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xml-stream.js
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xml-stream.js
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var events = require('events')
, expat = require('node-expat')
, FiniteAutomata = require('./finite-automata')
, Iconv = require('iconv').Iconv
;
// Retains link to hasOwnProperty.
var __own = Object.prototype.hasOwnProperty;
// Tests if object is empty (has no own properties).
function isEmpty(obj) {
for (var key in obj) if (__own.call(obj, key)) {
return false;
}
return true;
}
// XML entities.
var entities = {
'"': '"',
'&': '&',
'\'': ''',
'<': '<',
'>': '>'
};
// Escapes text for XML.
function escape(value) {
return value.replace(/"|&|'|<|>/g, function(entity) {
return entities[entity];
});
}
// Parser events to finite automata events mapping.
var faModes = {
'startElement': 'enter',
'endElement': 'leave',
'text': 'state'
};
// I accidentally the whole class.
module.exports = XmlStream;
// **XmlStream** is an XML stream filter based on Expat.
// It traverses a given stream and emits events for predefined selectors.
// Event listeners receive selected elements, context, and trace from root.
function XmlStream(stream, encoding) {
events.EventEmitter.call(this);
this._stream = stream;
this._fa = new FiniteAutomata();
this._lastState = 0;
this._startState = {};
this._finalStates = {};
this._emitData = false;
this._bufferLevel = 0;
this._preserveLevel = 0;
this._preserveWhitespace = 0;
this._collect = false;
// Set input stream encoding and create an iconv instance,
// if conversion is required. Default working encoding is UTF-8,
// so iconv is used when input is anything else, but UTF-8.
this._encoding = encoding || null;
this._encoder = makeEncoder(this._encoding);
// Start parsing.
parse.call(this);
}
// Either make an iconv instance, or not.
function makeEncoder(encoding) {
if (encoding && !/^utf-?8$/.test(encoding)) {
return new Iconv(encoding, 'utf8');
}
return null;
}
// Inherit events.EventEmitter.
XmlStream.super_ = events.EventEmitter;
XmlStream.prototype = Object.create(events.EventEmitter.prototype, {
constructor: {
value: XmlStream,
enumerable: false
}
});
// Adds a listener for the specified event.
//
// Supported events:
//
// * `data` on outgoing data chunk,
// * `end` when parsing has ended,
// * `startElement[: selector]` on opening tag for selector match,
// * `updateElement[: selector]` on finished node for selector match
// with its contents buffered,
// * `endElement[: selector]` on closing tag for selector match,
// * `text[: selector]` on tag text for selector match.
//
// When adding listeners for `startElement`, `updateElement`, and `text` the
// callback can modify the provided node, before it is sent to the consumer.
//
// Selector syntax is CSS-like and currently supports:
//
// * `ancestor descendant`
// * `parent > child`
XmlStream.prototype.on = function(eventName, listener) {
var event = parseEvent(eventName);
if (event !== null) {
// If we're dealing with a selector event,
// continue with selector-specific processing logic.
XmlStream.super_.prototype.on.call(this, event.name, listener);
var finalState = getFinalState.call(this, event.selector);
var self = this;
if (event.type === 'updateElement') {
this._fa.on('enter', finalState, function() {
self._bufferLevel++;
});
this._fa.on('leave', finalState, function(element, context, trace) {
self.emit(event.name, element, context, trace);
if (!--self._bufferLevel && self._emitData) {
emitElement.call(self, element, self._name, true);
}
});
} else {
var fn = function(element, context, trace) {
self.emit(event.name, element, context, trace);
};
this._fa.on(faModes[event.type], finalState, fn);
}
} else {
// Otherwise, we're dealing with a non-selector event.
if (eventName === 'data') {
this._emitData = true;
}
XmlStream.super_.prototype.on.call(this, eventName, listener);
}
};
// Collects elements with identical names, specified by a selector.
// They will reside in the parent element as an array.
XmlStream.prototype.collect = function(selector) {
selector = normalizeSelector(selector);
var finalState = getFinalState.call(this, selector);
var self = this;
this._fa.on('flag', finalState, function() {
self._collect = true;
});
};
// Preserves the order of element and text nodes inside elements
// that match the selector. Optionally, preserves whitespace.
