@e2fyi/streams
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Nodejs stream library for various use cases: e.g. Auto-tagging object streams, streaming to mongoDb via mongoose models, etc.
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<h1 class="page-title">Source: src/document-tagger.js</h1>
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<pre class="prettyprint source linenums"><code>'use strict';
const {Transform} = require('stream');
const defaultOpts = {writableObjectMode: true};
/**
* Settings for DocumentTagger.
* @memberof module:@e2fyi/streams
* @alias DocumentTaggerSettings
* @typedef {Object} DocumentTaggerSettings
* @property {String} autoIncrement - The auto-increment field to tag onto the
* stream object.
* @property {Boolean} ignoreNonObject - If `true`, no errors will be emitted
* when the chunk in the stream cannot be parsed into `Object`.
* @property {Boolean} readableObjectMode - If `true`, `Object` will be emitted
* from the stream, otherwise a `String` or `Buffer` representation or will
* emitted instead.
* @property {Boolean} objectMode - If `true`, `Object` will be emitted
* from the stream, otherwise a `String` or `Buffer` representation or will
* emitted instead. Overwrites `writableObjectMode`.
* @property {Function} filter - Function to filter the objects in the stream.
* Return `true` to keep the object.
* @property {Function|Object} mutate - Function or Object to mutate the stream.
* If an Object is provided, each stream object will be mutated with the
* `Object.assign(streamObj, mutateObj)`.
*/
/**
* `filtered` event. Emits the objects in the stream that are filtered out.
*
* @event DocumentTagger#filtered
* @type {object}
*/
/**
* Transform Object stream (objectMode=true) to tag with an autoIncrement id.
* An object or function can be optionally provided to mutate each object in
* the stream.
* @memberof module:@e2fyi/streams
* @extends stream.Transform
* @fires DocumentTagger#filtered
* @example
* const docTagger = new DocumentTagger({autoIncrement: 'id', mutate: { project: 'test' }});
* someReadableStreamFromArray([{text: 'abc'}, {text: 'efg'}])
* .pipe(docTagger)
* .pipe(process.stdout);
* // stdout >
* // {"text": "abc", "id": 0, "project": "test"}
* // {"text": "efg", "id": 1, "project": "test"}
*/
class DocumentTagger extends Transform {
/**
* Create a new DocumentTagger stream.
* @param {DocumentTaggerSettings} opts Settings for the stream.
*/
constructor(opts = defaultOpts) {
opts = Object.assign(opts, defaultOpts);
super(Object.assign(opts, defaultOpts));
this._counter_ = 0;
this._chunk_ = null;
this._ignoreNonObject_ = opts.ignoreNonObject;
this._autoIncrement_ = opts.autoIncrement;
this._filter_ = opts.filter;
this._toString_ = !(opts.readableObjectMode || opts.objectMode);
if (opts.mutate) {
this._mutate_ =
typeof opts.mutate === 'function'
? opts.mutate
: d => Object.assign(d, opts.mutate);
}
}
_transform(chunk, encoding, callback) {
// termination
if (!chunk) {
this.push(chunk);
return;
}
// if is buffer convert to Object
if (Buffer.isBuffer(chunk) || typeof chunk === 'string') {
if (this._chunk_) {
chunk = this._chunk_ + '' + chunk;
this._chunk_ = null;
}
try {
chunk = JSON.parse(chunk);
} catch (error) {
if (this._ignoreNonObject_) {
this._chunk_ = chunk;
callback();
return;
} else {
this.emit('error', error);
callback(error);
return;
}
}
}
// filters the chunk
if (this._filter_ && !this._filter_(chunk)) {
this.emit('filtered', chunk);
callback();
return;
}
// mutates the chunk
if (this._mutate_) {
chunk = this._mutate_(chunk);
}
// autoincrement and tag to chunk
if (chunk && this._autoIncrement_) {
chunk[this._autoIncrement_] = this._counter_++;
}
// convert to string if required
if (chunk && this._toString_) {
try {
chunk = JSON.stringify(chunk);
} catch (error) {
this.emit('error', error);
callback(error);
}
}
this.push(chunk);
callback();
}
}
module.exports = DocumentTagger;
</code></pre>
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<h2><a href="index.html">Home</a></h2><h3>Modules</h3><ul><li><a href="module-@e2fyi_streams.html">/streams</a></li></ul><h3>Classes</h3><ul><li><a href="module-@e2fyi_streams.DocumentTagger.html">DocumentTagger</a></li><li><a href="module-@e2fyi_streams.MongooseStream.html">MongooseStream</a></li></ul><h3>Events</h3><ul><li><a href="DocumentTagger.html#event:filtered">filtered</a></li><li><a href="MongooseStream.html#event:mongoose-bulk-write">mongoose-bulk-write</a></li></ul>
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Documentation generated by <a href="https://github.com/jsdoc3/jsdoc">JSDoc 3.6.0</a> on Thu Dec 14 2017 18:22:08 GMT+0800 (+08)
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