调用imagemagick做响应图片

设计出图后经常需要改下尺寸放在别的项目上使用，每次都是设计手工处理，其实图片服务可以做更多事情，比如借助强大的im，可以通过url控制图片尺寸

 var childProcess = require('child_process')
 var path = require('path')
     ,http = require('http')
     ,fs = require('fs')

 const dns_host = 'xxx.net' //图片源站地址
 const PATH_IMGS = '/home/work/demo/images' //目录存放
 const PATH_IMG_TMP = '/home/work/demo/images' //临时目录
 //图片尺寸参数
 // /pic/_hd/cd/19/d6d821de10662d5352ff2d6bbaf2_960_420.cj.100x100x15.jpg
 const REG_RESIZE_OPT = /\.(\d+)?x(\d+[\!\>\<]?)?x(\d+)?\.jpg/
 //图片质量 默认85
 //  /pic/_hd/cd/19/d6d821de10662d5352ff2d6bbaf2_960_420.cj.q100.100x100x15.jpg
 const REG_QUALITY_OPT = /\.q(\d+)\.jpg/  //图片质量参数

 http.createServer(function(req, res) {
     var imgurl = req.url
         ,cdn_path = imgurl
     var options = cdn_path.match(REG_RESIZE_OPT )
     var img_suffix = path.extname(cdn_path)
     var opt_img = {}
     if (options){
         opt_img =
             {
             "width" : options[1] || ''
             ,"height" : options[2] || ''
             ,"mode" : options[3] | 0 || 1
             ,"imgurl" : imgurl
             }
         cdn_path = cdn_path.replace(REG_RESIZE_OPT, img_suffix)
     }

     options = cdn_path.match(REG_QUALITY_OPT)
     if (options) {
         opt_img.quality = options[1] | 0
         cdn_path = cdn_path.replace(REG_QUALITY_OPT, img_suffix)
     }
     opt_img.quality = opt_img.quality || 85
     if (opt_img.quality >= 100) delete opt_img.quality

     http.get('http://' + dns_host + cdn_path , function(response){
         //因为图片size变了 去掉content-length
         delete response.headers['content-length']
         res.writeHead(response.statusCode , response.headers)
         if (200 !== response.statusCode) return response.pipe(res)

         var file_tmp = path.resolve(PATH_IMG_TMP , 'tmp_' + (+new Date).toString(24) + (img_suffix || ''))
         //抓取远程图片 临时存图
         var writeStream = fs.createWriteStream(file_tmp)
         response.pipe(writeStream)

         writeStream.on('error' ,function(err){
             console.log('err' , err)
             res.end(err.toString())
         })

         response.on('end' ,function(err){
             imgWorker(file_tmp , opt_img , (err ,imgsrc) => {
                 if (err) return res.end(err.toString())
                 imgsrc = imgsrc || file_tmp
                 var read_stream = fs.createReadStream(imgsrc)
                 read_stream.pipe(res)
                 read_stream.on('end' ,function(){
                     fs.unlink(file_tmp)
                 })
             })
         })

     })
 }).listen(8791) //web服务端口

 function mkdirp(p){
     p = path.dirname(p)
     if (fs.existsSync(p)) return

     p = p.split('/')
     var pathnow = ''
     p.forEach(function(pi){
         pathnow += pi + '/'
         if (!fs.existsSync(pathnow) )  fs.mkdirSync(pathnow)
      })

 }

 function imgWorker( file_tmp ,opt ,cbk){
     opt = opt || {}

     const bindPath = '/usr/local/ImageMagick/bin/'
     var bindIdentity = bindPath + 'identify'

