lib/fileapi/util.js

'use strict'

const {
  kState,
  kError,
  kResult,
  kAborted,
  kLastProgressEventFired
} = require('./symbols')
const { ProgressEvent } = require('./progressevent')
const { getEncoding } = require('./encoding')
const { DOMException } = require('../fetch/constants')
const { serializeAMimeType, parseMIMEType } = require('../fetch/dataURL')
const { types } = require('util')
const { StringDecoder } = require('string_decoder')
const { btoa } = require('buffer')

/** @type {PropertyDescriptor} */
const staticPropertyDescriptors = {
  enumerable: true,
  writable: false,
  configurable: false
}

/**
 * @see https://w3c.github.io/FileAPI/#readOperation
 * @param {import('./filereader').FileReader} fr
 * @param {import('buffer').Blob} blob
 * @param {string} type
 * @param {string?} encodingName
 */
function readOperation (fr, blob, type, encodingName) {
  // 1. If fr’s state is "loading", throw an InvalidStateError
  //    DOMException.
  if (fr[kState] === 'loading') {
    throw new DOMException('Invalid state', 'InvalidStateError')
  }

  // 2. Set fr’s state to "loading".
  fr[kState] = 'loading'

  // 3. Set fr’s result to null.
  fr[kResult] = null

  // 4. Set fr’s error to null.
  fr[kError] = null

  // 5. Let stream be the result of calling get stream on blob.
  /** @type {import('stream/web').ReadableStream} */
  const stream = blob.stream()

  // 6. Let reader be the result of getting a reader from stream.
  const reader = stream.getReader()

  // 7. Let bytes be an empty byte sequence.
  /** @type {Uint8Array[]} */
  const bytes = []

  // 8. Let chunkPromise be the result of reading a chunk from
  //    stream with reader.
  let chunkPromise = reader.read()

  // 9. Let isFirstChunk be true.
  let isFirstChunk = true

  // 10. In parallel, while true:
  // Note: "In parallel" just means non-blocking
  // Note 2: readOperation itself cannot be async as double
  // reading the body would then reject the promise, instead
  // of throwing an error.
  ;(async () => {
    while (!fr[kAborted]) {
      // 1. Wait for chunkPromise to be fulfilled or rejected.
      try {
        const { done, value } = await chunkPromise

        // 2. If chunkPromise is fulfilled, and isFirstChunk is
        //    true, queue a task to fire a progress event called
        //    loadstart at fr.
        if (isFirstChunk && !fr[kAborted]) {
          queueMicrotask(() => {
            fireAProgressEvent('loadstart', fr)
          })
        }

        // 3. Set isFirstChunk to false.
        isFirstChunk = false

        // 4. If chunkPromise is fulfilled with an object whose
        //    done property is false and whose value property is
        //    a Uint8Array object, run these steps:
        if (!done && types.isUint8Array(value)) {
          // 1. Let bs be the byte sequence represented by the
          //    Uint8Array object.

          // 2. Append bs to bytes.
          bytes.push(value)

          // 3. If roughly 50ms have passed since these steps
          //    were last invoked, queue a task to fire a
          //    progress event called progress at fr.
          if (
            (
              fr[kLastProgressEventFired] === undefined ||
              Date.now() - fr[kLastProgressEventFired] >= 50
            ) &&
            !fr[kAborted]
          ) {
            fr[kLastProgressEventFired] = Date.now()
            queueMicrotask(() => {
              fireAProgressEvent('progress', fr)
            })
          }

          // 4. Set chunkPromise to the result of reading a
          //    chunk from stream with reader.
          chunkPromise = reader.read()
        } else if (done) {
          // 5. Otherwise, if chunkPromise is fulfilled with an
          //    object whose done property is true, queue a task
          //    to run the following steps and abort this algorithm:
          queueMicrotask(() => {
            // 1. Set fr’s state to "done".
            fr[kState] = 'done'

            // 2. Let result be the result of package data given
            //    bytes, type, blob’s type, and encodingName.
            try {
              const result = packageData(bytes, type, blob.type, encodingName)

              // 4. Else:

              if (fr[kAborted]) {
                return
              }

              // 1. Set fr’s result to result.
              fr[kResult] = result

              // 2. Fire a progress event called load at the fr.
              fireAProgressEvent('load', fr)
            } catch (error) {
              // 3. If package data threw an exception error:

              // 1. Set fr’s error to error.
              fr[kError] = error

              // 2. Fire a progress event called error at fr.
              fireAProgressEvent('error', fr)
            }

            // 5. If fr’s state is not "loading", fire a progress
            //    event called loadend at the fr.
            if (fr[kState] !== 'loading') {
              fireAProgressEvent('loadend', fr)
            }
          })

          break
        }
      } catch (error) {
        if (fr[kAborted]) {
          return
        }

        // 6. Otherwise, if chunkPromise is rejected with an
        //    error error, queue a task to run the following
        //    steps and abort this algorithm:
        queueMicrotask(() => {
          // 1. Set fr’s state to "done".
          fr[kState] = 'done'

          // 2. Set fr’s error to error.
          fr[kError] = error

          // 3. Fire a progress event called error at fr.
          fireAProgressEvent('error', fr)

