@signalk/streams/from_json.js

Utilities for handling streams of Signal K data

/*
 * Copyright 2014-2015 Fabian Tollenaar <fabian@starting-point.nl>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0

 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* Usage:
 * As part of a PipedProvider in a settings file. Lets you pass json strings such as Signal K deltas coming from other sources such as TCP, UDP, Serial etc. Usually last in the list of providers for this pipe
 * Takes no options:

 {
   "type": "providers/from_json"
 },

 *
 */

const Transform = require('stream').Transform

function FromJson() {
  Transform.call(this, {
    objectMode: true
  })
}

require('util').inherits(FromJson, Transform)

FromJson.prototype._transform = function (chunk, encoding, done) {
  let parsed = null
  try {
    parsed = JSON.parse(chunk.toString())
  } catch (_) {
    console.error('Could not parse JSON:' + chunk.toString())
  }
  if (parsed) {
    this.push(parsed)
  }
  done()
}

module.exports = FromJson