Hubbub parser architecture ========================== Introduction ------------ Hubbub is a flexible HTML parser. It offers two interfaces: * a SAX-style event interface * a DOM-style tree-based interface Overview -------- Hubbub is comprised of four parts: * a charset handler * an input stream veneer * a tokeniser * a tree builder Charset handler --------------- The charset handler converts the raw data input into a requested encoding. Input stream veneer ------------------- The input stream veneer provides an abstract stream-like interface over the document buffer. This is used by the tokeniser. The document buffer will be encoded in either UTF-8 or UTF-16 (this is client-selectable). Tokeniser --------- The tokeniser divides the data held in the document buffer into chunks. It sends SAX-style events for each chunk. The tokeniser is agnostic to the charset the document buffer is stored in. Tree builder ------------ The tree builder constructs a DOM tree from the SAX events emitted by the tokeniser. The tree builder is tied to the document buffer charset. Memory usage and ownership -------------------------- Memory usage within the library is well defined, as is ownership of allocated memory. Raw input data provided by the library client is owned by the client. The document buffer is allocated on the fly by the library. The document buffer is created and resized by the charset handler. Its location is passed to the tree builder through a dedicated event. While parsing is occurring, the ownership of the document buffer lies with the charset handler. Upon parse completion, the tree builder may request ownership of the buffer. If it does not, the buffer will be freed on parser destruction. SAX events which refer to document segments contain direct references into the document buffer (i.e. no copying of data held in the document buffer occurs). The tree builder will allocate memory for use as DOM nodes. References to strings in the document buffer will be direct and will operate a copy-on-write strategy. All strings (excepting those which comprise part of the document buffer) and nodes within the DOM are reference counted. Upon a reference count reaching 0, the item is freed. The above strategy permits data copying to be kept to a minimum, hence minimising memory usage. Parse errors ------------ Notification of parse errors is made through a dedicated event similar to that used for notification of movement of the document buffer. This event contains the line/column offset of the error location, along with a message detailing the error.