// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// http://code.google.com/p/protobuf/
//
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//
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package com.google.protobuf;
import com.google.protobuf.Descriptors.Descriptor;
import com.google.protobuf.Descriptors.FieldDescriptor;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
/**
* A table of known extensions, searchable by name or field number. When
* parsing a protocol message that might have extensions, you must provide
* an {@code ExtensionRegistry} in which you have registered any extensions
* that you want to be able to parse. Otherwise, those extensions will just
* be treated like unknown fields.
*
* <p>For example, if you had the {@code .proto} file:
*
* <pre>
* option java_class = "MyProto";
*
* message Foo {
* extensions 1000 to max;
* }
*
* extend Foo {
* optional int32 bar;
* }
* </pre>
*
* Then you might write code like:
*
* <pre>
* ExtensionRegistry registry = ExtensionRegistry.newInstance();
* registry.add(MyProto.bar);
* MyProto.Foo message = MyProto.Foo.parseFrom(input, registry);
* </pre>
*
* <p>Background:
*
* <p>You might wonder why this is necessary. Two alternatives might come to
* mind. First, you might imagine a system where generated extensions are
* automatically registered when their containing classes are loaded. This
* is a popular technique, but is bad design; among other things, it creates a
* situation where behavior can change depending on what classes happen to be
* loaded. It also introduces a security vulnerability, because an
* unprivileged class could cause its code to be called unexpectedly from a
* privileged class by registering itself as an extension of the right type.
*
* <p>Another option you might consider is lazy parsing: do not parse an
* extension until it is first requested, at which point the caller must
* provide a type to use. This introduces a different set of problems. First,
* it would require a mutex lock any time an extension was accessed, which
* would be slow. Second, corrupt data would not be detected until first
* access, at which point it would be much harder to deal with it. Third, it
* could violate the expectation that message objects are immutable, since the
* type provided could be any arbitrary message class. An unpriviledged user
* could take advantage of this to inject a mutable object into a message
* belonging to priviledged code and create mischief.
*
* @author kenton@google.com Kenton Varda
*/
public final class ExtensionRegistry {
/** Construct a new, empty instance. */
public static ExtensionRegistry newInstance() {
return new ExtensionRegistry(
new HashMap<String, ExtensionInfo>(),
new HashMap<DescriptorIntPair, ExtensionInfo>());
}
/** Get the unmodifiable singleton empty instance. */
public static ExtensionRegistry getEmptyRegistry() {
return EMPTY;
}
/** Returns an unmodifiable view of the registry. */
public ExtensionRegistry getUnmodifiable() {
return new ExtensionRegistry(
Collections.unmodifiableMap(extensionsByName),
Collections.unmodifiableMap(extensionsByNumber));
}
/** A (Descriptor, Message) pair, returned by lookup methods. */
public static final class ExtensionInfo {
/** The extension's descriptor. */
public final FieldDescriptor descriptor;
/**
* A default instance of the extension's type, if it has a message type.
* Otherwise, {@code null}.
*/
public final Message defaultInstance;
private ExtensionInfo(FieldDescriptor descriptor) {
this.descriptor = descriptor;
this.defaultInstance = null;
}
private ExtensionInfo(FieldDescriptor descriptor, Message defaultInstance) {
this.descriptor = descriptor;
this.defaultInstance = defaultInstance;
}
}
/**
* Find an extension by fully-qualified field name, in the proto namespace.
* I.e. {@code result.descriptor.fullName()} will match {@code fullName} if
* a match is found.
*
* @return Information about the extension if found, or {@code null}
* otherwise.
*/
public ExtensionInfo findExtensionByName(String fullName) {
return extensionsByName.get(fullName);
}
/**
* Find an extension by containing type and field number.
*
* @return Information about the extension if found, or {@code null}
* otherwise.
*/
public ExtensionInfo findExtensionByNumber(Descriptor containingType,
int fieldNumber) {
return extensionsByNumber.get(
new DescriptorIntPair(containingType, fieldNumber));
}
/** Add an extension from a generated file to the registry. */
public void add(GeneratedMessage.GeneratedExtension<?, ?> extension) {
if (extension.getDescriptor().getJavaType() ==
FieldDescriptor.JavaType.MESSAGE) {
add(new ExtensionInfo(extension.getDescriptor(),
extension.getMessageDefaultInstance()));
} else {
add(new ExtensionInfo(extension.getDescriptor(), null));
}
}
/** Add a non-message-type extension to the registry by descriptor. */
public void add(FieldDescriptor type) {
if (type.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
throw new IllegalArgumentException(
"ExtensionRegistry.add() must be provided a default instance when " +
"adding an embedded message extension.");
}
add(new ExtensionInfo(type, null));
}
/** Add a message-type extension to the registry by descriptor. */
public void add(FieldDescriptor type, Message defaultInstance) {
if (type.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
throw new IllegalArgumentException(
"ExtensionRegistry.add() provided a default instance for a " +
"non-message extension.");
}
add(new ExtensionInfo(type, defaultInstance));
}
// =================================================================
// Private stuff.
private ExtensionRegistry(
Map<String, ExtensionInfo> extensionsByName,
Map<DescriptorIntPair, ExtensionInfo> extensionsByNumber) {
this.extensionsByName = extensionsByName;
this.extensionsByNumber = extensionsByNumber;
}
private final Map<String, ExtensionInfo> extensionsByName;
private final Map<DescriptorIntPair, ExtensionInfo> extensionsByNumber;
private static final ExtensionRegistry EMPTY =
new ExtensionRegistry(
Collections.<String, ExtensionInfo>emptyMap(),
Collections.<DescriptorIntPair, ExtensionInfo>emptyMap());
private void add(ExtensionInfo extension) {
if (!extension.descriptor.isExtension()) {
throw new IllegalArgumentException(
"ExtensionRegistry.add() was given a FieldDescriptor for a regular " +
"(non-extension) field.");
}
extensionsByName.put(extension.descriptor.getFullName(), extension);
extensionsByNumber.put(
new DescriptorIntPair(extension.descriptor.getContainingType(),
extension.descriptor.getNumber()),
extension);
FieldDescriptor field = extension.descriptor;
if (field.getContainingType().getOptions().getMessageSetWireFormat() &&
field.getType() == FieldDescriptor.Type.MESSAGE &&
field.isOptional() &&
field.getExtensionScope() == field.getMessageType()) {
// This is an extension of a MessageSet type defined within the extension
// type's own scope. For backwards-compatibility, allow it to be looked
// up by type name.
extensionsByName.put(field.getMessageType().getFullName(), extension);
}
}
/** A (GenericDescriptor, int) pair, used as a map key. */
private static final class DescriptorIntPair {
final Descriptor descriptor;
final int number;
DescriptorIntPair(Descriptor descriptor, int number) {
this.descriptor = descriptor;
this.number = number;
}
public int hashCode() {
return descriptor.hashCode() * ((1 << 16) - 1) + number;
}
public boolean equals(Object obj) {
if (!(obj instanceof DescriptorIntPair)) return false;
DescriptorIntPair other = (DescriptorIntPair)obj;
return descriptor == other.descriptor && number == other.number;
}
}
}