knowledge/node_modules/pg/lib/native/client.js

const nodeUtils = require('util')
// eslint-disable-next-line
var Native
// eslint-disable-next-line no-useless-catch
try {
  // Wrap this `require()` in a try-catch to avoid upstream bundlers from complaining that this might not be available since it is an optional import
  Native = require('pg-native')
} catch (e) {
  throw e
}
const TypeOverrides = require('../type-overrides')
const EventEmitter = require('events').EventEmitter
const util = require('util')
const ConnectionParameters = require('../connection-parameters')

const NativeQuery = require('./query')

const queryQueueLengthDeprecationNotice = nodeUtils.deprecate(
  () => {},
  'Calling client.query() when the client is already executing a query is deprecated and will be removed in pg@9.0. Use async/await or an external async flow control mechanism instead.'
)

const Client = (module.exports = function (config) {
  EventEmitter.call(this)
  config = config || {}

  this._Promise = config.Promise || global.Promise
  this._types = new TypeOverrides(config.types)

  this.native = new Native({
    types: this._types,
  })

  this._queryQueue = []
  this._ending = false
  this._connecting = false
  this._connected = false
  this._queryable = true

  // keep these on the object for legacy reasons
  // for the time being. TODO: deprecate all this jazz
  const cp = (this.connectionParameters = new ConnectionParameters(config))
  if (config.nativeConnectionString) cp.nativeConnectionString = config.nativeConnectionString
  this.user = cp.user

  // "hiding" the password so it doesn't show up in stack traces
  // or if the client is console.logged
  Object.defineProperty(this, 'password', {
    configurable: true,
    enumerable: false,
    writable: true,
    value: cp.password,
  })
  this.database = cp.database
  this.host = cp.host
  this.port = cp.port

  // a hash to hold named queries
  this.namedQueries = {}
})

Client.Query = NativeQuery

util.inherits(Client, EventEmitter)

Client.prototype._errorAllQueries = function (err) {
  const enqueueError = (query) => {
    process.nextTick(() => {
      query.native = this.native
      query.handleError(err)
    })
  }

  if (this._hasActiveQuery()) {
    enqueueError(this._activeQuery)
    this._activeQuery = null
  }

  this._queryQueue.forEach(enqueueError)
  this._queryQueue.length = 0
}

// connect to the backend
// pass an optional callback to be called once connected
// or with an error if there was a connection error
Client.prototype._connect = function (cb) {
  const self = this

  if (this._connecting) {
    process.nextTick(() => cb(new Error('Client has already been connected. You cannot reuse a client.')))
    return
  }

  this._connecting = true

  this.connectionParameters.getLibpqConnectionString(function (err, conString) {
    if (self.connectionParameters.nativeConnectionString) conString = self.connectionParameters.nativeConnectionString
    if (err) return cb(err)
    self.native.connect(conString, function (err) {
      if (err) {
        self.native.end()
        return cb(err)
      }

      // set internal states to connected
      self._connected = true

      // handle connection errors from the native layer
      self.native.on('error', function (err) {
        self._queryable = false
        self._errorAllQueries(err)
        self.emit('error', err)
      })

      self.native.on('notification', function (msg) {
        self.emit('notification', {
          channel: msg.relname,
          payload: msg.extra,
        })
      })

      // signal we are connected now
      self.emit('connect')
      self._pulseQueryQueue(true)

      cb(null, this)
    })
  })
}

Client.prototype.connect = function (callback) {
  if (callback) {
    this._connect(callback)
    return
  }

  return new this._Promise((resolve, reject) => {
    this._connect((error) => {
      if (error) {
        reject(error)
      } else {
        resolve(this)
      }
    })
  })
}

