IO: Add a method for reading lines

Change-Id: Ib7be76aa7ac889354ad4782e2b64d4221a0e25b9

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/IOReadLineTest.java

@@ -0,0 +1,116 @@
+/*
+ * Copyright (C) 2015, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.util;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.BufferedReader;
+import java.io.ByteArrayInputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
+import java.util.ArrayList;
+import java.util.Collection;
+
+import org.eclipse.jgit.lib.Constants;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class IOReadLineTest {
+	@Parameter(0)
+	public boolean buffered;
+
+	@Parameter(1)
+	public int sizeHint;
+
+	@SuppressWarnings("boxing")
+	@Parameters(name="buffered={0}, sizeHint={1}")
+	public static Collection<Object[]> getParameters() {
+		Boolean[] bv = {false, true};
+		Integer[] sv = {-1, 0, 1, 2, 3, 4, 64};
+		Collection<Object[]> params = new ArrayList<>(bv.length * sv.length);
+		for (boolean b : bv) {
+			for (Integer s : sv) {
+				params.add(new Object[]{b, s});
+			}
+		}
+		return params;
+	}
+
+	@Test
+	public void testReadLine() throws Exception {
+		Reader r = newReader("foo\nbar\nbaz\n");
+		assertEquals("foo\n", readLine(r));
+		assertEquals("bar\n", readLine(r));
+		assertEquals("baz\n", readLine(r));
+		assertEquals("", readLine(r));
+	}
+
+	@Test
+	public void testReadLineNoTrailingNewline() throws Exception {
+		Reader r = newReader("foo\nbar\nbaz");
+		assertEquals("foo\n", readLine(r));
+		assertEquals("bar\n", readLine(r));
+		assertEquals("baz", readLine(r));
+		assertEquals("", readLine(r));
+	}
+
+	private String readLine(Reader r) throws Exception {
+		return IO.readLine(r, sizeHint);
+	}
+
+	private Reader newReader(String in) {
+		Reader r = new InputStreamReader(
+				new ByteArrayInputStream(Constants.encode(in)));
+		if (buffered) {
+			r = new BufferedReader(r);
+		}
+		assertEquals(Boolean.valueOf(buffered),
+				Boolean.valueOf(r.markSupported()));
+		return r;
+	}
+}

org.eclipse.jgit/src/org/eclipse/jgit/util/IO.java

@@ -51,6 +51,7 @@ import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.Reader;
 import java.nio.ByteBuffer;
 import java.nio.channels.ReadableByteChannel;
 import java.text.MessageFormat;
@@ -371,6 +372,74 @@ public class IO {
 		return l;
 	}
 
+	/**
+	 * Read the next line from a reader.
+	 * <p>
+	 * Like {@link java.io.BufferedReader#readLine()}, but only treats {@code \n}
+	 * as end-of-line, and includes the trailing newline.
+	 *
+	 * @param in
+	 *            the reader to read from.
+	 * @param sizeHint
+	 *            hint for buffer sizing; 0 or negative for default.
+	 * @return the next line from the input, always ending in {@code \n} unless
+	 *         EOF was reached.
+	 * @throws IOException
+	 *             there was an error reading from the stream.
+	 */
+	public static String readLine(Reader in, int sizeHint) throws IOException {
+		if (in.markSupported()) {
+			if (sizeHint <= 0) {
+				sizeHint = 1024;
+			}
+			StringBuilder sb = new StringBuilder(sizeHint);
+			char[] buf = new char[sizeHint];
+			while (true) {
+				in.mark(sizeHint);
+				int n = in.read(buf);
+				if (n < 0) {
+					in.reset();
+					return sb.toString();
+				}
+				for (int i = 0; i < n; i++) {
+					if (buf[i] == '\n') {
+						resetAndSkipFully(in, ++i);
+						sb.append(buf, 0, i);
+						return sb.toString();
+					}
+				}
+				if (n > 0) {
+					sb.append(buf, 0, n);
+				}
+				resetAndSkipFully(in, n);
+			}
+		} else {
+			StringBuilder buf = sizeHint > 0
+					? new StringBuilder(sizeHint)
+					: new StringBuilder();
+			int i;
+			while ((i = in.read()) != -1) {
+				char c = (char) i;
+				buf.append(c);
+				if (c == '\n') {
+					break;
+				}
+			}
+			return buf.toString();
+		}
+	}
+
+	private static void resetAndSkipFully(Reader fd, long toSkip) throws IOException {
+		fd.reset();
+		while (toSkip > 0) {
+			long r = fd.skip(toSkip);
+			if (r <= 0) {
+				throw new EOFException(JGitText.get().shortSkipOfBlock);
+			}
+			toSkip -= r;
+		}
+	}
+
 	private IO() {
 		// Don't create instances of a static only utility.
 	}