exceljs/lib/csv/stream-converter.js

Excel Workbook Manager - Read and Write xlsx and csv Files.

// =======================================================================================================
// StreamConverter
//
// convert between encoding schemes in a stream
// Work in Progress - Will complete this at some point
let jconv;

class StreamConverter {
  constructor(inner, options) {
    this.inner = inner;

    options = options || {};
    this.innerEncoding = (options.innerEncoding || 'UTF8').toUpperCase();
    this.outerEncoding = (options.outerEncoding || 'UTF8').toUpperCase();

    this.innerBOM = options.innerBOM || null;
    this.outerBOM = options.outerBOM || null;

    this.writeStarted = false;
  }

  convertInwards(data) {
    if (data) {
      if (typeof data === 'string') {
        data = Buffer.from(data, this.outerEncoding);
      }

      if (this.innerEncoding !== this.outerEncoding) {
        data = jconv.convert(data, this.outerEncoding, this.innerEncoding);
      }
    }

    return data;
  }

  convertOutwards(data) {
    if (typeof data === 'string') {
      data = Buffer.from(data, this.innerEncoding);
    }

    if (this.innerEncoding !== this.outerEncoding) {
      data = jconv.convert(data, this.innerEncoding, this.outerEncoding);
    }
    return data;
  }

  addListener(event, handler) {
    this.inner.addListener(event, handler);
  }

  removeListener(event, handler) {
    this.inner.removeListener(event, handler);
  }

  write(data, encoding, callback) {
    if (encoding instanceof Function) {
      callback = encoding;
      encoding = undefined;
    }

    if (!this.writeStarted) {
      // if inner encoding has BOM, write it now
      if (this.innerBOM) {
        this.inner.write(this.innerBOM);
      }

      // if outer encoding has BOM, delete it now
      if (this.outerBOM) {
        if (data.length <= this.outerBOM.length) {
          if (callback) {
            callback();
          }
          return;
        }
        const bomless = Buffer.alloc(data.length - this.outerBOM.length);
        data.copy(bomless, 0, this.outerBOM.length, data.length);
        data = bomless;
      }

      this.writeStarted = true;
    }

    this.inner.write(this.convertInwards(data), encoding ? this.innerEncoding : undefined, callback);
  }

  read() {
    // TBD
  }

  pipe(destination, options) {
    const reverseConverter = new StreamConverter(destination, {
      innerEncoding: this.outerEncoding,
      outerEncoding: this.innerEncoding,
      innerBOM: this.outerBOM,
      outerBOM: this.innerBOM,
    });

    this.inner.pipe(reverseConverter, options);
  }

  close() {
    this.inner.close();
  }

  on(type, callback) {
    switch (type) {
      case 'data':
        this.inner.on('data', chunk => {
          callback(this.convertOutwards(chunk));
        });
        return this;
      default:
        this.inner.on(type, callback);
        return this;
    }
  }

  once(type, callback) {
    this.inner.once(type, callback);
  }

  end(chunk, encoding, callback) {
    this.inner.end(this.convertInwards(chunk), this.innerEncoding, callback);
  }

  emit(type, value) {
    this.inner.emit(type, value);
  }
}

module.exports = StreamConverter;