gradle-master/subprojects/internal-testing/src/main/groovy/org/gradle/util/internal/RedirectStdOutAndErr.java
/*
 * Copyright 2021 the original author or 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 org.gradle.util.internal;

import org.apache.commons.io.output.NullOutputStream;
import org.apache.commons.io.output.ProxyOutputStream;
import org.apache.commons.io.output.TeeOutputStream;
import org.junit.rules.MethodRule;
import org.junit.runners.model.FrameworkMethod;
import org.junit.runners.model.Statement;

import java.io.ByteArrayOutputStream;
import java.io.OutputStream;
import java.io.PrintStream;

/**
 * A Junit rule which replaces stdout and stderr with mocks for the duration of the test, and restores them at the end
 * of the test.
 */
public class RedirectStdOutAndErr implements MethodRule {
    private PrintStream originalStdOut;
    private PrintStream originalStdErr;
    private ByteArrayOutputStream stdoutContent = new ByteArrayOutputStream();
    private ByteArrayOutputStream stderrContent = new ByteArrayOutputStream();
    private RedirectingOutputStream stdOutRouter = new RedirectingOutputStream(NullOutputStream.NULL_OUTPUT_STREAM);
    private RedirectingOutputStream stdErrRouter = new RedirectingOutputStream(NullOutputStream.NULL_OUTPUT_STREAM);
    private PrintStream stdOutPrintStream = new PrintStream(new TeeOutputStream(stdoutContent, stdOutRouter));
    private PrintStream stdErrPrintStream = new PrintStream(new TeeOutputStream(stderrContent, stdErrRouter));

    @Override
    public Statement apply(final Statement base, FrameworkMethod method, Object target) {
        return new Statement() {
            @Override
            public void evaluate() throws Throwable {
                originalStdOut = System.out;
                originalStdErr = System.err;
                stdOutRouter.setOut(originalStdOut);
                stdErrRouter.setOut(originalStdErr);
                try {
                    System.setOut(stdOutPrintStream);
                    System.setErr(stdErrPrintStream);
                    base.evaluate();
                } finally {
                    System.setOut(originalStdOut);
                    System.setErr(originalStdErr);
                    stdOutRouter = null;
                    stdErrRouter = null;
                    stdOutPrintStream = null;
                    stdErrPrintStream = null;
                    stdoutContent = null;
                    stderrContent = null;
                }
            }
        };
    }

    public PrintStream getStdOutPrintStream() {
        return stdOutPrintStream;
    }

    public PrintStream getStdErrPrintStream() {
        return stdErrPrintStream;
    }

    public String getStdErr() {
        return stderrContent.toString();
    }

    public String getStdOut() {
        return stdoutContent.toString();
    }

    private static class RedirectingOutputStream extends ProxyOutputStream {
        RedirectingOutputStream(OutputStream out) {
            super(out);
        }

        void setOut(OutputStream out) {
            this.out = out;
        }
    }
}