// send a query to the server
// this method is highly overloaded to take
// 1) string query, optional array of parameters, optional function callback
// 2) object query with {
//    string query
//    optional array values,
//    optional function callback instead of as a separate parameter
//    optional string name to name & cache the query plan
//    optional string rowMode = 'array' for an array of results
//  }
Client.prototype.query = function (config, values, callback) {
  let query
  let result
  let readTimeout
  let readTimeoutTimer
  let queryCallback

  if (config === null || config === undefined) {
    throw new TypeError('Client was passed a null or undefined query')
  } else if (typeof config.submit === 'function') {
    readTimeout = config.query_timeout || this.connectionParameters.query_timeout
    result = query = config
    // accept query(new Query(...), (err, res) => { }) style
    if (typeof values === 'function') {
      config.callback = values
    }
  } else {
    readTimeout = config.query_timeout || this.connectionParameters.query_timeout
    query = new NativeQuery(config, values, callback)
    if (!query.callback) {
      let resolveOut, rejectOut
      result = new this._Promise((resolve, reject) => {
        resolveOut = resolve
        rejectOut = reject
      }).catch((err) => {
        Error.captureStackTrace(err)
        throw err
      })
      query.callback = (err, res) => (err ? rejectOut(err) : resolveOut(res))
    }
  }

  if (readTimeout) {
    queryCallback = query.callback || (() => {})

    readTimeoutTimer = setTimeout(() => {
      const error = new Error('Query read timeout')

      process.nextTick(() => {
        query.handleError(error, this.connection)
      })

      queryCallback(error)

      // we already returned an error,
      // just do nothing if query completes
      query.callback = () => {}

      // Remove from queue
      const index = this._queryQueue.indexOf(query)
      if (index > -1) {
        this._queryQueue.splice(index, 1)
      }

      this._pulseQueryQueue()
    }, readTimeout)

    query.callback = (err, res) => {
      clearTimeout(readTimeoutTimer)
      queryCallback(err, res)
    }
  }

  if (!this._queryable) {
    query.native = this.native
    process.nextTick(() => {
      query.handleError(new Error('Client has encountered a connection error and is not queryable'))
    })
    return result
  }

  if (this._ending) {
    query.native = this.native
    process.nextTick(() => {
      query.handleError(new Error('Client was closed and is not queryable'))
    })
    return result
  }

  if (this._queryQueue.length > 0) {
    queryQueueLengthDeprecationNotice()
  }

  this._queryQueue.push(query)
  this._pulseQueryQueue()
  return result
}

// disconnect from the backend server
Client.prototype.end = function (cb) {
  const self = this

  this._ending = true

  if (!this._connected) {
    this.once('connect', this.end.bind(this, cb))
  }
  let result
  if (!cb) {
    result = new this._Promise(function (resolve, reject) {
      cb = (err) => (err ? reject(err) : resolve())
    })
  }

  this.native.end(function () {
    self._connected = false

    self._errorAllQueries(new Error('Connection terminated'))

    process.nextTick(() => {
      self.emit('end')
      if (cb) cb()
    })
  })
  return result
}

Client.prototype._hasActiveQuery = function () {
  return this._activeQuery && this._activeQuery.state !== 'error' && this._activeQuery.state !== 'end'
}

Client.prototype._pulseQueryQueue = function (initialConnection) {
  if (!this._connected) {
    return
  }
  if (this._hasActiveQuery()) {
    return
  }
  const query = this._queryQueue.shift()
  if (!query) {
    if (!initialConnection) {
      this.emit('drain')
    }
    return
  }
  this._activeQuery = query
  query.submit(this)
  const self = this
  query.once('_done', function () {
    self._pulseQueryQueue()
  })
}

// attempt to cancel an in-progress query
Client.prototype.cancel = function (query) {
  if (this._activeQuery === query) {
    this.native.cancel(function () {})
  } else if (this._queryQueue.indexOf(query) !== -1) {
    this._queryQueue.splice(this._queryQueue.indexOf(query), 1)
  }
}

Client.prototype.ref = function () {}
Client.prototype.unref = function () {}

Client.prototype.setTypeParser = function (oid, format, parseFn) {
  return this._types.setTypeParser(oid, format, parseFn)
}

Client.prototype.getTypeParser = function (oid, format) {
  return this._types.getTypeParser(oid, format)
}

Client.prototype.isConnected = function () {
  return this._connected
}