Rails源代码分析（24）：ActionController::Streaming-优快云博客

本文链接：https://blog.youkuaiyun.com/jlaky/article/details/3482924

本文介绍了一种高效文件传输方法，包括send_file和send_data两个核心函数。send_file通过流式传输发送文件，适用于大文件传输；send_data则用于发送二进制数据作为文件下载。两者均支持设置内容类型、文件名等选项。

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这个module提供了两个方法：

1） send_file

# Sends the file by streaming it 4096 bytes at a time. This way the

# whole file doesn't need to be read into memory at once. This makes

# it feasible to send even large files.

# Be careful to sanitize the path parameter if it coming from a web

# page. <tt>send_file(params[:path])</tt> allows a malicious user to

# download any file on your server.

# Options:

# * <tt>:filename</tt> - suggests a filename for the browser to use.

# Defaults to <tt>File.basename(path)</tt>.

# * <tt>:type</tt> - specifies an HTTP content type.

# Defaults to 'application/octet-stream'.

# * <tt>:disposition</tt> - specifies whether the file will be shown inline or downloaded.

# Valid values are 'inline' and 'attachment' (default).

# * <tt>:stream</tt> - whether to send the file to the user agent as it is read (+true+)

# or to read the entire file before sending (+false+). Defaults to +true+.

# * <tt>:buffer_size</tt> - specifies size (in bytes) of the buffer used to stream the file.

# Defaults to 4096.

# * <tt>:status</tt> - specifies the status code to send with the response. Defaults to '200 OK'.

# * <tt>:url_based_filename</tt> - set to +true+ if you want the browser guess the filename from

# the URL, which is necessary for i18n filenames on certain browsers

# (setting <tt>:filename</tt> overrides this option).

# Simple download:

# send_file '/path/to.zip'

# Show a JPEG in the browser:

# send_file '/path/to.jpeg', :type => 'image/jpeg', :disposition => 'inline'

# Show a 404 page in the browser:

# send_file '/path/to/404.html', :type => 'text/html; charset=utf-8', :status => 404

2）send_data

# Send binary data to the user as a file download. May set content type, apparent file name,

# and specify whether to show data inline or download as an attachment.

# Options:

# * <tt>:filename</tt> - suggests a filename for the browser to use.

# * <tt>:type</tt> - specifies an HTTP content type.

# Defaults to 'application/octet-stream'.

# * <tt>:disposition</tt> - specifies whether the file will be shown inline or downloaded.

# Valid values are 'inline' and 'attachment' (default).

# * <tt>:status</tt> - specifies the status code to send with the response. Defaults to '200 OK'.

# Generic data download:

# send_data buffer

# Download a dynamically-generated tarball:

# send_data generate_tgz('dir'), :filename => 'dir.tgz'

# Display an image Active Record in the browser:

# send_data image.data, :type => image.content_type, :disposition => 'inline'

2 实现

  module Streaming
    DEFAULT_SEND_FILE_OPTIONS = {
      :type         => 'application/octet-stream'.freeze,
      :disposition  => 'attachment'.freeze,
      :stream       => true,
      :buffer_size  => 4096,
      :x_sendfile   => false
    }.freeze
    X_SENDFILE_HEADER = 'X-Sendfile'.freeze
    protected
      def send_file(path, options = {}) #:doc:
        raise MissingFile, "Cannot read file #{path}" unless File.file?(path) and File.readable?(path) # 确认文件可读
        options[:length]   ||= File.size(path)
        options[:filename] ||= File.basename(path) unless options[:url_based_filename]
        send_file_headers! options
        @performed_render = false
        if options[:x_sendfile] # 采用高速传输模式,不经过服务器的内存
          logger.info "Sending #{X_SENDFILE_HEADER} header #{path}" if logger
          head options[:status], X_SENDFILE_HEADER => path
        else # 采用经过内存的读取模式
          if options[:stream]
            # 如果:stream设置为true 那么一边读取一边发送
            render :status => options[:status], :text => Proc.new { |response, output|
              logger.info "Streaming file #{path}" unless logger.nil?
              len = options[:buffer_size] || 4096
              File.open(path, 'rb') do |file|
                while buf = file.read(len)
                  output.write(buf)
                end
              end
            }
          else
          # 如果:stream设置为false那么整个文件读取结束才发送
            logger.info "Sending file #{path}" unless logger.nil?
            File.open(path, 'rb') { |file| render :status => options[:status], :text => file.read }
          end
        end
      end
      # 直接发送data
     def send_data(data, options = {}) #:doc:
        logger.info "Sending data #{options[:filename]}" if logger
        send_file_headers! options.merge(:length => data.size)
        @performed_render = false
        render :status => options[:status], :text => data
      end
    private
      def send_file_headers!(options)
        options.update(DEFAULT_SEND_FILE_OPTIONS.merge(options))
        [:length, :type, :disposition].each do |arg|
          raise ArgumentError, ":#{arg} option required" if options[arg].nil?
        end #检查必须有的参数
        disposition = options[:disposition].dup || 'attachment'
        disposition <<= %(; filename="#{options[:filename]}") if options[:filename] #如果有:filename拼接到 Content-Disposition 
        headers.update(
          'Content-Length'            => options[:length],
          'Content-Type'              => options[:type].to_s.strip,  # fixes a problem with extra '/r' with some browsers
          'Content-Disposition'       => disposition,
          'Content-Transfer-Encoding' => 'binary'
        )
        # Fix a problem with IE 6.0 on opening downloaded files:
        # If Cache-Control: no-cache is set (which Rails does by default),
        # IE removes the file it just downloaded from its cache immediately
        # after it displays the "open/save" dialog, which means that if you
        # hit "open" the file isn't there anymore when the application that
        # is called for handling the download is run, so let's workaround that
        headers['Cache-Control'] = 'private' if headers['Cache-Control'] == 'no-cache'
      end
  end