check that titles are trimmed

titles starting or ending with whitespace are awkward, they should be
trimmed by the application

src/domain/domain_error.cpp

@@ -17,6 +17,8 @@ std::string error_message(fix::domain::domain_error error) {
     return "title may not contain '\\' or '`'";
   case domain_error::TITLE_HAS_NON_ASCII_CHARS:
     return "title may not contain non-ASCII characters";
+  case domain_error::TITLE_NOT_TRIMMED:
+    return "title may not start or end with whitespace";
   }
   return "unknown domain error";
 }

src/domain/domain_error.hpp

@@ -13,6 +13,7 @@ enum class domain_error {
   TITLE_HAS_NON_PRINTABLES = 12,
   TITLE_HAS_SPECIAL_PUNCTUATION = 13,
   TITLE_HAS_NON_ASCII_CHARS = 14,
+  TITLE_NOT_TRIMMED = 15,
 };
 
 template<typename T>

src/domain/title.cpp

@@ -3,6 +3,7 @@
 #include <cctype>
 #include <climits>
 #include <range/v3/algorithm/any_of.hpp>
+#include <range/v3/view/trim.hpp>
 
 using namespace fix::domain;
 
@@ -12,6 +13,11 @@ constexpr size_t MAX_LENGTH = 120;
 title::title(std::string_view text) : text{text} {}
 
 expected<title> title::create(std::string_view text) {
+  const auto trimmed_length = ranges::size(text | ranges::views::trim([](char c) { return isspace(c); }));
+  if (trimmed_length != text.length()) {
+    return unexpected(domain_error::TITLE_NOT_TRIMMED);
+  }
+
   if (text.length() < MIN_LENGTH) {
     return unexpected(domain_error::TITLE_TOO_SHORT);
   }

test/domain/title_test.cpp

@@ -74,3 +74,9 @@ TEST_CASE("Titles have a restricted character set") {
                FailsWithMessage("title may not contain non-ASCII characters"));
   }
 }
+
+TEST_CASE("Title text may not start or end with whitespace") {
+  const auto untrimmed_title = GENERATE("  may not start with blanks"sv, "nor end with blanks  "sv,
+                                        "\t\ttabs are whitespace"sv, "linebreaks, too\n"sv);
+  CHECK_THAT(title::create(untrimmed_title), FailsWithMessage("title may not start or end with whitespace"));
+}