Add ReverseFileReader from logging plugin

Change-Id: I8fcf1d9e686834dfad9d93c177b97b0ea19fd742
Reviewed-on: http://gerrit.dmdirc.com/2325
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

src/com/dmdirc/util/io/ReverseFileReader.java

@@ -0,0 +1,261 @@
+/*
+ * Copyright (c) 2006-2012 DMDirc Developers
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package com.dmdirc.util.io;
+
+import java.io.EOFException;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.Stack;
+
+/**
+ * Reads a file in reverse.
+ */
+public class ReverseFileReader {
+
+    /** File to manipulate. */
+    private RandomAccessFile file;
+
+    /** Number of bytes to skip backwards at a time. */
+    private byte seekLength = 50;
+
+    /**
+     * Create a new ReverseFileReader.
+     *
+     * @param filename File to open.
+     * @throws FileNotFoundException If the file is not a regular file.
+     * @throws SecurityException If a security manager exists and its checkRead method denies read access to the file.
+     * @throws IOException If there is an error seeking to the end of the file.
+     */
+    public ReverseFileReader(final String filename) throws FileNotFoundException,
+            SecurityException, IOException {
+        file = new RandomAccessFile(filename, "r");
+        reset();
+    }
+
+    /**
+     * Create a new ReverseFileReader.
+     *
+     * @param myFile Existing file to use.
+     * @throws FileNotFoundException If the file is not a regular file.
+     * @throws SecurityException If a security manager exists and its checkRead method denies read access to the file.
+     * @throws IOException If there is an error seeking to the end of the file.
+     */
+    public ReverseFileReader(final File myFile) throws FileNotFoundException,
+            SecurityException, IOException {
+        file = new RandomAccessFile(myFile, "r");
+        reset();
+    }
+
+    /**
+     * Reset the file pointer to the end of the file.
+     *
+     * @throws IOException If there is an error seeking, or the file is closed.
+     */
+    public void reset() throws IOException {
+        if (file == null) {
+            throw new IOException("File has been closed.");
+        }
+        file.seek(file.length());
+    }
+
+    /**
+     * Get the current seekLength.
+     *
+     * @return current seekLength
+     */
+    public byte getSeekLength() {
+        return seekLength;
+    }
+
+    /**
+     * Set the seekLength.
+     *
+     * @param newValue New value for seekLength
+     */
+    public void setSeekLength(final byte newValue) {
+        seekLength = newValue;
+    }
+
+    /**
+     * Close the file pointer.
+     * This should be called before removing the reference to this object
+     *
+     * @throws IOException If there is an error closing the file, or if it has been closed already.
+     */
+    public void close() throws IOException {
+        if (file == null) {
+            throw new IOException("File has been closed.");
+        }
+        file.close();
+        file = null;
+    }
+
+    /**
+     * Get the next full line.
+     *
+     * @return The next full line.
+     * @throws EOFException If there is no more lines.
+     * @throws IOException If an error reading or seeking occured, or if the fiel is closed.
+     */
+    public String getNextLine() throws EOFException, IOException {
+        if (file == null) {
+            throw new IOException("File has been closed.");
+        }
+        // Used to store result to output.
+
+        final ArrayList<Byte> line = new ArrayList<Byte>(seekLength);
+        // Used to store position in file pre-read
+        long fp = 0;
+        // Used to store position in file when this is called
+        long startfp = 0;
+        // Used to store read bytes
+        byte[] bytes;
+        // Distance seeked
+        int seekDistance = 0;
+
+        // Check current position, if 0 we are at the start of the file
+        // and should throw an exception.
+        startfp = file.getFilePointer();
+        if (startfp == 0) {
+            throw new EOFException("Reached Start of file");
+        }
+
+        // Keep looping untill we get a full line, or the end of the file
+        boolean keepLooping = true;
+        boolean gotNewLine;
+        while (keepLooping) {
+            gotNewLine = false;
+            // Get Current Position
+            fp = file.getFilePointer();
+
+            // Check how far to seek backwards (seekLength or to the start of the file)
+            if (fp < seekLength) {
+                // Seek to the start of the file;
+                seekDistance = (int) fp;
+                fp = 0;
+            } else {
+                // Seek to position current-seekLength
+                seekDistance = seekLength;
+                fp = fp - seekDistance;
+            }
+            // Seek!
+            file.seek(fp);
+
+            bytes = new byte[seekDistance];
+            // Read into the bytes array
+            file.read(bytes);
+
+            // And loop looking for data
+            // This uses seekDistance so that only wanted data is checked.
+            for (int i = seekDistance - 1; i >= 0; --i) {
+                // Check for New line Character, or a non carraige-return char
+                if (bytes[i] == '\n') {
+                    // Seek to the location of this character and exit this loop.
+                    file.seek(fp + i);
+                    gotNewLine = true;
+                    break;
+                } else if (bytes[i] != '\r') {
+                    // Add to the result, the loop will continue going.
+                    line.add(0, bytes[i]);
+                }
+            }
+
+            // We have now processed the data we read (Either added it all to the
+            // buffer, or found a newline character.)
+
+            if (fp == 0 && !gotNewLine) {
+                // This part of the loop started from the start of the file, but didn't
+                // find a new line anywhere. no more loops are posssible, so Treat
+                // this as "got new line"
+                gotNewLine = true;
+                file.seek(0);
+            }
+
+            // Do we need to continue?
+            if (gotNewLine) {
+                // We have found a new line somewhere, thus we don't need
+                // to read any more bytes, so exit the while loop!
+                keepLooping = false;
+            } else {
+                // We have not found a new line anywhere,
+                // Seek to the pre-read position, and repeat.
+                file.seek(fp);
+            }
+
+        }
+
+        // Return the data obtained.
+        byte[] result = new byte[line.size()];
+        for (int i = 0; i < line.size(); ++i) {
+            result[i] = line.get(i);
+        }
+        return new String(result, Charset.forName("UTF-8"));
+    }
+
+    /**
+     * Try and get x number of lines.
+     * If the file is closed, an empty stack will be returned.
+     *
+     * @param numLines Number of lines to try and get.
+     * @return The requested lines
+     */
+    public Stack<String> getLines(final int numLines) {
+        final Stack<String> result = new Stack<String>();
+        for (int i = 0; i < numLines; ++i) {
+            try {
+                result.push(getNextLine());
+            } catch (IOException e) {
+                break;
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Try and get x number of lines and return a \n delimited String.
+     * If the file is closed, an empty string will be returned.
+     *
+     * @param numLines Number of lines to try and get.
+     * @return The requested lines
+     */
+    public String getLinesAsString(final int numLines) {
+        final StringBuilder result = new StringBuilder();
+        for (int i = 0; i < numLines; ++i) {
+            try {
+                result.insert(0, "\n");
+                result.insert(0, getNextLine());
+            } catch (IOException e) {
+                break;
+            }
+        }
+        if (result.charAt(0) == '\n') {
+            result.deleteCharAt(0);
+        }
+        return result.toString();
+    }
+
+}

