Add ColumnFormatter/StringUtil classes for text output

The ColumnFormatter class will simplify output of column-oriented text
for SSH commands like ls-groups and others (including HTTP counterparts)
that may print user-supplied text that can contain tab and newline
characters that would screw up scripts using these commands for
automation. To deal with this, all text output is subject to C-style
escaping of all non-printable characters. The escaping in done in the
new StringUtil class.

So far this new functionality is only used by the ls-projects command
when the project description is printed. The escaping method used there
previously only took care of newline characters.

Change-Id: Ia605bbc44fc82d69d2f40b337319368aefd01eee

gerrit-server/src/main/java/com/google/gerrit/server/StringUtil.java

@@ -0,0 +1,54 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server;
+
+public class StringUtil {
+  /**
+   * An array of the string representations that should be used in place
+   * of the non-printable characters in the beginning of the ASCII table
+   * when escaping a string. The index of each element in the array
+   * corresponds to its ASCII value, i.e. the string representation of
+   * ASCII 0 is found in the first element of this array.
+   */
+  static String[] NON_PRINTABLE_CHARS =
+    { "\\x00", "\\x01", "\\x02", "\\x03", "\\x04", "\\x05", "\\x06", "\\a",
+      "\\b",   "\\t",   "\\n",   "\\v",   "\\f",   "\\r",   "\\x0e", "\\x0f",
+      "\\x10", "\\x11", "\\x12", "\\x13", "\\x14", "\\x15", "\\x16", "\\x17",
+      "\\x18", "\\x19", "\\x1a", "\\x1b", "\\x1c", "\\x1d", "\\x1e", "\\x1f" };
+
+  /**
+   * Escapes the input string so that all non-printable characters
+   * (0x00-0x1f) are represented as a hex escape (\x00, \x01, ...)
+   * or as a C-style escape sequence (\a, \b, \t, \n, \v, \f, or \r).
+   * Backslashes in the input string are doubled (\\).
+   */
+  public static String escapeString(final String str) {
+    // Allocate a buffer big enough to cover the case with a string needed
+    // very excessive escaping without having to reallocate the buffer.
+    final StringBuilder result = new StringBuilder(3 * str.length());
+
+    for (int i = 0; i < str.length(); i++) {
+      char c = str.charAt(i);
+      if (c < NON_PRINTABLE_CHARS.length) {
+        result.append(NON_PRINTABLE_CHARS[c]);
+      } else if (c == '\\') {
+        result.append("\\\\");
+      } else {
+        result.append(c);
+      }
+    }
+    return result.toString();
+  }
+}