opentrees-harvester/lib/wfs.js

/**
 * WFS helper functions.
 *
 * @module
 * @private
 */

const URL = require('url').URL
const xpath = require('xpath')
const xmldom = require('xmldom')

/**
 * Build WFS GetCapabilities URL.
 *
 * @param {string} url - WFS server URL
 * @returns {string}
 */
function buildGetCapabilitiesUrl(url) {
  const u = new URL(url)
  const base = `${u.origin}${u.pathname}`
  // Build GetCapabilities URL
  const searchParams = new URLSearchParams({
    service: 'WFS',
    request: 'GetCapabilities'
  })
  // Avoid encoding colons
  return `${base}?${decodeURIComponent(searchParams)}`
}

/**
 * Parse WFS GetCapabilities response.
 *
 * @param {string} xml – XML string
 * @returns {object} Parsed capabilities (version, outputFormats, typeNames,
 * resultTypes, resultPaging).
 */
function parseCapabilities(xml) {
  const parser = new xmldom.DOMParser()
  const tree = parser.parseFromString(xml)
  const namespaces = xpath.select('/*/@*', tree).reduce((obj, x) => {
    if (x.name.startsWith('xmlns')) {
      obj[x.name.replace(/^xmlns:?/, '')] = x.value
    }
    return obj
  }, {})
  const select = xpath.useNamespaces(namespaces)
  const version = select(
    '//ows:Operation[@name="GetCapabilities"]/ows:Parameter[@name="AcceptVersions"]/ows:AllowedValues/ows:Value' +
    '|//ows:Operation[@name="GetCapabilities"]/ows:Parameter[@name="AcceptVersions"]/ows:Value',
    tree
  )
    .map((x) => x.firstChild.data)
    .sort()
    .pop()
  const outputFormats = select(
    '//ows:Operation[@name="GetFeature"]/ows:Parameter[@name="outputFormat"]/ows:AllowedValues/ows:Value' +
    '|//ows:Operation[@name="GetFeature"]/ows:Parameter[@name="outputFormat"]/ows:Value',
    tree
  ).map((x) => x.firstChild.data)
  const typeNames = select(
    '//*[local-name()="FeatureType"]/*[local-name()="Name"]',
    tree
  ).map((x) => x.firstChild.data)
  const resultTypes = select(
    '//ows:Operation[@name="GetFeature"]/ows:Parameter[@name="resultType"]/ows:AllowedValues/ows:Value' +
    '|//ows:Operation[@name="GetFeature"]/ows:Parameter[@name="resultType"]/ows:Value',
    tree
  ).map((x) => x.firstChild.data)
  const resultPaging = select(
    '//ows:Constraint[@name="ImplementsResultPaging"]/ows:DefaultValue',
    tree
  ).map((x) => x.firstChild.data === 'TRUE').pop()
  return { version, outputFormats, typeNames, resultTypes, resultPaging }
}

/**
 * Choose the output format.
 *
 * @param {string[]} formats - List of output formats
 * @returns {string|null}
 */
function chooseOutputFormat(formats) {
  for (const format of formats) {
    const lowercase = format.toLowerCase()
    if (lowercase.includes('geopackage') || lowercase.includes('gpkg')) {
      return format
    }
    if (lowercase.includes('json')) {
      return format
    }
  }
  return null
}

/**
 * Build WFS GetFeature URL.
 *
 * @param {string} url - WFS server URL (ideally with typeName parameter)
 * @param {object} capabilities - Server capabilities
 * @param {boolean} paging - Whether to set a start index and max feature count
 * @returns {string}
 */
function buildGetFeatureUrl(url, capabilities, paging = false) {
  const u = new URL(url)
  const base = `${u.origin}${u.pathname}`
  let typeName
  for (const [key, value] of u.searchParams.entries()) {
    if (['typename', 'typenames'].includes(key.toLowerCase())) {
      typeName = value
    }
  }
  if (capabilities.typeNames.length === 0) {
    throw new Error(`[${url}] No feature types`)
  }
  if (typeName && !capabilities.typeNames.includes(typeName)) {
    throw new Error(`[${url}] ${typeName} not in feature types: ${capabilities.typeNames}`)
  }
  if (!typeName) {
    if (capabilities.typeNames.length > 1) {
      throw new Error(
        `[${url}] Select one of multiple feature types: ${capabilities.typeNames}`
      )
    }
    typeName = capabilities.typeNames[0]
  }
  // Build GetFeature URL
  const isV2 = capabilities.version >= '2.0.0'
  const searchParams = new URLSearchParams({
    service: 'WFS',
    version: capabilities.version,
    request: 'GetFeature',
    [isV2 ? 'typeNames' : 'typeName']: typeName,
    srsName: 'EPSG:4326'
  })
  const outputFormat = chooseOutputFormat(capabilities.outputFormats)
  if (outputFormat) {
    searchParams.set('outputFormat', outputFormat)
  }
  if (paging) {
    searchParams.set(isV2 ? 'count' : 'maxFeatures', 50000)
    searchParams.set('startIndex', 0)
  }
  // Avoid encoding colons
  return `${base}?${decodeURIComponent(searchParams)}`
}

module.exports = {
  buildGetFeatureUrl,
  buildGetCapabilitiesUrl,
  parseCapabilities,
  chooseOutputFormat
}