HttpWebResponse LastModified [英] HttpWebResponse LastModified

问题描述

HttpWebResponse.LastModified准确吗？它总是存在吗？我的项目是创建一种专注的网络爬虫，如果我将使用资源的哈希值或仅使用HttpWebResponse.LastModified属性检查资源的新鲜度，我就会陷入困境。

Is the HttpWebResponse.LastModified accurate? Is it always present? My project is to create a sort of a focused web crawler and I am stucked if I will use the hash value of a resource or just the HttpWebResponse.LastModified property to check the resource's "freshness".

使用哈希值意味着每次检查时都会流式传输资源。这对整体性能有很大影响。

Using the hash value means streaming the resource every time it's checked. This has a big impact on overall performance.

如果我只检查HttpWebResponse.LastModified，它是否准确？

If I will just check the HttpWebResponse.LastModified, is it accurate?

推荐答案

HttpWebResponse.LastModified返回HTTP Last-Modified 响应标头的值。

HttpWebResponse.LastModified returns the value of the HTTP Last-Modified response header.

HTTP响应标头由发送响应的HTTP服务器设置。如果它设置 Last-Modified 响应标头，并且是否将其设置为准确值，则完全取决于服务器。

HTTP response headers are set by the HTTP server sending the response. It's completely up to the server if it sets the Last-Modified response header, and whether it sets it to an accurate value or not.

Last-Modified 响应标头是HTTP中缓存验证模型的一部分。它通常与 If-Modified-Since 请求标头一起使用。您可能需要阅读 HTTP / 1.1，第6部分：缓存了解详情。

The Last-Modified response header is part of the Validation Model for Caching in HTTP. It is usually used in conjunction with the If-Modified-Since request header. You might want to read HTTP/1.1, part 6: Caching for the details.

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