This ensures that Oga can lex the following properly:
<input value="" />
Previously Ragel would stop upon finding the empty string. This was caused due
to the string rules being declared as following:
string_dquote = (dquote ^dquote+ dquote);
string_squote = (squote ^squote+ squote);
These rules only match strings _with_ content, not without. Since Ragel stops
consuming input the moment it finds unhandled data this resulted in incorrect
tokens being emitted.
Thanks to some heavy rubberducking with @whitequark the lexer is now a little
bit better at lexing T_TEXT nodes. For example, previously the following could
not be lexed properly:
"foo < bar"
There might still be some tweaking to do but we're getting there.
Using create_makefile('liboga/liboga') will compile liboga.so into
path-to-gem/lib/liboga/ and therefore require_relative in oga.rb will fail.
Therefore the right parameter for create_makefile is 'liboga' ->
path-to-gem/lib/liboga.so
The previous setup would consume too much. For example the following HTML:
<a><!--foo--><b><!--bar--></b></a>
would result in the following T_COMMENT token:
"foo--><b><!--bar"
The new setup requires the marking of a start position. I'm not a huge fan of
this but there doesn't appear to be a way around this.
Instead of using a raw Hash Oga now uses the XML::Attribute class for storing
information about element attributes.
Attributes are stored as an Array of XML::Attribute instances. This allows the
attributes to be more easily modified. If they were stored as a Hash you'd not
only have to update the attributes themselves but also the Hash that contains
them.
While using an Array has a slight runtime cost in most cases the amount of
attributes is small enough that this doesn't really pose a problem. If webscale
performance is desired at some point in the future Oga could most likely cache
the lookup of an attribute. This however is something for the future.
Using IO/StringIO objects one can parse large XML files without first having to
read the entire file into memory. This can potentially save a lot of memory at
the cost of a slightly slower runtime.
For IO like instances the lexer will consume the input line by line. If a
String is given it's consumed as a whole instead. A small side effect of
reading the input line by line is that text such as "foo\nbar" will be lexed as
two tokens instead of one.
Fixes#19.
Instead of directly accessing the `data` instance variable the C/Java code now
uses the method `read_data`. This is part of one of the various steps required
to allow Oga to read data from IO like instances. It also means I can freely
change the name of the instance variable without also having to change the
C/Java code.
This moves the element related rules to the element_head machine (where they
belong). This in turn makes it possible to lex ">" as a text node, previously
this was impossible.
After discussing this with @headius I've decided to do this the manual way
anyway. Apparently the basic load service stuff is deprecated and not very
reliable.
While I've tried to keep Oga pure Ruby for as long as possible the performance
of Ragel's Ruby output was not worth the trouble. For example, lexing 10MB of
XML would take 5 to 6 seconds at least. Nokogiri on the other hand can parse
that same XML into a DOM document in about 300 miliseconds. Such a big
performance difference is not acceptable.
To work around this the XML/HTML lexer will be implemented in C for
MRI/Rubinius and Java for JRuby. For now there's only a C extension as I
haven't read up yet on the JRuby API. The end goal is to provide some sort of
Ragel "template" that can be used to generate the corresponding C/Java
extension code. This would remove the need of duplicating the grammar and
associated code.
The native extension setup is a hybrid between native and Ruby. The raw Ragel
stuff happens in C/Java while the actual logic of actions happens in Ruby. This
adds a small amount of overhead but makes it much easier to maintain the lexer.
Even with this extra overhead the performance is much better than pure Ruby.
The 10MB of XML mentioned above is lexed in about 600 miliseconds. In other
words, it's 10 times faster.
Yorick Peterse
Benjamin Klotz