http: http status classification

Add `status_class` enum for possible http code groups (classes) and a function `classify_status` to get code's classification. Intended for general usage to prevent code like `if (http_code >= XXX && http_code < YYY)`

include/seastar/http/reply.hh

@@ -111,6 +111,38 @@ struct reply {
         network_connect_timeout = 599, //!< network_connect_timeout
     } _status;
 
+    /**
+     * HTTP status classes
+     * See https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
+     *
+     * 1xx: Informational - Request received, continuing process
+     * 2xx: Success - The action was successfully received, understood, and accepted
+     * 3xx: Redirection - Further action must be taken in order to complete the request
+     * 4xx: Client Error - The request contains bad syntax or cannot be fulfilled
+     * 5xx: Server Error - The server failed to fulfill an apparently valid request
+     */
+    enum class status_class : uint8_t {
+        informational = 1,
+        success = 2,
+        redirection = 3,
+        client_error = 4,
+        server_error = 5,
+        unclassified
+    };
+
+    /**
+     * Classify http status
+     * @param http_status the http status \ref status_type
+     * @return one of the \ref status_class values
+     */
+    static constexpr status_class classify_status(status_type http_status) {
+        auto sc = static_cast<std::underlying_type_t<status_type>>(http_status) / 100;
+        if (sc < 1 || sc > 5) [[unlikely]] {
+            return status_class::unclassified;
+        }
+        return static_cast<status_class>(sc);
+    }
+
     /**
      * The headers to be included in the reply.
      */

tests/unit/httpd_test.cc

@@ -1831,3 +1831,58 @@ BOOST_AUTO_TEST_CASE(test_path_decode_changed) {
     auto expected_chars = seastar::sstring{" "};
     BOOST_REQUIRE_EQUAL(result, expected_chars);
 }
+
+namespace seastar::http {
+std::ostream& boost_test_print_type(std::ostream& os, reply::status_class sc) {
+    constexpr std::string_view status_strings[] {
+        "1xx: Informational",
+        "2xx: Success",
+        "3xx: Redirection",
+        "4xx: Client Error",
+        "5xx: Server Error",
+        "Unclassified"
+    };
+    auto status = static_cast<std::underlying_type_t<reply::status_class>>(sc) - 1u;
+    if (status < std::size(status_strings)) {
+        return os << status_strings[status];
+    }
+    return os << "Unclassified";
+}
+} // namespace seastar::http
+
+BOOST_AUTO_TEST_CASE(test_http_status_classification) {
+    size_t informational = 0;
+    size_t success = 0;
+    size_t redirection = 0;
+    size_t client_error = 0;
+    size_t server_error = 0;
+    size_t unclassified = 0;
+    for (auto i = -100; i < 700; ++i) {
+        auto classification = http::reply::classify_status(static_cast<http::reply::status_type>(i));
+        if (i >= 100 && i < 200) {
+            ++informational;
+            BOOST_REQUIRE_EQUAL(classification, http::reply::status_class::informational);
+        } else if (i >= 200 && i < 300) {
+            ++success;
+            BOOST_REQUIRE_EQUAL(classification, http::reply::status_class::success);
+        } else if (i >= 300 && i < 400) {
+            ++redirection;
+            BOOST_REQUIRE_EQUAL(classification, http::reply::status_class::redirection);
+        } else if (i >= 400 && i < 500) {
+            ++client_error;
+            BOOST_REQUIRE_EQUAL(classification, http::reply::status_class::client_error);
+        } else if (i >= 500 && i < 600) {
+            ++server_error;
+            BOOST_REQUIRE_EQUAL(classification, http::reply::status_class::server_error);
+        } else {
+            ++unclassified;
+            BOOST_REQUIRE_EQUAL(classification, http::reply::status_class::unclassified);
+        }
+    }
+    BOOST_REQUIRE_EQUAL(informational, 100);
+    BOOST_REQUIRE_EQUAL(success, 100);
+    BOOST_REQUIRE_EQUAL(redirection, 100);
+    BOOST_REQUIRE_EQUAL(client_error, 100);
+    BOOST_REQUIRE_EQUAL(server_error, 100);
+    BOOST_REQUIRE_EQUAL(unclassified, 300);
+}