com.facebook.buck.rules.OutputKey.java Source code

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Here is the source code for com.facebook.buck.rules.OutputKey.java

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/*
 * Copyright 2012-present Facebook, Inc.
 *
 * 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.facebook.buck.rules;

import com.google.common.hash.HashCode;
import com.google.common.hash.Hashing;

import java.io.File;
import java.nio.ByteBuffer;

import javax.annotation.Nullable;

/**
 * OutputKey encapsulates computation of SHA-1 content hashing for outputs.
 */
public class OutputKey implements Comparable<OutputKey> {
    @Nullable
    private final HashCode hashCode;
    private final boolean idempotent;

    /**
     * OutputKeys that have no associated outputs (output == null) are treated as sentinels that are
     * distinct from other idempotent OutputKeys. OutputKeys associated with actual outputs are
     * non-idempotent if the outputs cannot be read during key generation.
     */
    public OutputKey(@Nullable File output) {
        if (output == null) {
            this.hashCode = null;
            this.idempotent = true;
        } else {
            this.hashCode = hashOutput(output);
            this.idempotent = (hashCode != null);
        }
    }

    @Nullable
    private HashCode hashOutput(File output) {
        if (output == null) {
            return null;
        }
        // Use RuleKey's Builder to do the hard work of hashing the output file.
        RuleKey.Builder builder = RuleKey.builder();
        builder.set(output.getPath(), output);
        RuleKey ruleKey = builder.build();
        if (!ruleKey.isIdempotent()) {
            return null;
        }
        return ruleKey.getHashCode();
    }

    public boolean isIdempotent() {
        return idempotent;
    }

    public boolean isSentinel() {
        return (isIdempotent() && hashCode == null);
    }

    /**
     * Sentinel OutputKeys are output as a string of 's' characters, and non-idempotent OutputKeys are
     * normally output as a string of 'x' characters, but when comparing two sets of OutputKeys in
     * textual form it is necessary to mangle one of the two sets, so that non-idempotent OutputKeys
     * are never considered equal.
     */
    public String toString(boolean mangleNonIdempotent) {
        if (isSentinel() || !isIdempotent()) {
            String replacementChar = isSentinel() ? "s" : (!mangleNonIdempotent ? "x" : "y");
            return new String(new char[Hashing.sha1().bits() / 4]).replace("\0", replacementChar);
        }
        return hashCode.toString();
    }

    @Override
    public String toString() {
        return toString(false);
    }

    /**
     * Order non-idempotent OutputKeys as less than sentinels, which in turn are less than all
     * idempotent non-sentinels.
     *
     * non-idempotent < sentinel < idempotent non-sentinel
     */
    @Override
    public int compareTo(OutputKey other) {
        // Handle non-idempotent keys.
        if (!isIdempotent()) {
            if (!other.isIdempotent()) {
                return 0;
            }
            return -1;
        } else if (!other.isIdempotent()) {
            return 1;
        }

        // Handle sentinel keys.
        if (isSentinel()) {
            if (other.isSentinel()) {
                return 0;
            }
            return -1;
        } else if (other.isSentinel()) {
            return 1;
        }

        // Handle idempotent non-sentinel keys.
        return ByteBuffer.wrap(hashCode.asBytes()).compareTo(ByteBuffer.wrap(other.hashCode.asBytes()));
    }

    /**
     * Treat non-idempotent OutputKeys as unequal to everything, including other non-idempotent
     * OutputKeys.
     */
    @Override
    public boolean equals(Object that) {
        if (!(that instanceof OutputKey)) {
            return false;
        }
        OutputKey other = (OutputKey) that;
        if (!isIdempotent() || !other.isIdempotent()) {
            return false;
        }
        return (compareTo(other) == 0);
    }

    @Override
    public int hashCode() {
        if (!isIdempotent()) {
            return 0;
        }
        return super.hashCode();
    }

    /**
     * Helper method used to avoid memoizing non-idempotent OutputKeys.
     */
    public static OutputKey filter(OutputKey outputKey) {
        if (!outputKey.isIdempotent()) {
            return null;
        }
        return outputKey;
    }
}