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// Copyright 2014 Google Inc. 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.util.io;
import static java.nio.charset.StandardCharsets.UTF_8;
import java.io.IOException;
import java.io.OutputStream;
/**
* A stream that writes to another one, emittig a prefix before every line
* it emits. This stream will also add a newline for every flush; so it's not
* useful for anything other than simple text data (e.g. log files). Here's
* an example which demonstrates how an explicit flush or a flush caused by
* a full buffer causes a newline to be added to the output.
*
* <code>
* foo bar
* baz ba[flush]ng
* boo
* </code>
*
* This results in this output being emitted:
*
* <code>
* my prefix: foo bar
* my prefix: ba
* my prefix: ng
* my prefix: boo
* </code>
*/
public final class LinePrefixingOutputStream extends LineFlushingOutputStream {
private byte[] linePrefix;
private final OutputStream sink;
public LinePrefixingOutputStream(String linePrefix, OutputStream sink) {
this.linePrefix = linePrefix.getBytes(UTF_8);
this.sink = sink;
}
@Override
protected void flushingHook() throws IOException {
synchronized (sink) {
if (len == 0) {
sink.flush();
return;
}
byte lastByte = buffer[len - 1];
boolean lineIsIncomplete = lastByte != NEWLINE;
sink.write(linePrefix);
sink.write(buffer, 0, len);
if (lineIsIncomplete) {
sink.write(NEWLINE);
}
sink.flush();
len = 0;
}
}
}
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