Add LineReader for reading lines with terminators

commonmark/src/main/java/org/commonmark/internal/util/LineReader.java

@@ -0,0 +1,149 @@
+package org.commonmark.internal.util;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.Reader;
+
+/**
+ * Reads lines from a reader like {@link java.io.BufferedReader} but also returns the line terminators.
+ * <p>
+ * Line terminators can be either a line feed {@code "\n"}, carriage return {@code "\r"}, or a carriage return followed
+ * by a line feed {@code "\r\n"}. Call {@link #getLineTerminator()} after {@link #readLine()} to obtain the
+ * corresponding line terminator. If a stream has a line at the end without a terminator, {@link #getLineTerminator()}
+ * returns {@code null}.
+ */
+public class LineReader implements Closeable {
+
+    // Same as java.io.BufferedReader
+    static final int CHAR_BUFFER_SIZE = 8192;
+    static final int EXPECTED_LINE_LENGTH = 80;
+
+    private Reader reader;
+    private char[] cbuf;
+
+    private int position = 0;
+    private int limit = 0;
+
+    private String lineTerminator = null;
+
+    public LineReader(Reader reader) {
+        this.reader = reader;
+        this.cbuf = new char[CHAR_BUFFER_SIZE];
+    }
+
+    /**
+     * Read a line of text.
+     *
+     * @return the line, or {@code null} when the end of the stream has been reached and no more lines can be read
+     */
+    public String readLine() throws IOException {
+        StringBuilder sb = null;
+        boolean cr = false;
+
+        while (true) {
+            if (position >= limit) {
+                fill();
+            }
+
+            if (cr) {
+                // We saw a CR before, check if we have CR LF or just CR.
+                if (position < limit && cbuf[position] == '\n') {
+                    position++;
+                    return line(sb.toString(), "\r\n");
+                } else {
+                    return line(sb.toString(), "\r");
+                }
+            }
+
+            if (position >= limit) {
+                // End of stream, return either the last line without terminator or null for end.
+                return line(sb != null ? sb.toString() : null, null);
+            }
+
+            int start = position;
+            int i = position;
+            for (; i < limit; i++) {
+                char c = cbuf[i];
+                if (c == '\n') {
+                    position = i + 1;
+                    return line(finish(sb, start, i), "\n");
+                } else if (c == '\r') {
+                    if (i + 1 < limit) {
+                        // We know what the next character is, so we can check now whether we have
+                        // a CR LF or just a CR and return.
+                        if (cbuf[i + 1] == '\n') {
+                            position = i + 2;
+                            return line(finish(sb, start, i), "\r\n");
+                        } else {
+                            position = i + 1;
+                            return line(finish(sb, start, i), "\r");
+                        }
+                    } else {
+                        // We don't know what the next character is yet, check on next iteration.
+                        cr = true;
+                        position = i + 1;
+                        break;
+                    }
+                }
+            }
+
+            if (position < i) {
+                position = i;
+            }
+
+            // Haven't found a finished line yet, copy the data from the buffer so that we can fill
+            // the buffer again.
+            if (sb == null) {
+                sb = new StringBuilder(EXPECTED_LINE_LENGTH);
+            }
+            sb.append(cbuf, start, i - start);
+        }
+    }
+
+    /**
+     * Return the line terminator of the last read line from {@link #readLine()}.
+     *
+     * @return {@code "\n"}, {@code "\r"}, {@code "\r\n"}, or {@code null}
+     */
+    public String getLineTerminator() {
+        return lineTerminator;
+    }
+
+    @Override
+    public void close() throws IOException {
+        if (reader == null) {
+            return;
+        }
+        try {
+            reader.close();
+        } finally {
+            reader = null;
+            cbuf = null;
+        }
+    }
+
+    private void fill() throws IOException {
+        int read;
+        do {
+            read = reader.read(cbuf, 0, cbuf.length);
+        } while (read == 0);
+        if (read > 0) {
+            limit = read;
+            position = 0;
+        }
+    }
+
+    private String line(String line, String lineTerminator) {
+        this.lineTerminator = lineTerminator;
+        return line;
+    }
+
+    private String finish(StringBuilder sb, int start, int end) {
+        int len = end - start;
+        if (sb == null) {
+            return new String(cbuf, start, len);
+        } else {
+            return sb.append(cbuf, start, len).toString();
+        }
+    }
+}

