morgan-json/index.js

A variant of `morgan.compile` that provides format functions that output JSON

'use strict';

var debug = require('diagnostics')('morgan-json');

/**
 * Compile a `morgan` format string into a `morgan` format function
 * that returns JSON.
 *
 * Adopted from `morgan.compile` from `morgan` under MIT.
 *
 * @param {string|Object} format
 * @param {Object} opts Options for how things are returned.
 *   - 'stringify': (default: true) If false returns an object literal
 * @return {function}
 * @public
 */
module.exports = function compile (format, opts) {
  if (format === '') {
    throw new Error('argument format string must not be empty');
  }

  if (typeof format !== 'string') {
    return compileObject(format, opts);
  }

  opts = opts || {};

  var fmt = format.replace(/"/g, '\\"');
  var stringify = opts.stringify !== false ? 'JSON.stringify' : '';
  var js = '  "use strict"\n  return ' + stringify + '({' + fmt.replace(/:([-\w]{2,})(?:\[([^\]]+)\])?([^:]+)?/g, function (_, name, arg, trail, offset, str) {
    var tokenName = String(JSON.stringify(name));
    var tokenArguments = 'req, res';
    var tokenFunction = 'tokens[' + tokenName + ']';
    var trailer = (trail || '').trimRight();

    if (arg !== undefined) {
      tokenArguments += ', ' + String(JSON.stringify(arg));
    }

    return '\n    ' + tokenName + ': (' + tokenFunction + '(' + tokenArguments + ') || "-") + ' + JSON.stringify(trailer) + ','
  }) + '\n  })';

  debug('\n%s', js);

  // eslint-disable-next-line no-new-func
  return new Function('tokens, req, res', js);
}

/**
 * Compile an Object with keys as `morgan` format strings into a `morgan` format function
 * that returns JSON. The JSON returned will have the same keys as the format Object.
 *
 * Adopted from `morgan.compile` from `morgan` under MIT.
 *
 * @param {string|Object} format
 * @param {Object} opts Options for how things are returned.
 *   - 'stringify': (default: true) If false returns an object literal
 * @return {function}
 * @public
 */
function compileObject (format, opts) {
  if (!format || typeof format !== 'object') {
    throw new Error('argument format must be a string or an object');
  }

  opts = opts || {};

  var keys = Object.keys(format);
  var stringify = opts.stringify !== false ? 'JSON.stringify' : '';
  var js = '  "use strict"\n  return ' + stringify + '({' + keys.map(function (key, i) {
    var assignment = '\n    "' + key + '": "' + format[key].replace(/:([-\w]{2,})(?:\[([^\]]+)\])?/g, function (_, name, arg) {
      var tokenArguments = 'req, res';
      var tokenFunction = 'tokens[' + String(JSON.stringify(name)) + ']';

      if (arg !== undefined) {
        tokenArguments += ', ' + String(JSON.stringify(arg));
      }

      return '" + (' + tokenFunction + '(' + tokenArguments + ') || "-") + "';
    }) + '"';

    return assignment;
  }) + '\n  })';

  debug('\n%s', js);

  // eslint-disable-next-line no-new-func
  return new Function('tokens, req, res', js);
};