Fixed length "String" type, for use in `ref-struct` type definitions.

ref-fixed-string.js

var ref = require('ref');

module.exports = FixedString;

/**
 * Fixed length "String" type, for use in Struct type definitions.
 * Null-terminates by default.
 * Throws an Error if there's not enough space available when setting a string.
 */

function FixedString (length, encoding, nullTerminate) {
  if (!(this instanceof FixedString)) {
    return new FixedString(length, encoding, nullTerminate);
  }
  this.size = length | 0;
  if (this.size <= 0) {
    throw new TypeError('fixed string requires a byte length!');
  }
  this.encoding = encoding;
  //this.nullTerminate = Boolean(nullTerminate);
}
FixedString.prototype = Object.create(ref.types.char, {
  constructor: {
    value: FixedString,
    enumerable: false,
    writable: true,
    configurable: true
  }
});

FixedString.prototype.get = function (buffer, offset) {
  var v = buffer.toString(this.encoding, offset, offset + this.size);

  // strip at null terminator
  var zero = v.indexOf('\0');
  if (zero !== -1) {
    return v.substring(0, zero);
  } else {
    return v;
  }
};

FixedString.prototype.set = function (buffer, offset, value) {
  var v = value + '\0'; // null terminate
  var b = Buffer.byteLength(v, this.encoding);
  if (this.size < b) {
    throw new Error('string ' + JSON.stringify(value) + ' requires ' + b
        + ' bytes, but only ' + this.size + ' available');
  }
  buffer.write(v, offset, undefined, this.encoding);
};