allow users to read bytes for BINARY and VARBINARY columns

spec/db_spec.cr

@@ -217,4 +217,21 @@ DB::DriverSpecs(MySql::Any).run do
       end
     end
   end
+
+  it "allows VARBINARY fields to be read as slices" do |db|
+    db.exec %(create table if not exists btest (b varbinary(16) not null);)
+    db.exec %(insert into btest (b) values (X'5a5a5a');)
+
+    DB.open db.uri do |db|
+      begin
+        db.query("select b from btest") do |rs|
+          rs.each do
+            rs.read(Bytes).should eq Bytes.new(3, 90_u8)
+          end
+        end
+      rescue e
+        fail("Expected no exception, but got \"#{e.message}\"")
+      end
+    end
+  end
 end

src/mysql/result_set.cr

@@ -88,6 +88,20 @@ class MySql::ResultSet < DB::ResultSet
     end
   end
 
+  # In order not to break existing functionality expecting strings, we only
+  # apply the binary check if bytes are requested in the read method call
+  def read(t : (Bytes | (Bytes | Nil)).class)
+    val = read
+
+    if !val
+      nil
+    elsif val.is_a?(String | Bytes)
+      val.to_slice
+    else
+      raise "#{self.class}#read returned a #{val.class}. A #{t} was expected."
+    end
+  end
+
   def read(t : Bool.class)
     MySql::Type.from_mysql(read.as(Int8))
   end