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https://github.com/jdesgats/lua-lolhtml

Lua binding for the lol-HTML rewriter/parser
https://github.com/jdesgats/lua-lolhtml

html lua parsing

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Lua binding for the lol-HTML rewriter/parser

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README 

        
Lua binding for lol-html

========================



This library is a Lua binding for [lol-html][lolhtml], a *Low output latency

streaming HTML parser/rewriter with CSS selector-based API*.



It can be used to either extract data from HTML documents or rewrite them

on-the-fly.



Installation

------------



You need a functional setup of Rust and Cargo to be able to build this module.

Please refer to the [Rust website][rust-install] or install it with your

distribution's package manager.



### Luarocks (version >= 3.0 required)



You can install this module with Luarocks:



```

luarocks install https://raw.githubusercontent.com/jdesgats/lua-lolhtml/master/rockspecs/lolhtml-dev-1.rockspec

```



### Manual build



First, be sure to clone this repository with its submodules. Then the provided

Makefile should be able to build the module.



```

git clone --recursive https://github.com/jdesgats/lua-lolhtml.git

make

```



Running the tests require [my fork][telescope] of Telescope:



```

luarocks install https://raw.githubusercontent.com/jdesgats/telescope/master/rockspecs/telescope-scm-1.rockspec

tsc spec/lolhtml.lua

```



Quick start

-----------



The workflow is usually:



1. Create a [*rewriter builder*](#rewriterbuilder-objects) object:

   ```lua

   local lolhtml = require "lolhtml"

   local my_builder = lolhtml.new_rewriter_builder()

   ```

2. Attach callbacks to it with the logic to transform your documents:

   ```lua

   my_builder:add_element_content_handlers {

     selector = lolhtml.new_selector("h1"),

     element_handler = function(el) el:set_attribute("class", "title") end

   }

   ```

3. Use the previous builder to create [*rewriter*](#rewriter-objects) objects,

   one for each HTML page you want to work on:

   ```lua

   local my_rewriter = lolhtml.new_rewriter {

     builder = my_builder,

     sink = function(s) print(s) end,

   }

   ```

4. Feed the rewriter with the actual HTML stream:

   ```lua

   for l in io.stdin:lines() do

     my_rewriter:write(l)

   end

   my_rewriter:close()

   ```



The `examples` directory contains a port of the original Rust examples from

lol-html. You can run them by feeding an HTML page as input:



```sh

curl -NL https://git.io/JeOSZ | lua examples/defer_scripts.lua

```



Status

------



**ALPHA VERSION**



This binding is not finished yet. Even if the test coverage is quite good and

pass and Valgrind is not complaining, bugs might still be present.



Also, the API is dot frozen and might change. Here are a non-exhaustive list

of things that I still consider:



* API naming: stay close of the original names, or choose shorter ones

* Selectors: should they be exposed at all? or compiled and cached transparently

* Some data could be exposed as attributes rather than methods, is it better?

* Tables vs. lots of arguments for some functions

* Error handling: when to raise errors, when to return `nil, err`



Reference

---------



This library tries to stay close of the original API, while being more Lua-ish

when appropriate. In particular it should not panic (as in triggering

`SIGABRT`), such case would be considered as a bug.



### Top-level objects



Object constructors:



* `lolhtml.new_selector`: see [`Selector`](#selector-objects)

* `lolhtml.new_rewriter_builder`: see [`RewriterBuilder`](#rewriterbuilder-objects)

* `lolhtml.new_rewriter`: see [`Rewriter`](#rewriter-objects)



Constants:



* `lolhtml.CONTINUE`

* `lolhtml.STOP`



### Selector objects



Selector object represent a parsed CSS selector that can be used to build

rewriter builders.



Selector objects don't have any methods or attributes. They are exposed only

for garbage collection purposes (and also as an optimization if you need to

reuse the same selector in multiple builders).



#### `lolhtml.new_selector(sel: string) => Selector | nil, err`



Builds a new [`Selector`](#selector-objects) object out of the give string.

Returns `nil, err` in case of syntax error.



### RewriterBuilder objects



The `RewriterBuilder` encapsulate the logic to make rewrites, usually they are

created at program startup and are used to instantiate many `Rewriter` objects.



All callbacks functions are called with a single argument whose type depend on

the type of callback. This argument should not outlive the callback and any

attempt to keep a reference of it to use it later will result in an error.



These functions can return:



* `lolhtml.CONTINUE`: instructs the parser to continue processing the HTML

  stream

* `lolhtml.STOP`: causes the parser to stop immediately, `write()` or `end()`

  methods of the rewriter will return an error code

* *nothing*: same as `lolhtml.CONTINUE`



If a callback raises an error, it will also causes the rewriter to stop

immediately. The error object or message will be returned as error by the

`write()` or `end()` methods of the rewriter.



#### `lolhtml.new_rewriter_builder() => RewriterBuilder`



Create a new `RewriterBuilder` object.



#### `RewriterBuilder:add_document_content_handlers(callbacks) => self`



Adds new document-level content handlers. This function might be called

multiple times to add multiple handlers.



The `callback` parameter must be a table with callbacks for different types

of events, the possible fields are:



* `doctype_handler`: called after parsing the Document Type declaration with

  a [`Doctype`](#doctype-objects) object.

* `comment_handler`: called whenever a comment is parsed with a

  [`Comment`](#comment-objects) object.

* `text_handler`: called when text nodes are parsed with a

  [`TextChunk`](#textchunk-objects) object.

