Allow escaping of non-printable characters in CSV output/input

This is a proposed solution for FasterXML#124. It introduces a new Feature, `ESCAPE_CONTROL_CHARS_WITH_ESCAPE_CHAR`,
which will apply the standard ASCII escapes from JSON to all characters that the CSV generator writes.

If this solution is workable, I will add tests.

csv/src/main/java/com/fasterxml/jackson/dataformat/csv/CsvCharacterEscapes.java

@@ -0,0 +1,101 @@
+package com.fasterxml.jackson.dataformat.csv;
+
+import com.fasterxml.jackson.core.SerializableString;
+import com.fasterxml.jackson.core.io.CharTypes;
+import com.fasterxml.jackson.core.io.CharacterEscapes;
+import com.fasterxml.jackson.dataformat.csv.CsvGenerator.Feature;
+
+/**
+ * Character escapes for CSV. There are multiple types of escapes.
+ *
+ * <ul>
+ * <li>no escapes - return all characters the same way they are defined</li>
+ * <li>quote escape - return all characters except the quote character which is escaped (backwards compat) </li>
+ * <li>control escape - same as {@link CharTypes#get7BitOutputEscapes()}, escape all control characters</li>
+ * <li> control and quote escape - do not double up quote, escape control characters and quote.</li>
+ * </ul>
+ */
+public final class CsvCharacterEscapes extends CharacterEscapes
+{
+
+    private static final long serialVersionUID = 1L;
+
+    // No character escapes, every character returned as is.
+    private static final CsvCharacterEscapes sNoEscapesInstance = new CsvCharacterEscapes(new int[0]);
+
+    // Only escape quotes, controlled by {@link Feature#ESCAPE_QUOTE_CHAR_WITH_ESCAPE_CHAR}.
+    private static final CsvCharacterEscapes sQuoteEscapesInstance;
+
+    // Only escape control chars, do *not* escape the quote char. See (@link Feature#ESCAPE_CONTROL_CHARS_WITH_ESCAPE_CHAR}.
+    private static final CsvCharacterEscapes sControlEscapesInstance;
+
+    // Escape control chars and the quote char.
+    private static final CsvCharacterEscapes sControlQuoteEscapesInstance = new CsvCharacterEscapes(CharacterEscapes.standardAsciiEscapesForJSON());
+
+    private static final CsvCharacterEscapes [] sEscapes;
+
+    static {
+        int[] quoteEscapes = new int[(int) '"' + 1];
+        quoteEscapes[(int) '"'] = '"';
+        sQuoteEscapesInstance = new CsvCharacterEscapes(quoteEscapes);
+
+        int[] controlEscapes = CharacterEscapes.standardAsciiEscapesForJSON();
+        controlEscapes['"'] = 0; // do not escape ", double it up.
+        sControlEscapesInstance = new CsvCharacterEscapes(controlEscapes);
+
+        sEscapes = new CsvCharacterEscapes[4];
+        sEscapes[0] = sNoEscapesInstance;
+        sEscapes[1] = sQuoteEscapesInstance;
+        sEscapes[2] = sControlEscapesInstance;
+        sEscapes[3] = sControlQuoteEscapesInstance;
+    }
+
+
+    private final int[] escapes;
+
+    private CsvCharacterEscapes(int[] escapes)
+    {
+        this.escapes = escapes;
+    }
+
+    public static CsvCharacterEscapes noEscapesInstance()
+    {
+        return sNoEscapesInstance;
+    }
+
+    public static CsvCharacterEscapes quoteEscapesInstance()
+    {
+        return sQuoteEscapesInstance;
+    }
+
+    public static CsvCharacterEscapes controlEscapesInstance()
+    {
+        return sControlEscapesInstance;
+    }
+
+    public static CsvCharacterEscapes controlQuoteEscapesInstance()
+    {
+        return sControlQuoteEscapesInstance;
+    }
+
+    public static CsvCharacterEscapes fromCsvFeatures(int csvFeatures)
+    {
+        int idx = 0;
+        idx |= CsvGenerator.Feature.ESCAPE_QUOTE_CHAR_WITH_ESCAPE_CHAR.enabledIn(csvFeatures) ? 1 : 0;
+        idx |= Feature.ESCAPE_CONTROL_CHARS_WITH_ESCAPE_CHAR.enabledIn(csvFeatures) ? 2 : 0;
+
+        return sEscapes[idx];
+    }
+
+    @Override
+    public SerializableString getEscapeSequence(int ch)
+    {
+        return null; // unused for CSV escapes
+    }
+
+    @Override
+    public int[] getEscapeCodesForAscii()
+    {
+        return escapes;
+    }
+}