test/com/dmdirc/util/io/ReverseFileReaderTest.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright (c) 2006-2012 DMDirc Developers
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package com.dmdirc.util.io;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.util.Stack;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class ReverseFileReaderTest {
+
+    @Test
+    public void testIndividual() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        assertEquals("Line 7", reader.getNextLine());
+        assertEquals("Line 6", reader.getNextLine());
+        assertEquals("Line 5", reader.getNextLine());
+        assertEquals("Line 4", reader.getNextLine());
+        assertEquals("Line 3", reader.getNextLine());
+        assertEquals("Line 2", reader.getNextLine());
+        assertEquals("Line 1", reader.getNextLine());
+        reader.close();
+    }
+
+    @Test
+    public void testCarriageReturn() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test4.txt").toURI()));
+        reader.getNextLine();
+        assertEquals("Normal line", reader.getNextLine());
+        reader.close();
+    }
+
+    @Test
+    public void testLongLine() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test4.txt").toURI()));
+        assertEquals("This is a line that is longer than 50 characters, so " +
+                "should cause the reader to have to scan back multiple times.",
+                reader.getNextLine());
+        reader.close();
+    }
+
+    @Test
+    public void testStack() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        final Stack<String> lines = reader.getLines(10);
+
+        assertEquals(7, lines.size());
+        assertEquals("Line 1", lines.pop());
+        assertEquals("Line 2", lines.pop());
+        assertEquals("Line 3", lines.pop());
+        assertEquals("Line 4", lines.pop());
+        assertEquals("Line 5", lines.pop());
+        assertEquals("Line 6", lines.pop());
+        assertEquals("Line 7", lines.pop());
+        reader.close();
+    }
+
+    @Test
+    public void testSmallStack() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        final Stack<String> lines = reader.getLines(3);
+
+        assertEquals(3, lines.size());
+        assertEquals("Line 5", lines.pop());
+        assertEquals("Line 6", lines.pop());
+        assertEquals("Line 7", lines.pop());
+        reader.close();
+    }
+
+    @Test
+    public void testReset() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        assertEquals("Line 7", reader.getNextLine());
+        assertEquals("Line 6", reader.getNextLine());
+        reader.reset();
+        assertEquals("Line 7", reader.getNextLine());
+        assertEquals("Line 6", reader.getNextLine());
+        assertEquals("Line 5", reader.getNextLine());
+        reader.close();
+    }
+
+    @Test(expected=IOException.class)
+    public void testIllegalClose() throws URISyntaxException, IOException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        reader.close();
+        reader.close();
+    }
+
+    @Test(expected=IOException.class)
+    public void testIllegalReset() throws URISyntaxException, IOException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        reader.close();
+        reader.reset();
+    }
+
+    @Test(expected=IOException.class)
+    public void testIllegalGetNextLine() throws URISyntaxException, IOException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        reader.close();
+        reader.getNextLine();
+    }
+
+    @Test
+    public void testSeekLength() throws IOException, URISyntaxException {
+        final ReverseFileReader reader = new ReverseFileReader(
+                new File(getClass().getResource("test1.txt").toURI()));
+        reader.setSeekLength((byte) 100);
+        assertEquals((byte) 100, reader.getSeekLength());
+    }
+
+}

test/com/dmdirc/util/io/test4.txt

@@ -0,0 +1,2 @@
+Normal line
+This is a line that is longer than 50 characters, so should cause the reader to have to scan back multiple times.