If Modified Since HTTP Header - WordPress Development.

I am trying to enable 304 If Modified Since HTTP header in my WordPress site. After doing lot of Googling I find out a site where the author said to put the following line at the very end of wordpress wp-config.php file. Here is the line of code.

The Last-Modified is mainly used for caching. It's sent back for resources for which you can track the modification time. The resources doesn't have to be files but anything. for instance pages which are generated from dB information where you have a UpdatedAt column. Its used in combination with the If-Modified-Since header which each browser sends in the Request (if it has received a Last.

If-Modified-Since: date. This request header is used with GET method to make it conditional: if the requested document has not changed since the time specified in this field the document will not be sent, but instead a Not Modified 304 reply. Format of this field is the same as for Date.

The Last-Modified response header specifies the last time a change was made in the returned content, in the form of a time stamp. ETag values are unique identifiers generated by the server and changed every time the object is modified. Either can be used to determine if cached content is up to date.

If you want to produce a date and time stamp for use in one of your HTTP headers (for example, the If-Modified-Since header), you can use the FORMATTIME command. The STRINGFORMAT option on the command converts the current date and time (in ABSTIME format), or a date and time produced by the application program, into the RFC 1123 format.

Testing my site with varvy SEO tool I see it complains about If-Modified-Since HTTP header. After reading about it I see it is a header use by e.g. Google to tell them, hey you don’t need to scan it again. I saw how to add the header to WP, but this functionality is suppose to be in a plugin and not on the theme. Since Autoptimize already knows when was the last modification (and cache.

Access-Control-Request-Headers: Included when the header is a complex header, such as If-Modified-Since, or a custom header such as Opera Mini's X-Forwarded-For. Access-Control-Allow-Headers: Lets the referer know if the headers it sent are okay.

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So two question really - is the If-Modified-Since HTTP Header still relevant and should I make sure this is included? And is there anything else I should be doing to make sure the spiders crawl our pages? (apart from keeping them nice, fresh and useful).

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A PUT request can return a Precondition Failed (412) response if the representation has been modified since the last request. The conditional PUT can help avoid the lost update problem. Conditional HTTP requests can be used with the Last-Modified and ETag headers. The Last-Modified header can represent dates with granularity of one second.