XmlStream.prototype.preserve = function(selector, whitespace) {
selector = normalizeSelector(selector);
var finalState = getFinalState.call(this, selector);
var self = this;
this._fa.on('enter', finalState, function() {
self._preserveLevel++;
if (whitespace) {
self._preserveWhitespace++;
}
});
this._fa.on('leave', finalState, function() {
self._preserveLevel--;
if (whitespace) {
self._preserveWhitespace--;
}
});
};
// Normalizes the selector and returns the new version and its parts.
function normalizeSelector(selector) {
var parts = selector.match(/[^\s>]+|>/ig);
selector = (parts) ? parts.join(' ') : '';
return {
normalized: selector,
parts: parts || []
};
}
// Parses the selector event string and returns event information.
function parseEvent(event) {
var eventParts = event.match(/^((?:start|end|update)Element|text):?(.*)/);
if (eventParts === null) {
return null;
}
var eventType = eventParts[1];
var selector = normalizeSelector(eventParts[2]);
return {
selector: selector,
type: eventType,
name: (eventParts[2]) ? eventType + ': ' + selector.normalized
: eventType
};
}
// Compiles a given selector object to a finite automata
// and returns its last state.
function getFinalState(selector) {
if (__own.call(this._finalStates, selector.normalized)) {
var finalState = this._finalStates[selector.normalized];
} else {
var n = selector.parts.length;
var immediate = false;
this._startState[this._lastState] = true;
for (var i = 0; i < n; i++) {
var part = selector.parts[i];
if (part === '>') {
immediate = true;
} else {
if (!immediate) {
this._fa.transition(this._lastState, '', this._lastState);
}
this._fa.transition(this._lastState, part, ++this._lastState);
immediate = false;
}
}
var finalState = this._lastState++;
this._finalStates[selector.normalized] = finalState;
}
return finalState;
}
// Emits XML for element opening tag.
function emitStart(name, attrs) {
this.emit('data', '<' + name);
for (var attr in attrs) if (__own.call(attrs, attr)) {
this.emit('data', ' ' + attr + '="' + escape(attrs[attr]) + '"');
}
this.emit('data', '>');
}
// Emits XML for element closing tag.
function emitEnd(name) {
this.emit('data', '</' + name + '>');
}
// Emits XML for element text.
function emitText(text) {
this.emit('data', escape(text));
}
// Emits a single element and its descendants, or an array of elements.
function emitElement(element, name, onLeave) {
if (Array.isArray(element)) {
var i;
for (i = 0; i < element.length - 1; i++) {
emitOneElement.call(this, element[i], name);
}
emitOneElement.call(this, element[i], name, onLeave);
} else {
emitOneElement.call(this, element, name, onLeave);
}
}
// Emits child element collection and their descendants.
// Works only with preserved nodes.
function emitChildren(elements) {
var i;
for (i = 0; i < elements.length; i++) {
var element = elements[i];
if (typeof element === 'object') {
emitStart.call(this, element.$name, element.$);
emitChildren.call(this, element.$children);
emitEnd.call(this, element.$name);
} else {
emitText.call(this, element);
}
}
}
// Recursively emits a given element and its descendants.
function emitOneElement(element, name, onLeave) {
if (typeof element === 'object') {
emitStart.call(this, name, element.$);
if (__own.call(element, '$children')) {
emitChildren.call(this, element.$children);
} else {
var hasText = false;
for (var child in element) {
if (__own.call(element, child) && child !== '$' && child != '$name') {
if (child === '$text') {
hasText = true;
} else {
emitElement.call(this, element[child], child);
}
}
}
if (hasText) {
emitText.call(this, element.$text);
}
}
} else {
emitStart.call(this, name, element.$);
emitText.call(this, element);
}
if (!onLeave) {
emitEnd.call(this, name);
}
}
// Starts parsing the source stream and emitting various events.
// The Expat parser is assigned several listeners for this purpose.
function parse() {
var self = this;
var xml = new expat.Parser('utf-8');
var stack = [];
var trace = {};
var curr = {
element: {},
collect: this._collect,
fullText: '',
space: 0,
path: '',
context: {}
};
var fa = this._fa;
fa.setState(this._startState);
// A listener is assigned on opening tag encounter.
