src/main/java/com/google/devtools/build/lib/skyframe/FileArtifactValue.java - bazel - Git at Google

 // Copyright 2014 The Bazel Authors. All rights reserved.
 //
 // 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 com.google.devtools.build.lib.skyframe;

 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Preconditions;
 import com.google.common.io.BaseEncoding;
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.actions.FileStateType;
 import com.google.devtools.build.lib.actions.cache.DigestUtils;
 import com.google.devtools.build.lib.actions.cache.Metadata;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
 import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.Symlinks;
 import com.google.devtools.build.skyframe.SkyValue;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Objects;
 import javax.annotation.Nullable;

 /**
  * Stores the actual metadata data of a file. We have the following cases:
  *
  * <ul>
  * <li> an ordinary file, in which case we would expect to see a digest and size;
  * <li> a directory, in which case we would expect to see an mtime;
  * <li> an intentionally omitted file which the build system is aware of but doesn't actually exist,
  *     where all access methods are unsupported;
  * <li> a "middleman marker" object, which has a null digest, 0 size, and mtime of 0.
  * <li> The "self data" of a TreeArtifact, where we would expect to see a digest representing the
  *     artifact's contents, and a size of 0.
  * </ul>
  */
 // TODO(janakr): make this an interface once JDK8 allows us to have static methods on interfaces.
 @Immutable @ThreadSafe
 public abstract class FileArtifactValue implements SkyValue, Metadata {
   private static final class SingletonMarkerValue extends FileArtifactValue implements Singleton {
     @Override
     public FileStateType getType() {
       return FileStateType.NONEXISTENT;
     }

     @Nullable
     @Override
     public byte[] getDigest() {
       return null;
     }

     @Override
     public long getSize() {
       return 0;
     }

     @Override
     public long getModifiedTime() {
       return 0;
     }

     @Override
     public boolean wasModifiedSinceDigest(Path path) throws IOException {
       return false;
     }

     @Override
     public String toString() {
       return "singleton marker artifact value (" + hashCode() + ")";
     }
   }

   private static final class OmittedFileValue extends FileArtifactValue implements Singleton {
     @Override
     public FileStateType getType() {
       return FileStateType.NONEXISTENT;
     }

     @Override
     public byte[] getDigest() {
       throw new UnsupportedOperationException();
     }

     @Override
     public long getSize() {
       throw new UnsupportedOperationException();
     }

     @Override
     public long getModifiedTime() {
       throw new UnsupportedOperationException();
     }

     @Override
     public boolean wasModifiedSinceDigest(Path path) throws IOException {
       return false;
     }

     @Override
     public String toString() {
       return "OMITTED_FILE_MARKER";
     }
   }

   @AutoCodec static final FileArtifactValue DEFAULT_MIDDLEMAN = new SingletonMarkerValue();
   /** Data that marks that a file is not present on the filesystem. */
   @VisibleForTesting @AutoCodec
   public static final FileArtifactValue MISSING_FILE_MARKER = new SingletonMarkerValue();

   /**
    * Represents an omitted file -- we are aware of it but it doesn't exist. All access methods are
    * unsupported.
    */
   @AutoCodec static final FileArtifactValue OMITTED_FILE_MARKER = new OmittedFileValue();

   @AutoCodec.VisibleForSerialization
   @AutoCodec
   static final class DirectoryArtifactValue extends FileArtifactValue {
     private final long mtime;

     @AutoCodec.VisibleForSerialization
     DirectoryArtifactValue(long mtime) {
       this.mtime = mtime;
     }

     @Override
     public FileStateType getType() {
       return FileStateType.DIRECTORY;
     }

     @Nullable
     @Override
     public byte[] getDigest() {
       return null;
     }

     @Override
     public long getModifiedTime() {
       return mtime;
     }

     @Override
     public long getSize() {
       return 0;
     }

     @Override
     public boolean wasModifiedSinceDigest(Path path) throws IOException {
       return false;
     }

     @Override
     public String toString() {
       return MoreObjects.toStringHelper(this).add("mtime", mtime).toString();
     }
   }

   @AutoCodec.VisibleForSerialization
   @AutoCodec
   static final class RegularFileArtifactValue extends FileArtifactValue {
     private final byte[] digest;
     @Nullable private final FileContentsProxy proxy;
     private final long size;

