overpass-frontend/src/loadFile.js

A JavaScript (NodeJS/Browser) library to easily access data from OpenStreetMap via Overpass API or from an OSM File. The objects can directly be used with LeafletJS or exported to GeoJSON. Data will be cached in the browser memory.

const fs = require('fs')
const bzip2 = require('bzip2')
const parseDataUrl = require('parse-data-url')

module.exports = function loadFile (url, options, callback) {
  let filename = url
  if ('filename' in options) {
    filename = options.filename
  }

  if (url.match(/^data:/)) {
    const parsed = parseDataUrl(url)
    if (!parsed) {
      const e = new Error('Error parsing data URL')
      return callback(e)
    }

    let content = parsed.toBuffer()

    const m = filename.match(/^(.*)\.bz2$/)
    if (m || parsed.contentType.match(/^application\/x-bzip/)) {
      try {
        content = bzip2decode(content)
      } catch (err) {
        return callback(err)
      }
      filename = m ? m[1] : filename
    }

    if (filename === url) {
      filename = parsed.contentType === 'application/json'
        ? 'file.osm.json'
        : 'file.osm'
    }

    return callback(null, content, filename)
  }

  if (typeof location === 'undefined' && !url.match(/^(http:|https:|)\/\//)) {
    fs.readFile(url,
      (err, content) => {
        if (err) {
          return callback(err)
        }

        const m = filename.match(/^(.*)\.bz2$/)
        if (m) {
          try {
            content = bzip2decode(content)
          } catch (err) {
            return callback(err)
          }
          filename = m[1]
        }

        callback(null, content, filename)
      }
    )

    return
  }

  const req = new global.XMLHttpRequest()

  req.onreadystatechange = function () {
    if (req.readyState === 4) {
      if (req.status === 200) {
        let content

        const m = filename.match(/^(.*)\.bz2$/)
        if (m) {
          try {
            content = bzip2decode(new Uint8Array(req.response))
          } catch (err) {
            return callback(err)
          }
          filename = m[1]
        } else {
          content = req.response
        }

        callback(null, content, filename)
      } else {
        callback(new Error('Received error ' + req.status + ' (' + req.statusText + ')'))
      }
    }
  }

  if (url.substr(0, 2) === '//') {
    if (typeof location === 'undefined') {
      url = 'https:' + url
    } else {
      url = global.location.protocol + url
    }
  }

  if (filename.match(/\.bz2$/)) {
    req.responseType = 'arraybuffer'
  }

  req.open('GET', url)
  req.send()
}

function bzip2decode (file) {
  let data

  try {
    data = bzip2.simple(bzip2.array(file))
  } catch (err) {
    throw new Error('Error decoding bzip2 stream')
  }

  let content = ''

  for (let i = 0; i < data.byteLength; i++) {
    content += String.fromCharCode(data[i])
  }

  return decodeURIComponent(escape(content))
}