fs-source/index.js

A file system source for the BOB streaming protocol.

'use strict'

const fs = require('fs')
const { Status } = require('bob-streams')

class FileSource {
  constructor (path, options) {
    if (options !== undefined && typeof options !== 'object') {
      throw new TypeError(`options MUST be an Object, found ${typeof options}`)
    }

    options = copyObject(options)

    if (path !== undefined && typeof path !== 'string') {
      throw new TypeError(`path MUST be a String, found ${typeof path}`)
    }

    this.path = path

    this.fd = options.fd === undefined ? null : options.fd
    this.flags = options.flags === undefined ? 'r' : options.flags
    this.mode = options.mode === undefined ? 0o666 : options.mode

    this.pos = 0

    if (options.start !== undefined) {
      if (typeof options.start !== 'number') {
        throw new TypeError(`options.start MUST be a Number, found ${typeof options.start}`)
      }
      if (options.end === undefined) {
        options.end = Infinity
      } else if (typeof options.end !== 'number') {
        throw new TypeError(`options.end MUST be a Number or undefined, found ${typeof options.end}`)
      }

      if (options.start > options.end) {
        const errVal = `{start: ${options.start}, end: ${options.end}}`
        throw new RangeError(`start must be greater than end, found ${errVal}`)
      }

      this.pos = options.start !== undefined ? options.start : 0
    }

    // XXX(Fishrock123):
    // streams3 opens the FD here, but I think error handling might be better if
    // it is opened during pull flow.
    //
    // That has some disadvantages, namely around telling when to actually open
    // the file, but also the delayment of error until after stream construction.
    //
    // if (typeof this.fd !== 'number')
    //   this.open()
  }

  bindSink (sink) {
    this.sink = sink
  }

  pull (error, buffer) {
    if (error) {
      if (typeof this.fd === 'number') {
        fs.close(this.fd, (closeError) => {
          this.fd = null
          this.sink.next(Status.error, closeError || error)
        })
      } else {
        return this.sink.next(Status.error, error)
      }
    }

    if (typeof this.fd !== 'number') {
      fs.open(this.path, this.flags, this.mode, (error, fd) => {
        if (error) {
          return this.sink.next(Status.error, error)
        }

        this.fd = fd

        this.readFromFile(buffer)
      })
    } else {
      this.readFromFile(buffer)
    }
  }

  readFromFile (buffer) {
    if (typeof this.fd !== 'number') {
      return this.pull(null, buffer)
    }

    fs.read(this.fd, buffer, 0, buffer.length, this.pos, (error, bytesRead) => {
      if (error) {
        fs.close(this.fd, (closeError) => {
          this.fd = null
          this.sink.next(Status.error, closeError || error)
        })
      } else {
        if (bytesRead > 0) {
          this.pos += bytesRead
          this.sink.next(Status.continue, null, buffer, bytesRead)
        } else {
          fs.close(this.fd, (closeError) => {
            this.fd = null
            if (closeError) {
              this.sink.next(Status.error, closeError)
            } else {
              this.sink.next(Status.end, null, buffer, 0)
            }
          })
        }
      }
    })
  }
}

module.exports = FileSource

/* ## Helpers ## */

function copyObject (source) {
  var target = {}
  for (var key in source) { target[key] = source[key] }
  return target
}