     @AutoCodec.VisibleForSerialization
     RegularFileArtifactValue(byte[] digest, @Nullable FileContentsProxy proxy, long size) {
       this.digest = Preconditions.checkNotNull(digest);
       this.proxy = proxy;
       this.size = size;
     }

     @Override
     public FileStateType getType() {
       return FileStateType.REGULAR_FILE;
     }

     @Override
     public byte[] getDigest() {
       return digest;
     }

     @Override
     public long getSize() {
       return size;
     }

     @Override
     public boolean wasModifiedSinceDigest(Path path) throws IOException {
       if (proxy == null) {
         return false;
       }
       FileStatus stat = path.statIfFound(Symlinks.FOLLOW);
       return stat == null || !stat.isFile() || !proxy.equals(FileContentsProxy.create(stat));
     }

     @Override
     public long getModifiedTime() {
       throw new UnsupportedOperationException(
           "regular file's mtime should never be called. (" + this + ")");
     }

     @Override
     public String toString() {
       return MoreObjects.toStringHelper(this)
           .add("digest", BaseEncoding.base16().lowerCase().encode(digest))
           .add("size", size)
           .add("proxy", proxy).toString();
     }

     @Override
     public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
       if (!(o instanceof RegularFileArtifactValue)) {
         return false;
       }
       RegularFileArtifactValue r = (RegularFileArtifactValue) o;
       return Arrays.equals(digest, r.digest) && Objects.equals(proxy, r.proxy) && size == r.size;
     }

     @Override
     public int hashCode() {
       return (proxy != null ? 127 * proxy.hashCode() : 0)
           + 37 * Long.hashCode(getSize()) + Arrays.hashCode(getDigest());
     }
   }

   static final class RemoteFileArtifactValue extends FileArtifactValue {
     private final byte[] digest;
     private final long size;
     private final long modifiedTime;
     private final int locationIndex;

     RemoteFileArtifactValue(byte[] digest, long size, long modifiedTime, int locationIndex) {
       this.digest = digest;
       this.size = size;
       this.modifiedTime = modifiedTime;
       this.locationIndex = locationIndex;
     }

     @Override
     public FileStateType getType() {
       return FileStateType.REGULAR_FILE;
     }

     @Override
     public byte[] getDigest() {
       return digest;
     }

     @Override
     public long getSize() {
       return size;
     }

     @Override
     public long getModifiedTime() {
       return modifiedTime;
     }

     @Override
     public int getLocationIndex() {
       return locationIndex;
     }

     @Override
     public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
       if (!(o instanceof RemoteFileArtifactValue)) {
         return false;
       }
       RemoteFileArtifactValue r = (RemoteFileArtifactValue) o;
       return Arrays.equals(digest, r.digest)
           && size == r.size
           && modifiedTime == r.modifiedTime
           && locationIndex == r.locationIndex;
     }

     @Override
     public int hashCode() {
       return Objects.hash(Arrays.hashCode(digest), size, modifiedTime, locationIndex);
     }

     @Override
     public boolean wasModifiedSinceDigest(Path path) {
       throw new UnsupportedOperationException();
     }
   }

   static FileArtifactValue create(Artifact artifact, FileValue fileValue) throws IOException {
     boolean isFile = fileValue.isFile();
     FileContentsProxy proxy = getProxyFromFileStateValue(fileValue.realFileStateValue());
     return create(artifact.getPath(), isFile, isFile ? fileValue.getSize() : 0, proxy,
         isFile ? fileValue.getDigest() : null);
   }

   static FileArtifactValue create(
       Artifact artifact, FileValue fileValue, @Nullable byte[] injectedDigest) throws IOException {
     boolean isFile = fileValue.isFile();
     FileContentsProxy proxy = getProxyFromFileStateValue(fileValue.realFileStateValue());
     return create(artifact.getPath(), isFile, isFile ? fileValue.getSize() : 0, proxy,
         injectedDigest);
   }

   @VisibleForTesting
   public static FileArtifactValue create(Artifact artifact) throws IOException {
     return create(artifact.getPath());
   }