* `doc_end_handler`: called at the end of the document with a

  [`DocumentEnd`](#documentend-objects) object.



All of the fields are optional. Calling a callback has a cost so leave out any

callback you don't need.



#### `RewriterBuilder:add_element_content_handlers(callbacks) => self`



Adds new element content handlers associated with a selector. This function

might be called multiple times to add multiple handlers for different

selectors.



The `callback` parameter must be a table with the selector and the callbacks

for different types of events, the possible fields are:



* `selector`: the [CSS selector](#selector-objects) to call the callbacks on

  (required)

* `comment_handler`: called whenever a comment is parsed with a

  [`Comment`](#comment-objects) object.

* `text_handler`: called when text nodes are parsed with a

  [`TextChunk`](#textchunk-objects) object.

* `element_handler`: called when an element is parsed with a

  [`Element`](#element-objects) object.



All of the fields are optional (except `selector`). Calling a callback has a

cost so leave out any callback you don't need.



### Rewriter objects



Rewriter object are processing a single HTML document and are instantiated with

a [`RewriterBuilder`](#rewriterbuilder-objects) object.



Each rewriter has an associated `sink`, which is a function called to output

the rewritten HTML.



#### `lolhtml.new_rewriter(options) => Rewriter | nil, err`



Creates a new reriter object. The `options` argument must be a table, the

following fields are allowed:



* `builder`: a `RewriterBuilder` object (required)

* `encoding`: the text encoding for the HTML stream. Can be a label for any of

  the web-compatible encodings with an exception for `UTF-16LE`, `UTF-16BE`,

  `ISO-2022-JP` and `replacement` (these non-ASCII-compatible encodings are

  not supported). (optional, default is `"utf-8"`)

* `preallocated_parsing_buffer_size`: Specifies the number of bytes that should

  be preallocated on HtmlRewriter instantiation for the internal parsing

  buffer. See [lol-html documentation][lolhtml-memory] for details. (optional,

  default is 1024)

* `max_allowed_memory_usage`: Sets a hard limit in bytes on memory consumption

  of a Rewriter instance. See [lol-html documentation][lolhtml-memory] for

  details. (optional, default is `SIZE_MAX`)

* `strict`: boolean, if set to true the rewriter bails out if it encounters

   markup that drives the HTML parser into ambigious state. See

  [lol-html documentation][lolhtml-strict] for details. (optional, default is

  `false`)



Returns the new Rewriter on success, or `nil` and an error message on failure.



#### `Rewriter:write(s) => self | nil, err`



Write HTML chunk to rewriter. Returns the rewriter itself on success, or `nil`

and an error message on failure. Failure happens if (incomplete list):



* A callback or a sink raises an error

* A previous invocation returned an error

* Called after `close`



#### `Rewriter:close(s) => self | nil, err`



Finalizes the rewriting process. Should be called once the last chunk of the

input is written. Returns the rewriter itself on success, or `nil` and an

error message on failure. Failure happens if (incomplete list):



* A callback or a sink raises an error

* A previous invocation returned an error

* Called more than once



### Doctype objects



#### `Doctype:get_name() => string|nil`

#### `Doctype:get_id() => string|nil`

#### `Doctype:get_system_id() => string|nil`



### Comment objects



#### `Comment:get_text() => string`

#### `Comment:set_text(string) => self|nil, err`

#### `Comment:before(string, is_html) => self|nil, err`

#### `Comment:after(string, is_html) => self|nil, err`

#### `Comment:replace(string, is_html) => self|nil, err`

#### `Comment:remove() => self|nil, err`

#### `Comment:is_removed() => boolean`



### TextChunk objects



#### `TextChunk:get_text() => string`

#### `TextChunk:is_last_in_text_node() => boolean`

#### `TextChunk:before(string, is_html) => self|nil, err`

#### `TextChunk:after(string, is_html) => self|nil, err`

#### `TextChunk:replace(string, is_html) => self|nil, err`

#### `TextChunk:remove() => self|nil, err`

#### `TextChunk:is_removed() => boolean`



### Element objects



#### `Element:get_tag_name() => string`

#### `Element:get_namespace_uri() => string`

#### `Element:get_attribute(name) => string|nil`

#### `Element:has_attribute(name) => boolean`

#### `Element:set_attribute(name, value) => self|nil, err`

#### `Element:remove_attribute(name) => self|nil, err`

#### `Element:attributes() => iterator`



Returns a Lua iterator triplet so the following construction is valid:



```lua

for attr_name, value in element:attribute() do

  ...

end

```



#### `Element:before(string, is_html) => self|nil, err`

#### `Element:after(string, is_html) => self|nil, err`

#### `Element:prepend(string, is_html) => self|nil, err`

#### `Element:append(string, is_html) => self|nil, err`

#### `Element:set_inner_content(string, is_html) => self|nil, err`

#### `Element:replace(string, is_html) => self|nil, err`

#### `Element:remove() => self|nil, err`

#### `Element:remove_and_keep_content() => self|nil, err`

#### `Element:is_removed() => boolean`



### DocumentEnd objects



#### `DocumentEnd:append(string, is_html) => self|nil, err`



[lolhtml]: https://github.com/cloudflare/lol-html

[lolhtml-memory]: https://docs.rs/lol_html/0.1.0/lol_html/struct.MemorySettings.html

[lolhtml-strict]: https://docs.rs/lol_html/0.1.0/lol_html/struct.Settings.html#structfield.stricti

[rust-install]: https://www.rust-lang.org/tools/install

[telescope]: https://github.com/jdesgats/telescope