commonmark/src/test/java/org/commonmark/internal/util/LineReaderTest.java

@@ -0,0 +1,128 @@
+package org.commonmark.internal.util;
+
+import org.junit.Test;
+
+import java.io.*;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Objects;
+
+import static java.util.stream.Collectors.joining;
+import static org.commonmark.internal.util.LineReader.CHAR_BUFFER_SIZE;
+import static org.junit.Assert.*;
+
+public class LineReaderTest {
+
+    @Test
+    public void testReadLine() throws IOException {
+        assertLines();
+
+        assertLines("", "\n");
+        assertLines("foo", "\n", "bar", "\n");
+        assertLines("foo", "\n", "bar", null);
+        assertLines("", "\n", "", "\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE - 1), "\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE), "\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE) + "b", "\n");
+
+        assertLines("", "\r\n");
+        assertLines("foo", "\r\n", "bar", "\r\n");
+        assertLines("foo", "\r\n", "bar", null);
+        assertLines("", "\r\n", "", "\r\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE - 2), "\r\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE - 1), "\r\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE), "\r\n");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE) + "b", "\r\n");
+
+        assertLines("", "\r");
+        assertLines("foo", "\r", "bar", "\r");
+        assertLines("foo", "\r", "bar", null);
+        assertLines("", "\r", "", "\r");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE - 1), "\r");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE), "\r");
+        assertLines(repeat("a", CHAR_BUFFER_SIZE) + "b", "\r");
+
+        assertLines("", "\n", "", "\r", "", "\r\n", "", "\n");
+        assertLines("what", "\r", "are", "\r", "", "\r", "you", "\r\n", "", "\r\n", "even", "\n", "doing", null);
+    }
+
+    @Test
+    public void testClose() throws IOException {
+        var reader = new InputStreamReader(new ByteArrayInputStream("test".getBytes(StandardCharsets.UTF_8)));
+        var lineReader = new LineReader(reader);
+        lineReader.close();
+        lineReader.close();
+        try {
+            reader.read();
+            fail("Expected read to throw after closing reader");
+        } catch (IOException e) {
+            // Expected
+        }
+    }
+
+    private void assertLines(String... s) throws IOException {
+        assertTrue("Expected parts needs to be even (pairs of content and terminator)", s.length % 2 == 0);
+        var input = Arrays.stream(s).filter(Objects::nonNull).collect(joining(""));
+
+        assertLines(new StringReader(input), s);
+        assertLines(new SlowStringReader(input), s);
+    }
+
+    private static void assertLines(Reader reader, String... expectedParts) throws IOException {
+        try (var lineReader = new LineReader(reader)) {
+            var lines = new ArrayList<>();
+            String line;
+            while ((line = lineReader.readLine()) != null) {
+                lines.add(line);
+                lines.add(lineReader.getLineTerminator());
+            }
+            assertNull(lineReader.getLineTerminator());
+            assertEquals(Arrays.asList(expectedParts), lines);
+        }
+    }
+
+    private static String repeat(String s, int count) {
+        StringBuilder sb = new StringBuilder(s.length() * count);
+        for (int i = 0; i < count; i++) {
+            sb.append(s);
+        }
+        return sb.toString();
+    }
+
+    /**
+     * Reader that only reads 0 or 1 chars at a time to test the corner cases.
+     */
+    private static class SlowStringReader extends Reader {
+
+        private final String s;
+        private int position = 0;
+        private boolean empty = false;
+
+        private SlowStringReader(String s) {
+            this.s = s;
+        }
+
+        @Override
+        public int read(char[] cbuf, int off, int len) throws IOException {
+            Objects.checkFromIndexSize(off, len, cbuf.length);
+            if (len == 0) {
+                return 0;
+            }
+            empty = !empty;
+            if (empty) {
+                // Return 0 every other time to test handling of 0.
+                return 0;
+            }
+            if (position >= s.length()) {
+                return -1;
+            }
+            cbuf[off] = s.charAt(position++);
+            return 1;
+        }
+
+        @Override
+        public void close() throws IOException {
+        }
+    }
+}