Fixes #27: Reject full 00 - 1F unicode range

lexer.go

diff --git a/lexer.go b/lexer.go
index 7cb789b..13fd84f 100644
--- a/lexer.go
+++ b/lexer.go
@@ -423,7 +423,11 @@
 				return l.errorf("invalid escape sequence: \\" + string(l.peek()))
 			}
 		} else {
-			growingString += string(l.peek())
+			r := l.peek()
+			if 0x00 <= r && r <= 0x1F {
+				return l.errorf("unescaped control character %U", r)
+			}
+			growingString += string(r)
 		}
 
 		if l.next() == eof {

lexer_test.go

diff --git a/lexer_test.go b/lexer_test.go
index d1cd130..23b231b 100644
--- a/lexer_test.go
+++ b/lexer_test.go
@@ -463,6 +463,19 @@
 	})
 }
 
+func TestKeyEqualStringNoEscape(t *testing.T) {
+	testFlow(t, "foo = \"hello \u0002\"", []token{
+		token{Position{1, 1}, tokenKey, "foo"},
+		token{Position{1, 5}, tokenEqual, "="},
+		token{Position{1, 8}, tokenError, "unescaped control character U+0002"},
+	})
+	testFlow(t, "foo = \"hello \u001F\"", []token{
+		token{Position{1, 1}, tokenKey, "foo"},
+		token{Position{1, 5}, tokenEqual, "="},
+		token{Position{1, 8}, tokenError, "unescaped control character U+001F"},
+	})
+}
+
 func TestLiteralString(t *testing.T) {
 	testFlow(t, `foo = 'C:\Users\nodejs\templates'`, []token{
 		token{Position{1, 1}, tokenKey, "foo"},
@@ -514,19 +527,33 @@
 		token{Position{1, 34}, tokenEOF, ""},
 	})
 
-	testFlow(t, "foo = \"\"\"\nhello\n\"literal\"\nworld\"\"\"", []token{
+	testFlow(t, "foo = \"\"\"\nhello\\\n\"literal\"\\\nworld\"\"\"", []token{
 		token{Position{1, 1}, tokenKey, "foo"},
 		token{Position{1, 5}, tokenEqual, "="},
-		token{Position{2, 1}, tokenString, "hello\n\"literal\"\nworld"},
+		token{Position{2, 1}, tokenString, "hello\"literal\"world"},
 		token{Position{4, 9}, tokenEOF, ""},
 	})
 
-	testFlow(t, "foo = \"\"\"\\\n    \\\n    \\\n    hello\nmultiline\nworld\"\"\"", []token{
+	testFlow(t, "foo = \"\"\"\\\n    \\\n    \\\n    hello\\\nmultiline\\\nworld\"\"\"", []token{
 		token{Position{1, 1}, tokenKey, "foo"},
 		token{Position{1, 5}, tokenEqual, "="},
-		token{Position{1, 10}, tokenString, "hello\nmultiline\nworld"},
+		token{Position{1, 10}, tokenString, "hellomultilineworld"},
 		token{Position{6, 9}, tokenEOF, ""},
 	})
+
+	testFlow(t, "key2 = \"\"\"\nThe quick brown \\\n\n\n  fox jumps over \\\n    the lazy dog.\"\"\"", []token{
+		token{Position{1, 1}, tokenKey, "key2"},
+		token{Position{1, 6}, tokenEqual, "="},
+		token{Position{2, 1}, tokenString, "The quick brown fox jumps over the lazy dog."},
+		token{Position{6, 21}, tokenEOF, ""},
+	})
+
+	testFlow(t, "key2 = \"\"\"\\\n       The quick brown \\\n       fox jumps over \\\n       the lazy dog.\\\n       \"\"\"", []token{
+		token{Position{1, 1}, tokenKey, "key2"},
+		token{Position{1, 6}, tokenEqual, "="},
+		token{Position{1, 11}, tokenString, "The quick brown fox jumps over the lazy dog."},
+		token{Position{5, 11}, tokenEOF, ""},
+	})
 }
 
 func TestUnicodeString(t *testing.T) {