#文件multer上传翻版

抄的multer 0.12.8版本（看清楚，首页就说了。。。）

simple-multer 是一个node.js 中间件 处理上传 multipart/form-data.

封装了busboy

##API

###安装

$ npm install simple-multer

###使用

var express = require('express')
var multer  = require('multer')

var app = express()
app.use(multer({ dest: './uploads/'}))

你能获得这些字段和文件

console.log(req.body)
console.log(req.files)

重点： simple-multer 不会处理任何不是multipart/form-data形式的表单

##simple-multer file object

一个 multer文件对象是一个包含一下属性的文件对象：

1. fieldname - 在表单中的字段名
2. originalname - 用户计算机上的文件名
3. name - 重命名文件名
4. encoding - 文件编码类型
5. mimetype - 描述文件类型
6. path - 本地文件上传的位置
7. extension - 文件的拓展
8. size - 文件的尺寸
9. truncated - 如果限制文件超过限制，将被截断
10. buffer - Raw data (是一个空的，除非 inMemory 参数 是真的）

##options multer 接受一个可选对象，最基本的选项dest ，告诉multer上传到哪里。如果你没有填写这个参数，文件将重命名并且上传到系统临时文件夹。 如果inMemory 选项为true，数据不会写入硬盘，但是这些数据会保持在文件缓冲区。

在默认情况下，multer 将会重命名文件为了避免文件名冲突，当然这个重命名函数，也能根据你的要求自己的要求重新定义

以下是multer 的可选参数：

• dest
• limits
• includeEmptyFields
• putSingleFilesInArray
• inMemory
• rename(fieldname, filename, req, res)
• renameDestDir(dest, req, res)
• onFileUploadStart(file, req, res)
• onFileUploadData(file, data, req, res)
• onFileUploadComplete(file, req, res)
• onParseStart()
• onParseEnd(req, next)
• onError()
• onFileSizeLimit(file)
• onFilesLimit()
• onFieldsLimit()
• onPartsLimit()

除了这些，multer 也支持 更多的先进的busboy 选项 比如：highWaterMark,fileHwm and defCharset

在普通 express web app 中，基本实例实例如下：

app.use(multer({
  dest: './uploads/',
  rename: function (fieldname, filename) {
    return filename.replace(/\W+/g, '-').toLowerCase() + Date.now()
  }
}))

以下是这些options 参数的细节和解释：

###dest

用于文件上传的路径

###limits

以下可选参数选址了对象的大小限制，这些参数奖直接传给busboy,参数的具体解释请查看busboy's page

• fieldNameSize - integer - Max field name size (Default: 100 bytes)
• fieldSize - integer - Max field value size (Default: 1MB)
• fields - integer - Max number of non-file fields (Default: Infinity)
• fileSize - integer - For multipart forms, the max file size (in bytes) (Default: Infinity)
• files - integer - For multipart forms, the max number of file fields (Default: Infinity)
• parts - integer - For multipart forms, the max number of parts (fields + files) (Default: Infinity)
• headerPairs - integer - For multipart forms, the max number of header key=>value pairs to parse Default: 2000 (same as node's http).

limits: {
  fieldNameSize: 100,
  files: 2,
  fields: 5
}

指定这些limits 能够帮助我们保护网站抵制 denial of service (DoS) attacks.

###includeEmptyFields

这个参数 决定是否让空的字段值 赋值到req.body上。默认为false

includeEmptyFields: true

###putSingleFilesInArray

putStringFilesInArray默认值是false.

putSingleFilesInArray: true

一些applications 或者 libraries，例如 Object models,期待 req.files 键值对总是指向数组。如果设置为true，multer将会确保所有的值指向同一个数组。

// the value points to a single file object
req.files['file1'] = [fileObject1]
// the value points to an array of file objects
req.files['file1'] = [fileObject1, fileObject2]

相比 multer 的默认putStringFilesArray 是false。如果req.files任意键的值是一个单一的文件，让后这个值等同一个一文件对象。如果这个value指向 复数文件，这个value等于一个数组文件objects

// the value points to a single file object
req.files['file1'] = fileObject1
// the value points to an array of file objects
req.files['file1'] = [fileObject1, fileObject2]

