zero-argument constructor and include
* a resource named {@code META-INF/services/io.grpc.ManagedChannelProvider} in their JAR. The
* file's contents should be the implementation's class name.
*
*
Implementations should not throw. If they do, it may interrupt class loading. If
* exceptions may reasonably occur for implementation-specific reasons, implementations should
* generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}.
*/
@Internal
public abstract class ManagedChannelProvider {
/**
* Returns the ClassLoader-wide default channel.
*
* @throws ProviderNotFoundException if no provider is available
*/
public static ManagedChannelProvider provider() {
ManagedChannelProvider provider = ManagedChannelRegistry.getDefaultRegistry().provider();
if (provider == null) {
throw new ProviderNotFoundException("No functional channel service provider found. "
+ "Try adding a dependency on the grpc-okhttp, grpc-netty, or grpc-netty-shaded "
+ "artifact");
}
return provider;
}
/**
* Whether this provider is available for use, taking the current environment into consideration.
* If {@code false}, no other methods are safe to be called.
*/
protected abstract boolean isAvailable();
/**
* A priority, from 0 to 10 that this provider should be used, taking the current environment into
* consideration. 5 should be considered the default, and then tweaked based on environment
* detection. A priority of 0 does not imply that the provider wouldn't work; just that it should
* be last in line.
*/
protected abstract int priority();
/**
* Creates a new builder with the given host and port.
*/
protected abstract ManagedChannelBuilder builderForAddress(String name, int port);
/**
* Creates a new builder with the given target URI.
*/
protected abstract ManagedChannelBuilder builderForTarget(String target);
/**
* Creates a new builder with the given target URI and credentials. Returns an error-string result
* if unable to understand the credentials.
*/
protected NewChannelBuilderResult newChannelBuilder(String target, ChannelCredentials creds) {
return NewChannelBuilderResult.error("ChannelCredentials are unsupported");
}
public static final class NewChannelBuilderResult {
private final ManagedChannelBuilder channelBuilder;
private final String error;
private NewChannelBuilderResult(ManagedChannelBuilder channelBuilder, String error) {
this.channelBuilder = channelBuilder;
this.error = error;
}
public static NewChannelBuilderResult channelBuilder(ManagedChannelBuilder builder) {
return new NewChannelBuilderResult(Preconditions.checkNotNull(builder), null);
}
public static NewChannelBuilderResult error(String error) {
return new NewChannelBuilderResult(null, Preconditions.checkNotNull(error));
}
public ManagedChannelBuilder getChannelBuilder() {
return channelBuilder;
}
public String getError() {
return error;
}
}
/**
* Thrown when no suitable {@link ManagedChannelProvider} objects can be found.
*/
public static final class ProviderNotFoundException extends RuntimeException {
private static final long serialVersionUID = 1;
public ProviderNotFoundException(String msg) {
super(msg);
}
}
}