borc/src/tagged.js

Encode and parse data in the Concise Binary Object Representation (CBOR) data format (RFC7049).

'use strict'

/**
 * A CBOR tagged item, where the tag does not have semantics specified at the
 * moment, or those semantics threw an error during parsing. Typically this will
 * be an extension point you're not yet expecting.
 */
class Tagged {
  /**
   * Creates an instance of Tagged.
   *
   * @param {number} tag - the number of the tag
   * @param {any} value - the value inside the tag
   * @param {Error} err - the error that was thrown parsing the tag, or null
   */
  constructor (tag, value, err) {
    this.tag = tag
    this.value = value
    this.err = err
    if (typeof this.tag !== 'number') {
      throw new Error('Invalid tag type (' + (typeof this.tag) + ')')
    }
    if ((this.tag < 0) || ((this.tag | 0) !== this.tag)) {
      throw new Error('Tag must be a positive integer: ' + this.tag)
    }
  }

  /**
   * Convert to a String
   *
   * @returns {string} string of the form '1(2)'
   */
  toString () {
    return `${this.tag}(${JSON.stringify(this.value)})`
  }

  /**
   * Push the simple value onto the CBOR stream
   *
   * @param {cbor.Encoder} gen - The generator to push onto
   * @returns {number}
   */
  encodeCBOR (gen) {
    gen._pushTag(this.tag)
    return gen.pushAny(this.value)
  }

  /**
   * If we have a converter for this type, do the conversion.  Some converters
   * are built-in.  Additional ones can be passed in.  If you want to remove
   * a built-in converter, pass a converter in whose value is 'null' instead
   * of a function.
   *
   * @param {Object} converters - keys in the object are a tag number, the value
   * is a function that takes the decoded CBOR and returns a JavaScript value
   * of the appropriate type.  Throw an exception in the function on errors.
   * @returns {any} - the converted item
   */
  convert (converters) {
    let er, f
    f = converters != null ? converters[this.tag] : undefined
    if (typeof f !== 'function') {
      f = Tagged['_tag' + this.tag]
      if (typeof f !== 'function') {
        return this
      }
    }
    try {
      return f.call(Tagged, this.value)
    } catch (error) {
      er = error
      this.err = er
      return this
    }
  }
}

module.exports = Tagged