如何在不读取 HTTP 资源的其余部分的情况下读取标头？

Question

我确信当我这样做时：

http = Net::HTTP.start uri.host, uri.port
request = Net::HTTP::Get.new uri
response = http.request request

我建立了某种与远程 HTTP 资源的连接，以便能够知道它的 Content-Type，而要真正加载整个资源，我然后调用 response.body。

但是要么我总是错了，要么是我现在访问的服务器出了问题，http.request 加载了我无法接受的整个远程文件：

[Net::HTTP debug] opening connection to v.redd.it:80...  
[Net::HTTP debug] opened  
[Net::HTTP debug] <- "GET /6otzwem1c7721/DASH_9_6_M?source=fallback HTTP/1.1\r\nAccept-Encoding: gzip;q=1.0,deflate;q=0.6,identity;q=0.3\r\nAccept: */*\r\nUser-Agent: Ruby\r\nHost: v.redd.it\r\nConnection: close\r\n\r\n"  
[Net::HTTP debug] -> "HTTP/1.1 200 OK\r\n"  
[Net::HTTP debug] -> "Last-Modified: Sat, 29 Dec 2018 11:25:57 GMT\r\n"  
[Net::HTTP debug] -> "ETag: \"662291aec20b252aaebcf54c3b1827af-42\"\r\n"  
[Net::HTTP debug] -> "Content-Type: video/mp4\r\n"  
[Net::HTTP debug] -> "Cache-Control: public, max-age=604800, s-maxage=86400, must-revalidate\r\n"  
[Net::HTTP debug] -> "Accept-Ranges: bytes\r\n"  
[Net::HTTP debug] -> "Content-Length: 218756120\r\n"  
[Net::HTTP debug] -> "Accept-Ranges: bytes\r\n"  
[Net::HTTP debug] -> "Date: Sun, 30 Dec 2018 13:44:21 GMT\r\n"  
[Net::HTTP debug] -> "Via: 1.1 varnish\r\n"  
[Net::HTTP debug] -> "Connection: close\r\n"  
[Net::HTTP debug] -> "X-Served-By: cache-fra19120-FRA\r\n"  
[Net::HTTP debug] -> "X-Cache: HIT\r\n"  
[Net::HTTP debug] -> "X-Cache-Hits: 0\r\n"  
[Net::HTTP debug] -> "X-Timer: S1546177461.284280,VS0,VE0\r\n"  
[Net::HTTP debug] -> "Server: snooserv\r\n"  
[Net::HTTP debug] -> "Vary: Origin\r\n"  
[Net::HTTP debug] -> "\r\n"  
[Net::HTTP debug] reading 218756120 bytes... 

我和 byebug 一起进去，直到找到它发生的地方：

[159, 168] in /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http/response.rb
   159:   def reading_body(sock, reqmethodallowbody)  #:nodoc: internal use only
   160:     @socket = sock
   161:     @body_exist = reqmethodallowbody && self.class.body_permitted?
   162:     begin
   163:       yield
=> 164:       self.body   # ensure to read body
   165:     ensure
   166:       @socket = nil
   167:     end
   168:   end
(byebug) where
--> #0  Net::HTTPResponse.reading_body(sock#Net::BufferedIO, reqmethodallowbody#TrueClass) at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http/response.rb:164
    #1  Net::HTTP.transport_request(req#Net::HTTP::Get) at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http.rb:1445
    #2  Net::HTTP.request(req#Net::HTTP::Get, body#NilClass, &block#NilClass) at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http.rb:1407
    #3  block in Net::HTTP.block in request(req#Net::HTTP::Get, body#NilClass, &block#NilClass) at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http.rb:1400
    #4  Net::HTTP.start at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http.rb:853
    #5  Net::HTTP.request(req#Net::HTTP::Get, body#NilClass, &block#NilClass) at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/net/http.rb:1398

是服务器的错吗？红宝石错？或者如果我想在不加载整个资源的情况下获取标头数据，我应该使用其他方法吗？

P.S.：我不需要第三方花哨的依赖，我只需要使用Net::HTTP。

Answer 1

取决于你真正想要完成的事情：

根本不在乎身体：

使用HEAD 代替GET：

uri = URI('http://example.com')
http = Net::HTTP.start uri.host, uri.port 
request = Net::HTTP::Head.new uri
response = http.request request
response.body
# => nil

有条件地加载正文

使用带有net/http 的块可以让您在实际加载主体之前进行钩子：

uri = URI('http://example.com')
res = nil

Net::HTTP.start(uri.host, uri.port) do |http|
  request = Net::HTTP::Get.new uri

  http.request request do |response|
    res = response
    break
  end
end

res
# => #<Net::HTTPOK 200 OK readbody=false> 
res['Content-Type']
# => "text/html; charset=UTF-8"