###inMemory 如果这个boolean值为true，multer将要写入磁盘的数据保存在file.buffer属性上。 这个 dest 选项仍然可以设置，而且path属性包含了推荐文件保存路径（The dest option is still populated and the path property contains the proposed path to save the file.） 默认值false

inMemory: true

警告： 如果inMemory 设定是true的话，在上传非常大的文件好，或者大量较小文件时，可能会使我们的内存消耗殆尽。

###rename(fieldname,filename,req,res) 这个函数用来重命名上传的文件名，返回的返回值作为文件的新名字（不包含拓展名）.这个fieldname 和 filename 的文件

rename: function (fieldname, filename, req, res) {
  return fieldname + filename + Date.now()
}

注意： req.body Warnings applies to this function

renameDestDir(dest, req, res)

Function to rename the directory in which to place uploaded files. The dest parameter is the default value originally assigned or passed into multer. The req and res are also passed into the function because they may contain information (eg session data) needed to create the path (eg get userid from the session).

renameDestDir: function(dest, req, res) {
  return dest + '/user1'  
}

Note that req.body Warnings applies to this function.

onFileUploadStart(file, req, res)

Event handler triggered when a file starts to be uploaded. A file object with the following properties are available to this function: fieldname, originalname, name, encoding, mimetype, path, extension.

onFileUploadStart: function (file, req, res) {
  console.log(file.fieldname + ' is starting ...')
}

You can even stop a file from being uploaded - just return false from the event handler. The file won't be processed or reach the file system.

onFileUploadStart: function (file, req, res) {
  if (file.originalname == 'virus.exe') return false;
}

Note that req.body Warnings applies to this function.

onFileUploadData(file, data, req, res)

Event handler triggered when a chunk of buffer is received. A buffer object along with a file object is available to the function.

onFileUploadData: function (file, data, req, res) {
  console.log(data.length + ' of ' + file.fieldname + ' arrived')
}

Note that req.body Warnings applies to this function.

onFileUploadComplete(file, req, res)

Event handler trigger when a file is completely uploaded. A file object is available to the function.

onFileUploadComplete: function (file, req, res) {
  console.log(file.fieldname + ' uploaded to  ' + file.path)
}

Note that req.body Warnings applies to this function.

onParseStart()

Event handler triggered when the form parsing starts.

onParseStart: function () {
  console.log('Form parsing started at: ', new Date())
}

onParseEnd(req, next)

Event handler triggered when the form parsing completes. The request object and the next objects are are passed to the function.

onParseEnd: function (req, next) {
  console.log('Form parsing completed at: ', new Date());

  // usage example: custom body parse
  req.body = require('qs').parse(req.body);

  // call the next middleware
  next();
}

Note: If you have created a onParseEnd event listener, you must manually call the next() function, else the request will be left hanging.

onError()

Event handler for any errors encountering while processing the form. The error object and the next object is available to the function. If you are handling errors yourself, make sure to terminate the request or call the next() function, else the request will be left hanging.

onError: function (error, next) {
  console.log(error)
  next(error)
}

onFileSizeLimit()

Event handler triggered when a file size exceeds the specification in the limit object. No more files will be parsed after the limit is reached.

onFileSizeLimit: function (file) {
  console.log('Failed: ', file.originalname)
  fs.unlink('./' + file.path) // delete the partially written file
}

onFilesLimit()

Event handler triggered when the number of files exceed the specification in the limit object. No more files will be parsed after the limit is reached.

onFilesLimit: function () {
  console.log('Crossed file limit!')
}

onFieldsLimit()

Event handler triggered when the number of fields exceed the specification in the limit object. No more fields will be parsed after the limit is reached.

onFieldsLimit: function () {
  console.log('Crossed fields limit!')
}

onPartsLimit()

Event handler triggered when the number of parts exceed the specification in the limit object. No more files or fields will be parsed after the limit is reached.

onPartsLimit: function () {
  console.log('Crossed parts limit!')
}

##req.body Warnings

警告： req.body 在文件上传之后 完整解析。过早的访问req.boy会发生很多错误。req和res参数被增加到一些functions中，方便程序猿访问。 例如 session 变量 或者 socket.io 对象。