Filter out escape sequence 'character set' select

Some terminals (xterm) supports two different 'character sets' ('G0' and
'G1'), which can be switched with 'SI' (shift in, '\017') and 'SO'
(shift out, '\016'). Each character set can be configured separately
and can be chosen from a list of pre-defined sets like 'ASCII Set' and
'Special Graphics'.

Running `TERM=xterm tput sgr0` to reset the terminal returns an escape
sequence starting with 'ESC ( 0', which selects the 'ASCII Set' for
'G0'. This currently is not understood by the Jenkins AnsiColor plugin.

Filter out those sequences, as they otherwise clutter the output.

<https://www.in-ulm.de/~mascheck/various/alternate_charset/> has a nice
description for characters sets

This is issue <#29>, a
upstream port of <https://issues.jenkins-ci.org/browse/JENKINS-24387>

jansi/src/main/java/org/fusesource/jansi/AnsiOutputStream.java

@@ -64,6 +64,7 @@ public AnsiOutputStream(OutputStream os) {
     private static final int LOOKING_FOR_OSC_COMMAND_END = 6;
     private static final int LOOKING_FOR_OSC_PARAM = 7;
     private static final int LOOKING_FOR_ST = 8;
+    private static final int LOOKING_FOR_CHARSET = 9;
 
     int state = LOOKING_FOR_FIRST_ESC_CHAR;
 
@@ -72,6 +73,8 @@ public AnsiOutputStream(OutputStream os) {
     private static final int SECOND_OSC_CHAR = ']';
     private static final int BEL = 7;
     private static final int SECOND_ST_CHAR = '\\';
+    private static final int SECOND_CHARSET0_CHAR = '(';
+    private static final int SECOND_CHARSET1_CHAR = ')';
 
     @Override
     public synchronized void write(int data) throws IOException {
@@ -91,6 +94,12 @@ public synchronized void write(int data) throws IOException {
                     state = LOOKING_FOR_NEXT_ARG;
                 } else if (data == SECOND_OSC_CHAR) {
                     state = LOOKING_FOR_OSC_COMMAND;
+                } else if (data == SECOND_CHARSET0_CHAR) {
+                    options.add(new Integer('0'));
+                    state = LOOKING_FOR_CHARSET;
+                } else if (data == SECOND_CHARSET1_CHAR) {
+                    options.add(new Integer('1'));
+                    state = LOOKING_FOR_CHARSET;
                 } else {
                     reset(false);
                 }
@@ -193,6 +202,11 @@ public synchronized void write(int data) throws IOException {
                     state = LOOKING_FOR_OSC_PARAM;
                 }
                 break;
+
+            case LOOKING_FOR_CHARSET:
+                options.add(new Character((char) data));
+                reset(processCharsetSelect(options));
+                break;
         }
 
         // Is it just too long?
@@ -731,6 +745,21 @@ protected void processChangeWindowTitle(String label) {
     protected void processUnknownOperatingSystemCommand(int command, String param) {
     }
 
+    /**
+     * Process character set sequence.
+     * @param options
+     * @return true if the charcter set select command was processed.
+     */
+    private boolean processCharsetSelect(ArrayList<Object> options) throws IOException {
+        int set = optionInt(options, 0);
+        char seq = ((Character) options.get(1)).charValue();
+        processCharsetSelect(set, seq);
+        return true;
+    }
+
+    protected void processCharsetSelect(int set, char seq) {
+    }
+
     private int optionInt(ArrayList<Object> options, int index) {
         if (options.size() <= index)
             throw new IllegalArgumentException();

jansi/src/test/java/org/fusesource/jansi/HtmlAnsiOutputStreamTest.java

@@ -76,6 +76,12 @@ public void testUTF8Character() throws IOException {
                 colorize("\u3053\u3093\u306b\u3061\u306f"));
     }
 
+    @Test
+    public void testResetCharacterSet() throws IOException {
+        assertEquals(colorize("(\033(0)"), "()");
+        assertEquals(colorize("(\033)0)"), "()");
+    }
+
     private String colorize(String text) throws IOException {
         ByteArrayOutputStream os = new ByteArrayOutputStream();
         HtmlAnsiOutputStream hos = new HtmlAnsiOutputStream(os);