HTTP HEAD方法为动态生成的文件获取什么响应头？ [英] What response header should HTTP HEAD method get for a dynamically generated file?
问题描述
http规范说明了HEAD请求：
The http spec says about the HEAD request:
HEAD方法与GET相同，但服务器必须不是
在响应中返回消息体。元信息在HTTP头中包含
以响应HEAD请求应该与响应GET请求时发送的信息相同
。
The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The metainformation contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request.
Content-Length实体标题字段指示
实体主体的大小，以十进制数的OCTET发送对于收件人，或者在
HEAD方法的情况下，如果请求是GET，那么
已发送的实体主体的大小。
The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.
因此，如果请求的资源是动态生成的，对于 HEAD 请求，资源 ALSO 生成？是否应该 Content-Length 标头或 Transfer-Encoding：chunked 标头？
So if the requested resource is dynamically generated, for the HEAD request, will the resource ALSO be generated? Should there a Content-Length header or Transfer-Encoding: chunked header?
（我觉得这是关于如何实现HTTP协议。）
(I feel this is about how to implement the HTTP protocol.)
我没有看到规范要求是否要发送Content-Length标头或如何将其发送给动态生成的资源。这种动态资源将使用分块传输编码发送，如果使用 GET Content-Length 标头>方法。因此，如果HEAD响应应该模仿GET响应，则不应发送Contnet-Length。
I don't see the spec mandates whether to send Content-Length header or how to send it for a dynamically generated resource. Such dynamic resource will be sent with chunked transfer encoding and there'll be no Content-Length header if accessed with a GET method. So, if HEAD response should mimic GET response, the Contnet-Length should not be sent either.
推荐答案
a）那不是HTTP规范。它是1999年过时的RFC 2616的W3C副本。
a) That's not the HTTP spec. It is the W3C copy of the now obsolete RFC 2616, dated 1999.
b）关于当前规范，请参阅 https://greenbytes.de/tech/webdav/rfc7231.html#HEAD
b) For the current spec, see https://greenbytes.de/tech/webdav/rfc7231.html#HEAD
回答你的问题：如果你不知道有效载荷大小而没有实际生成它，那么在HEAD响应中不发送Content-Length就可以了。
To answer your question: if you don't know the payload size without actually generating it, not sending Content-Length in the HEAD response is ok.
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