   @VisibleForTesting
   public static FileArtifactValue create(Path path) throws IOException {
     // Caution: there's a race condition between stating the file and computing the
     // digest. We need to stat first, since we're using the stat to detect changes.
     // We follow symlinks here to be consistent with getDigest.
     FileStatus stat = path.stat(Symlinks.FOLLOW);
     return create(path, stat.isFile(), stat.getSize(), FileContentsProxy.create(stat), null);
   }

   private static FileArtifactValue create(
       Path path, boolean isFile, long size, FileContentsProxy proxy, @Nullable byte[] digest)
           throws IOException {
     if (!isFile) {
       // In this case, we need to store the mtime because the action cache uses mtime for
       // directories to determine if this artifact has changed. We want this code path to go away
       // somehow (maybe by implementing FileSet in Skyframe).
       return new DirectoryArtifactValue(path.getLastModifiedTime());
     }
     if (digest == null) {
       digest = DigestUtils.getDigestOrFail(path, size);
     }
     Preconditions.checkState(digest != null, path);
     return new RegularFileArtifactValue(digest, proxy, size);
   }

   public static FileArtifactValue createForVirtualActionInput(byte[] digest, long size) {
     return new RegularFileArtifactValue(digest, /*proxy=*/ null, size);
   }

   public static FileArtifactValue createNormalFile(
       byte[] digest, @Nullable FileContentsProxy proxy, long size) {
     return new RegularFileArtifactValue(digest, proxy, size);
   }

   static FileArtifactValue createNormalFile(FileValue fileValue) {
     FileContentsProxy proxy = getProxyFromFileStateValue(fileValue.realFileStateValue());
     return new RegularFileArtifactValue(fileValue.getDigest(), proxy, fileValue.getSize());
   }

   private static FileContentsProxy getProxyFromFileStateValue(FileStateValue value) {
     if (value instanceof FileStateValue.RegularFileStateValue) {
       return ((FileStateValue.RegularFileStateValue) value).getContentsProxy();
     } else if (value instanceof FileStateValue.SpecialFileStateValue) {
       return ((FileStateValue.SpecialFileStateValue) value).getContentsProxy();
     }
     return null;
   }

   @VisibleForTesting
   public static FileArtifactValue createNormalFile(byte[] digest, long size) {
     return createNormalFile(digest, /*proxy=*/null, size);
   }

   public static FileArtifactValue createDirectory(long mtime) {
     return new DirectoryArtifactValue(mtime);
   }

   /**
    * Creates a FileArtifactValue used as a 'proxy' input for other ArtifactValues.
    * These are used in {@link com.google.devtools.build.lib.actions.ActionCacheChecker}.
    */
   static FileArtifactValue createProxy(byte[] digest) {
     Preconditions.checkNotNull(digest);
     return createNormalFile(digest, /*proxy=*/ null, /*size=*/ 0);
   }

   @Override
   public abstract FileStateType getType();

   @Nullable
   @Override
   public abstract byte[] getDigest();

   @Override
   public abstract long getSize();

   @Override
   public abstract long getModifiedTime();

   /**
    * Provides a best-effort determination whether the file was changed since the digest was
    * computed. This method performs file system I/O, so may be expensive. It's primarily intended to
    * avoid storing bad cache entries in an action cache. It should return true if there is a chance
    * that the file was modified since the digest was computed. Better not upload if we are not sure
    * that the cache entry is reliable.
    */
   public abstract boolean wasModifiedSinceDigest(Path path) throws IOException;

   @Override
   public boolean equals(Object o) {
     if (this == o) {
       return true;
     }
     if (!(o instanceof Metadata)) {
       return false;
     }
     if ((this instanceof Singleton) || (o instanceof Singleton)) {
       return false;
     }
     Metadata m = (Metadata) o;
     if (getType() != m.getType()) {
       return false;
     }
     if (getDigest() != null) {
       return Arrays.equals(getDigest(), m.getDigest()) && getSize() == m.getSize();
     } else {
       return getModifiedTime() == m.getModifiedTime();
     }
   }

