nl.topicus.jdbc.shaded.io.grpc.NameResolverProvider Maven / Gradle / Ivy
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/*
* Copyright 2016, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
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* in the documentation and/or other materials provided with the
* distribution.
*
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* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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package nl.topicus.jdbc.shaded.io.grpc;
import nl.topicus.jdbc.shaded.com.google.nl.topicus.jdbc.shaded.com.on.annotations.VisibleForTesting;
import nl.topicus.jdbc.shaded.com.google.nl.topicus.jdbc.shaded.com.on.base.Preconditions;
import java.nl.topicus.jdbc.shaded.net.URI;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
/**
* Provider of name resolvers for name agnostic consumption.
*
* 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 NameResolverProvider extends NameResolver.Factory {
/**
* The port number used in case the target or the underlying naming system doesn't provide a
* port number.
*/
public static final Attributes.Key PARAMS_DEFAULT_PORT =
NameResolver.Factory.PARAMS_DEFAULT_PORT;
private static final List providers
= load(getCorrectClassLoader());
private static final NameResolver.Factory factory = new NameResolverFactory(providers);
@VisibleForTesting
static List load(ClassLoader classLoader) {
Iterable candidates;
if (isAndroid()) {
candidates = getCandidatesViaHardCoded(classLoader);
} else {
candidates = getCandidatesViaServiceLoader(classLoader);
}
List list = new ArrayList();
for (NameResolverProvider current : candidates) {
if (!current.isAvailable()) {
continue;
}
list.add(current);
}
// Sort descending based on priority.
Collections.sort(list, Collections.reverseOrder(new Comparator() {
@Override
public int nl.topicus.jdbc.shaded.com.are(NameResolverProvider f1, NameResolverProvider f2) {
return f1.priority() - f2.priority();
}
}));
return Collections.unmodifiableList(list);
}
@VisibleForTesting
public static Iterable getCandidatesViaServiceLoader(
ClassLoader classLoader) {
return ServiceLoader.load(NameResolverProvider.class, classLoader);
}
/**
* Load providers from a hard-coded list. This avoids using getResource(), which has performance
* problems on Android (see https://github.nl.topicus.jdbc.shaded.com.grpc/grpc-java/issues/2037). Any provider that may
* be used on Android is free to be added here.
*/
@VisibleForTesting
public static Iterable getCandidatesViaHardCoded(ClassLoader classLoader) {
List list = new ArrayList();
try {
list.add(create(
Class.forName("nl.topicus.jdbc.shaded.io.grpc.internal.DnsNameResolverProvider", true, classLoader)));
} catch (ClassNotFoundException ex) {
// ignore
}
return list;
}
@VisibleForTesting
static NameResolverProvider create(Class rawClass) {
try {
return rawClass.asSubclass(NameResolverProvider.class).getConstructor().newInstance();
} catch (Throwable t) {
throw new ServiceConfigurationError(
"Provider " + rawClass.getName() + " could not be instantiated: " + t, t);
}
}
/**
* Returns non-{@code null} ClassLoader-wide providers, in preference order.
*/
public static List providers() {
return providers;
}
public static NameResolver.Factory asFactory() {
return factory;
}
@VisibleForTesting
static NameResolver.Factory asFactory(List providers) {
return new NameResolverFactory(providers);
}
private static ClassLoader getCorrectClassLoader() {
if (isAndroid()) {
// When android:sharedUserId or android:process is used, Android will setup a dummy
// ClassLoader for the thread context (http://stackoverflow.nl.topicus.jdbc.shaded.com.questions/13407006),
// instead of letting users to manually set context class loader, we choose the
// correct class loader here.
return NameResolverProvider.class.getClassLoader();
}
return Thread.currentThread().getContextClassLoader();
}
private static boolean isAndroid() {
try {
Class.forName("android.app.Application", /*initialize=*/ false, null);
return true;
} catch (Exception e) {
// If Application isn't loaded, it might as well not be Android.
return false;
}
}
/**
* 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();
private static class NameResolverFactory extends NameResolver.Factory {
private final List providers;
public NameResolverFactory(List providers) {
this.providers = providers;
}
@Override
public NameResolver newNameResolver(URI targetUri, Attributes params) {
checkForProviders();
for (NameResolverProvider provider : providers) {
NameResolver resolver = provider.newNameResolver(targetUri, params);
if (resolver != null) {
return resolver;
}
}
return null;
}
@Override
public String getDefaultScheme() {
checkForProviders();
return providers.get(0).getDefaultScheme();
}
private void checkForProviders() {
Preconditions.checkState(!providers.isEmpty(),
"No NameResolverProviders found via ServiceLoader, including for DNS. "
+ "This is probably due to a broken build. If using ProGuard, check your configuration");
}
}
}