HTTP requests a static TXT file, the first response is 304, and the second response is 200 analysis

1. HTTP requests a static TXT file, the first response is 304, and the second time is 200. as shown in Figure 1

Figure 1

2. Reference URL:https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Status/304. HTTP 304 does not change the content of the request that does not need to be transferred again, that is, the content of the cache can be used. This is usually in some safe methods (SAFE), such as GET or HEAD or the header information is attached to the request: if-none-match or if-modified-since. The request header for the first response 304 includes: If-Modified-Since: Thu, 27 May 2021 06:10:50 GMT. as shown in Figure 2

Figure 2

3. Reference URL:https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Headers/If-Modified-Since. If-modified-since is a conditional request header, the server will only return the resource if the requested resource has been modified after a given date and time, and the status code is 200 . If the requested resource has not been modified since then, a 304 response without the body of the message is returned, and the last modification time will be in the last-modified header. Unlike if-unmodified-since, if-modified-since can only be used in GET or HEAD requests.

4. The request header of the second response 200 is not included: If-Modified-Since: Thu, 27 May 2021 06:10:50 GMT. as shown in Figure 3

Figure 3