   @Override
   public int hashCode() {
     if (this instanceof Singleton) {
       return System.identityHashCode(this);
     }
     // Hash digest by content, not reference.
     if (getDigest() != null) {
       return 37 * Long.hashCode(getSize()) + Arrays.hashCode(getDigest());
     } else {
       return Long.hashCode(getModifiedTime());
     }
   }
 }
	// Copyright 2014 The Bazel Authors. All rights reserved.
	//
	// 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 com.google.devtools.build.lib.skyframe;

	import com.google.common.annotations.VisibleForTesting;
	import com.google.common.base.MoreObjects;
	import com.google.common.base.Preconditions;
	import com.google.common.io.BaseEncoding;
	import com.google.devtools.build.lib.actions.Artifact;
	import com.google.devtools.build.lib.actions.FileStateType;
	import com.google.devtools.build.lib.actions.cache.DigestUtils;
	import com.google.devtools.build.lib.actions.cache.Metadata;
	import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
	import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
	import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
	import com.google.devtools.build.lib.vfs.FileStatus;
	import com.google.devtools.build.lib.vfs.Path;
	import com.google.devtools.build.lib.vfs.Symlinks;
	import com.google.devtools.build.skyframe.SkyValue;
	import java.io.IOException;
	import java.util.Arrays;
	import java.util.Objects;
	import javax.annotation.Nullable;

	/**
	* Stores the actual metadata data of a file. We have the following cases:
	*
	* <ul>
	* <li> an ordinary file, in which case we would expect to see a digest and size;
	* <li> a directory, in which case we would expect to see an mtime;
	* <li> an intentionally omitted file which the build system is aware of but doesn't actually exist,
	* where all access methods are unsupported;
	* <li> a "middleman marker" object, which has a null digest, 0 size, and mtime of 0.
	* <li> The "self data" of a TreeArtifact, where we would expect to see a digest representing the
	* artifact's contents, and a size of 0.
	* </ul>
	*/
	// TODO(janakr): make this an interface once JDK8 allows us to have static methods on interfaces.
	@Immutable @ThreadSafe
	public abstract class FileArtifactValue implements SkyValue, Metadata {
	private static final class SingletonMarkerValue extends FileArtifactValue implements Singleton {
	@Override
	public FileStateType getType() {
	return FileStateType.NONEXISTENT;
	}

	@Nullable
	@Override
	public byte[] getDigest() {
	return null;
	}

	@Override
	public long getSize() {
	return 0;
	}

	@Override
	public long getModifiedTime() {
	return 0;
	}

	@Override
	public boolean wasModifiedSinceDigest(Path path) throws IOException {
	return false;
	}

	@Override
	public String toString() {
	return "singleton marker artifact value (" + hashCode() + ")";
	}
	}

	private static final class OmittedFileValue extends FileArtifactValue implements Singleton {
	@Override
	public FileStateType getType() {
	return FileStateType.NONEXISTENT;
	}

	@Override
	public byte[] getDigest() {
	throw new UnsupportedOperationException();
	}

	@Override
	public long getSize() {
	throw new UnsupportedOperationException();
	}

	@Override
	public long getModifiedTime() {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean wasModifiedSinceDigest(Path path) throws IOException {
	return false;
	}

	@Override
	public String toString() {
	return "OMITTED_FILE_MARKER";
	}
	}

	@AutoCodec static final FileArtifactValue DEFAULT_MIDDLEMAN = new SingletonMarkerValue();
	/** Data that marks that a file is not present on the filesystem. */
	@VisibleForTesting @AutoCodec
	public static final FileArtifactValue MISSING_FILE_MARKER = new SingletonMarkerValue();

	/**
	* Represents an omitted file -- we are aware of it but it doesn't exist. All access methods are
	* unsupported.
	*/
	@AutoCodec static final FileArtifactValue OMITTED_FILE_MARKER = new OmittedFileValue();

	@AutoCodec.VisibleForSerialization
	@AutoCodec
	static final class DirectoryArtifactValue extends FileArtifactValue {
	private final long mtime;

	@AutoCodec.VisibleForSerialization
	DirectoryArtifactValue(long mtime) {
	this.mtime = mtime;
	}

	@Override
	public FileStateType getType() {
	return FileStateType.DIRECTORY;
	}

	@Nullable
	@Override
	public byte[] getDigest() {
	return null;
	}

	@Override
	public long getModifiedTime() {
	return mtime;
	}

	@Override
	public long getSize() {
	return 0;
	}

	@Override
	public boolean wasModifiedSinceDigest(Path path) throws IOException {
	return false;
	}

	@Override
	public String toString() {
	return MoreObjects.toStringHelper(this).add("mtime", mtime).toString();
	}
	}

	@AutoCodec.VisibleForSerialization
	@AutoCodec
	static final class RegularFileArtifactValue extends FileArtifactValue {
	private final byte[] digest;
	@Nullable private final FileContentsProxy proxy;
	private final long size;

