COMMON: Add U32String version of toPrintable

This only escapes ASCII control characters, not characters wih
codepoints > 127.

common/ustr.cpp

@@ -267,4 +267,41 @@ char* U32String::itoa(int num, char* str, int base) {
 	return str;
 }
 
+U32String toPrintable(const U32String &in, bool keepNewLines) {
+	U32String res;
+
+	const char *tr = "\x01\x01\x02\x03\x04\x05\x06" "a"
+				  //"\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f";
+					   "b" "t" "n" "v" "f" "r\x0e\x0f"
+					"\x10\x11\x12\x13\x14\x15\x16\x17"
+					"\x18\x19\x1a" "e\x1c\x1d\x1e\x1f";
+
+	for (const u32char_type_t *p = in.c_str(); *p; p++) {
+		if (*p == '\n') {
+			if (keepNewLines)
+				res += *p;
+			else
+				res += U32String("\\n");
+
+			continue;
+		}
+
+		if (*p < 0x20 || *p == '\'' || *p == '\"' || *p == '\\') {
+			res += '\\';
+
+			if (*p < 0x20) {
+				if (tr[*p] < 0x20)
+					res += Common::String::format("x%02x", *p);
+				else
+					res += tr[*p];
+			} else {
+				res += *p;	// We will escape it
+			}
+		} else
+			res += *p;
+	}
+
+	return res;
+}
+
 } // End of namespace Common

common/ustr.h

@@ -200,6 +200,18 @@ U32String operator+(const U32String &x, const U32String &y);
 /** Append the given @p y character to the given @p x string. */
 U32String operator+(const U32String &x, U32String::value_type y);
 
+/**
+ * Converts string with all non-printable characters properly escaped
+ * with use of C++ escape sequences.
+ * Unlike the String version, this does not escape characters with
+ * codepoints > 127.
+ *
+ * @param src The source string.
+ * @param keepNewLines Whether keep newlines or convert them to '\n', default: true.
+ * @return The converted string.
+ */
+U32String toPrintable(const U32String &src, bool keepNewLines = true);
+
 /** @} */
 
 } // End of namespace Common