     /*
      * mode 0 等比
      * mode 1 剪切
      * mode 2 压缩填充
      * */
     if (!opt.height) opt.mode = 0

     convert()

     function convert(){
         var binConvert = bindPath + 'convert'
         var img_save_path = PATH_IMGS + opt.imgurl
         mkdirp(img_save_path)
         /*
         convert -resize 1024 file.jpg newfile.jpg
         得到图片宽为1024，高根据原始图片比例计算而来

         convert -resize x768 file.jpg newfile.jpg
         得到的图片高位768，宽根据原始图片比例计算而来

         convert -resize 1024×768! file.jpg newfile.jpg
         固定宽高缩放，不考虑原是图宽高的比例，把图片缩放到指定大小。

         convert -resize “1024×768>” file.jpg newfile.jpg
         只有当src.jpg的宽大于1024或高大于768时候，才进行缩小处理，否则生成newfile.jpg和file.jpg具有一样的尺寸。

         convert -resize “1024×768<” file.jpg newfile.jpg
         只有当src.jpg的宽小于1024或高小于768时候，才进行放大处理，否则生成newfile.jpg和file.jpg具有一样的尺寸。

         http://www.imagemagick.org/discourse-server/viewtopic.php?t=18545

         */

         var childArgs = []

         /*
          * NorthWest, North, NorthEast, West, Center, East, SouthWest, South, SouthEast
          * NorthWest是左上角对齐 ，SouthEast是右下角对齐
          * 通过resize参数第二位可以控制对应对齐方式 默认Center 居中
          */
         if (opt.mode) {
             var _m = opt.mode.toString()
             var gravity = ['NorthWest', 'North', 'NorthEast', 'West'
                         , 'Center', 'East', 'SouthWest', 'South', 'SouthEast']
                             [(_m.slice(1,2) || 4) | 0]
             var color = ['' ,'white' ,'black'][(_m.slice(2,3) || 0) | 0]
             opt.mode = _m.slice(0,1) | 0
         }
         switch (opt.mode){
             case 2:
                 /*
                  * mode为2x 图片压缩填入指定尺寸 底色填充
                  * you can resize to the larger dimension and then pad the image
                  * convert image -resize "275x275" -gravity center -background white -extent 275x275 resultimage
                  */
                 childArgs.push('-resize')
                 childArgs.push(opt.width + 'x' + opt.height )
                 childArgs.push('-gravity')
                 childArgs.push(gravity)
                 if (color) {
                     childArgs.push('-background')
                     childArgs.push(color)
                 }

                 childArgs.push('-extent')
                 childArgs.push( opt.width + 'x' +  opt.height  )
                 break
             case 1:
                 /*
                 * mode为1x 图片拉伸 溢出剪切
                 */
                 var    cut = '+0+0'
                 childArgs.push('-resize')
                 childArgs.push(opt.width + 'x' + opt.height + '^')
                 childArgs.push('-gravity')
                 childArgs.push(gravity)

                 childArgs.push('-crop')
                 childArgs.push( opt.width + 'x' +  opt.height + cut )

                 break
             default:
                 /*
                 * 原图等比例缩放  比例不符合时以原图为准
                 */
                 var opt_size = opt.width || ''
                 if (opt.height) opt_size += 'x' + opt.height
                 if (opt_size){
                     childArgs.push('-resize')
                     childArgs.push(opt_size)
                 }
         }
         //去除元数据 相机信息 ps信息等
         childArgs.push('+profile')
         childArgs.push('"*"')
         childArgs.push('-strip')

         if (opt.quality){
             childArgs.push('-quality')
             childArgs.push(opt.quality)
         }

         childArgs.push(file_tmp)
         childArgs.push(img_save_path)

         console.log(childArgs)

         childProcess.execFile(binConvert, childArgs, function(err, stdout, stderr) {
             err && console.log(err)
             cbk(err  , img_save_path)
         })
     }

 }

node前端是nginx 对处理过的图片就可以直接使用了

 server {
     listen  80;
     server_name xxx.com;

     location /favicon.ico {
         return 418;
     }

     location / {
         root /home/work/demo/images ;
         try_files $uri $uri/  @router;

     }
     location @router {
         proxy_pass http://127.0.0.1:8791;
     }
 }