	@AutoCodec.VisibleForSerialization
	RegularFileArtifactValue(byte[] digest, @Nullable FileContentsProxy proxy, long size) {
	this.digest = Preconditions.checkNotNull(digest);
	this.proxy = proxy;
	this.size = size;
	}

	@Override
	public FileStateType getType() {
	return FileStateType.REGULAR_FILE;
	}

	@Override
	public byte[] getDigest() {
	return digest;
	}

	@Override
	public long getSize() {
	return size;
	}

	@Override
	public boolean wasModifiedSinceDigest(Path path) throws IOException {
	if (proxy == null) {
	return false;
	}
	FileStatus stat = path.statIfFound(Symlinks.FOLLOW);
	return stat == null \|\| !stat.isFile() \|\| !proxy.equals(FileContentsProxy.create(stat));
	}

	@Override
	public long getModifiedTime() {
	throw new UnsupportedOperationException(
	"regular file's mtime should never be called. (" + this + ")");
	}

	@Override
	public String toString() {
	return MoreObjects.toStringHelper(this)
	.add("digest", BaseEncoding.base16().lowerCase().encode(digest))
	.add("size", size)
	.add("proxy", proxy).toString();
	}

	@Override
	public boolean equals(Object o) {
	if (this == o) {
	return true;
	}
	if (!(o instanceof RegularFileArtifactValue)) {
	return false;
	}
	RegularFileArtifactValue r = (RegularFileArtifactValue) o;
	return Arrays.equals(digest, r.digest) && Objects.equals(proxy, r.proxy) && size == r.size;
	}

	@Override
	public int hashCode() {
	return (proxy != null ? 127 * proxy.hashCode() : 0)
	+ 37 * Long.hashCode(getSize()) + Arrays.hashCode(getDigest());
	}
	}

	static final class RemoteFileArtifactValue extends FileArtifactValue {
	private final byte[] digest;
	private final long size;
	private final long modifiedTime;
	private final int locationIndex;

	RemoteFileArtifactValue(byte[] digest, long size, long modifiedTime, int locationIndex) {
	this.digest = digest;
	this.size = size;
	this.modifiedTime = modifiedTime;
	this.locationIndex = locationIndex;
	}

	@Override
	public FileStateType getType() {
	return FileStateType.REGULAR_FILE;
	}

	@Override
	public byte[] getDigest() {
	return digest;
	}

	@Override
	public long getSize() {
	return size;
	}

	@Override
	public long getModifiedTime() {
	return modifiedTime;
	}

	@Override
	public int getLocationIndex() {
	return locationIndex;
	}

	@Override
	public boolean equals(Object o) {
	if (this == o) {
	return true;
	}
	if (!(o instanceof RemoteFileArtifactValue)) {
	return false;
	}
	RemoteFileArtifactValue r = (RemoteFileArtifactValue) o;
	return Arrays.equals(digest, r.digest)
	&& size == r.size
	&& modifiedTime == r.modifiedTime
	&& locationIndex == r.locationIndex;
	}

	@Override
	public int hashCode() {
	return Objects.hash(Arrays.hashCode(digest), size, modifiedTime, locationIndex);
	}

	@Override
	public boolean wasModifiedSinceDigest(Path path) {
	throw new UnsupportedOperationException();
	}
	}

	static FileArtifactValue create(Artifact artifact, FileValue fileValue) throws IOException {
	boolean isFile = fileValue.isFile();
	FileContentsProxy proxy = getProxyFromFileStateValue(fileValue.realFileStateValue());
	return create(artifact.getPath(), isFile, isFile ? fileValue.getSize() : 0, proxy,
	isFile ? fileValue.getDigest() : null);
	}

	static FileArtifactValue create(
	Artifact artifact, FileValue fileValue, @Nullable byte[] injectedDigest) throws IOException {
	boolean isFile = fileValue.isFile();
	FileContentsProxy proxy = getProxyFromFileStateValue(fileValue.realFileStateValue());
	return create(artifact.getPath(), isFile, isFile ? fileValue.getSize() : 0, proxy,
	injectedDigest);
	}

	@VisibleForTesting
	public static FileArtifactValue create(Artifact artifact) throws IOException {
	return create(artifact.getPath());
	}

