body-parser/lib/types/json.js

Node.js body parsing middleware

/*!
 * body-parser
 * Copyright(c) 2014 Jonathan Ong
 * Copyright(c) 2014-2015 Douglas Christopher Wilson
 * MIT Licensed
 */

'use strict'

/**
 * Module dependencies.
 * @private
 */

var createError = require('http-errors')
var debug = require('debug')('body-parser:json')
var isFinished = require('on-finished').isFinished
var read = require('../read')
var typeis = require('type-is')
var { getCharset, normalizeOptions } = require('../utils')

/**
 * Module exports.
 */

module.exports = json

/**
 * RegExp to match the first non-space in a string.
 *
 * Allowed whitespace is defined in RFC 7159:
 *
 *    ws = *(
 *            %x20 /              ; Space
 *            %x09 /              ; Horizontal tab
 *            %x0A /              ; Line feed or New line
 *            %x0D )              ; Carriage return
 */

var FIRST_CHAR_REGEXP = /^[\x20\x09\x0a\x0d]*([^\x20\x09\x0a\x0d])/ // eslint-disable-line no-control-regex

var JSON_SYNTAX_CHAR = '#'
var JSON_SYNTAX_REGEXP = /#+/g

/**
 * Create a middleware to parse JSON bodies.
 *
 * @param {object} [options]
 * @return {function}
 * @public
 */

function json (options) {
  var { inflate, limit, verify, shouldParse } = normalizeOptions(options, 'application/json')

  var reviver = options?.reviver
  var strict = options?.strict !== false

  function parse (body) {
    if (body.length === 0) {
      // special-case empty json body, as it's a common client-side mistake
      // TODO: maybe make this configurable or part of "strict" option
      return {}
    }

    if (strict) {
      var first = firstchar(body)

      if (first !== '{' && first !== '[') {
        debug('strict violation')
        throw createStrictSyntaxError(body, first)
      }
    }

    try {
      debug('parse json')
      return JSON.parse(body, reviver)
    } catch (e) {
      throw normalizeJsonSyntaxError(e, {
        message: e.message,
        stack: e.stack
      })
    }
  }

  return function jsonParser (req, res, next) {
    if (isFinished(req)) {
      debug('body already parsed')
      next()
      return
    }

    if (!('body' in req)) {
      req.body = undefined
    }

    // skip requests without bodies
    if (!typeis.hasBody(req)) {
      debug('skip empty body')
      next()
      return
    }

    debug('content-type %j', req.headers['content-type'])

    // determine if request should be parsed
    if (!shouldParse(req)) {
      debug('skip parsing')
      next()
      return
    }

    // assert charset per RFC 7159 sec 8.1
    var charset = getCharset(req) || 'utf-8'
    if (charset.slice(0, 4) !== 'utf-') {
      debug('invalid charset')
      next(createError(415, 'unsupported charset "' + charset.toUpperCase() + '"', {
        charset: charset,
        type: 'charset.unsupported'
      }))
      return
    }

    // read
    read(req, res, next, parse, debug, {
      encoding: charset,
      inflate,
      limit,
      verify
    })
  }
}

/**
 * Create strict violation syntax error matching native error.
 *
 * @param {string} str
 * @param {string} char
 * @return {Error}
 * @private
 */

function createStrictSyntaxError (str, char) {
  var index = str.indexOf(char)
  var partial = ''

  if (index !== -1) {
    partial = str.substring(0, index) + JSON_SYNTAX_CHAR

    for (var i = index + 1; i < str.length; i++) {
      partial += JSON_SYNTAX_CHAR
    }
  }

  try {
    JSON.parse(partial); /* istanbul ignore next */ throw new SyntaxError('strict violation')
  } catch (e) {
    return normalizeJsonSyntaxError(e, {
      message: e.message.replace(JSON_SYNTAX_REGEXP, function (placeholder) {
        return str.substring(index, index + placeholder.length)
      }),
      stack: e.stack
    })
  }
}

/**
 * Get the first non-whitespace character in a string.
 *
 * @param {string} str
 * @return {function}
 * @private
 */

function firstchar (str) {
  var match = FIRST_CHAR_REGEXP.exec(str)

  return match
    ? match[1]
    : undefined
}

/**
 * Normalize a SyntaxError for JSON.parse.
 *
 * @param {SyntaxError} error
 * @param {object} obj
 * @return {SyntaxError}
 */

function normalizeJsonSyntaxError (error, obj) {
  var keys = Object.getOwnPropertyNames(error)

  for (var i = 0; i < keys.length; i++) {
    var key = keys[i]
    if (key !== 'stack' && key !== 'message') {
      delete error[key]
    }
  }

  // replace stack before message for Node.js 0.10 and below
  error.stack = obj.stack.replace(error.message, obj.message)
  error.message = obj.message

  return error
}