在AppEngine上对上传的二进制数据进行Base64编码

Question

我一直在尝试将用户（在这个情况下是一个可信的管理员）的图像数据进行Base64编码，这样可以尽量减少对BlobStore的调用。每次我尝试编码时，都会收到一个错误提示：

Error uploading image: 'ascii' codec can't decode byte 0x89 in position 0: ordinal not in range(128)

我在网上搜索了这个错误（不太重要的部分），发现可能和Unicode有关（？）。模板部分只是一个基本的上传表单，而处理程序包含以下代码：

  def post(self,id):
    logging.info("ImagestoreHandler#post %s", self.request.path)
    fileupload = self.request.POST.get("file",None)
    if fileupload is None : return self.error(400)

    content_type = fileupload.type or getContentType( fileupload.filename )
    if content_type is None: 
      self.error(400)
      self.response.headers['Content-Type'] = 'text/plain'
      self.response.out.write( "Unsupported image type: " + fileupload.filename )
      return
    logging.debug( "File upload: %s, mime type: %s", fileupload.filename, content_type )

    try:
      (img_name, img_url) = self._store_image(
        fileupload.filename, fileupload.file, content_type )
      self.response.headers['Location'] = img_url
      ex=None
    except Exception, err:
      logging.exception( "Error while storing image" )
      self.error(400)
      self.response.headers['Content-Type'] = 'text/plain'
      self.response.out.write("Error uploading image: " + str(err))
      return
    #self.redirect(urlBase % img.key() )  #dummy redirect is acceptable for non-AJAX clients,
    # location header should be acceptable for true REST clients, however AJAX requests 
    # might not be able to access the location header so we'll write a 200 response with 
    # the new URL in the response body:

    acceptType = self.request.accept.best_match( listRenderers.keys() )
    out = self.response.out
    if acceptType == 'application/json':
      self.response.headers['Content-Type'] = 'application/json'
      out.write( '{"name":"%s","href":"%s"}' % ( img_name, img_url ) )
    elif re.search( 'html|xml', acceptType ):
      self.response.headers['Content-Type'] = 'text/html'
      out.write( '<a href="%s">%s</a>' % ( img_url, img_name) )

  def _store_image(self, name, file, content_type):
    """POST handler delegates to this method for actual image storage; as
    a result, alternate implementation may easily override the storage
    mechanism without rewriting the same content-type handling. 

    This method returns a tuple of file name and image URL."""

    img_enc = base64.b64encode(file.read())
    img_enc_struct = "data:%s;base64,%s" % (content_type, img_enc)

    img = Image( name=name, data=img_enc_struct )
    img.put()
    logging.info("Saved image to key %s", img.key() ) 
    return ( str(img.name), img.key() )

我的图像模型：

from google.appengine.ext import db

class Image(db.Model):

  name = db.StringProperty(required=True)
  data = db.TextProperty(required=True)
  created = db.DateTimeProperty(auto_now_add=True)
  owner = db.UserProperty(auto_current_user_add=True)

非常感谢任何帮助。这段代码，除了我在_store_image中的图像编码，来自gvdent的blooger分支，链接在这里。

Answer 1

你的商店图片代码可能是这样的……

img = Image( name=name, data=file.read() )
img.put()
return ( str(img.name), img.key() )

把二进制数据做成base64编码可能会让数据变得更大，同时也会增加处理这些数据时的时间。

而Blobstore使用的存储结构和数据存储是一样的，所以它只是让文件上传和下载变得更简单。