// Here we traverse the configured finite automata use the stack
// to form the context and trace for selector event emission.
xml.on('startElement', function(name, attr) {
self.emit('startElement', name, attr);
stack.push(curr);
trace[curr.path] = curr.element;
var context = Object.create(curr.context);
var element = {
$: attr,
$name: name,
$text: ''
};
var parent = curr.element;
curr = {
element: element,
collect: false,
fullText: '',
space: 0,
path: curr.path + '/' + name,
context: context
};
self._collect = false;
fa.enter(name, [element, context, trace]);
if (self._preserveLevel > 0) {
element.$children = [];
}
name = element.$name;
curr.collect = self._collect;
if (curr.collect) {
var container;
if (__own.call(parent, name)) {
container = parent[name];
container.push(element);
} else {
container = [element];
parent[name] = container;
}
} else {
parent[name] = element;
context[name] = element;
}
if (self._bufferLevel === 0 && self._emitData) {
emitStart.call(self, name, element.$);
}
});
// A listener is assigned on closing tag encounter.
// Current node structure object is finalized. A selector listener is
// invoked with current node, context, and trace; these arguments are
// removed from the stack afterwards.
xml.on('endElement', function(name) {
self.emit('endElement', name);
var prev = stack.pop();
var element = curr.element;
var text = curr.fullText;
var attr = element.$;
if (typeof attr !== 'object') {
attr = {};
}
var name = element.$name;
self._name = name;
delete element.$;
delete element.$text;
delete element.$name;
var val = element;
if (isEmpty(element) && isEmpty(attr)) {
val = text;
} else if (!isEmpty(attr)) {
element.$ = attr;
}
if (text !== '') {
element.$text = text;
}
if (self._bufferLevel > 0 || self._preserveLevel > 0) {
element.$name = name;
}
curr.context[name] = val;
if (curr.collect) {
var container = prev.element[name];
container[container.length - 1] = val;
} else {
prev.element[name] = val;
}
fa.leave([element, curr.context, trace]);
if (self._preserveLevel > 0) {
prev.element.$children.push(val);
}
if (self._bufferLevel === 0 && self._emitData) {
emitEnd.call(self, name);
}
curr = prev;
this._collect = curr.collect;
});
// Collect node text part by part
// (and trim leading and trailing whitespace).
xml.on('text', function(text) {
curr.element.$text = text;
fa.run('state', [curr.element, curr.context, trace]);
if (self._bufferLevel === 0 && self._emitData) {
emitText.call(self, text);
}
var trimmed = curr.element.$text.trim();
var spaced = curr.element.$text.substr(0, 1);
spaced = (spaced !== '') && (spaced.trim() === '');
var after = curr.element.$text.substr(-1, 1);
after = (after !== '') && (after.trim() === '');
switch (curr.space) {
// No words yet (pass through spaces).
case 0:
if (trimmed !== '') {
curr.space = after ? 2 : 1;
}
break;
// Immediately after text or entity.
case 1:
if (trimmed === '') {
curr.space = 2;
} else {
if (spaced) {
curr.fullText += ' ';
}
if (after) {
curr.space = 2;
}
}
break;
// Some words were emitted, pass through spaces again.
// Emit spaces only when a word is encountered afterwards.
case 2:
if (trimmed !== '') {
curr.fullText += ' ';
curr.space = 1;
}
break;
}
text = self._preserveWhitespace > 0 ? text : trimmed;
if (self._preserveLevel > 0) {
if (text !== '') {
curr.element.$children.push(text);
}
}
curr.fullText += text;
});
// This prelude array and string are used during encoding detection.
// Incoming buffers are collected and parsing is postponed,
// but only until the first tag.
var prelude = '';
var preludeBuffers = [];
// Parse incoming chunk.
// Convert to UTF-8 or emit errors when appropriate.
var parseChunk = function(data) {
if (self._encoder) {
data = self._encoder.convert(data);
}
if (!xml.parse(data, false)) {
self.emit('error', xml.getError());
}
}
// Pass data from stream to parser.
this._stream.on('data', function(data) {
if (self._encoding) {
parseChunk(data);
} else {
// We can't parse when the encoding is unknown, so we'll look into
// the XML declaration, if there is one. For this, we need to buffer
// incoming data until a full tag is received.
preludeBuffers.push(data);
prelude += data.toString();
if (/^\s*<[^>]+>/.test(prelude)) {
var matches = prelude.match(/^\s*<\?xml[^>]+encoding="(.+)"[^>]*\?>/);
self._encoding = matches ? matches[1] : 'utf8';
self._encoder = makeEncoder(self._encoding);
for (var i = 0, n = preludeBuffers.length; i < n; i++) {
parseChunk(preludeBuffers[i]);
}
}
}
});
// End parsing on stream EOF and emit an *end* event ourselves.
this._stream.on('end', function() {
if (!xml.parse('', true)) {
self.emit('error', xml.getError());
}
self.emit('end');
});
}