          // 4. If fr’s state is not "loading", fire a progress
          //    event called loadend at fr.
          if (fr[kState] !== 'loading') {
            fireAProgressEvent('loadend', fr)
          }
        })

        break
      }
    }
  })()
}

/**
 * @see https://w3c.github.io/FileAPI/#fire-a-progress-event
 * @see https://dom.spec.whatwg.org/#concept-event-fire
 * @param {string} e The name of the event
 * @param {import('./filereader').FileReader} reader
 */
function fireAProgressEvent (e, reader) {
  // The progress event e does not bubble. e.bubbles must be false
  // The progress event e is NOT cancelable. e.cancelable must be false
  const event = new ProgressEvent(e, {
    bubbles: false,
    cancelable: false
  })

  reader.dispatchEvent(event)
}

/**
 * @see https://w3c.github.io/FileAPI/#blob-package-data
 * @param {Uint8Array[]} bytes
 * @param {string} type
 * @param {string?} mimeType
 * @param {string?} encodingName
 */
function packageData (bytes, type, mimeType, encodingName) {
  // 1. A Blob has an associated package data algorithm, given
  //    bytes, a type, a optional mimeType, and a optional
  //    encodingName, which switches on type and runs the
  //    associated steps:

  switch (type) {
    case 'DataURL': {
      // 1. Return bytes as a DataURL [RFC2397] subject to
      //    the considerations below:
      //  * Use mimeType as part of the Data URL if it is
      //    available in keeping with the Data URL
      //    specification [RFC2397].
      //  * If mimeType is not available return a Data URL
      //    without a media-type. [RFC2397].

      // https://datatracker.ietf.org/doc/html/rfc2397#section-3
      // dataurl    := "data:" [ mediatype ] [ ";base64" ] "," data
      // mediatype  := [ type "/" subtype ] *( ";" parameter )
      // data       := *urlchar
      // parameter  := attribute "=" value
      let dataURL = 'data:'

      const parsed = parseMIMEType(mimeType || 'application/octet-stream')

      if (parsed !== 'failure') {
        dataURL += serializeAMimeType(parsed)
      }

      dataURL += ';base64,'

      const decoder = new StringDecoder('latin1')

      for (const chunk of bytes) {
        dataURL += btoa(decoder.write(chunk))
      }

      dataURL += btoa(decoder.end())

      return dataURL
    }
    case 'Text': {
      // 1. Let encoding be failure
      let encoding = 'failure'

      // 2. If the encodingName is present, set encoding to the
      //    result of getting an encoding from encodingName.
      if (encodingName) {
        encoding = getEncoding(encodingName)
      }

      // 3. If encoding is failure, and mimeType is present:
      if (encoding === 'failure' && mimeType) {
        // 1. Let type be the result of parse a MIME type
        //    given mimeType.
        const type = parseMIMEType(mimeType)

        // 2. If type is not failure, set encoding to the result
        //    of getting an encoding from type’s parameters["charset"].
        if (type !== 'failure') {
          encoding = getEncoding(type.parameters.get('charset'))
        }
      }

      // 4. If encoding is failure, then set encoding to UTF-8.
      if (encoding === 'failure') {
        encoding = 'UTF-8'
      }

      // 5. Decode bytes using fallback encoding encoding, and
      //    return the result.
      return decode(bytes, encoding)
    }
    case 'ArrayBuffer': {
      // Return a new ArrayBuffer whose contents are bytes.
      const sequence = combineByteSequences(bytes)

      return sequence.buffer
    }
    case 'BinaryString': {
      // Return bytes as a binary string, in which every byte
      //  is represented by a code unit of equal value [0..255].
      let binaryString = ''

      const decoder = new StringDecoder('latin1')

      for (const chunk of bytes) {
        binaryString += decoder.write(chunk)
      }

      binaryString += decoder.end()

      return binaryString
    }
  }
}

/**
 * @see https://encoding.spec.whatwg.org/#decode
 * @param {Uint8Array[]} ioQueue
 * @param {string} encoding
 */
function decode (ioQueue, encoding) {
  const bytes = combineByteSequences(ioQueue)

  // 1. Let BOMEncoding be the result of BOM sniffing ioQueue.
  const BOMEncoding = BOMSniffing(bytes)

  let slice = 0

  // 2. If BOMEncoding is non-null:
  if (BOMEncoding !== null) {
    // 1. Set encoding to BOMEncoding.
    encoding = BOMEncoding

    // 2. Read three bytes from ioQueue, if BOMEncoding is
    //    UTF-8; otherwise read two bytes.
    //    (Do nothing with those bytes.)
    slice = BOMEncoding === 'UTF-8' ? 3 : 2
  }

  // 3. Process a queue with an instance of encoding’s
  //    decoder, ioQueue, output, and "replacement".

  // 4. Return output.

  const sliced = bytes.slice(slice)
  return new TextDecoder(encoding).decode(sliced)
}

/**
 * @see https://encoding.spec.whatwg.org/#bom-sniff
 * @param {Uint8Array} ioQueue
 */
function BOMSniffing (ioQueue) {
  // 1. Let BOM be the result of peeking 3 bytes from ioQueue,
  //    converted to a byte sequence.
  const [a, b, c] = ioQueue

  // 2. For each of the rows in the table below, starting with
  //    the first one and going down, if BOM starts with the
  //    bytes given in the first column, then return the
  //    encoding given in the cell in the second column of that
  //    row. Otherwise, return null.
  if (a === 0xEF && b === 0xBB && c === 0xBF) {
    return 'UTF-8'
  } else if (a === 0xFE && b === 0xFF) {
    return 'UTF-16BE'
  } else if (a === 0xFF && b === 0xFE) {
    return 'UTF-16LE'
  }

  return null
}

/**
 * @param {Uint8Array[]} sequences
 */
function combineByteSequences (sequences) {
  const size = sequences.reduce((a, b) => {
    return a + b.byteLength
  }, 0)

  let offset = 0

  return sequences.reduce((a, b) => {
    a.set(b, offset)
    offset += b.byteLength
    return a
  }, new Uint8Array(size))
}

module.exports = {
  staticPropertyDescriptors,
  readOperation,
  fireAProgressEvent
}