102 lines
2.1 KiB
JavaScript
102 lines
2.1 KiB
JavaScript
'use strict'
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const { Inaccessible, InvalidResponse } = require('../core/base-service/errors')
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// Map from URL to { timestamp: last fetch time, data: data }.
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let regularUpdateCache = Object.create(null)
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// url: a string, scraper: a function that takes string data at that URL.
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// interval: number in milliseconds.
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// cb: a callback function that takes an error and data returned by the scraper.
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//
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// To use this from a service:
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//
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// const { promisify } = require('util')
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// const { regularUpdate } = require('../../lib/regular-update')
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//
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// function getThing() {
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// return promisify(regularUpdate)({
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// url: ...,
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// ...
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// })
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// }
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//
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// in handle():
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//
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// const thing = await getThing()
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function regularUpdate(
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{
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url,
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intervalMillis,
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json = true,
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scraper = buffer => buffer,
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options = {},
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request = require('request'),
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},
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cb
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) {
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const timestamp = Date.now()
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const cached = regularUpdateCache[url]
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if (cached != null && timestamp - cached.timestamp < intervalMillis) {
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cb(null, cached.data)
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return
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}
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request(url, options, (err, res, buffer) => {
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if (err != null) {
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cb(
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new Inaccessible({
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prettyMessage: 'intermediate resource inaccessible',
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underlyingError: err,
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})
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)
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return
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}
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if (res.statusCode < 200 || res.statusCode >= 300) {
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cb(
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new InvalidResponse({
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prettyMessage: 'intermediate resource inaccessible',
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})
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)
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}
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let reqData
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if (json) {
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try {
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reqData = JSON.parse(buffer)
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} catch (e) {
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cb(
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new InvalidResponse({
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prettyMessage: 'unparseable intermediate json response',
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underlyingError: e,
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})
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)
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return
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}
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} else {
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reqData = buffer
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}
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let data
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try {
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data = scraper(reqData)
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} catch (e) {
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cb(e)
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return
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}
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regularUpdateCache[url] = { timestamp, data }
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cb(null, data)
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})
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}
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function clearRegularUpdateCache() {
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regularUpdateCache = Object.create(null)
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}
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module.exports = {
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regularUpdate,
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clearRegularUpdateCache,
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}
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