csv/src/main/java/com/fasterxml/jackson/dataformat/csv/CsvFactory.java

@@ -419,6 +419,8 @@ protected CsvGenerator _createGenerator(IOContext ctxt, Writer out) throws IOExc
         CsvGenerator gen = new CsvGenerator(ctxt, _generatorFeatures, _csvGeneratorFeatures,
                 _objectCodec, out, _schema);
         // any other initializations? No?
+
+        gen.setCharacterEscapes(CsvCharacterEscapes.fromCsvFeatures(_csvGeneratorFeatures));
         return gen;
     }
 

csv/src/main/java/com/fasterxml/jackson/dataformat/csv/CsvGenerator.java

@@ -7,6 +7,7 @@
 
 import com.fasterxml.jackson.core.*;
 import com.fasterxml.jackson.core.base.GeneratorBase;
+import com.fasterxml.jackson.core.io.CharacterEscapes;
 import com.fasterxml.jackson.core.json.JsonWriteContext;
 import com.fasterxml.jackson.core.io.IOContext;
 import com.fasterxml.jackson.dataformat.csv.impl.CsvEncoder;
@@ -81,7 +82,19 @@ public enum Feature
          *
          * @since 2.9.3
          */
-        ESCAPE_QUOTE_CHAR_WITH_ESCAPE_CHAR(false)
+        ESCAPE_QUOTE_CHAR_WITH_ESCAPE_CHAR(false),
+
+        /**
+         * Feature that determines whether control characters (non-printable) are escaped using the
+         * configured escape character. This feature allows LF and CR characters to be output as <pre>\n</pre>
+         * and <pre>\r</pre> instead of being echoed out. This is a compatibility feature for some
+         * parsers that can not read such output back in.
+         * <p>
+         * Default value is false so that control characters are echoed out (backwards compatible).
+         *
+         * @since 2.9.9
+         */
+        ESCAPE_CONTROL_CHARS_WITH_ESCAPE_CHAR(false)
         ;
 
         protected final boolean _defaultState;
@@ -146,6 +159,8 @@ private Feature(boolean defaultState) {
     // note: can not be final since we may need to re-create it for new schema
     protected CsvEncoder _writer;
 
+    protected CharacterEscapes _characterEscapes = null;
+
     /*
     /**********************************************************
     /* Output state
@@ -220,6 +235,8 @@ public CsvGenerator(IOContext ctxt, int jsonFeatures, int csvFeatures,
         _formatFeatures = csvFeatures;
         _schema = schema;
         _writer = new CsvEncoder(ctxt, csvFeatures, out, schema);
+
+        _writer.setOutputEscapes(CsvCharacterEscapes.fromCsvFeatures(csvFeatures).getEscapeCodesForAscii());
     }
 
     public CsvGenerator(IOContext ctxt, int jsonFeatures, int csvFeatures,
@@ -312,6 +329,22 @@ public JsonGenerator overrideFormatFeatures(int values, int mask)
         return this;
     }
 
+    public JsonGenerator setCharacterEscapes(CharacterEscapes esc) {
+        this._characterEscapes = esc;
+        if (esc != null) {
+            this._writer.setOutputEscapes(esc.getEscapeCodesForAscii());
+        } else {
+            this._writer.setOutputEscapes(CsvCharacterEscapes.fromCsvFeatures(_formatFeatures).getEscapeCodesForAscii());
+        }
+
+        return this;
+    }
+
+    public CharacterEscapes getCharacterEscapes() {
+        return this._characterEscapes;
+    }
+
+
     /*
     /**********************************************************
     /* Public API, capability introspection methods