MariaDB determine json from Extended Metadata

In MariaDB the JSON of a result value is from
the extended metadata of the protocol.

This is returned when PROTOCOL_41 is in
the connection flags.

ref: https://mariadb.com/docs/server/reference/clientserver-protocol/4-server-response-packets/result-set-packets#extended-metadata

Author: grooverdan

ext/mysql2/result.c

@@ -240,6 +240,18 @@ static VALUE rb_mysql_result_fetch_field(VALUE self, unsigned int idx, int symbo
   return rb_field;
 }
 
+static int rb_mariadb_json_type(const MYSQL_FIELD *field) {
+#if defined(MARIADB_PACKAGE_VERSION)
+    MARIADB_CONST_STRING field_attr;
+
+    if (!mariadb_field_attr(&field_attr, field,
+                            MARIADB_FIELD_ATTR_FORMAT_NAME)) {
+      return field_attr.length == 4 && strncmp(field_attr.str, "json", 4) == 0;
+    }
+#endif
+    return 0;
+}
+
 static VALUE rb_mysql_result_fetch_field_type(VALUE self, unsigned int idx) {
   VALUE rb_field_type;
   GET_RESULT(self);
@@ -309,7 +321,9 @@ static VALUE rb_mysql_result_fetch_field_type(VALUE self, unsigned int idx) {
         rb_field_type = rb_sprintf("decimal(%d,%d)", precision, field->decimals);
         break;
       case MYSQL_TYPE_STRING:       // char[]
-        if (field->flags & ENUM_FLAG) {
+	if (rb_mariadb_json_type(field)) {
+          rb_field_type = rb_str_new_cstr("json");
+	} else if (field->flags & ENUM_FLAG) {
           rb_field_type = rb_str_new_cstr("enum");
         } else if (field->flags & SET_FLAG) {
           rb_field_type = rb_str_new_cstr("set");
@@ -324,17 +338,27 @@ static VALUE rb_mysql_result_fetch_field_type(VALUE self, unsigned int idx) {
       case MYSQL_TYPE_VAR_STRING:   // char[]
         if (field->charsetnr == MYSQL2_BINARY_CHARSET) {
           rb_field_type = rb_sprintf("varbinary(%ld)", field->length);
-        } else {
+        } else if (rb_mariadb_json_type(field)) {
+          rb_field_type = rb_str_new_cstr("json");
+	} else {
           rb_field_type = rb_sprintf("varchar(%ld)", field->length / MYSQL2_MAX_BYTES_PER_CHAR);
         }
         break;
       case MYSQL_TYPE_VARCHAR:      // char[]
+	if (rb_mariadb_json_type(field)) {
+          rb_field_type = rb_str_new_cstr("json");
+	  break;
+	}
         rb_field_type = rb_sprintf("varchar(%ld)", field->length / MYSQL2_MAX_BYTES_PER_CHAR);
         break;
       case MYSQL_TYPE_TINY_BLOB:    // char[]
         rb_field_type = rb_str_new_cstr("tinyblob");
         break;
       case MYSQL_TYPE_BLOB:         // char[]
+	if (rb_mariadb_json_type(field)) {
+          rb_field_type = rb_str_new_cstr("json");
+	  break;
+	}
         if (field->charsetnr == MYSQL2_BINARY_CHARSET) {
           switch(field->length) {
             case 255:

spec/mysql2/result_spec.rb

@@ -199,9 +199,7 @@
       expect(result.field_types).to eql(expected_types)
     end
 
-    it "should return json type on mysql 8.0" do
-      next unless /8.\d+.\d+/ =~ @client.server_info[:version]
-
+    it "should return json type" do
       result = @client.query("SELECT JSON_OBJECT('key', 'value')")
       expect(result.field_types).to eql(['json'])
     end