	@VisibleForTesting
	public static FileArtifactValue create(Path path) throws IOException {
	// Caution: there's a race condition between stating the file and computing the
	// digest. We need to stat first, since we're using the stat to detect changes.
	// We follow symlinks here to be consistent with getDigest.
	FileStatus stat = path.stat(Symlinks.FOLLOW);
	return create(path, stat.isFile(), stat.getSize(), FileContentsProxy.create(stat), null);
	}

	private static FileArtifactValue create(
	Path path, boolean isFile, long size, FileContentsProxy proxy, @Nullable byte[] digest)
	throws IOException {
	if (!isFile) {
	// In this case, we need to store the mtime because the action cache uses mtime for
	// directories to determine if this artifact has changed. We want this code path to go away
	// somehow (maybe by implementing FileSet in Skyframe).
	return new DirectoryArtifactValue(path.getLastModifiedTime());
	}
	if (digest == null) {
	digest = DigestUtils.getDigestOrFail(path, size);
	}
	Preconditions.checkState(digest != null, path);
	return new RegularFileArtifactValue(digest, proxy, size);
	}

	public static FileArtifactValue createForVirtualActionInput(byte[] digest, long size) {
	return new RegularFileArtifactValue(digest, /proxy=/ null, size);
	}

	public static FileArtifactValue createNormalFile(
	byte[] digest, @Nullable FileContentsProxy proxy, long size) {
	return new RegularFileArtifactValue(digest, proxy, size);
	}

	static FileArtifactValue createNormalFile(FileValue fileValue) {
	FileContentsProxy proxy = getProxyFromFileStateValue(fileValue.realFileStateValue());
	return new RegularFileArtifactValue(fileValue.getDigest(), proxy, fileValue.getSize());
	}

	private static FileContentsProxy getProxyFromFileStateValue(FileStateValue value) {
	if (value instanceof FileStateValue.RegularFileStateValue) {
	return ((FileStateValue.RegularFileStateValue) value).getContentsProxy();
	} else if (value instanceof FileStateValue.SpecialFileStateValue) {
	return ((FileStateValue.SpecialFileStateValue) value).getContentsProxy();
	}
	return null;
	}

	@VisibleForTesting
	public static FileArtifactValue createNormalFile(byte[] digest, long size) {
	return createNormalFile(digest, /proxy=/null, size);
	}

	public static FileArtifactValue createDirectory(long mtime) {
	return new DirectoryArtifactValue(mtime);
	}

	/**
	* Creates a FileArtifactValue used as a 'proxy' input for other ArtifactValues.
	* These are used in {@link com.google.devtools.build.lib.actions.ActionCacheChecker}.
	*/
	static FileArtifactValue createProxy(byte[] digest) {
	Preconditions.checkNotNull(digest);
	return createNormalFile(digest, /proxy=/ null, /size=/ 0);
	}

	@Override
	public abstract FileStateType getType();

	@Nullable
	@Override
	public abstract byte[] getDigest();

	@Override
	public abstract long getSize();

	@Override
	public abstract long getModifiedTime();

	/**
	* Provides a best-effort determination whether the file was changed since the digest was
	* computed. This method performs file system I/O, so may be expensive. It's primarily intended to
	* avoid storing bad cache entries in an action cache. It should return true if there is a chance
	* that the file was modified since the digest was computed. Better not upload if we are not sure
	* that the cache entry is reliable.
	*/
	public abstract boolean wasModifiedSinceDigest(Path path) throws IOException;

	@Override
	public boolean equals(Object o) {
	if (this == o) {
	return true;
	}
	if (!(o instanceof Metadata)) {
	return false;
	}
	if ((this instanceof Singleton) \|\| (o instanceof Singleton)) {
	return false;
	}
	Metadata m = (Metadata) o;
	if (getType() != m.getType()) {
	return false;
	}
	if (getDigest() != null) {
	return Arrays.equals(getDigest(), m.getDigest()) && getSize() == m.getSize();
	} else {
	return getModifiedTime() == m.getModifiedTime();
	}
	}

	@Override
	public int hashCode() {
	if (this instanceof Singleton) {
	return System.identityHashCode(this);
	}
	// Hash digest by content, not reference.
	if (getDigest() != null) {
	return 37 * Long.hashCode(getSize()) + Arrays.hashCode(getDigest());
	} else {
	return Long.hashCode(getModifiedTime());
	}
	}
	}